Provicialis ad eviroetal chage i the Early Cretaceous – Paleoceanographic and stratigraphic applications of calcareous nannofossils and geochemistry

Dissertation

zur Erlangung des Grades eines Doktors der Naturwissenschaften an der Fakultät für Geowissenschaften der Ruhr-Universität Bochum

vorgelegt von Carla Möller geboren in Dortmund

Bochum, Mai 2017

Data! Data! Data! he ried ipatietly. I a’t ake riks without lay.

Sherlock Holmes

Erklärung

Ich versichere an Eides statt, dass ich die eingereichte Dissertation selbstständig und ohne unzulässige fremde Hilfe verfasst, andere als die in ihr angegebene Literatur nicht benutzt und dass ich alle ganz oder annähernd übernommenen Textstellen sowie verwendete Grafiken, Tabellen und Auswertungsprogramme kenntlich gemacht habe. Außerdem versichere ich, dass die vorgelegte elektronische mit der schriftlichen Version der Dissertation übereinstimmt und die Abhandlung in dieser oder ähnlicher Form noch nicht anderweitig als Promotionsleistung vorgelegt und bewertet wurde.

(Carla Möller)

Declaration of authorship

This thesis consists of five chapters. Chapter 1 is an introduction to the present thesis. Chapters 2, and 3 are papers which have been published in peer-reviewed journals, chapter 4 is a manuscript that has been submitted for publication. Chapter 5 contains the conclusions of the present thesis. All data generated and used for this thesis is enclosed with the electronic version.

Chapter 2 Möller, C., Mutterlose, J., Alsen, P., 2015. Integrated stratigraphy of Lower Cretaceous sediments (Ryazanian–Hauterivian) from North-East Greenland. Palaeogeography, Palaeoclimatology, Palaeoecology 437, 85-97. Belemnite rostra for the analysis were supplied by J. Mutterlose and P. Alsen. C. Möller sampled the shells and analyzed the data. The paper was written by C. Möller with contributions from J. Mutterlose and P. Alsen. Comments and suggestions of two anonymous reviewers have been included in the final version.

Chapter 3 Möller, C., Bornemann, A., Mutterlose, J., submitted. Size changes of calcareous nannofossils and the nature of the Weissert Event (Early Cretaceous).

C. Möller performed the sampling of one of the cores. Also the preparation of the microscope slides, and the analyses of the calcareous nannofossil assemblages in the samples from northern Germany was done by C. Möller. A. Bornemann supplied microscope slides and biometric data for Watznaueria barnesia for the third core; all other biometric measurements as well as data analyses were done by C. Möller. The paper was written by C. Möller with contributions from A. Bornemann and J. Mutterlose.

Chapter 4 Möller, C., Mutterlose, J., 2014. Middle Hauterivian biostratigraphy and palaeoceanography of the Lower Saxony Basin (Northwest Germany). Zeitschrift der Deutschen Geowissenschaftlichen Gesellschaft 165 (4), 501-520. C. Möller performed the sample preparation, the qualitative and quantitative analysis of the nannofossil assemblages, and data analysis. The analyzed belemnite samples were supplied by J. Mutterlose. C. Möller wrote the paper with contributions from J. Mutterlose. Comments and suggestions of Martin Hiss (Geologischer Dienst NRW) and one anonymous reviewer have been implemented into the final version.

