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Ecological and environmental consequences of oceanic anoxic events and the Cretaceous-Paleogene mass extinction event [Elektronische Ressource] : a molecular-isotopic approach / vorgelegt von Julio C. Sepúlveda Arellano

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Ecological and environmental consequences of Oceanic Anoxic Events and the Cretaceous-Paleogene mass extinction event: a molecular-isotopic approachDissertation zur Erlangung des Doktorgrades der Naturwissenschaften - Dr. rer. Nat. – Am Fachbereich Geowissenschaften der Universität Bremen vorgelegt von Julio C. Sepúlveda Arellano Bremen September 2008 Thesis committee 1. Supervisor: Prof. Kai-Uwe Hinrichs, University of Bremen, Germany 2. Co-Supervisor: Prof. Roger E. Summons, Massachusetts Institute of Technology, USA 3. Member: Prof. Jörn Peckmann, University of Bremen, Germany 4. Member: Prof. Wolfgang Bach, University of Bremany Thesis defense thMonday, 17 November 2008 Faculty of Geosciences, University of BremenMira niñita, te voy a llevar a ver la luna brillando en el mar… Para Annette y Amaya TABLE OF CONTENTSAbstract Thesis abstract……………………………………………………………. I Kurzfassung……………………………………………………………...III Acknowledgements.……………………………………………………………………...VList of Figures………………………………………………………………………….VIIList of Tables…………………………………………………………………………....IXList of Abbreviations…………………………………………………………………....XChapter I: Introduction………………………………………………………………..1 General introduction………………………………………………………2 1. Biological and geological processes influencing the global…………..2 carbon and nutrient cycles2. Oceanic anoxia during the Cretaceous………………………………...4 3. Cretaceous-Paleogene mass extinction event ……………………….10 4.

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Ecological and environmental consequences of Oceanic Anoxic

s-Paleogene mass extinction event: a Events and the Cretaceou

molecular-isotopic approach

Dissertation

zur Erlangung des Doktorgrades

der Naturwissenschaften

- Dr. rer. Nat. –

Fachbereich Geowissenschaften Am

en ität Bremder Univers

vorgelegt von

Julio C. Sepúlveda Arellano

en Brem

ber 2008 Septem

ittee mThesis com

1. Supervisor: Prof. Kai-Uwe Hinrichs, University of Bre

any en, Germm

of. Roger E. Summons, Mar2. Co-Supervisor: Pte of Technology, USA ssachusetts Institu

any en, Germann, University of Brember: Prof. Jörn Peckm3. Mem

4. Member: Prof. Wolfgang Bach, University of Bremen, Germany

se Thesis defen

Monday, 17

th

November 2008

fces, University oFaculty of Geoscienen Brem

r… ar la luna brillando en el mMira niñita, te voy a llevar a ve

aya Para Annette y Am

Abstract

TABLE OF CONTENTS

Thesis abstract……………………………………………………………. I

Kurzfassung……………………………………………………………...III

……………………………………………………………………...Vledgements.Acknow

………………………………………………………………………….VIIresList of Figu

…………………………………………………………………………....IXList of Tables

…………………………………………………………………....XList of Abbreviations

Introduction………………………………………………………………..1 Chapter I:

General

Chapter II:

1.

2.

3.

4.

5.

6.

7.

8.

introduction………………………………………………………2

sses influencing the global…………..2 Biological and geological proce

carbon and nutrient cycles

s………………………………...4 e Cretaceouxia during thOceanic ano

ss extinction event …as-Paleogene mCretaceou…………………….10

arker concept…………………………………………………...18 Biom

tions based on the use of……………22ental reconstrucPaleoenvironm

arkers and compound specific isotope ratios lipid biom

Research foci and objectives……………….………………………...26

Contribution to publications…………………………………………27

References……………………………………………………………30

ental and ecological………….41 environmMolecular-isotopic evidence of

changes across the Cenom-Turonian boundary in theanian

of central Jordan Levant Platform

Chapter III:Chapter IV:Chapter V:

s in the Late………………………85 ciOceanographic and climatic dynam

DP Site 1259): s Equatorial Atlantic (OCretaceou

pound-specific stable isotope approachA com

ents ganic-rich sedimation of orinto the form

Rapid Resurgence of Marine Productivity after the …………………...115

ction Event s-Paleogene Mass ExtinCretaceou

nuscript………………………………………………….116 aPrinted m1.

entary online inforSupplem2.ation…………………………………129 m

rks and Perspectives…………………………………141 amConcluding Re

1.

2.

3.

4.

Conclusions…………………………………………………………142

Perspectives…………………………………………………………146

Presentations and other activities……………..…………………….149

Erklärung……………………………………………………………151

THESIS ABSTRACT

Abstract Thesis

in aim of this thesis was to study the biotic and abiotic consequences ofaThe mextreme environmental conditions during Cretaceous Oceanic Anoxic Events (OAE), and
the recovery of prievent through the use of lipid biommary production at the Cretaceous-Paleogene (K-Pg) markers, compound-specific stable isotopes, and bulk ass extinction
geochemistry. This multiproxy approach contributes new evidence for understanding the
intricate environmental and biological interactions occurring during these important
rth’s history, which were responsible for rapid biological turnover that aevents in Eical cycles. eochempacted bioggreatly im Two OAEs covering the Late Cretaceous were studied - the Coniacian-Turonian vant illion years ago, Ma) in an intra-shelf basin of the LeBoundary OAE2 (~ 93.5 m in Central Jordan, and the Coniacian OAE3 (~ 88-89 Ma) at the western Platformequatorial Atlantic off the coast of Surinam (ODP Site 1259, Demerara Rise). OAE2 at
Jordan was characterized by sea-level changes that resulted in water column stratification
ocline, hypersalinity, and oxygen depletion, whereas evidence of with a fluctuating chemsteranes and hopanoids, including 2-mphotic zone euxinia (PZE) was only found after the termethyl hopanes (2-MeH), and 13ination of this event. Abundant C enriched aryl
isoprenoids suggest that the observed enviecological successions of planktonic assemblages domronmental changes were accominated by algae, inclupanied by ding
dinoflagellates, cyanobacteria and green-sulfur bacteria. The synchronous occurrence of 15portance of N values around 0‰ provides evidence for the im2-MeH and n at this stratified/anoxic ary productio-fixation fueling primcyanobacteria and N2continental platform. OAE3 at Demerara Rise was characterized by apparently cyclic,
concomitant variations of stable isotopic composition of carbon and hydrogen (13C and
D, respectively) of marine- and terrestrial-derived n-alkanes. This pattern suggested a
s. Intervals of enhanced marine rine and terrestrial systematight coupling between mproductivity were evidenced by positive 13C excursions of the algal marker n-C17, likely
related to increased growth rates and primary productivity. Parallel 13C enrichments in
C29 and C31 n-alkanes of higher land plant waxes suggest simultaneous changes of

I

Thesis Abstract

resulting in increased ospheric COs. Lowered concentrations of atmterrestrial ecosystem2

importance of C4 plants was one possible scenario explaining the observed molecular-

isotopic patterns. These intervals were also accompanied by D enrichments in n-C17

suggestive of changes in Dwater, likely due to variations in the evaporation/precipitation

balance and continental runoff. Overall, these results revealed a complex interplay of the

climatic and oceanographic regime and a potential coupling of marine and terrestrial

environmental changes.

g (~ 65.5 Ma) was studied in an ss extinction event at the K-PaIn addition, the m

, ned “Fish Clay” layer at Stevns Klint the renowexceptionally expanded section of

ark. At this location, decreased photosynthesis resulting fromDenm the low solar

transmission after the meteorite impact may have lasted less than 50 years. A highly

arkers and increased heterotrophic bacterial activity inished contribution of algal biomdim

was characteristic of the 2-mm-thick organic-rich layer deposited immediately after the

ction. This result e onset of recovery in algal produboundary. This period preceded th

odels suggesting a rapid resurgence of carbon fixation and strongly supported m

pact event, and provided a more r imjoaecological reorganization after this m

prehensive view of the biotic recovery compared to more traditional microfossil com

studies.

II

KURZFASSUNG

Kurzfassung

die biotischen und abiotischen Reaktionen Diese Dissertation untersucht einerseits auf extreme Um(OAE) und andererseits die Erholungphase der Primweltbedingungen während der kreidezeitlichärproduzenten imen „Oceanic Anoxic Events“ Anschluss an das
g) Grenze. Zu diesem Zweck wurden Aussterbeereignis der Kreide-Paläogen (K-Pponenten-spezifische stabile Isotope und arker, komische Biomorganisch-geochemgeochemische Gesamtparameter analysiert. Diese Multiproxy-Studie beleuchtet die
plexe Wechselbeziehung zwischen Umwelt und Biologie, während dieser wichtigen komn biologischen „Turnover“ e, die für einen schnelleEreignisse der Erdgeschicht ische Kreisläufeverantwortlich waren und weitreichende Auswirkungen auf biogeochemhatten. - der Oberkreide wurden untersucht – das OAE2 der ConiaciumZwei OAEs Intraschelf-Becken der Levant-Ma) im Grenze (~ 93.5 Millionen Jahre, TuroniumPlattform in Zentraljordanien, und das OAE3 des Coniacium (~ 88-89 Ma) im westlichen
äquatorialen Atlantik nahe der Küste Surinams (ODP Site 1259, Demerara Rise). Zu den
Jordanien gehörten Meeresspiegelschwankungen, nalen des OAE2 iprägnanten Merkmeinhergehend mit einer Stratifizierung der Wassersäule, variierender Position der
Chemokline, Hypersalinität und SOAE2 Hinweise für eine euxinische, phoauerstoff Mangel; während nach Beendigung des tische Zone (PZE) vorlagen. Erhöhte
Konzentrationen an Steranen und Hopanoiden, einschließlich 2-Methyl Hopanen (2-13C angereicherten Aryl-Isoprenoiden, weisen darauf hin, dass die MeH) und ökologischen Sukzession, der von Algen weltveränderungen von einer beobachteten Uminierten Plankton-kterien, Grün-Schwefel Bakterien) dom(inkl. Dinoflagellaten, CyanobaVergesellschaftungen begleitet wurden. Des Weiteren lässt das synchrone Auftreten von 2-MeH und 15N-Werten um 0‰ auf die Bedeutung von Cyanobakterien und N2-
ärproduktion unter den bestehenden Fixierung als die treibende Kraft der Primn Bedingungen schließen. stratifizierten/anoxischeDie enge Kopplung zwischen marinem und terrestrischem System war
charakteristisch für das OAE3 am Demerara Rise und ging einher mit einer zyklischen
Variation der stabilen Kohlenstoff- und Wasserstoff-Isotopenzusammensetzung (13C

III

Kurzfassung

und D) in marinen sowie terrestrischen n-Alkanen. Episoden mit gesteigerter mariner
Produktivität waren gekennzeichnet durch positive 13C-Anomalien des Algenbiomarkers

C17 n-Alkan, welche voraussichtlich durch einen Anstieg in der Wachstumsrate sowie der
Primärproduktion hervorgerufen wurden. Die parallele 13C Anreicherung in C29 und C31
achse höherer Landplanzen) lässt auf eine simultane arker für W-Alkanen (Biomn ögliche Erklärung fürs schließen. Eine mVeränderung des terrestrischen Ökosystem-Konzentration und osphärischen COen könnte eine Verringerung der atmdieses Phänom2 diese -Pflanzen sein. Zusätzlich wurdenender Bedeutung von Cdadurch zunehm4

Intervalle mit D-Anreicherungen in n-C17 begleitet, welche auf Variationen in der
Abfluss hinweisen. ag und kontinentalem Evaporation/NiederschlBalance zwischenDiese Ergebnisse verdeutlichen das komplexe Zusammenspiel von klimatischen und
rinen und aozeanographischen Faktoren und legen eine Kopplung zwischen mweltveränderungen nahe. terrestrischen UmDas Aussterbeereignis der K-Pg Grenze (~ 65.5 Ma) wurde an einem außergewöhnlich mächtigem Profil des „Fish Clay“ bei Stevns Klint (Dänemark)
teoriten Impakt verursachte, e Muntersucht. An dieser Lokation führte, die von einemhotosyntheserate, die einen geringere solare Einstrahlung zu einer Reduzierung der Parkeranalysen in der daran spannte. Biom von weniger als 50 Jahre umZeitrauminanz von ächtigen, organikreichen Lage ergaben eine Domanschließenden 2-mm mheterotrophen, bakteriellen Prozessen, die dem erneuten Aufblühen der Algen-Vergesellschaftungen vorausgingen. Die Ergebnisse dieser Studie unterstützen Modelle Kohlenstoff-Fixierung und ökologischen edereinsetzen der idie ein schnelles Wit bieten sie einen pakt-Ereignis befürworten. Som ImRestrukturierung nach diesem Vergleich zu traditionellen fassenderen Einblick in die biotische Entwicklung imumStudien basierend auf Mikrofossilien.

IV

ACKNOWLEDGEMENTS

ents Acknowledgem

Formworked with Cretaceouerly trained as a mas rocks before comrine biologist ing to Bremand oceanographer, I had never seen or en. It was here and during the
realization of my PhD that I was fortunate to meet people who introduced me to the
re I would like eistry, geobiology, and geology. Hfascinating worlds of organic geochemto express my immense gratefulness to those who contributed to my work and life in
Bremen during these three and half years. I would like to start thanking my supervisor,
ding the opportunity to join his group and for guieProf. Kai-Uwe Hinrichs, for giving mmy way through my PhD with such a great enthusiasm. Thanks Kai, for trusting me so
much, for giving me your support, and for opening my eyes and letting me develop my
own ideas with complete freedom. I would also like to thank my co-supervisor, Prof.
at his lab at MIT, and for expressing so much eons, for receiving mRoger E. Summ research, always providing encouraging suggestions that greatly yinterest on mrk o understanding of the K/Pg event. I look forward to continuing our wycontributed to mat Cambridge. I am also indebted to Profs. Jörn Peckmann and Wolfgang Bach, for
accepting being members of my thesis committee. The EUROPROX Program and the
einschaft are thanked for funding my studies. Deutsche Forschungsgemed in this thesis would not have been possible rt of the work includaA great pwithout the help from many people. Many thanks to my friend Jens Wendler, for making
the discussions about the Cretaceous’ world such an enjoyable experience, and for the nts of music together with Egon. To Arne Leider, who supported emoinspiring mimportant parts of my project during his undergraduate and master thesis, and to Jeff
er student. Very special thanks with the K/Pg project as a summeSalacup, for helping mgoes to Xavi Prieto, who besides being a great friend kept the lab running wonderfully well, and to Pamela Rossel for being like my sister during these years (gracias chiquitita).
I’m highly thankful to Steffi Tille, Ulrike Beckert, Jenny Wendt, Patrick Simundic, Tim
vert l Markus EoKahs, Monika Segl, and Hella Buschhoff for their support in the lab. Tand Daniel Birgel, for guiding my first steps into lipid analysis and mass spectrometry.
To Birgit Schmincke, for her immense support, and for making my life easier when I had
to deal with administrative stuff (which I still don’t fully understand), as well as Marion

V

Acknowledgements

the Organic Geochemistry oMilling-Goldbach, Maria Petrogiannis, and Anja Stöckl. To, Frauke, Simone, Arne, Xavi, Pame, Kai, Verena, land Geobiology groups: Julius, Flveig, Nadine, Benni, Tobi H., Ester, Yu-obi E., SoMarcus, Daniel, Birgit, Marcos, TShih, Marlene, Matthias K., Matthias S., Xiaolei, Sebastien, Jörn, Florian, Jan, Boonraksa, Monika, Steffi T., Steffi L., and Henning, for providing this place with the

tant support and friendship. To Beth! Orcutt, osphere, and for their consbest working atm

for proof reading several parts of this thesis even when being on a cruise in the middle of

best ythe Pacific Ocean, and for her great friendship and discussions about politics. To mking this world a better place to live - always keep that afriend Sergio Contreras, for mgreat smile on your face, buddy. To my German teacher, Ursula Meyers, for giving me
the hope that some day I will finally learn the language, Vielen dank liebe Ula!
fellow students, postdocs, proponents yTo the EUROPROX group, including m

and speakers. To the Geobiology Group at MIT, for receiving me for half a year; special
an, Carolyn Colonero, and Alla Skorokhod for their generous thanks go to Laura Shermyhelp. To m, HOI, Ricardo, Cristina & Margarita, Chanda & Tim friends at W

ny good friends abert, Sébastien, Konrad, Carlos & Jessica. To mYingTsong, Grace & Rowith whom I shared great moments in Bremen, especially at the Lagerhaus and
e, Barbara & Marius, Gulnaz & Cécile & Rick, Elvan & JeromHeartbreak Hotel: Petra,elle, Jeroen, Ed, Ines, Uli, Christian, Luisa, Jean, Isab,Xavier, Catalina, Igaratza, Ilhamniel & Gina, Lars H., Elsabe J., Sybille, and Frank. To Mahyar aMarkus, Eva, Magaly, D y, for the best Iron Maiden gigs of mith” Mohtadi and his brother Mehran“Adrian Sm

ilvio “Maestro” Pantoja and Carina Lange, and er supervisors in Chile, S formylife. To mmy friends in Concepción for being always so close despite of the distance. To my German family, Siegrun, Hans, Brigitte, Christoph & Diane, and Henny,
for receiving me with so much love and for giving me the warm feeling of a family.
siblings Constanza, Consuelo, and y parents Julio and Patricia, and myTo mt now and ever, and for believing in my Felipe, for their unconditional love and suppor

. es-Yves Cousteau since I was a childs inspired by Jacqudreamst wonderful o life forever in the myFinally, to the two persons that changed mway, filling my life with love and making me a proud partner and father, this work and all
aya. two loves, Annette and Amymy efforts are dedicated to m

VI

Figure I.1:

Figure I.2:

Figure I.3:

: Figure I.4

Figure I.5.

Figure I.6.

Figure I.7.

Figure I.8.

Figure I.9

Figure II.1.

Figure II.2.

Figure II.3.

Figure II.4.

Figure II.5.