I. Table of contents II. ABSTRACT ...... IV III. KURZFASSUNG ...... VII IV. ACKNOWLEDGEMENTS ...... X 1 INTRODUCTION ...... 1 1.1. Thesis structure ...... 1 1.2. Calcareous nannofossils ...... 2 1.2.1. Biology ...... 3 1.2.2. Nannoliths ...... 6 1.2.3. Evolution and fossil record of calcareous nannofossils ...... 9 1.2.4. Significance of coccolithophores for ocean chemistry and biogeochemical cycles ...... 11 1.2.5. Applications ...... 15 1.3. The Early Cretaceous ...... 16 1.3.1. Climate ...... 16 1.3.2. Sea level and ocean circulation ...... 19 1.3.3. Environmental change and Oceanic Anoxic Events ...... 21 1.4. Aims and objectives...... 26 1.5. References ...... 27 2 INTEGRATED STRATIGRAPHY OF LOWER CRETACEOUS SEDIMENTS (RYAZANIAN-HAUTERIVIAN) FROM NORTH-EAST GREENLAND ...... 42 2.1. Introduction ...... 43 2.2. Geological setting ...... 45 2.3. Section ...... 45 2.4. Material and methods ...... 46 2.5. Results ...... 47 2.5.1. Element composition...... 47 2.5.2. Strontium isotopes ...... 47 2.5.3. Stable carbon and oxygen isotopes...... 49 2.6. Discussion ...... 49 2.6.1. The Ryazanian-Valanginian boundary ...... 49 2.6.2. The Weissert Event and the Valanginian nannoconid decline ...... 52 2.6.3. The lower / upper Valanginian boundary ...... 57 2.6.4. The Valanginian / Hauterivian boundary ...... 57 2.6.5. Lowermost Cretaceous palaeotemperatures ...... 58 2.7. Conclusions ...... 59 2.8. Acknowledgements ...... 60 2.9. References ...... 60 3 SIZE CHANGES OF CALCAREOUS NANNOFOSSILS AND THE NATURE OF THE WEISSERT EVENT (EARLY CRETACEOUS) ...... 67 3.1. Introduction ...... 68 3.2. Study sites and stratigraphy ...... 69 3.2.1. Lower Saxony Basin, Northern Germany ...... 69 3.2.2. Blake Bahama Basin, western Atlantic Ocean ...... 70 3.3. Material and methods ...... 71 i

3.3.1. Nannofossil biostratigraphy ...... 71 3.3.2. Counting ...... 71 3.3.3. Biometry ...... 71 3.3.4. Organic carbon isotopes...... 75 3.4. Results ...... 75 3.4.1. Nannofossil biostratigraphy ...... 75 3.4.2. Nannofossil abundances and preservation...... 75 3.4.3. Absolute and relative abundances of Nannoconus spp...... 76 3.4.4. Biometry ...... 76 13 3.4.5. Organic carbon isotopes (δ Corg)...... 78 3.5. Discussion ...... 80 3.5.1. Preservation ...... 80 3.5.2. Ocean acidification and toxic trace metals...... 80 3.5.3. Temperature – the climate of the late Valanginian ...... 81 3.5.4. Loss of ecological niches ...... 82 3.5.5. The Valanginian nannoconid decline ...... 85 3.5.6. Implications for the interpretation of the Weissert Event ...... 86 3.6. Conclusions ...... 89 3.7. Acknowledgements ...... 90 3.8. References ...... 90 4 MIDDLE HAUTERIVIAN BIOSTRATIGRAPHY AND PALEOCEANOGRAPHY OF THE LOWER SAXONY BASIN (NORTHWEST GERMANY) ...... 99

ABSTRACT ...... 99 KURZFASSUNG ...... 100 4.1. Introduction ...... 101 4.2. Geological Setting ...... 102 4.3. Studied sections and stratigraphy ...... 104 4.3.1. Emlichheim section ...... 104 4.3.2. Resse section ...... 105 4.4. Material and methods ...... 105 4.4.1. Calcareous nannofossils ...... 105 4.4.2. Geochemistry ...... 107 4.5. Results ...... 107 4.5.1. Calcareous nannofossil biostratigraphy ...... 107 4.5.2. Nannofossil preservation, diversity and abundance ...... 111 4.5.3. Calcareous nannofossil ecology – relative abundances of selected species ...... 112 4.5.4. Geochemistry ...... 115 4.6. Discussion ...... 116 4.6.1. Biostratigraphy ...... 116 4.6.2. Palaeoecology ...... 117 4.6.3. Palaeotemperatures ...... 118 4.6.4. Palaeoceanography and sequence stratigraphy ...... 121 4.7. Conclusions ...... 124 4.8. Acknowledgements ...... 124 4.9. References ...... 125 5 CONCLUSIONS AND PERSPECTIVES ...... 129 5.1. Conclusions ...... 129 5.1.1. Stratigraphy...... 129 ii