LIST OF FIGURES

List of Figures

phytoplanktonic groups and carbon cycle…….3 niaParallel evolution of m

Conceptual model of the main mechanisms triggering ocean anoxia……..6

odels explaining enhanced productivity and Two conceptual m

preservation of organic carbon…………………………………………….8

Carbon-isos ……………..9 rd and sea-level of the Late Cretaceoutope reco

ss extinction events during the Phanerozoic…………………..11 aMajor m

The stratotype K-Pg section at El Kef, Tunisia………………………….16

ark………………….17 The Fish Clay at Kulstirenden, Stevns Klint, Denm

arkers………………………………………….19 ains of life and biomDom

ethyl hopanoid index throughout the Phanerozoic……………...23 The 2-m

Map of the studied area in Jordan………………………………………..46

istry of GM-3 section at Jordan…………………………..51 Bulk geochem

s…………………………………53 atogram Characteristic total ion chrom

pound classes………………….54 Relative percentage contribution of com

arker ratios………………………………………………...59 Selected biom

VII

List of Figures

Figure II.6. Selected ion chromatogram (m/z 191) displaying hopanes……………...61
Figure II.7. Selected ion chromatogram (m/z 133/134) displaying aryl isoprenoids...63
Figure II.8. Compound-specific carbon isotopic composition………………………..67
during OAE2…72 odel for the Levant PlatformConceptual depositional mFigure II.9. rara Rise……………………..90 emMap of study area, ODP Site 1259, DeFigure III.1. ) of Site 1259……………………..91 istry (TOC and CaCOBulk geochemFigure III.2. 3 -alkanes………………………...96 nand concentration and of Distribution Figure III.3. Figure III.4. Compound-specific isotopic composition of n-alkanes………………...100
ental interpretation at Site 1259……………….102 ary and environmSummFigure III.5. istry at Kulstirenden……………………………………..119 Bulk geochemFigure IV.1. Figure IV.2. Biomarker-based maturity and source parameters……………………...122
Map of study area at Stevns Klint………………………………………135 Figure IV.3. ples………………….136 s of selected samatogramTotal ion current chromFigure IV.4. Figure IV.5. GC–MS-MRM-mode chromatograms of C27-C31 triterpanes…………..137
Figure IV.6. GC–MS-MRM-mode chromatograms of steranes……………………...138

VIII

Table I.1.

Table I.2.

Table I.3.

Table II.1.

Table II.2.

Table II.3.

Table IV.1

LIST OF TABLES

List of Tables

s……………..5 e Cretaceouts during thary of oceanic anoxic evenA summ

raples of lipid biomExamkers as indicators of biological sources and

ental reconstruction…………………………………………….21 environm

arkers…………………..24 biomies derives fromental proxPaleoenvironm

Jordan…………………50 ents fromistry of analyzed sedimBulk geochem

arker ratios at Jordan……………………………………...56 Selected biom

Compound-specific carbon isotopic composition......................................68

MRM–GC–MS–MS precursor to product transitions…………………..133

IX

List of Abbreviations

2-MeHI CaCO Calcium 3CPI Carbon CTB Cenom13 C 13Ccarb
13Corg
15 N  Stable D DCM DichloromDIC Dissolved DSDP p FC Fish GC-irMS GC-MS GammGI Gigatons Gt HomHHI CretaceouK-Pg ky LCA Long-chain Ly Lycopane Million Ma d cmMeOH MethanoMRM-GG-MS OAE

X

LIST OF ABBREVIATIONS

2-Methyl hopane index carbonate index preference oundary Banian-Turonian Stable carbon isotopic composition (‰) Stable carbon isotopic composition of bulk carbonates (‰) tter (‰)aStable carbon isotopic composition of organic mStable nitrogen isotopic composition of bulk sediment (‰)
(‰) position comisotopic hydrogen ethane carbon inorganic Deep Sea Drilling Program Isotopic fractionation Clay ass spectrometry atography-isotope ratio-mGas chromss spectrometry aatography mGas chromindex acerane

index ohopane oundary bs-Paleogene Kilo years or thousand years e -alkann

years Meters of composite depth l Metastable reaction monitoring gas chromatography mass
etry spectromt xic evenOceanic ano

ODP

OMZ Oxygen

CO 2

Ph Phytane

Pr Pristane

Pr/Ph Pristan

P-T Perm

PZE Photic

SCA Short-chain

SSS Sea

SST

TOC

Ocean Drilling Program

minimum zone

Partial pressure of CO

ratio tane e/phy

ian-Triassic

euxinia zone

e -alkann

salinsurface ity

2

perature Sea surface tem

Total organic carbon

List of Abbreviations

XI

CHAPTER I

INTRODUCTION

Chapter I

1

GENERAL INTRODUCTION

Chapter I

ental,nmThis introductory section provides an overview of the envirobiogeochemical, and biological processes (and feedback mechanisms) controlling the
ent of anoxia/euxinia in t and sustainmneglobal carbon cycle, and leading to the developmes, with special focus on the Late Cretaceous ents over geological timrine environmamPeriod (~ 94-65.5 million years, Ma). Additionally, this section introduces the main
ss extinction event at the Cretaceous-Paleogene Boundary, and atheories explaining the m and g extinctionechanisms controllin mits biotic and abiotic consequences includingarkers and stable isotopes in the study of survival. Finally, the concept of lipid bioments is discussed. paleoenvironm

OCESSES INFLUENCIBIOLOGICAL AND GEOLOGICAL PR I.1.NG THE

GOBAL CARBON AND NUTRIENT CYCLES

of modern eukaryotic phytoplankton inant groupsThe evolution of the three dom(coccolithophores, dinoflagellates, and diatoms) reached ecological predominance during
the Mesozoic and changed both ecosystem structure and biogeochemical cycles
(Falkowski et al., 2004). Due to their capacity for rapid growth, marine microorganisms
(Arrigo, 2005) and have shaped the geological jor drivers of global nutrient cycles aare m 1999). The latter cean and atmosphere (Hayes et al.,ox state of ocarbon cycle and the redary producers e three groups of primthe evolutionary history of thescan be exemplified by since the Early Jurassic, the increase of organic carbon burial efficiency in marine
sediments, and the long-term enrichment in 13C of the mobile carbon reservoir (Fig. I.1;

Katz, 2005). These changes were tightly coupled to the continental rifting responsible for n. Sea level changes, on the other hand, nsion and coastline extethe ocean’s configuratiotinents and allowed the flourishing of the conregulated nutrient influx fromphytoplanktonic groups along continental margins. Carbon burial over geological time
scales has also influenced the partial pressure of atmospheric CO2 (CO2) and climate
which is suggested to have favored, for an and Hayes, 1992; Hayes et al., 1999), (Freem

2

Chapter I

instance, the expansion of the C4-type photosynthetic system in terrestrial plants (e.g.,
ni et al., 1999; 2005). Kuypers et al., 1999; Paga

eukaFigure Iryotic .1.phy Long-termtoplankton, an relationsd cahip rbon betwcyclee for en sea lethe past 240 vel change,Ma (Katz, the e 2005vol). Futionaromry tr left to ajectories of right, sea malevel jor
curve; number of calcareous nannoplankton species and genera; number of dinoflagellate cysts species and
genera; numb13er of diatom species and genera; 13C of bulk carbonate; 13C of organic carbon; 87Sr/86Sr as
an indicator of C input from continental erosion. Modified from Katz (2005), see original reference for
data sources. details about rfurthe

The long-term trend of biological and geochemical evolution was interrupted by alies which occurred during discrete ical anomperiods of biotic crises and geochem88; Leckie et al.,intervals of widespread ocean anoxia in the Cretaceous (Arthur et al., 19 rks the end of the Cretaceous (Alvarez et al., ass extinction event that ma2002), and the mtal stress during nee of these intervals of environm1980; D'Hondt, 2005). It is during somryotes including ely prokarine planktonic groups, namathe Cretaceous that other moautotrophic archaea, played a key ecological and photosynthetic cyanobacteria and chemical role globally (Kuypers et al., 2001; 2002a; 2004b). Nitrogen fixation by geochem variations COary productivity and cyanobacteria is suggested to have controlled prim2

3

Chapter I

escales (Falkowski, 1997). However, the role of prokaryotic organismson geological timduring the mass extinction event at the end of the Cretaceous remains largely unknown.

E CRETACIOUS NG THOCEANIC ANOXIA DURI I.2.

Ocean anoxia and euxinia accompanied several events during the Phanerozoic
ndary ian-Triassic boullion year, Ma) including biotic crises during the Permi(last 545 m02). The Cretaceous Period, and the Cretaceous (Leckie et al., 20),(e.g., Grice et al., 2005 beginning of the Paleogene the end of the Jurassic (145.5 ± 4 Ma) to the extending fromate, (65.5 ± 0.5 Ma), witnessed some of the most extraordinary changes in climical cycles, and biotic turnover observed during the last 250 oceanography, biogeochemMa of Earth’s history (e.g., Leckie et al., 2002).

Oceanic anoxic events and forcing mechanisms. The realization that vast areas of the
world oceans might have experienced oxygen-depleted conditions and euxinia during
Cretaceous time arose from the observation that organic-carbon-rich sediments (black
ric settings, including coastal and open teed in a variety of paleo-bathymshales) formocean areas, and epicontinental seas (Schlanger and Jenkyns, 1976; Jenkyns, 1980).
These events have been named oceanic anoxic events (OAE; Schlanger and Jenkyns,
rine anoxia (in the aals of widespread me interv1976), and are thought to represent timounts of organic carbon on the of large aments) and burial n and/or sedimwater colum88). Black shales ocean floor (e.g., Schlanger and Jenkyns, 1976; Arthur et al., 1987; 19are mudrocks characterized by a high organic content (usually > 1%) with a color varying
gray to olive-brown to black. Black shales are usually devoid of benthonic diume mfrom rthur and Sageman, 1994); they can also beinations (Afauna and contain distinct lamhighly enriched in several redox-sensitive and sulfide-forming trace metals (Brumsack,
d 2006). Several OAEs varying in duration and geographical extension have been describe between the Early Aptian and the Santonian (see summary Table I.1). The two mostanian-Turonian Boundary and the Cenome early Aptian OAE1a OAEs are thwidespreadOAE2 (Arthur et al., 1987; Schlanger et al., 1987). On the other hand, the Coniacian-

4

Chapter I

e (e.g., Meyers et al., 2006). Santonian OAE3 appears as the most extended in timparatively less attention than its counterparts, likely due to However, it has received comits regional restriction to the Atlantic basin (Wagner et al., 2004), in spite of the evidence
atic-oceanographic processes controlling theplex, and orbitally-driven climof com interval (Nederbragt et al., 2007). deposition of black shales during this

Table I.1. A summary of the mid-Cretaceous Oceanic Anoxic events (Meyers, 2006)

Event Common name Geological time Absolute duration
OAE 3 “None” Coniacian-Santonian 87.3–84.6 Ma (~ 2.7 My)
OAE 2 Bonarelli event Latest Cenomanian 93.8–93.5 Ma (~ 300 ky)
OAE 1d Breistroffer event Late Albian 100.6–100.2 Ma (~ 400 ky)
OAE 1c Tollebuc event Late Albian 103.7–103.4 Ma (~ 300 ky)
OAE 1b (several) Urbino event Early Albian 110.9–110.6 Ma (~ 300 ky)
Paquier event Early Albian 112.0–111.6 Ma (~ 400 ky)
Jacob event Late Aptian 113.6–113.2 Ma (~ 400 ky)
OAE 1a Selli event Early Aptian 124.2–123.4 Ma (~ 800 ky)

Although an intense discussion about the main mechanisms controlling black
shales formation has occurred during the last few decades, elevated levels of primary
productivity in surface waters, as well as increased organic matter preservation under
st plausible explanations (e.g., ooxygen-deficient conditions, are considered as mté and Köster, 1998; Kuypers et al., 2002b; Mort et al., 2007). However, smaSinninghe Dthe actual trigger mechanism has not clearly been identified. The interaction of factors
such as enhanced ocean crust production, volcanic activity, and massive magmatic
ed to have caused the assumepisodes (Leckie et al., 2002; Turgeon and Creaser, 2008) are elevated concentrations of atmospheric CO2 (Bice and Norris, 2002; Bice et al., 2006)
peratures ceptionally high sea surface temate with exand the associated greenhouse climd to low (Schouten et al., 2003; Bice et al., 2006; Forster et al., 2007) and high-iat mlatitudes (Jenkyns et al., 2004). The latter contributed to the presence of ice-free poles and a weaker than modern equator-to-pole surface-temperature gradient (Poulsen et al.,
to the chanisme1999). Rising sea level has been also advocated as an important mation of black shales, responsible for the flooding of extended coastal areas, the mfortransfer of continental nutrients into the ocean, and the formation of epicontinental seas

5

Chapter I

(cf., Arthur et al., 1987; Schlanger et al., 1987; Leckie et al., 2002). Finally, increased thermohaline stratification due to high sea surface temperatures and continental runoff
miof the western Tethys and North Atlaght have affected deep-water formntic (e.g., Erbacher et al., 2001). ation and elevated carbon burial in restricted basins
Recent model results suggest that reduced oxygen solubility during warm climates
nfiguration have a more important role in and nutrient-trapping controlled by continent comp, 2008). A inia than stagnant circulation (Meyer and Ku oceanic euxllingcontrodevelopmsequence of probable forcing ment of anoxia and euxinia is summechanismsarized in Figure I.2. Active volcanism and feedback loops involved in the during
the Cretaceous was assumed to be the main trigger of elevated CO2 levels and resulted
continental weathering and higher delivery ing, and an intensification ofin global warmrates of nutrients (phosphate) into the oceans. This led to increased marine productivity
organic maand export to the deep ocean protter respiration through sulfate reduction and decreased oxmoting oxygen depletion and euxinia, due toygen solubility at both
nditions facilitated phosphate relatively high ocean temperatures. Reducing co

Figure I.2. Conceptual model displaying the main components involved in the establishment and
relationsmaintenance hips are deof euxinia inotedn the by “normocean, and feedbacal arrows” ank md indiechanismcate the direction of the s (Meyer and Kump, response; ne2008). Positives gative
relationships are denoted by “circular arrow heads” and indicate that the response is in the opposite
direction. (-) and (+) denotes negative and positive feedback loops, respectively.

6

Chapter I

mobilization from sediments, thus keeping a positive feedback loop on productivity and

persistent euxinic conditions until volcanism ceased (Meyer and Kump, 2008).

Although the proxy record covering the Cretaceous provides evidence for the

echanismntioned meinteraction of several of the ms as responsible for oxygen depletion

and the formation of black shales, it remains difficult to conceive how marine primary

. Besides salinity emproduction could have been sustained for an extended period of ti

rological cycle, gnified runoff under an accelerated hyda due to mstratification

oceanographic models also include the role of sustained enhanced upwelling under

erved in modern favorable atmospheric circulation (Figure I.3; Meyers, 2006). As obs

coastal environments dominated by permanent or semi-permanent upwelling conditions

ary such as the eastern Pacific, Indian, and western Atlantic oceans, high rates of prim

gen-poor and nutrient-rich production are fueled by the vertical transport of oxy

and, the development of oxygen ing to a high oxygen demsubsurface waters, lead

minimum zones (OMZ), and to excellent preservation of organic matter in surface

, 2004; Cowie, 2005). and Levinents (e.g., Hellysedim Analogous oceanographic

ion of black shales conditions have been invoked to explain the orbitally-driven deposit

02b;s off the coast of northwest Africa (e.g., Kuypers et al., 20during the Cretaceou

erica (Nederbragt et al., Lüning et al., 2004; Kolonic et al., 2005) and northeast South Am

2007; Friedrich et al., 2008).

7

Chapter I

mFigure I.odels charac3. Two terizing a hiconceghly ptual
nd a strongly productive aanoxia and estratified enviruxionmnia in ocents favoring ean
Meyers, rgin settings (fromamnce for 2006; see original referepanel r details). Upper furtheling represents coastal upwelproductivity anconditions characterizedd th by high e
developmLower panel reent of a presemant a rked OMZ. strongly
with a mstratified and prarked pycnocline oductive sysduetem to
Downward continental runoff. fluxes to the arrows indicatsee orgaa floor. nic matter

Biological and geochemical consequences of OAEsOAEs represent periods of a major . perturbation of the global carbon and nutrient cycles, as evidenced by a marked positive
(Fig. I.4) attributed to a change in thecarbon isotopic excursion in the geological record increased tal inorganic carbon pool that resulted fromisotopic composition of the tomarine productivity and burial of 13C-depleted organic ma13tter (Arthur et al., 1988).
During photosynthesis, phytoplankton discrimisotopic depletion of the organic matter and an enrichminate against ent C, which results inof the remaining inorganic an
carbon pool (e.g., Freemcoincide with episodes of biotic turnover in an and Hathe mayes, 1992). The occurrence of carbon-isotope events rine fossil record, which has promoted
the use of carbon-isotope curves and correlation as a global stratigraphic tool (Jarvis et al., 2006; Fig. I.4). Environmental changes associated with OAEs are reported to have caused
Leckie et al., 2002). On the other hand, somaccelerated rates of speciation and extinction of planktonic calcareous organisme OAEs have been related to the flourishing s (e.g.,
ary producers (Kuypers et al., 2001; 2004b). portant primof planktonic archaea as imMarine archaeal lipids found in sediments of the North Atlantic Ocean deposited during

8

Chapter I

tter present in ainate the bulk of organic mthe early Albian OAE1b are suggested to dom

black shales, indicating that planktonic chemoautotrophic archaea played an important

tion of black shales (Kuypers et al., 2001;amecological role and contributed to the for

ally, n2002a). Additiononium trogen deficiency due to denitrification and anaerobic ammi

oxidation in anoxic waters during OAEs might have given N2-fixing cyanobacteria a

comed to have petitive advantage over algae (Kuypers et al., 2004b). This group seem

blage over a vast array of coastal ic assemportant fraction of the planktonprised an imcom

ents during OAEs, and was likely responsible for the supply ofand open ocean environm

fixed nitrogen for other members of the planktonic community (Kuypers et al., 2004b;

a et al., 2008). et al., 2006; Kashiyamitrescu and Brassell, 2005; OhkouchiDum

Figure I.4. For figure caption see next page

9

Chapter I

Figure I.4. Relationship between carbon-isotope record and sea level change for the Late Albian – Early
Campan13ian (Jarvis et al., 2006). Left panel is a smoothed (5-point moving average) version of the English
Chalk Siberia, India, and NWC composite age-ca Europe librated c(see Jaurvervis et comal., pared 2006). Gray areas with sea-level curves fromrepresent isotopes the Russian Platform events associated to and
p between isotopic anomalies (OAEs) and itive relationshiurbations of the carbon cycle. Note the pospertsea level, especially well developed during the Cenomanian-Turonian Boundary OAE2.