5.1.2. A model for environmental change during the Valanginian Weissert Event ...... 130 5.1.3. Paleoceanography of the Lower Saxony Basin in the Valanginian – Hauterivian ...... 133 5.2. Perspectives ...... 134 5.3. References ...... 136 6 TAXONOMIC INDEX ...... 140 7 CURRICULUM VITAE ...... 145

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II. Abstract

Calcareous nannofossils, the tiny calcareous hard parts produced by single-celled algae, are a useful tool for biostratigraphy due to their worldwide distribution, high abundance, and small size. Calcifying single celled algae have been an important part of the phytoplankton for nearly 200 Ma, and are still one of the main groups of phytoplankton in the modern oceans. As planktic primary producers, they depend on environmental parameters such as water temperature, light, and nutrient availability. The distribution, abundance and diversity of their fossil remains therefore can provide a detailed record of past marine environments.

The early Early Cretaceous (Berriasian – Hauterivian, 145-129 Ma) was a time of strong faunal provincialism and sea-level lowstand. The lack of seaways between ocean basins allowed only very limited floral and faunal exchange. Such endemism poses a challenge for over-regional biostratigraphic correlation of lowermost Cretaceous sedimentary successions. During these times, the Lower Saxony Basin (LSB) represented one of the few seaways which connected the Boreal Ocean in the north with the Tethys Ocean in lower latitudes. In the LSB, isolation and endemism alternate with phases of faunal and floral exchange, documented by the occurrence of fossil taxa of Boreal or Tethyan origin, respectively. The study of this basin is therefore of high interest for biostratigraphy as well as paleoceanography.

The climate of the Early Cretaceous is a matter of intensive debate. Evidence for cooling episodes during the Lower Cretaceous interrupting the warm, equable Mesozoic climate, and reconstructions pointing towards warm, humid conditions, are discussed controversially. In the upper Valanginian (136-133 Ma), a 1.5‰ positie carbon isotope excursion is detectable globally in marine carbonates and organic matter. This so-called Weissert Event coincided with volcanic activity of the Paraná-Etendeka large igneous province (LIP). A demise of carbonate platforms in the Tethys and changes in calcareous nannofossil

assemblages document a perturbation of marine environments during this time.

In any set of proxy data, the effects of local and regional conditions interfere with global trends. For a correct interpretation of past conditions, studies should therefore ideally comprise data representing different marine settings distributed over different latitudes. A prerequisite for the reconstruction of past paleoceanography and paleoclimate is a reliable over-regional correlation of sediment successions provided by a firm stratigraphic framework. This thesis presents integrated stratigraphy (87Sr/86“r, δ13C, ammonite biostratigraphy, calcareous nannofossil biostratigraphy) of Lower Cretaceous sections from the Boreal Realm. Based on the stratigraphic findings, quantitative analyses of calcareous nannofossil iv

assemblages, and biometry of three coccolith species (Biscutum constans, Watznaueria barnesiae, Zeugrhabdotus erectus) are used for reconstructions of Early Cretaceous climate and oceanography, and provide implications for nannofossil paleoecology. The main findings of this thesis are:

1) Integrated stratigraphy (87Sr/86“r, δ13C, ammonite biostratigraphy, calcareous nannofossil biostratigraphy) results in a revision of the Lower Cretaceous (Ryazanian – Hauterivian) of North-East Greenland. The revision of the stratigraphic ranges of two nannofossil index species (Sollasites arcuatus, Micrantholithus speetonensis) imply changes for the nannofossil zonation of the Boreal Lower Cretaceous. Calcareous nannofossil biostratigraphy of mid-Hauterivian sediment successions from the LSB modify previous biostratigraphic age assignments for the Gildehaus Sandstone in western Germany, suggesting a late early Hauterivian age for the base of the formation.

2) As a result of the stratigraphic revisions, the Valanginian decline of the calcareous nannofossil genus Nannoconus, well known from the Tethys, was identified in North-East Greenland. The first documentation of this nannoconid crisis associated with the Weissert Event, as far north as Greenland indicates that it is a global event, not limited to the Tethys.