NCTION EVENT CRETACEOUS-PALEOGENE MASS EXTI I.3.

rded at the Cretaceous-Paleogene Boundary (K/Pg; ss extinction event recoaThe m65.5 million years ago) is the most recent of the so called “big five” Phanerozoic mass
rks the end of the Mesozoic era (Sepkoski Jr, 1996; Figure I.5). Two-aextinctions and m tinction,thirds of all living species on Earth, including the dinosaurs, went into exwhereas the total diversity of fossilized marine genera declined by about 50% (Sepkoski
Jr, 1996; Figure I.5). ive and ssaAlthough several hypotheses have been suggested to explain the mabrupt nature of the K/Pg, it was not until the early eighties that a revolutionary theory
alously high concentrations entirely. Based on anom changed its geological interpretationof iridium (a rare element in the earth’ crust) found in deep-sea limestones deposited at
several localities during the boundary, Alvarez et al., (1980) suggested that an asteroid 10 ± 4 kilometers in diameter must have impacted the Earth, resulting in the ejection of a
s, causing darkness and phere for several yeardust cloud of pulverized rock into the stratosulated ss extinction. The theory stima mthe disruption of photosynthesis that led to during the following years; the subsequent considerable scientific and public interestrldwide (e.g., Alvarez et al., oaly in several other sections w anomdiscovery of the iridiumpact cratering (Bohor et al., 1984) m1980), as well as shocked quartz characteristic of ioffered further evidence. But the discovery of a buried 180-km-diameter circular crater in
the Yucatan Peninsula (Chicxulub crater) one decade later (Hildebrand et al., 1991; Pope
ost three pact occurred at the K/Pg. After almteorite imeet al., 1991), indicated that a mdecades since its publication and the focus of intense scientific discussion, a compelling
the Alvarez’s hypothesis and provided its ount of geological evidence has supported am ing, 2007).rtance (see Ryder, 1996; Kwide accep

10

Chapter I

Figure I.5. Biodiversity by the number of genera during the Phanerozoic (Sepkoski Jr, 1996). Cm =
Cambthe so called “big rian fafivuna, Pz = Palee” maozoic fass extinction events una, Md =moderduring tn fahunae Phane.rozoic Notice the abrupt dec(black arroreases ws), such as the in diveK-Pg. rsity during

An alternative and/or parallel mechanism described to have contributed to the
ss extinction event at the K/Pg is the generation of a large igneous province on the am n as the Deccanent is knowia (Keller, 2003). This evDeccan Plateau of west-central IndPg boundary (Keller et al., 2008), and it /Traps; it is dated within less than 1 Ma of the Kmay correspond to the greatest episode of continental flood basalt volcanism in the
Phanerozoic. The Deccan Traps are responsible for flooding about 2.6 x 106 km2 of India
with basaltic lavas, releasing 5 x 1017 moles of mantle CO2 into Earth’s atmosphere over
ssive aental consequences of such a ma duration 0.53-1.36 Ma (McLean, 1985). Environmate, a ffecting the global climing avolcanic activity include a greenhouse warmoting istry and promperturbation of the entire carbon cycle likely affecting ocean chemocean acidification, and sea level and sedimentation changes, i.e., a combination of
ility and extinction (e.g., McLean, 1985). factors contributing to ecological instabained a ing it has remecise duration and timHowever, due to uncertainties about its prrather speculative theory, although recent dating results placing the Deccan traps eruption

11

Chapter I

close to the K/Pg have strengthened its relationship with the mass extinction (Chenet et
ller et al., 2008). eal., 2007; K several environmThe immeental and biological consequediate causes of the extinction remnces of the meain under discussion; however, teor impact on a global
scale have been proposed (c.f., Kring, 2007). Models have suggested that the nature of the impacted material (a submerged marine carbonate platform), and the energy released
by the impact (0.7-3.4 x 1031 ergs), could have generated over 200 Gt of SO2 and vapor
(Pope et al., 1994; 1997; Kring, 2007). This probably water, and over 500 Gt of CO2 produced an aerosol plume towards the stratosphere that caused more than a decade of
rain, and disruption of ocean circulationission, global cooling, acid reduced solar transm(Pope et al., 1994; 1997). Recent constraints of the global cooling event suggest that its
and deeper waters) might have lasted ing of both surface effects on ocean circulation (coolation of sulfuric and ). Acid rain derived by the formfor ~ 2 k.y. (Galeotti et al., 2004t been sufficient to acidify ght have noi sulfate aerosols, however, mnitric acids fromocean basins (D'Hondt et al., 1994). Wildfires are thought to have occurred almost
olbach et al., 1988) and worldwide due to the widespread distribution of soot (Watic hydrocarbons (Venkatesan and Dahl, 1989; Arinobu et al., 1999) in polycyclic arom spike. Based on stable carbon isotopemboundary samples coinciding with the iridiuabove-ground biomvalues of terrestrial biomass and atmarkers, and using a carbon mosphere, it has been suggested that about 18-24% ofass balance between terrestrial the
busted at the K/Pg ass could have been instantaneously comterrestrial above-ground biomated to have injected elevated concentrations of e estimildfires ar(Arinobu et al., 1999). WCO2 into the atmWolbach et al., 1988). An alternative theory hosphere resulting in an interval of greenhouse warmas recently challenged the global wildfire ing (Crutzen, 1987;
the hypothesis though; based on the discovery of carbon cenospheres derived frombustion of pulverized coal or fuel-oil droplets, it has been suggested that plete comincombusted an organic-rich target crust (Harvey et al., 2008). pact comthe im

12

Chapter I

otic recovery.iBiological and geochemical effects; bportant One of the most im

biological consequences of the impact was the shutdown of photosynthesis and the

ission the reduction of sunlight transmfromcollapse of the global food chain that resulted . However, the disruption of due to a dust cover in the stratosphere (Alvarez et al., 1980)

pact production of sulfate aerosols from the photosynthesis appears to be related to the imtarget rock (Pope et al., 1994; 1997; 1998), and to the soot produced by global wildfires pact dust theory (Pope, 2002). The reduced solar (c.f., Kring, 2007), rather than to the imated to have lasted for up to about a decade (Pope et al., ission has been estimtransm1994; 1997).

ents affected the global osynthesis in pelagic environmThe disruption of photve carbon isotopic excursion in biogenic carbon cycle as observed by a pronounced negatios et al., 1989; D'Hondt et al., 1998). carbonates worldwide (Hsü et al., 1982; Zachinifera obtained fromCarbon isotope records of planktic and benthic foram deep-sea

ace tween surfeal” isotopic gradient bbasins exhibit an abrupt disturbance of the “normand deep ocean waters at the K/Pg, assumed to represent the ceasing of organic matter

Hondt et al., 1998). This export to the sea floor (Hsü et al., 1982; Zachos et al., 1989; D'

en interpreted to characterize two different scenarios; the first one aly has beisotopic anom

ary production or an unusually low level of plete shutdown of primincludes the combiological production in surface waters after the impact (Hsü et al., 1982). This theory

has been described as the “Strangelove Ocean” model or an ocean “without life” (see
review by D'Hondt, 2005). An alternative theory, also known as the “living ocean” model
(Adams et al., 2004), involves a rapid recovery of primary production in surface waters
tter to the deep ocean (D'Hondt aafter the impact but a sustained low export of organic mpact open-ocean at the structure of the post-imhes tet al., 1998). The latter assume of large pelagic grazers or a decreased pletely altered (e.g., absencs was comecosystem

tter into aminished packaging of organic mean size of phytoplankton), resulting in a dim

Hondt et al., 1998). Independent xport to the deep ocean (D'large particles and reduced e

of the scenario, both fossil and geochemical records suggest that the evolutionary and

out 3 Ma of the ical recovery of the oceans occurred in two steps after abbiogeochems et al., 2004; Hondt et al., 1998; AdamK/Pg, (Hsü et al., 1982; Zachos et al., 1989; D'e required to plies that the time long observed recovery imhCoxall et al., 2006). T

13

Chapter I

ely long al food webs was extrem and to restore normregenerate the pelagic ecosystemediate physical effects of the impared to the immcompact. Primary productivity following the K/Pg might not have diminished to the same
extent and duration evrecords from planktic and benthic foraerywhere, though, espemicially at high-latitudnifera obtained in Antarctica indicates thes. Carbon isotope at the
(Stott and Keffects of the imepact on productivity mnnett, 1989). The recovery of the ecosystemight have been sm in Antarctica and Denmaller than at lower latitudes ark has
r, 1994). Records of been calculated to have occurred in ~ 500 ky (Barrera and Kelle and radiolarian) obtained from New Zealand indicate that siliceous plankton (diatomght have been relatively high during the first 1 Ma following the K/Pg ibioproductivity m). , 1995; Hollis et al., 2003(Hollis et al. by selective extinction; the shutdown Survival across the boundary was governedof photosynthesis affected trophic webs that more strongly depended on living plant pared to those based on detritus (Sheehan and Hansen, 1986; Sheehan et al., tter comam1996). Among marine microplankton, the groups more strongly forced to extinction
planktonic foramincluded calcareous nannoplankton (coccoliths, nannoliths, and inifera (MacLeod et al., 1997). Detritivorous organisms such as mcalcispheres) and arine
ought to have buffered extinction at the benthic scavengers and deposit feeders are the that photosynthesis was halted boundary due to their ability to survive during the timtinction appeared to have provided (Sheehan and Hansen, 1986). Selective exary producers with benthic cysts or resting paratively high survival rates to primcomstages such as dinoflagellates (Brinkhuis and Zachariasse, 1988; Brinkhuis et al., 1998; Wendler et al., 2002), and to neritic and opportunistic species (Sheehan et al., 1996), notably at high latitude regions (Keller et al., 1993). Dinoflagellate cysts do not show boundary (Brinkhuis and Zachariasse, ss the K/Pgaccelerated rates of extinction acroelled s-walled cyst-producing species dw1988), and both organic-walled and calcareouEvidence for a rapid recovery of mduring the earliest Paleocene (Brinkhuis et al., 1998; Wendler and Warine primary production has been found in neritic illems, 2002).
environmpelagic systements and close to continental ms. Isotopic and geochemaical evrgins, comidence frompared to relatively long recoveries of Caravaca, Spain, suggests that
ky (Kaiho et al., 1999). This ary production occurred in about 7-13 a recovery of prim

14

Chapter I

Hokkaido, Japan, which revealed a ker record fromarresult is consistent with a biomrecovery in algal production at about 9 ky after the K-Pg (Mita and Shimoyama, 1999).
ary production in the globally distributed rine primaHowever, the resurgence of mestones nian limae Late Maastrichtian from the Early Dboundary clay layer separating thains poorly constrained. The latter is explained by the fact that the biotic recovery remsils. crofosi classically addressed by the study of calcareous mafter the K/Pg has beenited due to poor fossil preservation and reworking Microfossil-based studies can be lim(Schmitz et al., 1992; Kaiho and Lamolda, 1999; Hart et al., 2004), and they disregard
ctures such as eukaryotic ossil struary producers lacking hard-fubiquitous primcroalgae and prokaryotic cyanobacteria. Moreover, alternative strategies of survival imsuch as mixotrophy have received little or no attention when evaluating ecological
recovery; e.g., small planktonic algae (<5 m) can account for about 40-95% of
stratified oceanic temperate waters (Zubkov andfotic layer obacterivory in the euphTarran, 2008).

. The official K-Pg boundary Global yer and the Fish ClayThe boundary clay laStratotype Section and Point (GSSP) at El Kef, Tunisia, contains all the internationally g the K-Pg (Fig. I.6; Keller et al., 1995). One of the key features accepted criteria defininrking the transition from the Late Maastrichtian to the earliest aof the boundary layer mied worldwide. At El Kef, the boundary is Danian is a clay layer that can be identifcharacterized by the presence of a 2-mm-thick red layer enriched in iridium, nickel-rich
spinels, and clay spherules, and it is assumed to represent the “fallout” lamina resulting
from the impact (sometimes also referred as “fire layer”). This layer is followed by a 50-
-poor clay which exhibits a 2-3‰ negative -thick dark, organic-rich, and carbonatecmexcursion in 13C interpreted to represent the global shutdown of marine productivity.
The K/Pg boundary is defined at the base of the red layer, also characterized by fossil “biomof Paleogene species (Karker” events such as the extineller et al., 1995). However, large differences in the thickness of ction of Cretaceous species and the first appearance
a few dwide. The thickness varies fromong sections worlmthe clay layer are found amillimeters/centimeters in pelagic environments (e.g., deep sea cores), and up to several
eters. tens of centim

15

Chapter I

Figure I.6. Geochemical profiles and other criteria defining the K/Pg boundary at El Kef, Tunisia (Keller et
al., 1995). From left to right, calcium carbonate content, 13C of bulk carbonate, iridium concentration,
abundance of Ni-rich spinels, total organic carbon content, and planktonic foraminifera extinction and
evolution. Dark gray area represents the position of the red layer, whereas the light gray area represents the
organic-rich clay layer.

ish Clay” the K/Pg is the so called “FOne of the classical sites for the study of19thboundary layer at Stevns Klint, Denm century (see Christensen et al., 1973). The renowned section at Højerup (~ 7 cark, which has been intensively studied since the m
thick) has been subdivided into six different beds according to lithology (Christensen et
lying within the fish clay (Fig. I.7). Bed-I corresponds to the Late our of themal., 1973), fMaastrichtian gray chalk, a calcareous silt with abundant bryozoans representing a typical
Late Cretaceous fossil asbase of the fish clay (often considered as blage. Bed-II at the sema transition into the red layer) is a 1-2 cm-thick gray and layered marl. Bed-III
corresponds to the red layer (sometimes dark in color), a1-2 cm-thick silty marl with
is a ents. Bed-IV and other rare elemidiumpyrite concretions and high concentrations of irrl, which contains a high ainated, organic-rich m-thick dark to light gray, lam3-5 cm carbonate. Bed-V is a light, content of clays and a relatively low content of calciumstreaked and veined marl up to 7-cm-thick, and contains white chalk fragments; bed-VI
correspond to the so called “Cerithium-limestone”, a white, sometimes slightly yellow
inated nature of the fish clay estone which overlies the fish clay. The lamindurated lim

16

Chapter I

and the lack of bioturbation (e.g., Christensen et al., 1973; Hart et al., 2004), the presence sulfate reduction (Schmitz, crobialiof pyrite, and sulfur isotopes suggestive of intense m1985), indicate deposition under oxygen-depleted conditions. Recently, Hart et al., (2004)
of the section at Højerup. It is located -thick) counterpart 40-cmdescribed an extended (~ed for e features describe samat Kulstirenden (northern part of Stevns Klint) and shares ththe fish clay at Højerup. Taking into account the relatively high organic content of the itz et al., 1988), this section offers an extraordinary opportunity to study fish clay (Schmat a high resolution. To date, lipid-based eters ical paramarkers and other geochembiomrly studies of the fish clay astudies at the K/Pg have yielded contradictory results. Esuggested that preservation of organic material might have been compromised by high
oneit, it and Beller, 1987; Meyers and Simonebacterial reworking and weathering (Sim1990), whereas more recent studies from a section in Hokkaido, Japan, provided some of
primary production after the K/Pg (Mita and the first indications of a rapid recovery ofShimoyama, 1999; Shimoyama et al., 2001), thus highlighting the potential of these
studies. In combination with more sensitive techniques such as Metastable Reaction
Monitoring Gas Chromatography Mass Spectrometry (MRM-GC-MS), biomarker studies
in the fish clay at Kulstirenden might offer a completely new perspective for our
diate aftermath of the K/Pg boundary. eunderstanding of the biotic recovery in the imm

Figure I.7. Subdivision of the Cretaceous-Paleogene
ark. Klint, Denmn, Stevns ry layer at KulstirendeboundaFigure modified from Hart et al. (2004). Subdivision of
different beds is based on the interpretation given to the fish
clay at Højerup (Christensen et al., 1973). See text for the
description of the different beds (I-VI)

17

BIOMARKER CONCEPT I.4.

Chapter I

“Biological markers or biomarkers can be defined as complex molecular fossils
derived from biochemicals, particularly lipids, in once-living organisms” (Peters et al.,
plies that the presence of a given lipid in an ntal concept imem2005). The fundaenvironmental samrelated to a particular organismple (e.g., water column, sedim or to a group of organismsents, rocks, fossil fuels, etc.) can be inhabiting a distinctive
ited arker are a limportant characteristics defining a bioment. Thus, two imenvironmber of known biological precursor(s), and a good preservation potential in numsedimentary records. Biomarkers therefore can be used for constraining biotic/abiotic
parameters of ancient environments, such as the ecology of marine primary producers,
rine versus terrestrial), and habitat of their atter (e.g., madifferent sources of organic mrine aarkers found in mLipid biomprecursors (e.g., water depth, oxygenation). sedimentary records can originate from all three domains of life (i.e., archaea, bacteria,
rally in eukaryotes (e.g., algae and higher and eukaryotes); e.g., steroids occur genee heterotrophic somplants), hopanoids are exclusively synthesized by bacteria (e.g.,bacteria and cyanobacteria), and acyclic and cyclic isoprenoid glycerol ether lipids are arkers, aea (Fig. I.8; see Table I.2 for relationships between biom the archrestricted toprecursors, and characteristic environments; Peters et al., 2005). In living organisms,
lipids serve a wide range of roles as membrane fluidity regulators, rigidifiers, barriers to
ergy sources (e.g., triacylglycerols of fatty proton exchange (e.g., steroids, hopanoids), enacids), energy acquisition (e.g., pigments), metabolism (e.g., hormones, vitamins), and
protective coating (e.g., leaf waxes). ary production from lipid rine primaIn order to reconstruct a history of m their genesis arkers fromarker proxies, one must understand the evolution of biombiomby marine phytoplankton to their preservation in marine sediments. First, organic matter
surface waters to the sea floor either by phytoplankton can be exported fromproduced bythe sinking of dense fecal pellets from zooplankton grazing or via the formation of
marine aggregates. During transit through the water column, the organic matter can

18

Chapter I

Figure I.8. Tree of life exhibiting the three main domains of life and their characteristic lipids. Bacteria and
hopanoids; pictures depict heterotrophic bacteria and cyanobacteria (http://universe-review.ca). Archaea
and archaeol; pictures depict archaeal cells (http://web.mit.edu). Eukarya and steroids; pictures depict
oups (http://www.learner.org). grdifferent phytoplanktonic

iundergo intense mall fraction (generally less than crobial degradation; usually only a sm

0.1%) of the photosynthetically-produced organic matter in surface waters eventually

accumulates in sediments (Wakeham and Lee, 1993). Of the organic matter that actually

accumulates in the sediments, biomarkers can provide information regarding depositional

conditions, diagenesis (biological, physical, and chemical alterations of organic matter at

temperatures < 50°C during burial), thermal maturation during catagenesis (thermal

peratures ~50-150°C), biodegradation, lithology, and age (Peters et al., alteration at tem

arkers can result in a series of transformations such as 2005). Diagenesis of biom

on, sulfurization, isomineralization, defunctionalizatioxidation/merisation, and

atization (e.g., Peters et al., 2005). Defunctionalization of biolipids (loss of arom

19

Chapter I

carboxylation, and functional groups) can occur due to dehydration, reduction, and deatic, most ation of hydrocarbon skeletons, either saturated or arommleads to the forcommonly preserved in geological records. The incorporation of sulfur into biolipids
during the early stages of diagenesis (sulfurization) occurs due to the reaction of
inorganic sulfur species (sulfide, polysulfides) with functional groups (e.g., hydroxyl group, double bonds), and in the absence of iron which otherwise would lead to the

formation of pyrite. This process can result in the formation of low- and high-molecular-
incorporation, olecular and intermolecular Spounds (intramweight organic sulfur comids and organic matter portant role for the preservation of liprespectively), and plays an imin organic-rich sediments from euxinic environments (e.g., Sinninghe Damsté and de
erization) s (isomerans et al., 1996a). The interconversion of isomLeeuw, 1990; Koopmarkers and configurational aturated biomgration of double bonds in unsisuch as the misomerization involving the intramolecular movement of hydrogen and methyl groups,

can provide important information regarding thermal maturity (e.g., Farrimond et al.,
1998). Molecular maturity parameters are based on the recognition of systematic changes
in biomarker composition with increasing burial depth (and thus thermal maturation);

lly stable (non-aers, a thermtwo stereoisomthey are based on the relative abundance of

ally unstable with the original biological configuration (e.g., biological) and a thermond et al., 1998). Farrim

The stable isotopic composition of lipids (especially carbon and hydrogen) comprises an additional and important source of paleoenvironmental information. For
carbon isotopes, for example, the isotopic composition of a naturally occurring biomarker

depends on the carbon source utilized, the isotopic fractionation associated with carbon and biosynthesis, and carbon budgets (Hayes, 1993). Thus, the tabolismeilation, massimstable carbon isotopic composition of a biomarker can provide important information
about its parent organism(s), carbon source, position within an ancient ecosystem, and
ples of the ental conditions (Hayes, 1993; Hayes, 2001). Specific examenvironmapplication of stable carbon and hydrogen isotopes in paleo-studies are given in following section.

20

Chapter I Table I.2.sources and Exdeampositional enviples of selected ronmebiomnt (aftarkerser (inclPeters et al., uding thos2005; e usesee d inorigi thisn thesis) as indicaal citation for further references) tors of biological
Compound Biological precursor Environment
nC15, nC17, nC19 Algae Lacustrine, marine
nC27, nC29, nC31 Higher plants Terrigenous
Mid-chain monomethylalkanes Cyanobacteria Hypersaline
Pristane/phytane (low) Phototrophs, archaea Anoxic, high salinity
C20 HBI, C25 HBI Diatoms Marine, lacustrine
C31-C40 head-to-head isoprenoids Archaea Unspecific
C27-29 steranes Algae and higher plants Various
Marine noflagellates, haptophytes thyl-cholestanes Die23,24-DimC(4-de30 24sm-nethyl) -propyl-cholestanes Chrysophyte algae Marine
4-Methylsteranes Some bacteria, dinoflagellates Lacustrine or marine
Diasteranes Algae/higher plants Clay-rich rocks
c or younger Triassiine, MarDinosteranes Dinoflagellates 25,28,30-trisnorhopane Bacteria Anoxic marine, upwelling?
C35 17,21(H)-hopane Bacteria Reducing to anoxic
2-Methylhopanes Cyanobacteria Enclosed basin
3-Methylhopanes Methanotrophic bacteria Lacustrine?
Gammacerane Tetrahymanol from ciliates Stratified water, hypersaline
18-Oleanane Cretaceous or younger, terrestrial Continent
13C-rich 2,3,6-trimethyl-subtituted aryl Chlorplants obiaceae, anaerobic green Photic zone euxinia
isoprenoids, isorenieratene, isorenieratane sulfur bacteria
21

Chapter I

PALEOENVIRONMENTAL RECONSTRUCTIONS BASED ON THE USE I.5.

MPOUND SPECIOF LIPID BIOMARKERS AND COFIC ISOTOPE

RATIOS

Molecular-isotopic signatures can comprise the only means to decipher past
ecosystems and biological inputs for organisms that leave no morphological imprint in
the geological record, and in sedimentary settings, where preservation of hard-fossils is precluded. As an example, our understanding about the crucial role of photosynthetic e scales, and ical cycles over geological timcyanobacteria in the evolution of geochemtheir role as important photoautotrophs during some OAEs would have been difficult to
arkers and stable isotopes. The combined presence of 2-methyl assess without using biomSummons et al., 1999), and bulk hopanes diagnostic of cyanobacteria (expressed as the 2-mnitrogen isotopes indicative of nitrogen fixation, has ethyl hopane index (2-MeHI);
in source for nutrient N during Cretaceous atrophy was the mbeen used to infer that diazoOAEs (Kuypers et al., 2004b; Fig. I.9.). This interpretation has been recently supported by the stable nitrogen isotopic composition of geoporphyrins extracted from black shales
stion that diazotrophic cyanobacteria were deposited during OAE2, which led to the suggemajor primary producers and contributed to the formation of black shales (Ohkouchi et
ed to have played a key ecological role at the al., 2006). Cyanobacteria also seemPermian-Triassic (P-T) mass extinction event. Biomarker evidence obtained from
Meishan sections in Zhejiang, South China, indicates that maxima in the 2-MeHI
ian-Triassic boundary ss extinction at the Permaoccurred after two episodes of faunal mal responses to the catastrophic events that caused the crobii(PTB), likely reflecting mtion data from the extinction and ecosystem changes (Xie et al., 2005). New high-resolule pport for multip 2-MeHI and provides sue locality shows even higher values ofsam e Early Triassic (Cao et al., in review),ental change in thepisodes of paleoenvironmss extinction ais mgreatly highlighting the ecological role of cyanobacteria during thevent. This aspect, however, has not yet been addressed for the mass extinction

22

Chapter I

Figure I.9. 2-methylhopanoid index through geological time obtained from oils and organic-rich sediments
(Knoll et al., 2007). Notice the increased values during Mesozoic OAEs and at the Permian-Triassic
boundary.

ch could contribute to a better understanding of the associated event at the K-Pg, whiecological reorganization and recovery. be used as paarkers can alsoBiomental “proxies”. A given leoenvironm

perature) can be reconstructed indirectly by ental variable of interest (e.g., temenvironm

using a single or multiple lipids, by combining different isomers, or from their stable

isotopic composition. Some of the most pertinent properties accessible to molecular

lied for Cretaceous OAEs, are ently app those frequingproxies for paleo-studies, includ

CO2 (seeperature (SST), sea surface salinity (SSS), oxygenation, and sea surface tem

Table I.3 for a summ. ary)ically enriched isorenieratane, derived from topce of isoFor instance, the presen

during Cretaceous OAEs, has ents depositedgreen sulfur bacteria in organic-rich sedim

been used to suggest the widespread occurrence of photic zone euxinia (PZE) during

gner amsté and Köster, 1998; Kuypers et al., 2004a; Wthese intervals (e.g., Sinninghe Daet al., 2004; Kolonic et al., 2005; Beckmann et al., 2008). Since Chlorobiaceae inhabit
water depths deeper than most algae, where concentrations of CO2 are high (chemocline),
the combined carbon isotopic composition of isorenieratane and algal markers has been
during OAEs (van Breugel et al., 2006). used to constrain the recycling of respired CO2pically enriched panied by the presence of isotommonly accomEvidence for PZE is co

23

Chapter I

gammacerane, suggesting the presence of biomass derived from marine ciliates thriving
, which provides Chlorobiaceaeocline and feeding on isotopically enriched at the chemfurther evidence for water column stratification (e.g., Sinninghe Damsté et al., 1995). The
ratio, based on the enhanced preservation of lycopane under anoxic -Cnlycopane/31g changes in palaeoxicity conditions, is also suggested as an indicator for tracinté et al., 2003). sm(Sinninghe Da

Table I.3. Selected paleoenvironmental proxies derived from lipid biomarkers
Parameter Proxy Rationale Source Reference
Sea surface Uk’37 index Unsaturation degree of Haptophyte Brassell et al., 1986;
temperature long-chain ketones algae Brassell, 1993
(alkenones)
TEX86 index Distribution of glycerol Membrane Schouten et al., 2002
lipids of dialkyl glycerol planktonic tetraethers (GDGTs) with different number of archaea
e ringsncyclopentaOxygenation, Isorenieratene, Indicators of photic zone Green sulfur Summons and
water-column isorenieratane, euxinia bacteria Powell, 1987;
stratification aryl isoprenoids Koopmans et al.,
1996b
Gammacerane Present in stratified, Ciliates ten Haven et al.,
index anoxic, and/or 1989; Sinninghe
hypersaline environments Damsté et al., 1995
Extended hopanes Present in euxinic and/or Bacteria de Leeuw and
(homohopane hypersaline environments Sinninghe Damsté,
index) 1990; Peters and
Moldowan, 1991
Lycopane/n-C31 Preferential preservation Ly = marine Schulte et al., 2000;
ratio of lycopane under anoxic photoautotroph? Sinninghe Damsté et
conditions n-C31 = land- al., 2003
plants
Phytane/pristane Degradation of phytol marine ten Haven et al.,
ratio under anoxic and oxic photoautotroph 1987
conditions Partial 13C alkenone Knowledge of isotopic Haptophyte Freeman and Hayes,
pressure of 13C phytane fractionation factors are Aquatic algae 1992; Pagani et al.,
CO2 (CO2) 13C sterols needed Aquatic algae 2005; Sinninghe
sté et al., 2008 DamSea surface D alkenones Salinity effect on Haptophyte Schouten et al., 2006
salinity fractionation algae
D n-C17 Aquatic algae Pagani et al., 2006

, nierateneIsoregenation, Oxywater-cstratification olumn isoaryrenl isopieratanrenoie, ds
Gammacerane x ndei nes d hopaExtendei(hndeomx) ohopane
Lycopane/n-C31
ratio ne Phytane/pristaratio 13C alkenone Partial pressure of 13C phytane
CO2 (CO2) 13C sterols
Sea surface D alkenones
salinity D n-C17

24

Chapter I

The carbon isotopic fractionation associated with the photosynthetic fixation of

CO2 is significantly correlated with the concentration of dissolved CO2 in the

entary records, in position of lipids found in sediment. Thus, the isotopic comenvironm

combination with empirically-obtained isotopic fractionation factors of lipids in

CO2 in ancient ospheric biological precursors, can be used to reconstruct changes in atm

ents (Freemenvironmapproach has been used to calculate high an and Hayes, 1992). This

CO2 levels for the Cretaceous greenhouse climate (Freeman and Hayes, 1992; Kuypers

et al., 1999; Bice et al., 2006; Sinninghe Damsté et al., 2008), which may be related to the

elevated reconstructed SST of Cretaceous oceans (Schouten et al., 2003; Forster et al.,

2007). CO2 reconstructions for the Cenomanian-Turonian OAE2 based on the

position of algal- and terrestrial-derived pound-specific carbon isotopic comcom

e presence of a large and abrupt fall in arkers, have been used to suggest thbiom

atmospheric CO2 concentrations which might have been responsible for the invoked

plants on land during the Cretaceous (Kuypers et al., 1999; Sinninghe expansion of C4

té et al., 2008). smDa

onstrated that the stable hydrogen isotopic ents have demCulture experim

fractionation associated with the synthesis of long chain alkenones in hapthophyte algae

is linearly correlated with salinity, suggesting a potential use for salinity reconstructions

bination with other is approach, in comhents (Schouten et al., 2006). Tin ancient environm

proxies, has reflected abrupt variations in SSS during the Late Holocene freshening of the

ation of Mediterranean mBlack Sea (van der Meer et al., 2008), and during the for

arkerse approach has been applied to biomsapropels (van der Meer et al., 2007). The sam

with a less specific source such as n-C17 alkane to reconstruct hydrological changes in the

Arctic ocean during the Paleocene-Eocene thermal maximum (Pagani et al., 2006).

ains less constrained. us oceans remHowever, its application for Cretaceo

25

I.6.RESEARCH FOCI AND OBJECTIVES

Chapter I

Through the combined use of molecular biomarkers, stable isotopes, and bulk
eters, the general scope of this thesis is to study the response of ical paramgeochemmarine planktonic ecosystems to extreme environmental stress during the Cretaceous and
at the K-Pg boundary.

research topics with specific goals: inaThis thesis can be divided into three m

of The Cenomanian-Turonian Boundary OAE-2 at the Levant carbonate platform 1.Central Jordan.  The main objective of this project is to assess the ecological and geochemical
consequences of anoxia/euxinia during OAE2. panied by ecological I asses whether episodes of anoxia/euxinia were accom changes in the community of marine primary producers, i.e, successions
between algae and photosynthetic bacteria.  Additionally, it is aimed to construct a conceptual model illustrating the
mechanisms leading to the development of oxygen depletion and the
ents. deposition of organic-rich sedim

2. The Coniacian OAE-3 at the eastern equatorial Atlantic (ODP Site 1259, Demerara
). Rise off the coast of Surinam This project aims to unravel the oceanographic and climatic dynamics leading
oduction through the use of compound-ary prrine primato variations in mrine- and terrestrial-derived aspecific stable carbon and hydrogen isotopes in mn-alkanes. An especial emphasis is giving to the role of upwelling and
ary production. tained high primcontinental runoff on sus Additionally, it is aimed to study the effects of varying primary production on
ents. the eccentricity-driven deposition of carbonate- and organic-rich sedimTo achieve this, a sedimentary sequence covering and entire cycle of
ied. alternated facies is stud

26

Chapter I

3. The Cretaceous-Paleogene mass extinction event: The Fish Clay section at Stevns
Klint, Denmark. rine photosynthesis recovered rapidly during the aI test the hypothesis that m immediate aftermath of the K/Pg after incoming solar radiation levels returned
ost entirely by using al”. As yet, this topic has been addressed almto “normmposition, whereas crofossils and their stable carbon and oxygen isotopic coims without hard-fossil no detailed recovery of photosynthetic organismarkers in a high-resolution onic biomstructures exists. By studying phytoplanktar, I expect sh Clay at Denmi exceptionally thick section of the Frecord of anary production in order to provide a variations in primto resolve short-termehensive view of the biotic recovery at the K-Pg. prmore com

CONTRIBUTIONS TO PUBLICATIONS I.7.

This thesis includes the full version of three manuscripts in different stages for
publication in international, peer-reviewed journals. Chapter II is accepted for publication
pending moderate revisions; chapter III is the first draft of a manuscript in preparation;
ission. chapter IV is ready for subm

CHAPTER II – full manuscript ges across the idence of environmental and ecological chanr-isotopic evMolecula Cenomanian-Turonian boundary in the Levant Platform of central Jordanndler, Arne Leider, Hans-Joachim Kuss, Roger E. Summons, eJulio Sepúlveda, Jens Wand Kai-Uwe Hinrichs d laboratory work for the emJulio Sepúlveda developed research strategy, perforpreparation and analysis of samples by GC-MS, MRM-GC-MS, and GC-irMS, processed
ndler developed research strategy, eWand interpreted data, and produced figures. Jens performed fieldtrip and sampling, and produced biostratigraphy and bulk geochemical
data. Arne Leider assisted with laboratory work for the preparation and analysis of

27

Chapter I

of his undergraduate thesis. ples for GC-MS and GC-irMS, and processed data as partsam

pling. ed fieldtrip and sam Kuss developed research strategy, and performHans-Joachimons facilitated his laboratory at MIT and contributed with data Roger E. Summ

interpretation. Kai-Uwe Hinrichs developed research strategy and contributed with data interpretation. Julio Sepúlveda wrote the paper with contributions from Kai-Uwe ndler. All co-authors provided editorial eoger E. Summons, and Jens WHinrichs, Rcomments. Accepted for publication with moderate comments (August 2008) in Organic

Geochemistry

aft of full manuscript rCHAPTER III – first d

ntic l Atlae Late Cretaceous EquatoriaOceanographic and climatic dynamics in th

proach into the formation of (ODP Site 1259): a compound-specific stable isotope ap

organic-rich sediments ider, and Kai-Uwe Hinrichs eJulio Sepúlveda, Arne Led part of the laboratory Julio Sepúlveda developed research strategy, perform

ples by GC-MS and GC-irMS, interpretedsis of samn and analywork for the preparatioted the laboratory work for the preparation data and produced figures. Arne Leider conducples for GC-MS and GC-irMand analysis of samS, and contributed with data processing

ster thesis. Kai-Uwe Hinrichs developed research strategy and a his mas part of

contributed to data interpretation. Julio Sepúlveda wrote the paper with contributions Kai-Uwe Hinrichs. fromFirst draft of manuscript in preparation for submission to Earth and Planetary

Science Letters

28

CHAPTER IV – full manuscript

Rapid Resurgence of Marine P

Extinction Event

Chapter I

after the Cretaceous-Paleogene Mass oductivityr

ons, and Kai-Uwe Hinrichs Julio Sepúlveda, Jens Wendler, Roger E. Summ

Julio Sepúlveda developed research strategy, performed fieldtrip and sam

pling,

ples for GC-MS and rk for the preparation and analysis of samoed laboratory wperform

MRM-GC-MS, processed and interpreted data, and produced figures. Jens W

guided fieldtrip and sam

pling, and provided geological background for data

ndler e

tated his laboratory ons developed research strategy, faciliinterpretation. Roger E. Summ

. Kai-Uwe Hinrichs developed research with data interpretationted contribuat MIT, and

mstrategy, perforpling, and contributed with data interpretation. Julio ed fieldtrip and sam

all co-authors. Sepúlveda wrote the paper with contributions from

ission to Manuscript ready for subm

Nature 29

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38

Chapter I

39

40

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CHAPTER II

Chapter II

Molecular-isotopic evidence of environmental and ecological changes ary in the Levant Platform of across the Cenomanian-Turonian boundcentral Jordan

Julio Sepúlveda1,2,*, Jens Wendler3,§, Arne Leider2, Hans-Joachim Kuss3,
2 4, and Kai-Uwe HinrichsRoger E. Summons

008) ents (August 2oderate comm with mAccepted for publication Organic Geochemistryin

1International Graduate College – Proxies in Earth History (EUROPROX), University of Bremen, 28334
any en, GermBrem2Organic Geochemistry Group, Department of Geosciences, University of Bremen, 28334 Bremen,
any Germ3Geochronology Group, Department of Geosciences, University of Bremen, 28334 Bremen, Germany
4CaDepambridrtmge MA 0213ent of Earth, Atmosphe9, USA ric and Planetary Sciences, Massachusetts Institute of Technology,

*Corresponding author: Tel.: +49 421 218 65742; fax: 49 421 218 65715. E-mail address: sepulved@uni-
bremen.de (J. Sepúlveda)
§UnivPresent address: Institute ersität Jena, 07749 Jenaof , GermEarth any Sciences, Faculty of Chemistry and Earth Sciences, Friedrich-Schiller-

Keywords: Cretaceous, Cenomanian, Turonian, Jordan, oceanic anoxic event, euxinia,
arkers, stable isotopes, cyanobacteria. lipid biom

41

oxic Event 2anian - Turonian Oceanic AnCenom

ABSTRACT

We evaluated the structure of planktonic communities and paleoenvironmental
conditions throughout the Cenomanian-Turonian Oceanic Anoxic Event (OAE2) by
studying bulk geochemical properties and the molecular-isotopic composition of source-
Levant Platformspecific hydrocarbons from organic-rich sedim, Central Jordan. High concentrations of desmeethyl and 4-mnts deposited in an intra-shelf basin at the ethyl steranes
as well as dinosteranes indicated that marine algae including dinoflagellates were the
main primary producing organisms. The presence of 2-methyl hopanes and low 15N

the contribution of topically enriched aryl isoprenoids, evidenceddition to isovalues, in adely. Changes in the relative ectivand green-sulfur bacteria, respN-fixing cyanobacteria contribution of biomarkers revealed successions in planktonic communities associated
The OAE2 interval was n stratification.with sea level changes and water colum waters, and a n, anoxic bottome water columcharacterized by a strong stratification of thdeep chemocline, as evidenced by high gammacerane and homohopane indices, and the
isorenieratane and its dabsence of photic zone euxinia merivatives ina post-OAE black shales point to a shoaling of the rkers, respectively. However, the presence of
chemocline and protracted euxinic conditions that extended into the photic zone. These
exceptionally high abundance of chlorophyll-ents were also characterized by an sedimderived pristane and phytane (up to 2 mg g-1 TOC) likely as a result of high primary
tter preservation. Our results provide further evidence for the aproduction and organic mary production during the portance of cyanobacteria and nitrogen fixation fueling primimdeposition of black shales, not only in open ocean settings but also in stratified/anoxic s during OAE2. continental platform