3) A decrease in size of B. constans coccoliths was detected in the Valanginian paralleling the Weissert Event. The observations are similar to the darfig of B. ostas durig the major Oceanic Anoxic Events of the mid-Cretaceous, the Aptian OAE1a and the Cenomanian/ Turonian OAE2. Both during the Weissert Event and the Aptian OAE1a, declining abundances of nannoconids coincided with the size decrease of B. constans. Potential causes for these nannofossil events, that are currently discussed include a) ocean acidification, b) toxic trace metals, and c) light attenuation. Ocean acidification during

the Valanginian is unlikely, as it requires more rapid volcanogenic outgassing of CO2 than reconstructed for the Paraná-Etendeka LIP. Neither are there indications of massive submarine volcanism that could have released large amounts of toxic trace metals to the oceans. The Valanginian shift towards a humid climate with intense continental weathering, however, is in agreement with a scenario of high water turbidity due to an increased rate of detrital input to the ocean. Evidence for intensified weathering during OAE1a and OAE2 indicates, that this scenario might apply also to these events. Therefore, the finding of a B. constans size decrease during the Weissert Event is in favor of the light attenuation model.

4) The mid-Hauterivian was a time of climatic and oceanographic change, that resulted in the LSB in the rapid replacement of the endemic ammonite fauna by Tethyan and Boreal taxa. With the pronounced increase observed in the absolute abundances of calcareous nannofossils, this present study

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documents the change in the marine ecosystem of the LSB. Warm humid conditions likely characterized this time, along with a basin-wide regression, during which the sandstone units of the Gildehaus Formation were deposited at the western margin of the LSB. Based on the presence of nannofossils documented here, a hemipelagic depositional setting is inferred for the Gildehaus Sandstone, where the coarse siliciclastics probably represent a mass-flow deposit.

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III. Kurzfassung

Aufgrund ihrer weltweiten Verbreitung, großen Häufigkeit und geringen Größe sind kalkige Nannofossilien, die winzigen Kalziumkarbonat-Überreste einzelliger Algen, ein wirkungsvolles biostratigraphisches Instrument. Kalzifizierende einzellige Algen sind seit beinahe 200 Ma ein wichtiger Bestandteil des Phytoplanktons, und sind auch in den heutigen Ozeanen eine der größten Phytoplanktongruppen. Als planktische Primärproduzenten sind sie abhängig von grundlegenden Umweltparametern wie Wassertemperatur, Licht und Nährstoffangebot. Die Verteilungsmuster, Häufigkeit und Diversität ihrer fossilen Überreste können daher detaillierte Archive mariner Lebensräume der Vergangenheit liefern.

Die frühe Frühe Kreide (Berrias – Hauterive, 145–129 Ma) war geprägt von niedrigem Meeresspiegel und starkem Provinzialismus von Faunen und Floren. Mangelnde Meeresverbindungen zwischen den Ozeanbecken ließen nur sehr begrenzten Austausch von Organismen zu. Solch ein Endemismus stellt eine Herausforderung für überregionale biostratigraphische Korrelation der Sedimentfolgen der untersten Kreide dar. Während dieser Zeit war das Niedersächsiche Becken (NB) einer der wenigen marinen Verbindungen zwischen dem Borealen Ozean im Norden und dem Tethys Ozean in äquatorialen Breiten. Isolation des NB und Endemismus wechseln sich ab mit Phasen von Faunen- und Florenaustausch, dokumentiert durch das Auftreten von fossiler Taxa borealer bzw. tethyaler Herkunft. Untersuchungen des NB sind daher sowohl für die Biostratigraphie als auch Paläozeanographie von großer Bedeutung.

Das Klima der Frühen Kreide wird kontrovers diskutiert. Hinweise auf Kälteperioden während der Frühen Kreide, die das gleichmäßig warme Klima des Mesozoikums unterbrachen, stehen Rekonstruktionen warmer, humider Bedingungen gegenüber. Eine Anomalie in der Kohlenstoffisotopie von +1.5‰ ist weltweit in marinen Karbonaten und organischem Material des oberen Valangin (136-133 Ma) messbar. Dieses sogenannte Weissert Event korreliert zeitlich mit dem Paraná-Etendeka Vulkanismus (Paraná- Etendeka Large Igneous Province). Der Untergang von Karbonat-Plattformen in der Tethys und Wechsel in den kalkigen Nannofossil Vergesellschaftungen dokumentieren die einhergehende Veränderung mariner Ökosysteme.