42

II.1.INTRODUCTION

Chapter II

black shales in coastal and openes of widespread deposition of organic-richTimtinental seas are known as Oceanic Anoxic Events as well as in epiconocean areas,inent during the Mesozoic and appear (OAEs; (Jenkyns, 1980)). They are especially promhigh sea suto coincide with extreme climrface tematic and operatures (Bice et al., 2006; Forster et al., 2007; Schouten et al.,ceanographic conditions, such as exceptionally
2003), rising sea level (e.g., (Arthur et al., 1987); (Schlanger et al., 1987)) and changes in oceanic circulation (e.g., (Erbacher et al., 2001)). OAEs are related to exceptional
episodes of increased marine primary production, the depletion of oxygen and massive
zones, increased rates of organic carbon burial and a umexpansion of oxygen minimconsequent perturbation of the global carbon cycle evidenced by a marked positive
(Schlanger et al., carbon isotopic excursion (CIE; (Jenkyns, 1980); (Arthur et al., 1987); y producers (e.g., (2001; Kuypers et al., ar1987), and perturbations in the ecology of primrine productivity due to a1999; Kuypers et al., 2004b; Leckie et al., 2002)). Enhanced mn eased preservation due to water columan increased supply of nutrients and incr

stratification are among the main proposed models to explain the deposition of black
rine ashales during OAEs (e.g., (Meyers, 2006)). However, the relationship between mtter under ad preservation of organic mproductivity (e.g., (Kuypers et al., 2002b)) ananoxic conditions (e.g., (Sinninghe Damsté & Köster, 1998)) remains contentious (Mort
et al., 2007a). ary producers can provide a rine prima changes in communities of mDecipheringditions controlling primary production, ental connmirobetter understanding of paleoenvnutrients and carbon cycling during these events. Here, the use of source-specific lipid
to be of crucial position have demonstrated arkers and their carbon isotopic combioms without hard skeletons such as portance in deciphering the role of organismimons & Kenig, 2001); prokaryotes (Kuypers et al., 2001; Kuypers et al., 2004b; Simitrescu(Dum al., 2006); (Knoll et al., 2007). Archaeal 2005); (Ohkouchi et & Brassell,tter present in ainant component of the organic mains have been reported as the domremearly Albian black shales deposited during the OAE1b in the North Atlantic Ocean, and

43

oxic Event 2anian - Turonian Oceanic AnCenom

blage (Kuypers et al., of the planktonic assemportance as constituents thus reflect their im2001; 2002a). On the other hand, nitrogen-fixing cyanobacteria have been suggested to be a major autotrophic planktonic group in open ocean and costal areas during some
OAEs, and are responsible for supplying nitrogen for other phytoplanktonic production itrescu & Brassell, 2005); (Ohkouchi et al., 2006); (Kuypers et al., 2004b); (Duma et al., 2008). (Kashiyamical multi-proxy approach, we constrain the relationship between Using a geochemental conditions associated with OAE2 (e.g., nutrient supply, euxinia, and paleoenvironmary producers in an intra-shelf basin in sea level changes) and the paleoecology of prim ly, we evaluate the role of. Particularthe southern Tethys ocean, i.e., the Levant Platforminated by N-fixing cyanobacteria in fueling algal production in this coastal setting dom. oxygen-depleted waters and loss of nitrogen via denitrification

Prior StudiesII.1.1.

entological and stratigraphical description (including A detailed geological, sedim has been provided ctions further north and south) of the Levant Platform seplatform 2003). Biostratigraphic, paleontological and lithological elsewhere (2005; Schulze et al.,panion paper e present study are part of a comanalyses of the outcrop sections used in th(Wendler et al., in review). The Levant carbonate platform extended over the passive
margin of the Arabo-Nubian shield during Cenomanian-Turonian (C-T) times. The
basin (Karak-Silla m of an intra-platforresent depositsoutcrop sections in this area repBasin), which was only intermittently disconnected from the open marine environment as
evidenced by the formation of occasional evaporites (Kuss et al., 2003). The prevailing ent while restricted water tional environment a neritic deposi carbonates documplatform ent characterized by dysoxic/anoxic episodescirculation and a deep subtidal environmk inous blacoccurred during transgressions and OAE2 (Schulze et al., 2005). Bitumbenthic foramshales, thin laminations, organic-rich minifers are all consistent with the prevalence of dysoxic conudstones, and the presence of small opportunistic ditions (Schulze
et al., 2005).

44

ETHODS ALS AND MMATERIII.2.

II.2.1.Samples

Chapter II

The outcrop sections, Ghawr Al Mazar (GM3) and Kuthrubbah (KB3) are about
apart (Fig. II.1.) and approxim30 km the paleo-coastline. distant fromately 150 km tra-platform basin rim and is characterized, fromnal to the iSection GM3 was proximinous ites, transitioning into a platy, bitum to top, by green clays and marls, dolombottomlimestone beds, brown marly clays, grey marls capped by limestones at the top (Fig.
basin and mII.2.). Section KB3 represents deeper parts of the Karak-Silla intraplatforples were l of 150 samales. A totaprised of an extended series of organic-rich black shcom the 36 m thick GM3 C-T boundary section (31°15’34” N; 35°35’41” E; collected from ical analyses, 150 were. For bulk geochemple spacing of 10 to 25 cmFig. II.1.) at samanalyzed for total organic carbon (TOC) and 118 for carbonate carbon isotopes (13Ccarb)
((Wendler et al., in review)), whereas 38 were analyzed for organic carbon (13Corg) and
nitrogen (15Norg) isotopes. For lipid biomarkers, we selected 8 samples of organic-rich
T Boundary, and -3 section spawning the Late Cenomanian, the C the GMsequences from black shales, dark fromEarly Turonian (127-239; Table II.1.). Their lithology variedmarls, and laminated bituminous marls (Table II.1.), whereas their deposition occurred
rdlze et ence (Schu order sequduring variable sea-level conditions, spanning roughly one 3al., 2005); J. Wendler, pers. commun.). Additionally, two organic-rich black shales, taken
thick KB3 section (31°09’13” N; 35°36’06”25 m the Early Turonian interval of the fromAE2 an expanded counterpart of the post-Oples represent E) were analyzed. These samun.). ple 238 in GM3 section (J. Wendler, pers. commblack-shale interval typified by sam

45

oxic Event 2anian - Turonian Oceanic AnCenom

Figure II.1. a) Study area showing the location of sections GM3 and KB3 (filled circles). Insert represents
an expanded view of the Arabian Peninsula. b) Configuration of the Levant Platform during the Late
2000). ., (after Philip et alanian Cenom

rements Bulk measuII.2.2.

les were cleaned by removing their outer parts with a saw and then pmRock sa

13

crushed to powder in an agate mortar. TOC and 13Ccarb measurements are described

ples prepared for carbonate-freeelsewhere (Wendler et al., in review). Powdered sam

organic carbon and nitrogen isotopes were decalcified using solvent-washed HCl 10%

until no further reaction was observed. Subsequently, the residues w

re rinsed with e

solvent-washed Milli-Q water, centrifuged, and dried for 72 hours at 60 °C. The isotopic

analyses were carried out using a Finnigan MAT Delta Plus coupled to a Carlo-Erba

ent analyzer at the University oelemen. Bremf

46

Lipid analysis II.2.3.

Chapter II

Rock samples were cleaned further by sonication for 5 minutes in solvent-rinsed

Milli-Q water. Samples were then dried overnight at 60 °C. Between 5 and 10 g of rock

ples were extracted in a ogenized. Samwere ground to powder in an agate mortar and hom

MARS microwave system (CEM Corporation) using a solvent mixture of

until the solvent extracts (at least 3x,ethanol (DCM:MeOH) 3:1 ethane:mdichlorom

became colorless) at 80°C for 20 minutes. Before extraction, 2 g of hexatriacontane,

ethyl octadecanoic acid were added as thyl esther, 1-nonadecanol and 2-mebehenic acid m

biid extracts (TLE) were cominternal standards. Total lipned after centrifugation and

concentrated under a stream of nitrogen using a Turbovap. TLEs were then separated into

asphaltenes and maltenes using small Pasteur pipettes filled with combusted glass wool
lfur was ental su, and eluted with hexane and DCM, respectively. Elemand NaSO4ltenes using acid-activated copper (4 N HCl, rinsed consecutively a the moved fromrem

n-with Milli-Q, MeOH, DCM, and ltenes were fractionated into four ahexane). The m

sorbent; gfractions of different polarities using Supelco LC-NH2 glass cartridges (500 m

atography-coupled gas chrom(Hinrichs et al., 2000)). Hydrocarbons were identified by

mass spectrometry (GC-MS) using a Thermo Electron Trace instrument equipped with a

film thickness), and n (0.32 mm ID, 0.25 m DB-5MS fused silica capillary colum30-m

ture program used was: injection at 60°C, perausing helium as the carrier gas. The GC tem2 min. isothermal; from 60°C to 150°C at 15°C min-1; from 150°C to 320°C at 4°C min-1;
20 min. isothermal. Identification of compounds was based on GC retention times and

mre reference data. parisons to literatuss spectral coma

-MS in Catics were also analyzed by GSaturated hydrocarbons and arommetastable reaction monitoring (MRM-GC-MS) and selected ion monitoring (SIM-GC-

a mass ass AutoSpec-Ultimused a Micromodes respectively. For this we MS) m

spectrom atograph. The GC was fitted witht 6890N gas chrometer interfaced to an Agilen

a DB-1 fused silica capillary column (60 m; 0.25 mm I.D.; 0.25 μm film thickness; J &

W Scientific) and the carrier gas was helium. The GC temperature program used was:
injection at 60°C, 2 min. isothermal; from 60°C to 150°C at 10°C min-1; from 150°C to
315°C at 3°C min-1; 24 min isothermal. The AutoSpec source was operated in EI-mode at

47

oxic Event 2anian - Turonian Oceanic AnCenom

250° C, 70 eV ionization energy, and 8 kV accelerating voltage. Data were acquired and ass Ltd.). processed using MassLynx 4.0 (MicromCompound-specific isotope analyses were performed by gas chromatography-
combustion-isotope ratio mass spectrometry (GC-C- irm-MS) consisting of a Thermo
o ace to a Thermo Electron GCC-II-interfElectron Trace GC coupled via a ThermElectron Delta Plus XP mass spectrometer. GC conditions were identical to those
described above. Carbon isotope ratios are reported as  values (13C, in ‰) relative to
the VPDB standard. Multiple CO2-pulses of known 13C value at the beginning and end
n (~ 0.22‰ or better) was ent precisioof each run were used for calibration. Instrumregularly checked by injecting a mixture of n-alkanes (n-C15 to n-C29) with known
isotopic compositions.

er cleavage ation and ethDesulfurizII.2.4.

d in asphaltenes and polar fractions of emRaney nickel desulfurization was perforin goal was aselected samples at MIT as described elsewhere (Grice et al., 1998b). Our mto evaluate preferential preservation of phytane due to sulfurization during early

diagenesis. 2 g of 3-n-Octadecylthiophene (CHIRON AS), 7-methylbenzo[b]naphthol
[2,3-d]thiophene (CHIRON AS), and hexatriacontane were added as internal standards. mns all silica colu smcentrated, loaded inThe residue was extracted 3x with DCM, con eand separated in five fractions using the following elution sequence: a) 3/8 dead volum(DV) of hexane for saturated and unsaturated hydrocarbons; b) 2 DV of hexane/DCM 8/2 /EtOAc 8/2 for alcohols; e) atics; c) 2 DV of DCM for ketones; d) 2 DV of DCMfor aromscan mode on a Microm2 DV of /EtOAc for acids. Hydrocarbons and aromass AutoSpec-Ultima as described above for MRatics were analyzed by GC-MS in full M-GCMS, over
ss range of 50 to 600 Daltons. Data were acquired and processed using MassLynx aa m4.0 (Micromass Ltd.). Ether bond cleavage was carried out in selected polar fractions as described evaluate the potential contribution of et al., 1998), in order toonselsewhere (Summn- extracted with ucts were subsequentlyphytane from archaeal diethers. Cleavage prodhexane (3x) and n-hexane/DCM 4/1 (2x) using a Pasteur pipette. Samples were loaded

48

Chapter II

ane -hexnns and separated into hydrocarbons and polar fractions using onto silica columbons were analyzed by GC-MS as described ts, respectively. Hydrocarand EtOAc as eluen

above for desulfurization products. 2 for as standardg of hexatriacontane was used

n. quantificatio

RESULTS AND DISCUSSION II.3.

emistry Bulk geochII.3.1.

The TOC content varied between close to zero and 3.10 % along the section with ters (Fig. II.2.). The TOC content of ethe highest values found at 57-70 and 75-79 mparatively higher than at GM3 (up to 6.8%; Table II.1.). ples from KB3 was comsam13Ccarb in GM3 fluctuated between -4 and +4‰ with a sharp negative excursion at the
lower part of the section, followed by a marked positive carbon isotopic excursion (CIE)
between 55 and 70 meters (grey area in Figure II.2.). Rather uniform values around +1‰
characterized the post-CIE interval. 13Ccarb values of samples from KB3 section were
slightly lower than those from GM3 (Table II.1.). The 13Ccarb record was correlated with
the Pueblo (USA) stratotype section that defines the position and duration of 500-600 ka
of OAE2 (gray area in Figure 2; (Wendler et al., in review)). The 13Corg varied between -
ser resolution (Fig. II.2.), the organic values track the 27 and -22‰. Despite its coar13 record reasonably faithfully with a negative CIE to values around -26‰ just prior Ccarbto the OAE and a positive CIE to values around -22 to -25‰ in the OAE. The 13Corg in

KB3 samples displayed values around -25‰ (Table II.1.). The C reflects a perturbation

in the global carbon cycle and encodes thination by phytoplankton e C-isotopic discrimduring photosynthesis under condenhanced global burial of organic maitions of increased marine produtter during OAE2 (Arthur et al., 1988; Scholle & ctivity and the
Arthur, 1980).

49

oxic Event 2anian - Turonian Oceanic AnCenom

orgN15c -0.6 -1.2 1.7 1.1 0.1 0.0 -0.1 0.9 2.0 0.5
carb13C -25.0 -25.3 -23.9 -24.2 -24.4 -24.3 -24.6 -23.3 -24.1 -26.1
carb13C 1.3 0.8 5.5 2.2 3.2 2.1 2.4 2.8 4.4 2.0
bax Tm(°C) - - 425 425 433 432 432 433 436 462
bCaCO3 (%) 85.9 86.4 49.9 54.8 59.0 66.9 64.6 70.0 63.5 18.3
TOC (%) 6.5 6.9 1.3 2.9 0.8 1.8 1.9 1.5 3.1 0.8
Relative Stratigraphy Post-OAE2 Post-OAE2 Post-OAE2 Post-OAE2 Post-OAE2 Post-OAE2 OAE2 OAE2 OAE2 Pre-OAE2
Lithology black shale black shale inous brown marl inated, bitumlaminous brown marl inated, bitumlaminous brown marl inated, bitumlaminous brown marl inated, bitumlam clainous dark-brown marlybitum stoneyrl abrown mdark-brown marl black shale
ical characterization ochem Geis study. hnts used for tesedimof
aDepth s) eterm( 18.6 17.4 77.17 76.87 76.60 74.95 69.60 62.73 58.36 52.40
Table II.1.ple Sam KB3-70* KB3-68* GM3-239 GM3-238* GM3-237 GM3-232 GM3-213 GM3-188 GM3-159 GM3-127

is study. hnts used for tesedimof Lithologyical characterization

d cludexbe enot n n canic nitrogeterial although inorgaanic m orgastly

o. cpers, rndleWe interval (J. e timemun.) mm
saesenting theprples reponding sam*Corresapoindicate low ers bLow numbd data) (unpublishendlerJens Wecsadecalcified on d Measureterial although inorgaanic m orgastlyont mrepreseumed to les and asspm
outcrop. e hsition in t

50

Chapter II

d y anogloof section lefton thephic lr et al (in rtical bars ack lbr ojaed for su= tract; TST t; tracsm = bit; gn isistry hem nic kl bufc nied decalcifi apic ote iso E2. C of orga Lith13C o13N of
.2.Figure IIistry hemk geocbulrs rtical bae VGM3.the lithographic o refer tpanelstratigrae ncand sequeand sea leveisions, vsubdindleeWtracks of Filled vereview). mt four represenunits with eight shale (BS) 39) -227les (1psam. HST arkerslipid bioms tract; LST mehighstand systsm= lowstand syste= transgressive systeomite ulod = olodGeoc bed. umgyps follows: a) indicated as total orgaofntage percecarbon;carbonates; c) matter; d)ples. The grey aresamitivsope ts threpresenfining OAexcursion de
15 b)

51

oxic Event 2anian - Turonian Oceanic AnCenom

The 15Norg record fluctuated between -1 and +2‰, with positive values prior to
the CIE and towards the top of the section, and the most depleted values during OAE2
(Fig. II.2.). InKB3 samples 15N values ranged between -1.2 and -0.6‰ (Table II.1.).
The 15N of bulk sediments has been used for assessing the occurrence of nitrogen
fixation (e.g., (Kuypers et al., 2004b); (Ohkouchi et al., 2006)), and denitrification (Jenkyns et al., 2007) during the deposition of Cretaceous black shales. Due to the low N-
isotopic fractionation of cyanobacteria during N2 fixation, 15Norg values between 0 and -
3 ‰ are characteristic of sediments with high predominance of cyanobacterial markers
a et al., 2008). On the other (Kuypers et al., 2004b); (Ohkouchi et al., 2006); (Kashiyaments as observed in rine sedimahand, denitrification leads to enriched values in mQuaternary sediments of upwelling areas (e.g., (Ganeshram et al., 2000)). Although
15Norg is influenced by multiple factors, we can surmise that diazotrophy was an
2 However, the scattered nature of the portant process in the study area during OAEime (Fig. II.2.). portance of this process varied over timdata suggests that relative im

II.3.2.ical sources ons and their biologHydrocarb

The aliphatic fraction of the samples from GM3 was dominated by desmethyl
steranes, 4-methyl steranes, triterpanes, n-alkanes, branched alkanes and phytane and
ances varied greatly through the section their relative abundpristane (Fig. II.3.). However, the KB3 section, exhibited a le 238, as well as coeval samples frompm(Fig. II.4.). Sanor contribution of hopanes, a irized by a markers characteunique distribution of biompounds, and a high abundance high abundance of saturated and unsaturated steroidal comarbon oncentration of hydroced cof Ph and Pr (Figs. II.3., II.4.). The total summcompounds displayed maximum values in sample GM3-238 (one order of magnitude
ples) (Fig. II.4.). higher than other sam

52

Figure II.

3.

Total ion chromatogram

s from GC-MS analy

sis

fiof

Chapter II

ve characteristic aliphatic fractions from

the GM3 and KB3 sections. a) sample GM3-127 located below the isotopic excursion of OAE2; b) sample

ted in the mGM3-188 loca

iddle of the isotopic excursion; c) sample GM3-237 positioned above the

isotopic excursion; d) sample GM3-238 positioned above the isotopic excursion and with a characteristic

high abundance of pristane and phytane; e) sample KB3-68, equivalent to sample 238 in GM3 and also

exhibiting high pristane and phytane. Inserts in figures b and d show the area dominated by steranes and

hopanes in greater detail. See legend for compounds identification and Table 1 for identities of samples.

53

oxic Event 2anian - Turonian Oceanic AnCenom

GM3 Figure IIsection. .4. ReNumlative percebers innt the right reage contripresebution nt the cof moancein comntration pounof hyd classes drocarbons stafound innda the alrdized by TOiphatic fractions in C.

Normal, branched and isoprenoid alkanes II.3.2.1.

na-Alkanes were mted by Cinly represen

ologues and their distribution hom35 15-

through the section did not show a clear trend, with neither unim

54

odal nor bimodal

Chapter II

distributions dominating. In general, concentrations of short-chain homologues (< n-C20;
SC) were low compared to mid- (n-C21-25; MC) and long-chain (> n-C26; LC)
counterparts (Table II.2.), except for the majority of non-OAE samples which maximized
at n-C18 or n-C19. LC maximized at C27, C29, and C31 and exhibited a slight odd-over-even
mapredomrked even-over-odd predominance, except for sample 238 with no preference, whereas MC exhibited a inance as evidenced by their carbon preference index (CPI
in Table II.2.). Samples from KB3 showed mostly SC and MC homologues. SC n-alkanes
are mostly derived from aquatic algae and microorganisms (Cranwell et al., 1987),
whereas LC homologues with a pronounced odd-over-even predominance are
characteristic of epicuticular waxes of vascular plants (Eglinton & Hamilton, 1967). Thes, the high abundance of those in the Ceference of LCobserved slight odd-over-even pr15-25 range and the absence of other biomarkers typical of terrestrial contribution (e.g.,
oleanane), point to a mainly mixed algal/microbial origin of the organic matter.
the latter was almost absent in most of the samAcyclic isoprenoids were represented by phytane (Ph) and pristane (Pr), although ples from GM3 section. These two
pounds were unusually concentrated in sample 238 representing up to 33% of thecom-1signal was widespread with the samtotal hydrocarbon fraction and accounting up toe patte 2.2 mg g TOCrn observed in corresponding sam (Figs. II.3., II.4.). This ples from
scuss this further in section 3.6. dieKB3. WTwo series of odd-carbon numbered C19-25 5,5-diethylalkanes and C19 and C21 3,3-
z 127 and 99, /using the mples 232 and 237 diethylalkanes were detected in samrespectively (Fig. II.3.). Series of branched alkanes with one or two quaternary carbon
ples and have been suggested to s (BAQCs) are commonly found in geological samatomr a oial; see (Kenig et al., 2003); (2005) fost likely bacterhave a biological source (monly used plastic bags comminants fromr source as contamdetailed review), although theiterial has been reported recently (Grosjean & Logan, apling of geological mduring sam2007). C18 and C20 alkylcyclopentanes were also found in samples 232 and 237 (Fig.
contamII.3.). Such comination by plastic bags (Grosjeanpounds have been also suggested to originate as the result of & Logan, 2007). An even carbon numbered
series of C18-22 3-methyl alkanes was observed in few samples, although most
ple 232. inently in samprom

55

oxic Event 2anian - Turonian Oceanic AnCenom

and cultures and are thus used as biomarkers for these ts ay found in cyanobacterial monlthyl alkanes are commeMono m
1995b); (Köster et al., 1999)). s (e.g., (Kenig et al., organism

d. d. d. d. d. d. AI n.e) Tm08 ++ 14 ++ 19 ++ 08 n.27 n.06 n.13 n.12 n.(Ts +Ts/ 0. - 0.0.0. 0.0. 0. 0.22R) hopanes 22S/(22S +  20 19 11 29 27 14 09 21 21 31)) 0.0.0.0.0.C0.0.0.0. 32+C3020R) steranes +C28+C20S/(20S + 26(C 08 08 05 09 04 06 04 09 07 29x 0.C2 )) / ((-ster 33.6 0..5 0..5 0..4 0..7 0..4 0..6 0..5 0..0 dC29% +C31
60+Cun.) 29m+Cm-ster 27o.8 58.3 38.2 46.8 31.5 28.5 26.5 50.9 37.8 . c28)+(CC% pers

c-ster 27Cb 25-35% .1 2152.8 2245.3 2132.2 2239.5 202020.2 19.7 2239.0 2227.8 3337, rndleWe31+C29+C27+C25((C) R + S  -2927 / (CR) R + S  -2927 / (CR) R + S  -2927 / (CRtectedet d/ interval (J. e timem  
no2 3 4 4 2 0 2 aCPI + S + S + S
al., 1993)) = 1.1.1.1.1.1.- - d., .15-3527-35292827 sa4 1.-C-C4 6 4 2 2 6 t; +, present; nnn0.0.0.0.0.0. (Marzi et - - esenting the/ -C-C Ceranes =t s Ceranes =t s Ceranes =t s
arker ratios. 15-3521-26anPI2;2 0.4 3 5 2 4 3 prund292827nn0.0.0.0.0.0.- - x (C C C Comples reofofof/ Indes = ++, ab15-3515-20bution bution ected bibution

-Cn-Cn - - 0 0.2 0.3 0.3 0.0.0 0.1 0.0 0. rence feiiri. SelTable II.2ple Sam *07-KB3 *86-KB3 932-3GM8* 32-3GM 732-3GM 232-3GM 312-3GM 881-3GM 951-3GM ponding sam*CorresaCarbon PrebRelative contrcRelative contdRelative contrerenoidAryl Isop

56

SteroidsII.3.2.2.

Chapter II

All bitumens presented abundant desmethyl steranes and 4-methyl steranes
including dinosteranes (Fig. II.3.). The dominant compounds were C27-29 5, 14,
17(H)-20R desmethyl steranes with small contribution from the 5, 14, 17(H)-20S
excursion to the top and mcounterparts (Fig. II.3.). 24-Ethylaxicholestane was dommized in samples 232 and 237 (Table II.2.). 4-inant from the base of the isotopic
ethyl-24-ethylcholestanes and Methylcholestanes and ergostanes along with 4-mdinosteranes were in evidence. Dinosteranes were identified by their mass spectra and by
-paring their elution order with published data (Summons et al., 1987); (van Kaamcomethyl steranes and abundances of total 4-mPeters et al., 1997); (Grice et al., 1998b). The 2abundance increased up sectdinosteranes was tightly correlated along the section (rion and remained high from the end of OAE2 onwards, = 0.98), whereas their relative
except for a decrease in sample 238 (Fig. II.5.). Sample 238, and those from the KB3
ethyl steranes and section, showed a distinctive pattern. Apart from the presence of desm4-methyl steranes, rearranged C27-29 diaster-13(17)-enes (m/z 257), C27-29 4-methyl
sterenes (m/z 271), and C-ring monoaromatic steranes (m/z 253) and methyl
monoaromatic steranes (m/z 267) were abundant (Fig. II.3.). With the exception of
samthe hydrocarbon fraction in mple 238 (where Ph domost of the bituminated), steroidal compounds were the domens, were present at relatively high inant terpenoids in
the KB3 ple 238 and in those fromized in samconcentrations during OAE2, and maximsection (Figs. II.3., II.4.). Sterols are produced by eukaryotic algae, protists and multicellular eukaryotes
(e.g., (Volkman et al., 1998)). Algae and metazoa are the likely main producers of C27
sterols whereas C29 sterols are often attributed to marine green algae (Knoll et al., 2007),
freshwater microalgae (e.g., (Volkman et al., 1999); (Kodner et al., 2008)), and land-
an et al., 1998)). 4-Methyl-24-ethyl cholestane and dinosteranes plants (e.g., (Volkmons et al., 1987)). stly from dinoflagellates (de Leeuw et al., 1983); (Summoderive methyl steranes are positively correlated with dinosteranes Other side-chain alkylated 4-me biological the samed to originate fromand dinoflagellate remains and thus assum

57

oxic Event 2anian - Turonian Oceanic AnCenom

pounds specifically those comprecursors (e.g., (Grice et al., 1998b)). Apart from

ethyl thane oxidizing bacteria (Jahnke et al., 1999), 4-me midentified as originating from

steroids are mostly algal in origin (e.g., (de Leeuw et al., 1983)). In addition to marine

ples, they are commonly found in evaporitic (e.g., (Grice et al., 1998b)) and sam

et al., 1998b)) environmfreshwater (e.g., (Goodwin et al., 1988); (Griceents indicating a

s. The high noflagellate source organismiinantly dwide tolerance of their predom

abundance of C27-29 desmethyl steranes, 4-methyl steranes and dinosteranes indicates that
nt ofponeportant comautochthonous phytoplankton, including dinoflagellates, were an im

ing the deposition of these black shales. tter produced and preserved durathe organic m

Changes in the composition of steroids point towards successions in assemblage of

ental changes (Knoll et al., 2007). The relative ary producers due to environmprim

contribution of C27-29 desmethyl steranes relative to C30-35 hopanes exhibited a general
decrease up section, except for a maximum in sample 238 (Fig. II.5.). This trend is

hyl steranes and dinosteranes, teminversely correlated with the relative contribution of 4-

which increased from the base of the CIE upwards except for a minimum in sample 238

(Fig. II.5.), and is likely to represent the developmental specific paleoenvironment of

conditions (Thomas et al., 1993). Dinoflagellates evidently became an increasingly

imdevelopmportant coment of water columponent of the phytoplanktonic commn stratification (Fig. II.5.; see unity in conjunction with the section 3.7), and a

transgressional phase and sea level high stand associated with the development of more

endler et al., in review). rine conditions during OAE2 (Waopen m

58

Chapter II

HopaFigure II.5nes; indi. Selected biomcates the relative contarker ratios. a)ribution of eukary Steranes overotic vers hopaus bactenes ratio = Crial organic m27-29 a steranes / Ctter. b) Relative 30-35
contribution of 4-methyl steranes = C28-30 4-methyl steranes / (C28-30 4-methyl steranes + C27-29 
steranes); indicates the relative contribution of dinoflagellates to the total eukaryotic assemblage. c)
stratification. Gammacerane d) IndeHomohopax = gammacerane / ne Index = C(gam35/ (C31-35macerane + C 17, 2130 (H) S and+ C 3017  , 21R(H) S ); indicative of + R homohopawater columnes); n
hopane/ (Cindicative of water col31 2-Me umn -hopane + Cstra30 tification, -hopane); hypeirsalinity and endicates the uxinirelative a. e) co2-Methyl Hntribution of coypane Indeanobacteria. x = C31 -

s Pentacyclic triterpenoidII.3.2.3.

Series of 17, 21(H) and 17, 21(H)-C27-35 hopanes, with minor 17, 21(H)
isomers and C28 almost absent, were identified in all samples based on the m/z 191 ion
chromatogram (Fig. 6). C30 -hopane was dominant in the lowermost two samples,
except in sample 238 (Fig. II.6.). As well, inated in the rest, whereas gammacerane dom hop-17(21)-enes were present and their relative contributions increased and CC3130upwards. Sample 238 and those from the KB3 section exhibited a more important
contribution of C29-C30 hop-17(21)-enes. The high abundance of hopanes in our samples
nable hydrocarbons; Fig. II.4.) indicates em(generally between 25 and 36 % of the GC-aportant input of bacterial bioman imer et al., 1984). ass (Ourisson et al., 1987), (Rohm pounds was higher towards theThe contribution of hopanes in relation to steroidal comend of OAE2 and afterwards, except for a minimum in sample 238 (Fig. II.5.). The latter

59

oxic Event 2anian - Turonian Oceanic AnCenom

is consistent with an increase in the relative contribution of extended C31-35 hopanes up

ohopane xpressed by the homximum in samples 232 and 237 as easection reaching a m

index (HHI; Fig. II.5.). This could represent an increasing contribution of cyanobacteria,

also indicated by the presence of C18-22 3-methyl alkanes (particularly in samples 232 and

237).

C31 2-methylhopane was identified and quantified using the m/z 426  205

ethylhopane index (2MeHI) increased reaction from MRM-GC-MS analysis. The 2-m

sharply from a minimum at the base of the section to maximum values during the CIE,

ples 238, whereas fairly stable values between 4 and 5% were observed until sam

followed by a slight decrease at the top of the section (Figure II.5.). In section KB3, the

aanes are proposed as diagnostic m2MeHI varied between 5 and 7%. 2-Methyl hoprkers

portant iously described as imal., 1999) and have been prevof cyanobacteria (Summons et

u itrescarkers in black shales deposited during OAEs (Kuypers et al., 2004b); (Dumbiom

& Brassell, 2005). Values of the 2MeHI up to 6 identify the presence of cyanobacteria in

ll as their role as producers of extended hopanes. Co-occurring ent, as wethe environmlow 15Norg values are also consistent with nitrogen fixation by cyanobacteria (Table

II.1.). A recent study (Rashby et al., 2007) found an unusual array of triterpenoids

anol and ethylated BHP, tetrahymethyl bacteriohopanetetrol, non-mincluding 2-m

additional methylated triterpenoids of the gammacerane type in the non-marine purple

anols and hopanoids have . Methylated tetrahymRhodopseudomonas palustris bacterium

also been reported in a closely-related soil bacterium, Bradyrhizobium japonicum (Bravo

et al., 2001), reinforcing the knowledge that sources of 2-methylhopanes encompass

organismwever, despite encountering abundant s other than cyanobacteria. Ho

our GC-MS data show no evidence of ples (see below),gammaceranes in all OAE2 sam

cannot readily be invoked as the source of R. palustristhylated gammaceranes. Thus, em

co-occurring 2-methylhopanes. Moreover, there do not appear to be any previous reports

of methylated gammaceranes in modern or ancient sediments.

Gammacerane is commonly found in anoxic and hypersaline environments (de

Leeuw & Sinninghe Damsté, 1990), it derives from tetrahymanol (ten Haven et al.,

1989), and is synthesized by bacterivorous ciliates or purple bacteria living at or below a

water column stratification and anoxia tor ofocline. It is often used as an indicachem

60

(Sinninghe Da

té et al., 1995a; 1sm

995b). Gamm

Chapter II

acerane was abundant in all analyzed

ples, indicating the presence of a stratified water columsam

n during the time of

deposition o black shales. Redox conditions are discussed in detail in section 3.7. f

Figure I section.

I.6. S

lected ion ce

romhs (matogram

/z

191) s

howing the

distr

bution i

triterpeof

noids i

n

3 GM

61

oxic Event 2anian - Turonian Oceanic AnCenom

ne and derivatives taIsorenieraII.3.2.4.

Isorenieratane was found in trace amounts in sample 127 at the base of the section

and most notably in sample 238. The latter, together with samples from KB3 section,

agenetic products, aryl and exhibited a notable contribution of isorenieratane and its di

1987); (Koopmans et al., 1996b); (Sinninghe diaryl isoprenoids (Summons & Powell,

Damsté et al., 2001); Fig. II.7.). Aryl and diaryl isoprenoids were present in the range

C13-C22 and C18-C22, respectively, and all samples displayed a similar distribution (Fig.

II.7.), although concentrations were higher in KB3 samples than in 238. A C33 diaryl

isoprenoid was also identified as an important component of the m/z 133 and 134 ion

photosynthetic green sulfurs (Fig. II.7.). Isorenieratane derives fromatogramchrom

ing in stratified water columbacteria (Chlorobiaceae producing isorenieratene) liv ns with

a relatively shallow chemocline. They are strict anaerobes and simultaneously require

light and H2S for growth (e.g., (Liaaen-Jensen, 1978); (Summons & Powell, 1987);

té et al., 2001)). Isorenieratane and its smans et al., 1996b); (Sinninghe Da(Koopm

diagenetic derivatives are generally interpreted as indicators of euxinic conditions in the

photic zone and are common in Cretaceous black shales, especially those deposited

sté & Köster, 1998); (Kuypers et al., during the C-T interval (e.g., (Sinninghe Dam

ce of isorenieratane and aryl isoprenoids 2004a); (Kolonic et al., 2005)). Thus, the presen

Chlorobiaceae as a component of the in these samples indicates the presence of

planktonic assemblage, also confirmed by their 13C-enriched nature (see section 3.5).

62

Chapter II

of tion pond

ple GM3-238 corres sam distribuehowing th70 s3-d KBn68, a3-
fromramtogale of chromddiids. Peaks in the m
moractions frbon focarhydr238, KBe GM3-lp sam
triangle) isoprenon(ope(filled circle) and diaryl of 134)/z 133/s (matogramlected ion chrome S
.7.Figure IIaryl triangle), isorenieratane (filled pounds. mooidal cto ster

63

oxic Event 2anian - Turonian Oceanic AnCenom

Thermal maturity II.3.3.

The high proportion of 17, 21(H) and 17, 21(H) hopanes with a marked 22R

over 22S predominance indicates that the organic matter is relatively immature (Fig.

II.6.). The presence of 17, 21(H) hopanes, although in small amounts, supports this.