In allen Proxies vergangener Umweltbedingungen überlagern sich lokale, regionale und globale Effekte. Rekonstruktionen sollten daher idealerweise auf Daten von unterschiedlichen marinen Ablagerungsräume und einem weiten Spektrum geographischer Breiten basieren. Voraussetzung für Paläozeanographie-und Paläoklimarekonstruktionen ist die zuverlässige überregionale Korrelation von Sedimentabfolgen. Die

vii vorliegende Dissertation stellt eine Stratigraphie von Unterkreidesedimenten des Boreal vor, basierend auf der Integration verschiedener stratigraphische Methoden (87Sr/86Sr, δ13C, Ammonitenbiostratigraphie, Nannofossilbiostratigraphie). Quantitative Analysen kalkiger Nannofossil-Vergesellschaftungen sowie Biometrie von drei Coccolithenspezies (Biscutum constans, Watznaueria barnesiae, Zeugrhabdotus erectus) werden für die Rekonstruktion von Klima und Ozeanographie der Frühen Kreide genutzt, und lassen Schlussfolgerungen für die Nannofossil-Palökologie zu. Die wichtigsten Ergebnisse dieser Arbeit sind:

1) Ein integrativer stratigraphischer Ansatz basierend auf 87Sr/86Sr-Daten, Kohlenstoffisotopie, Ammonitenbiostratigraphie und Nannofossilbiostratigraphie der Unterkreide Nordostgrönlands ermöglichte die Berichtigung der stratigraphischen Reichweiten von zwei Nannofossil Indexspezies (Sollasites arcuatus, Micrantholithus speetonensis). Daraus ergeben sich Änderungen der Nannofossil-Zonierung der borealen Unterkreide. Nannofossil Biostratigraphie von Sedimenten des mittleren Hauterive des NB modifiziert vorherige Altersbestimmung des Gildehaus Sandsteins in Nordwestdeutschland. Die Basis der Formation wird nun dem späten frühen Hauterive zugeordnet. 2) Aufgrund der stratigraphischen Korrekturen konnte der Häufigkeitsrückgang des kreidezeitlichen Nannofossilgattung Nannoconus, gut bekannt aus dem Valangin der Tethys, in Nordostgrönland nachgewiesen werden. Die erste Dokumentation der mit dem Weissert Evetn einhergehenden Nannoconidenkrise in so nördlichen Breiten deutet darauf hin, dass es sich um ein globales Ereignis handelte, das nicht auf den Tethys-Ozean beschränkt war. 3) Eine Größenverminderung von Coccolithen der Nannofossilspezies B. constans während des Valangin, parallel zum Weissert Event, konnte festgestellt werden. Die Beobachtungen ähneln der Verzwergung von B. constans während der Ozeanischen Anoxischen Events (OAE) der mittleren Kreide, dem Apt-zeitlichen OAE1a und dem OAE2 an der Cenoman/Turon-Grenze. Sowohl während des Weissert Events als auch während dem OAE1a ereignet sich parallel zu der Verkleinerung von B. constans ein Häufigkeitsrückgang von Nannoconiden. Mögliche Ursachen für diese Beobachtungen an Nannofossilien, die derzeit diskutiert werden, sind a) Ozeanversauerung, b) toxische Spurenmetalle und c) verringerte Lichtintensität. Es ist unwahrscheinlich, dass

während des Valangins eine Ozeanversauerung stattgefunden hat, da dafür höhere CO2- Ausstoßraten nötig wären als sie für den zeitgleichen Paraná-Etendeka Vulkanismus rekonstruiert werden. Ebenfalls fehlen Hinweise auf massiven submarinen Vulkanismus, der für hohe Konzentrationen toxischer Metalle in den Ozeanen verantwortlich sein könnte. Der viii