The 22S/(22S + 22R) ratio of C31 17, 21(H) hopane varied between 0.1 and 0.3 (Table
~ 0.6 (Peters et al., 2005). The relationship the end-point value ofII.2.) and far from

between C27 18-trisnorhopane (Ts) and C27 17-trisnorhopane (Tm), expressed as the
able II.2.). The 0.02 to 0.27 (T) ratio, displayed values ranging frommTs/(Ts + T

relationship between C29  22S/(22S + 22R) steranes generally varied between 0.03
ad 0.09 (Table II.2.). These values are also well below the end-point of 0.5 (Peters et al., e presence of rearranged htter. Ta2005) and indicate relatively immature organic m KB3 section ethyl sterenes in sample 238 and in those fromdiasterenes, sterenes, and 4-m Rock-Eval pyrolysis (J. values obtained fromsupport this conclusion as do low TxmaWendler, unpublished data; Table II.1.).

mposition of selected biomarkers and potential sources Isotopic coII.3.4.

arkers was n of selected biompositiopound-specific C-isotopic comThe comcompared to the 13Corg record to gain information regarding their potential biological
precursors (Fig. II.8.). The C27-29 steranes exhibited similar values through the section and
these fluctuated between -30.9 and -27.7‰; like the 13Corg record they showed a positive
E2 and returned to pre-OAE2 values in the upper Aexcursion of ~ 2‰ at the base of Opart of the CIE, except for a second maximum at the top of the section (Fig. II.8.). The
almost identical isotopic composition of the three major steranes points toward a common
biological source likely being an algal community typical of Cretaceous surface waters
itrescu & Brassell, 2005)). A significant (e.g. (Kuypers et al., 2002a), (2002b); (Dum

contribution of C29 from terrestrial plants thus appears unlikely. C30 -hopane varied
-28.7 to -24.3‰ and presented a positive excursion of ~3.2‰ at the beginning of fromOAE2 and peaked in the middle of the CIE. A second maximum, as for the steranes, was

64

Chapter II

observed at the top of the section (Fig. II.8.). The 13C of gammacerane varied between -
27 and -22‰ and displayed a similar trend than C30 -hopane although with a smaller
positive excursion (~1.6‰; Fig. II.8.). The 13C-enriched nature of gammacerane
heterotrophic tent with its origin frompared to steranes and hopanes, is consiscomorganisms (bacteria or ciliates) living near the chemocline and partially feeding on 13C-
sté et al., 1995a). In ig et al., 1995a); (Sinninghe Damtter (Kenaenriched organic mgeneral, biomarkers tracked the 13Corg profile, and except for gammacerane, they were
isotopically depleted (Fig. II.8.). C27-29 steranes and C30 -hopane presented an offset of
TOC values, respectively, consistent with the depleted nature ~ 4-6‰ and 0.4-1.7‰ fromof lipids relative to the total biomass (Hayes, 2001). 13C values for C30 -hopane and
ins in pounds have their orig these comgammacerane fell close to TOC suggesting thatcommon with the bulk of the preserved organic matter likely comprising heterotrophic
13C-enriched bacterial bacteria, ciliates, and cyanobacteria (Fig. II.8.). Relatively oautotrophs has been previously described products compared to those of eukaryotic photin environments domsequence in Italy (e.g., (Kenig et al., 1995a)), and the C-T boundary in the Equatorial inated by cyanobacteria, such as the Vena del Geso evaporitic
Atlantic (Kuypers et al., 2004b). Moreover, heavy 13Corg values were observed in rocks
a et diazotrophic cyanobacteria (Kashiyaminated by the C-T boundary in Italy domfromechanism concentrating mely effective COal., 2008). Cyanobacteria possess an extrem2(Badger & Price, 2003) and their derived lipids are less depleted than eukaryotic opic fractionation during carbon fixation counterparts due to the reduced carbon isottter in our a(Sakata et al., 1997). Evidence of cyanobacterial contribution to organic mples is supported by the 2MeHI, which exhibited higher values (3 to 6) during OAE2 samand the post-OAE2 interval (Fig. II.5.) together with relatively depleted 15Norg values
opposed to(Table II.2.) suggestive of N P occurred (N/P lower than Redfie2 fixation. The latter imld), i.e., conditions beneficial toplies that a deficiency in N as nitrogen
fixing cyanobacteria (Trespiration of organic mayrrell, 1999). Deplettter during the onset of OAion of oxygen in the water columE2 would have promoted n through
oval of nitrate and release of phosphate, both denitrification with the subsequent rem N-fixing cyanobacteria. Sulfidic conditionsoting the expansion ofnecessary factors promin deep waters may have impacted the availability of trace metals crucial for enzymes

65

oxic Event 2anian - Turonian Oceanic AnCenom

nbar & Knoll, 2002). N-fixing cyanobacteria associated with the biological N-cycle (A

may have been critical for sustaining elevated levels of primary production and export of

OAEs (Kuypers et al., 2004b). The high organic carbon to the sea floor during

plexity of their distribution suggest that abundances of steroidal hydrocarbons and com

productivity by eukaryotic algae flourished. However, since our samples would have

integrated long periods of time (~104 yr), it is not possible to discern any particular

ccessions in physpatial or secular su unities.toplankton comm

Among aryl isoprenoids, isotopic data were only obtained for C14 compounds in

ples. This is because a relativeKB3 samn in tioly high concentration and reduced co-elu

these samples allowed for higher precision measurements. The C14 aryl isoprenoid

showed the most enriched 13C values among all the studied compounds (~ -17‰; Table

3), consistent with an origin from green sulfur bacteria using the reversed tricarboxylic

acid cycle for carbon fixation ((Evans et al., 1966). The 13C of Ph and Pr in sample

ilar and suggestive of aarkably simGM3-238 and its counterparts from KB3 are rem

ilar hydrogen isotopic values latter is supported by simcommon source (Table II.3.). The

(J. Sepúlveda, unpublished data).

66

 8.Figure II.GM3 section. interval.

Chapter II

1313Axis “C of bulk Y” was zoomorganic carbon and comed in between 76 pound-sand 78.5 mpecific eters. Grey area C values of selected birepresents the omarkers fromOAE2

67

oxic Event 2anian - Turonian Oceanic AnCenom

Table II.3. Compound-specific carbon isotopic composition of pristane, phytane, and C14 aryl isoprenoids
ples. sam2 in post-OAE

Sample Phytane Pristane C14 Aryl Isoprenoid
13C (‰) 13C (‰) 13C (‰)

- -28.7 ± 0.7 -28.0 ± 1.6 GM3-238

-17.1 ± 0.1 -28.7 ± 0.5 -27.8 ± 0.8 KB3-70

-17.4 ± 2.5 -29.0 ± 0.8 -28.3 ± 0.9 KB3-68

Sulfur-bound lipids II.3.5.

The desulfurization of asphaltenes and polar fractions of selected samples from

both sections only yielded small amounts of hydrocarbons, namely C18-24 n-alkanes with
an odd-over-even predominance and maximum at n-C21H44, and phytane. The m/z 133
did not reveal isorenieratane or its tic fractionsaatograms of aromand 134 chrom

derivatives. The low yield of hydrocarbons after Raney-Nickel desulfurization suggests that the sulfurization of functionalized lipids during the early stages of diagenesis was

minor either due to low concentrations of reactive sulfur species or due to high iron

ocesses ral pninghe Damsté & de Leeuw, 1990). Alternatively, postdepositioncontent (Sin

esis. ed during early diagenmpound formcan also affect the stability of sulfur-bound co

al cleavage, as evidenced by the relatively weak nature of Desulfurization through therm

S-S and C-S bonds after hydrous pyrolysis (< 260°C), has also been invoked as a

m affecting the release of sulfur-bound hydrocarbons during catagenesis echanism

(Koopmans et al., 1996a). However, this mechanism can be excluded for the thermally

ature samples (Tables II.1. and II.2.; Fig. II.3.d). imm

68

d phytane Sources of pristane anII.3.6.

Chapter II

a the degradation of the phytyl side chain of chlorophyll-Ph and Pr derive from and -a, as well as from bacteriochlorophyll- photosynthetic algae and cyanobacteriafromb from purple sulfur bacteria (Brooks et al., 1969). Additional sources could possibly
include lipids from methanogenic and halophilic archaea (e.g., (Rowland, 1990), as well
nd Prount of Ph amas tocopherols for Pr (Goossens et al., 1984). We interpret the high ain sample 238 and those from KB3 to mostly derive from the phytyl chain of chlorophyll-
a froma) The isotopic com photosynthetic algae (eukaryotic phytposition of Ph and Pr is similar to steroidal cooplankton) based on the following criteria: mpounds of eukaryotic
m fropoundsn of distinctive steroidal comsource; b) the corresponding high concentratioalgae and the relatively low contribution of hopanes characteristic of cyanobacteria; and c) the absence of Ph and biphythane after ether-cleavage of polar fractions suggesting that a contribution of Ph from archaeol and caldarchaeol representative of marine
. is not likely (Kuypers et al., 2002a)),ic archaea (e.g.,plankton has only been reported inance of Ph and PrTo our knowledge, such a high predoments where sulfurization of functional inic environmin few cases and associated with eux ce et al., 1996; 1998a; 1998b); (Kenig et al.,lipids takes place ((Keely et al., 1993); (Gri1995a)). Extremely high concentrations of Ph (up to 9000 g gTOC-1) were found in a
house Basin, France (Keely et al., 1993) and the Oligocene Mulrl sequence fromamexplained to result from sulfurization during early diagenesis and subsequent temperature
Ph and steroids, cleavage of the sulfur bonds during catagenesis. High concentrations ofand a lack of even over odd predominance of n-alkanes (as observed in sample GM3-238
and those from KB3) have been explained by the same mechanisms in immature and
ans et al., 1996a). However, as explained in section 3.5, thissulfur-rich rocks (Koopmdesulfurization mechanism is contradictory to the immature nature of our samples.
tenes yielded insignificant Although the desulfurization of polar fractions and asphale occurrence of sulfurization during early ounts of hydrocarbons, it does not exclude thamdiagenesis. Chemical weathering can also account for unselective alteration of organic
matter (Petsch et al., 2000). Additionally, the abiotic reduction (hydrogenation) of
functionalized lipid into partly reduced counterparts under the presence of H2S/HS-, with

69

oxic Event 2anian - Turonian Oceanic AnCenom

or without an intermediate sulfurization step, has been proposed as a major preservation

lecular level (Hebting et al., 2006). opathway of organic carbon at a m

KB3 were deposited under high algal le GM3-238 and its counterparts frompmSa

productivity and the accumulation of organic matter under euxinic conditions. High

concentrations of H2S might have favored the presence of a simple trophic structure with
tter in the water ainished degradation of organic mlow heterotrophic activity, and a dim

column and sediments, allowing the preservation of a relatively unaltered algal lipid

pared to sterols in can be found in high proportion comaposition. Chlorophyll-com

certain marine dinoflagellates (Hallegraeff et al., 1991). Temporary limitation of specific

pared lipids comccurrence of pigment-derivedresources can also contribute to the high o

mbrane-derived lipids in their precursoreto ms. Under conditions of scarce resources such

as light and nutrients, slow-growing phytoplankton can synthesize additional “resource

ents, consequently influencing the s such as pigmponentachinery” comacquisition m

eier et al., 2004); (Arrigo, 2005). etry (Klausmcellular stoichiom

aRedox conditions and pII.3.7.mental reconstruction leoenviron

The presence of gammacerane in the entire set of analyzed samples suggests the

r columpresence of a stratified and anoxic waten during their deposition, whereas

terpreted as variations in the degree of can be ine contribution its relativchanges instratification (e.g., (Sinninghe Damsté et al., 1995a). The gammacerane index (GI)

a ed, increased and reach of the sectionexhibited relatively low values at the base

maximum in the middle of the CIE and remained high upward (Fig. II.5.). The relative
contribution of extended C31-35 hopanes increased up section and reached a maximum in
ples 232 and 237 (Fig. II.5.). An increased samcontribution of extended hopanes probably

indicates an better preservation of their precursor bacteriohopanetetrol in sulfide-rich and

anoxic sedim ents (de Leeuwents (Peters & Moldowan, 1991), and hypersaline environm

crease of salinity té, 1990). Both indices indicate a progressive insm& Sinninghe Da

and/or thermal stratification of the water column and euxinic conditions in the bottom

ple 238 during the deposition of black shales. The Pr/Ph ratio was only calculated in sam

section (0.34 – 0.44) (T KB3 (0.33) and in those fromable II.3.) and is indicative of

70

Chapter II

strongly reducing conditions during deposition (Didyk et al., 1978); (de Leeuw & total phosphorous té, 1990); (ten Haven et al., 1985), (1987). A lowsmSinninghe Daples deposited during and after OAE2 in GM3 section (J. content has been found in samWendler, unpublished data) and corroborates the presence of anoxic conditions at the
s (Mort et al., 2007b). during these intervalent interfacewater-sedimand its diagenetic products, the isotopically renieratane ce of isoThe presenple 238 and in KB3 section point to the presence enriched aryl isoprenoids, found in samof Chlorobiaceae and the existence of photic zone euxinia (e.g., (Sinninghe Damsté et al.,
1995a); (van Kaam-Peters & Sinninghe Damsté, 1997). Gammacerane and isorenieratane
cient ocline in an the chemfhave been used for reconstructing changes of the depth oenvironments (e.g., (Sinninghe Damsté et al., 1995a). The occurrence of gammacerane
reflect the occurrence the section ples fromand the absence of isorenieratane in most samed below the photic zone. On the ocline positionmn with a chemof a stratified water coluple nd isorenieratane (as observed in samacerane ammother hand, the presence of both gaocline in mn with a shallow che238 and KB3 section) points to a stratified water columLevant platform during the deposition of odel for the the photic zone. A conceptual morganic-rich sediments is proposed in Figure II.9. A likely mechanisms triggering water
column stratification and bathymetrical changes of the chemocline is salinity
ation, and/or evaporation, as stratification as a result of changes in sea level, water circulsté et al., i-restricted environments (Kenig et al., 1995a); (Sinninghe Damobserved in semonfiguration of the Karak-Silla-Basin, the study area ” c1995a). Due to the “intra-platformexperienced different periods of connection ns and el fluctuatioe to sea-levwas sensitivand isolation from open marine conditions (Kuss et al., 2003). The presence of four
“gypsum beds” along the section indicates evaporitic conditions during low sea level
conditions (gb1-4 in Fig. II.2.), whereas geochemical and microfossil data indicate
onditions in the lower part of GM3 section, porally restricted lagoonal and brackish ctemand a maximum flooding shortly below the C-T boundary (Wendler et al., in review). We
ciated with the isotopic excursion to have favored the interpret the flooding event assoformation of dense waters that filled the intrashelf-basin of the Levant Platform and
n and the resulted in the observed stratification and anoxia in both the water columsediments (Fig. II.9.). This maximum sea level has been indicated as one of the major

71

oxic Event 2anian - Turonian Oceanic AnCenom

forcing mechanisms triggering high productivity and the deposition of organic carbon in

globally widespread basins (e.g., (Arthur et al., 1987). The flooding of extended coastal

ion and generation of ents, together with high evaporat low latitude environmareas in arid

warm and salty waters in marginal seas are considered as important processes leading to

stratification during sible for ediate waters responthe generation of dense deep and interm

OAEs (e.g., (Brass et al., 1982); (Arthur et al., 1987).

Figure II.9. Conceptual model of two representative depositional environments. a) An OAE2 scenario
would represent transgressive and high-stand conditions, flooding of coastal areas, and formation of dense
waters and stratification of the water column. The sea level rise exchanged surface waters with the
neighboring open ocean supplying nutrients that supported high rates of primary production. Nitrate was
removed by denitrification in anoxic waters hence favoring nitrogen fixation. Photic zone euxinia was
likely precluded by a deepening of the chemocline. b) The post-OAE2 scenario (samples GM3-238, KB3-
68, and KB3-70) represents decreasing sea level where restricted conditions are established. Photic zone
euxinia developed due to shoaling of the chemocline. The bathymetrical profile was modified from Schulze
et al. (2005) and exaggerated for schematic reasons. Dark and light grey boxes on top represent facies belts
and reconstructed depositional environments, respectively, according to Schulze et al. (2005).

72

CONCLUSIONS II.4.

Chapter II

Source-specific biomarker parameters obtained from bitumens of organic-rich
st-central Jordan indicated theanian-Turonian boundary of werocks from the Cenompresence of immature marine organic matter, mostly derived from algae including
dinoflagellates, as well as photosynthetic bacteria such as cyanobacteria and Chlorobiaceae, and bacterivorous ciliates. Terrestrial input was apparently minimal.
Successions in planktonic communities seem to be strongly associated with sea level
n stratification, e.g. the direct relationship between water changes and water column stratification and the relative contribution of dinoflagellates. The carbon isotopic columcomposition of hopanes, together with the presence of low 15Norg values and the
occurrence of 2-methyl hopanes suggest that N-fixing cyanobacteria were an important
component of the planktonic assemblage, accounting for an essential part of the organic
portant provide further evidence about the imecarbon deposited in the black shales. Wrole of these microorganisms as primary producers as well as nitrogen fixation for fueling
ents during OAEs. ary production in stratified/anoxic coastal environmprime gammacerane and homohopane ratio and theters, such as the Pr/PhRedox paramthroughout OAE2 and aindexes, indicate the presence of a stratifiefter. A shoaling of the chemocline and the developmd, euxinic and likely hypersaline water colument of photic n
enced by the presence of in a post-OAE interval as evidia occurredzone euxinisorenieratane and isotopic enrichment of the C14 aryl isoprenoid. This event was
e and pristine of algal origin, likely to characterized by high concentrations of phytanental stress and the under conditions of environmary productionrepresent high primpreservation of lipids under euxinic conditions. Two main conceptual models to explain stratification of the water column and the
T boundary are proposed. 1) Throughout OAE2, the -ent of anoxia during the Cdevelopme rising sea level, and the expected high flooding of extended areas associated to thation of salty-peratures, probably promoted the form due to increased temevaporationdense water masses in shallow coastal areas that filled the basin creating strong salinity

73

oxic Event 2anian - Turonian Oceanic AnCenom

stratification. 2) During the deposition of post-OAE2 black shales, intermittent isolation
of the basin and restricted circulation during low sea level stages most likely triggered
stratification of the water column and a shoaling of the chemocline promoting photic
zone euxinia.

ACKNOWLEDGEMENTS II.5.

einschaft (DFG) as part utsche Forschungsgemd by the DeThis research was fundeate College “Proxies in Earth History” (EUROPROX) and the of the European Graduonero, M. Segl, an, C. Col thank X. Prieto, S. Tille, L. ShermeDFG project Ku642-221. WU. Beckert, and P. Simundic for their valuable laboratory assistance, D. Birgel and M.
etry, R. Stein at the Alfred ss spectroma mElvert for helpful discussion and assistance inWegener Institute, Bremerhaven for laboratory facilities, and A. Masri and the Jordan
paign logistics. R.E. Summonsfield camGeological Survey (NRA) for providing ideal issenschaftskolleg, and , the Hanse-Wology Programwas supported by the NASA Exobithe Alexander von Humboldt-Stiftung Foundation. J. Sepúlveda acknowledges the DFG nth o for supporting his doctoral studies and a six mand the EUROPROX program. research visit to the Summons Laboratory at MIT

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84

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II Chapter I

Chapter III

Oceanographic and climatic dynamics in the Late Cretaceous

1259): A compound-specific stable Equatorial Atlantic (ODP Site

isotope approach into the formation of organic-rich sediments

Julio Sepúlveda1,2,*, Arne Leider2, Kai-Uwe Hinrichs2

First draft of article in prEarth and Planetary Science Letters eparation for subm(Septemission to ber 2008)

1International Graduate College – Proxies in Earth History (EUROPROX), University of Bremen, Germany

2OrGeosganic Geciences, Locehemobeneistry r StraGroup, ssMe, UniveArsRUM – Center for ity of Bremen, Mari28359 Bremne Enviroen, Genmrmany ental Sciences and Department of

*Corresponding author: Tel.: +49 421 218 65742; fax: 49 421 218 65715. E-mail address: sepulved@uni-
bremen.de (J. Sepúlveda)

KeywordsDrilling Program, Lipid biom: Late Cretaceous, Coniacian, Oceanic arkers, Stable isotopes. Anoxic Event, Demerara Rise, Ocean

85

Equatorial Atlantic E3 at the AConiacian O

ABSTRACT

The stable isotopic composition of carbon and hydrogen (13C and D) of aquatic-

and terrestrial-plant-derived n-alkanes from a 800-ky-long Coniacian record from the
western equatorial Atlantic (Ocean Drilling Program Site 1259, Demerara Rise) was used
ation of cyclic ns involved in the formatic variatioto assess oceanographic and clim-n short-chain ents. Two different aquatic sources ofcarbonate- and organic-rich sedim13C values, marine algae and cyanobacteria A) were identified based on their alkanes (SC(n-C17 and n-C21 with 13C values of -34 to -27.2), and heterotrophic bacteria (n-C16 n-C18
with 13C values of -31.6 to 24.5‰). For most part of the record the 13C of long-chain n-

alkanes (LCA) is consistent with an origin from land plants using C3 metabolism. Periods
of enhanced marine productivity were identified by positive 13C excursions in n-C17,
ese howth rates of phytoplankton under eutrophic conditions. Trlikely reflecting rapid gtive of enhanced upwelling and ils indicacrofossiperiods coincided with the presence of mwere accompanied by 13C enrichments of C29 and C31 n-alkanes thought to reflect
changes in continental vegetation, e.g., increasing contribution of C4 plants, a shift
possibly coupled with enhanced marine productivity and organic matter burial and

associated changes in CO2. In addition, these periods were marked by D enrichments in

n-C17 suggestive of changes in Dwater due to variations in the hydrological czcle,
. Our results generally agreed with rine-terrestrial systemasuggesting a tightly coupled mcurrent depositional models for the formation of eccentricity-driven cyclic sedimentary
sequences; however, they revealed a more complex interplay of the climatic and
e. oceanographic regim

86

INTRODUCTION III.1.

Chapter III

The massive burial of organic matter over vast areas of the Cretaceous’ oceans,
known as oceanic anoxic events (OAE; Jenkyns, 1980), has been the focus of intense
ate and the carbon cycle (e.g., Arthur et al., climplications for global research due to its imary production 1987; Schlanger et al., 1987; Kuypers et al., 1999). Elevated levels of primin surface waters and/or preservation of organic matter under oxygen-depleted conditions
are the most prominent scenarios to explain the formation of black shales (Sinninghe
té and Köster, 1998; Kuypers et al., 2002; Mort et al., 2007). This situation has been smDasuggested to result from the interaction of unusual and extreme environmental conditions
such as elevated concentrations of atmospheric CO2 (Bice et al., 2006), high sea surface
peratures (Schouten et al., 2003; Bice et al., 2006; Forster et al., 2007), rising sea temlevel (e.g., Arthur et al., 1987; Schlanger et al., 1987), massive magmatic episodes
lation (e.g., Erbacher et al., ceanic circu008), and changes in od Creaser, 2(Turgeon anains difficult to explain the occurrence of such extraordinary 2001). However, it remenvironmental conditions for extended periods of time. The Coniacian-Santonian interval
7 Ma; ration (~ 2.OAEs, in spite of its du(OAE3) has received less attention than other Meyers et al., 2006) and recent evidence of a complex oceanic-atmospheric interaction
ation of black-shales (Nederbragt et al., 2007; Friedrich et al., massociated to the for2008).

Ocean Drilling Program (ODP) Leg 207 successfully recovered Late Cretaceous
, providing continuous records merara Rise off the coast of Surinam the Deents fromsedimrbacher et al., 2004), of extended black shale sequences covering the Albian-Santonian (Ety for studying paleoceanographic and and offering an extraordinary opportunipaleoclimatic processes in the Equatorial Atlantic. These sediments are characterized by
the cyclic alternation of organic-rich layers, mostly composed of fecal pellets and lenses
aof organic m pelagic carbonate-rich beds posed oftter, and of carbonate-rich layers comion of carbonate-rich et al., 2007). The depositiniferal packstones (Nederbragt or foram to be affected by increased carbonate production and intervals of winnowing layers seem

87

Equatorial Atlantic E3 at the AConiacian O

under vigorous atmospheric and oceanic circulation, and thus to upwelling intensity,
rbonate dilution by layers seem to be related to increased cawhereas organic-rich7). The cyclic t et al., 200tense upwelling (Nederbragterrigenous fluxes and less indeposition of these sediments appears to be strongly linked to orbital Milancovitch
inly in the eccentricity frequency (Flögel et al., 2008b; Friedrich et al., 2008), acycles, mwith a minimumSite 959 in the tropical African m contribution of obliquity (Fargin, where orbital frequencies with shorter phasing lögel et al., 2008b). This differs from ODP
clearly dominate cyclic river discharge and black shale formation (Beckmann et al.,
inifera in Demarara 2005). Cyclic changes in the abundance of planktic and benthic foramRise are suggested to reflect changes in the mean latitudinal position of the Intertropical
Convergence zone (ITCZ) leading to fluctuations in the precipitation/upwelling regime,
and promoting changes in surface water productivity and the presence of a very shallow
um zone (OMZ; Friedrich et al., 2008). However, the influence of thenimioxygen model simulations suggest rine productivity is controversial; maITCZ on upwelling and mthat black-shale formation in the equatorial Atlantic was triggered by climatic variability
gner, ad to southern latitudes rather than by changes in the ITCZ (Flögel and Wiin m2006). Furthermore, high resolution records of redox variability (März et al., 2008)
suggest the alternation of perthan as found in studies based on bulk geochemmanent oxygen-depleted waters and euxiniistry (Flögel et al., 2008a; Friedrich et al., a in shorter cycles
15N values in Coniacian sediments 2008). Additionally, the presence of low but variable from Demerara Rise suggests that diazotrophy was the main source of nutrient nitrogen
plying the presence of upwelled ation, imduring certain intervals of black-shale form and Arthur, 2007). Thus, oceanographic waters with a low inorganic N/P ratio (Juniumght have interacted during the ied m assumprocesses of higher complexity than usuallyLate Cretaceous. We study the molecular distribution and isotopic composition of marine- and
terrestrial-derived n-alkanes from a sedimentary sequence spanning the Early Coniacian
at Derich sedimmeents described elsewhere to be driven by orbital eccentricity (Nrara Rise. This record includes two cycles of alternating carbonate- and organicederbragt et al., -
study the relationship between eiedrich et al., 2008). W2007; Flögel et al., 2008a; Frprimary production, upwelling intensity, and continental runoff as main triggers for the

88

Chapter III

ents by providing new insights into the coupling of both cyclic deposition of these sedim

rine and terrestrial carbon reservoirs. am

III.2.ETHODS ALS AND MMATERI

Study area and samples III.2.1.

arine plateau located at ~ 5 °N in the wide submra Rise is a ~ 220-kmeraThe Dem

e and the western tropical Atlantic, it stretches for ~ 380 km along the coast of Surinam

rly located south of Senegal at ~ 0° N ofemFrench Guyanas (Fig. III.1.), and it was for

paleolatitude during Cretaceous times (Erbacher et al., 2004). Rifting and faulting

processes separated the Guinea and Demerara Plateaus along an east-west–striking fault

system during the Early Cretaceous, rapidly subsiding and reaching water depth of ~

ter depths vary from aanian (Arthur and Natland, 1979). W by the Late Cenom2000 m

oabout 700 m on the plateau to mre than 4500 m at the abyssal plain and distal Orinoco

st area (Erbacher et al., 2004). ODP Site 1259 Hole C (9°18.0240 N, erth WoFan in the N

54°11.9694 W) was drilled on the northern slope of the Rise at a water depth of 2354 m

(Fig. III.1.). Sediments are characterized by dark-laminated organic-rich claystones,

occasionally interrupted by dark-light laminae or coarser greyish carbonate-rich intervals

ical analyses . Molecular and bulk geochem(Erbacher et al., 2004; Nederbragt et al., 2007)

indicate the presence of thermally immature marine-derived algal and bacterial organic

tter (Erbacher et al., 2004; Meyers et al., 2006). am

89

Equatorial Atlantic E3 at the AConiacian O

regiFigure IonsII. above 1.. (a) Map ssea level, howing a white areas reglobal present oceaplate-tectonic ns, recblack linesonstruction defor pict plat80 Ma BP. e boundariesGray. Black areas redots present
indicate locations of reported Late Cretaceous organic matter-rich deposits (Wagner et al., 2004 and
references therein). (b) Close-up of the equatorial Proto-Atlantic, with Demerara Rise enclosed by the
rectangle. (c) Present-day bathymetry of Demerara Rise with drill sites including 1259 (from März et al.,
). 0082

For the present study a total of 71 samples were obtained at a resolution of ~ 3.5

cm from a 3.56-m-long section (depth interval 505.70 - 509.26 mcd; Fig. III.2.),

including sections 12R-5, 12R-CC, 13R-1, 13R-2, and 13R-3. These samples correspond

inifera zonecatus) and planktonic foramto calcareous nannofossil zone CC13 (M. fur

ann et al., 2008; Friedrich et al., KS23 (D. concavata) and are Coniacian in age (Bornem

/Ma for Site 1259 during the mR) of 5 centation rates (LS2008). Average linear sedim

ntation of about 712 ky for the emConiacian (Erbacher et al., 2004) yield a period of sedi

intervals of ecause it contains twoterval. This section was selected bstudied in

rich sedimternations of carbonate- and organic-characteristic cyclic alents (Fig. III.2.), as

st of the record from ODP Site 1259, and recently described to represent ofound along m

90

comFigure Iposite deII.2. Tpth o(mtal orgacd) of nic caODrbon (TOCP Site 1259. L) aned caft panel srbonate cohows a ntent 25-m-long (CaCO3) against desequence of cypth in meters of clic alternations of
carbonate- and organic-rich intervals (gray and white areas, respectively). Right panel shows the interval
udy. used in this st

Chapter III

OC)

ic carbon (T

entation (Friedrich et al., 2008). Total organim

-driven sedeccentricity

) varies easured at high resolution (every 1.5 cm) values m

carbonate (CaCOand calcium3

ann et al.,

between 2 and 22%, and between 41 and 91%, respectively (Fig. III.2.; Bornem

2008; Friedrich et al., 2008).

91

Equatorial Atlantic E3 at the AConiacian O

hy – mass spectrometry (GC-MS) Lipid analysis, gas chromatograp III.2.2.

ation, all glassware was combusted at inIn order to reduce laboratory contamethane (DCM), and thanol (MeOH), dichlorome450°C for eight hours and rinsed with ment were ground to powder in an agate hexane before use. Between 5 and 20 g of sedimmortar and homogenized. Samples were extracted in a MARS microwave system (CEM
xture of DCM:MeOH 3:1 (at least 3x, until the solvent iCorporation) using a solvent mextracts became colorless) at 80°C for 20 minutes. Before extraction, 2 g of
hexatriacontane, docosanoic acid, 1-nonadecanol and 2-methyl octadecanoic acid were
bined after centrifugation added as internal standards. Total lipid extracts (TLE) were com of nitrogen using a Turbovap LV Evaporator. TLEs and concentrated under a streamcombusted glass wool and NaSOwere then separated into asphaltenes and m4altenes using sm, and eluted with hexane and DCM, respectively. all Pasteur pipettes filled with
Elemental sulfur was removed from the maltenes using acid-activated copper (4 N HCl,
ely with Milli-Q, MeOH, DCM, and hexane). Maltenes weresecutivrinsed confractionated into hydrocarbons, ketones and esters, alcohols, and fatty acids using Supelco DSC-NH2 solid phase extraction glass columns (6 mL, 500 mg sorbent; Hinrichs
sasatography-met al., 2000). Hydrocarbons were identified by coupled gas chrom elsewhere (Sepúlveda et al., accepted) etry (GC-MS) as describedspectromAfter GC-hydrocarbons by using urea adduction. SamMS analysis, n-alkanes were separated fromples were concentrated under a N branched and cyclic 2 flow,
dissolved in 3 ml of hexane/DCM 2:1, mixed with 2 ml of saturated urea solution in
MeOH (20 g Urea in 120 ml MeOH), and stored at -25 °C for 20 minutes. Later, solvent
and the steps described above were repeated twice. streamwas blown down under a N2Then, samples were evaporated; urea crystals were washed with 10 ml of hexane and
anched and cyclic for 15 seconds. The hexane phase, including brcentrifuged at 2000 rpmpounds, was pipetted off and collected as nocomn-adduct fraction; this step was repeated three times. Urea crystals were then dissolved with 5 ml of Milli-Q water and mixed with
10 ml of hexane/DCM 4:1. The solvent phase was pipetted off and saved as the adduct
was concentrated and transferred tofraction including n-alkanes; this step was repeated three tim inserts using hexane and analyzed by GC-MS as es. The adducted fraction

92

Chapter III

hod (yield of about 50-70%) was obtained by tedescribed above. The efficiency of the mcomparing the concentration of n-alkanes before and after urea adduction, and by using
an injection standard (20 g n-C22 anteiso alkane).

alysis Isotopic an III.2.3.

ed by gas specific carbon and hydrogen isotope analyses were performpound-Comchromatography-combustion-isotope ratio mass spectrometry (GC-C- irm-MS) consisting
bustion via a Thermo Finnigan GC Comedof a Thermo Finnigan Trace GC Ultra couplIII interface to a Thermo Finnigan Delta Plus XP mass spectrometer. For carbon isotope
analyses the GC was equipped with a RTX-5MS fused silica capillary column (30 m;
perature conditions were identical to thickness) and the tem film0.25 mm ID; 0.25 m was equipped with a er gas. The interface was used as carrithose described above. Heliumcombustion oven at 940 °C. Carbon isotope ratios are reported as  values (13C, in ‰)
relative to the VPDB standard. Multiple CO2-pulses of known 13C value at the
ent precision (~ 0.22‰ ch run were used for calibration. Instrumbeginning and end of eaor better) was regularly checked by injecting a mixture of n-alkanes (n-C15 to n-C29) with
known isotopic compositions. The isotopic composition of biomarkers was determined
position (docosanoic acid). now isotopic comrelative to an injection standard of kquipped with a RTX-5MS fused ents the GC was eeasuremFor hydrogen isotope msilica capillary column (60 m; 0.25 mm ID; 0.25 m film thickness), and the temperature
perature pyrolysis reactor above. A high-temconditions were identical to those described at 1440 °C pyrolyzed the sample quantitatively to H2 gas before introduction into the MS.
Pulses of hydrogen with known isotopic composition were used as the primary reference.
The H3 factor (Sessions et al., 2001) was monitored daily by using H2 gas at different
(better than 5‰) was evaluated daily by essures. The accuracy of the systemrpartial pusing a certified standard mixture of 15 n-alkanes (C16-C30) with known isotopic
Biogeochemical ann, mposition, and a 5-fold range of concentrations (A. SchimmelcomLaboratories, Indiana University). D values were corrected to the VSMOW scale by co-
injecting three standards with known isotopic composition (C10, C20, and C30 fatty acid

93

Equatorial Atlantic E3 at the AConiacian O

have been Vthyl esters) plus naphthalene. Only peak intensities larger than 1500 memconsidered for D values.

RESULTS AND DISCUSSION III.3.

urces Concentrations of selected hydrocarbons and biological so III.3.1.

n-Alkanes were mainly represented by the C15-35 homologues with a general
dominance of short-chain n-alkanes (SCA) between n-C15 and n-C21 (Fig. III.3.).
Concentrations of the most abundant homologues (n-C16,17,18,21) varied between 0.2 and
190 g gdw-1 and paralleled with depth; in general, they exhibited higher concentrations

during organic-rich intervals between 506.36 and 507.26 mcd, and between 508.46 and
d (Fig. III.3.). This trend did not change significantly when concentrations c508.75 mwere normalized to TOC (data not shown). SCA are mostly derived from aquatic algae
cteria (Han and Calvin, 1969; Cranwell s including photosynthetic bacroorganismiand met al., 1987). Even numbered SCA homologues between C12 and C22 are generally linked
to bacterial sources (Grimalt and Albaigés, 1987), whereas n-C17 usually derives from
photosynthetic algae and cyanobacteria (Han and Calvin, 1969; Cranwell et al., 1987), -ne halthough it can be also found in purple sulfur bacteria (Jones and Young, 1970). TC21 homologue has been reported as the major n-alkane present in the marine diatom
Rhizosolenia setigera (Blumer et al., 1971) and has been observed as dominant n-alkane
ples from high productivity areas off Walvis Bay (Hinrichs et in selected Pleistocene samd for these four homologues suggests al., 1999). The concentration pattern observeents. coupled production in the water column and/or preservation in sedimLong-chain n-alkanes (LCA) were characterized by C27-35 homologues with an
PI) values up to bon preference index (Cinance as evidenced by carodd-over-even predom12, characteristic of epicuticular waxes of vascular plants (Fig. III.3.; Eglinton and
Hamilton, 1967). Concentrations of n-C29, n-C31, and n-C33 paralleled with depth and
varied between almost zero and 20 g gdw-1; the lowest values were found below and

above 508 and 506.36 mcd, respectively, whereas maximum values were present between

94

Chapter III

e rather specific source of LCAs, their d (Fig. III.3.). Considering thc506.5 and 507.9 m

t of terrestrial organic matteronly used to track changes in the inpun is commconcentratio

ainto the m (e.g., Meyers, 1997). Concentrations of LCA were generally up to rine realm

one order of magnitude lower than SCAs, consistent with a largely marine origin of the

aorganic mnn et al., 2008). atter (cf., Meyers et al., 2006; Beckm

Concentrations of the acyclic isoprenoids phytane (Ph), pristane (Pr), and

lycopane (Ly) varied between almost zero and 25 g gdw, and showed similar downcore

profiles as SCA (Fig. III.2.). In aquatic environments, Ph and Pr derive mostly from the

found in madegradation of the phytyl side chain of chlorophyll-ny photosynthetic algae a

and cyanobacteria, as well as from bacteriochlorophyll-a and -b derived from purple

al sources of Ph could possibly in9). Additionsulfur bacteria (Brooks et al., 196clude

thanogenic and halophilic archaea (Rowland, 1990), as well as tocopherols e mlipids from

(antioxidants in plants and algal lipid membranes) for Pr (Goossens et al., 1984). In

marine environments they are usually interpreted to derive from photosynthetic primary

producers unless their carbon isotopic composition suggests a different source. Ly is

both oxic and anoxic environments ples froment samabundant in water and sedim

(Wakeham et al., 1993). Potential biological precursors include methanogenic archaea

(Brassell et al., 1981) and phototrophic algae (Wakeham et al., 1993). The similarity of

pounds are linked to profiles of SCA, Ph, Pr, and Ly suggest that variations of these com

rchanges in pary production in surface waters. im

influenced by sulfurization during early arkers such as Ph can be severelyBiom

ans et al., 1996), and this process has been ents (Koopmdiagenesis in euxinic environm

reported to occur at Demerara Rise (Beckmann et al., 2008; März et al., 2008). TOC

exhibits a good correlation with total S in the studied section (data not shown), whereas

biomarkers do not show a clear correlation with TOC (e.g., maximum TOC at 508.81

mcd. parallels a minimum in biomarkers). This suggests a cautious interpretation of

pound-productivity variations based on concentrations; thus, we also focus on the com

arkers. position of biomspecific isotopic com

95

Equatorial Atlantic E3 at the AConiacian O

96