Valanginzeitliche Trend zu humideren Bedingungen und verstärkter kontinentaler Verwitterung passt zu einem Szenario trüberen Wassers aufgrund erhöhten Eintrags von Detritus in die Ozeane. Da es Hinweise auf verstärkte Verwitterung auch während OAE1a und OAE2 gibt, könnte das Modell auch auf diese Events zutreffen. Daher unterstützt die Beobachtung der Größenverminderung von B. constans während des Weissert Events das Modell der verringerten Lichtintensität als Ursache. 4) Das mittlere Hauterive war eine Zeit klimatischen und ozeanographischen Wandels, der im NB zu einem schnellen Wechsel von endemischen Ammonitenfaunen zu borealen und tethyalen Formen führte. Der deutliche Anstieg der Häufigkeiten kalkiger Nannofossilien dokumentiert diese Veränderungen im marinen Ökosystem. Der Übergang vom frühen zum späten Hauterive war chrakterisiert durch warme, humide Bedingungen, und einer Beckenweiten Regression, während der die Sandsteine der Gildehaus Formation am westlichen Rand des NB abgelagert wurden. Der Nannofossilgehalt weist auf einen hemipelagischen Ablagerungsraum des Gildehaussandsteins hin, in dem die groben Siliziklastika einen Massenstrom darstellen.

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IV. Acknowledgements

First of all, I would like to express my gratitude to Jörg Mutterlose for enabling me to write this thesis. He continuously supported my work on the PhD project and provided practical help whenever needed. I am proud to be a member of Zack-society. Further I would like to thank Ulrich Heimhofer for agreeing to be the second supervisor of my PhD, and for valuable advice during my work.

I appreciate very much the work of Janina Falkenberg, Kirsten Kleefuß and Lena Wulff, whose efforts in the lab were most valuable for my PhD project. Christian Linnert is thanked for proof-reading, useful advice and discussions during the work on this thesis. I would like to thank my colleagues and friends at the institute, Ibtisam Beik, Victor Giraldo Gomez, Rene Hoffmann, Nathalie Lübke, Philipp Meissner, Mathias Müller, Tobias Püttmann, Christoph Schneider, Ferdinand Stöckhert and Sara Wassmann for support, discussions, company at lunchtimes, the occasional beer in the evening and generally a good time. Apart from discussions, valuable advice and proof reading, I would like to thank Kevin Stevens for solidarity and a good measure of nonsense during these years of sharing an office. Caroline Mantey is warmly thanked for friendship and company throughout our time at this institute.

Thanks to Elisabetta Erba I was able to go to Milano for a two-month research stay. My thanks for advice and discussions go also to Cinzia Bottini, Cristina Casellato and Giulia Faucher.

Ursula Justus and the Research School of the Ruhr-Universität Bochum are thanked for support, advice, and encouragement. I am grateful for financial support granted by the Wilhelm and Günter Esser-Stiftung during the final phase of this PhD project.

Last but not least I want to thank Michi, my parents, and all my family, friends, and housemates for their continuous support and sympathy during the last years.

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Introduction

1 Introduction

The preset dissertatio ith the title Proiialis ad gloal eiroetal hage i the Earl Cretaceous - Paleoceanographic and stratigraphic applications of calcareous nannofossils and geochemistr is suitted as a dotoral thesis to the fault of Geosiees of the Ruhr-Universität Bochum. The objectives of this thesis are revision and refinement of the age assignments for Lower Cretaceous sediment successions of the Boreal Realm, and reconstructions of Early Cretaceous climate and oceanography, with a focus on the environmental perturbation during this time.

1.1. Thesis structure This thesis consists of five chapters. Chapter 1 introduces the topic and methods of the thesis. Chapters 2, 3 and 4 are manuscripts that have been published in or have been submitted to international peer reviewed journals. Chapter 5 discusses the conclusions that can be drawn from this thesis, as well as perspectives for future research.

Chapter 1 consists of three parts. The first part introduces calcareous nannofossils, their biology, evolution and biogeochemical significance, as well as their applications in biostratigraphy and paleoceanography. The second part gives an overview over climate and oceanography of the Early Cretaceous period (145 – 100 Ma), addressing the controversial views of the Early Cretaceous climate. This part also introduces environmental perturbations during the Mesozoic and Cenozoic, introducing the concept of Oceanic Anoxic Events, short phases of environmental perturbation in the Mesozoic and Cenozoic. The third part explains the aims and objectives of the present thesis.

Chapter 2, published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology (Issue 437, pp. 85- 97, 2015), presents a revised stratigraphic zonation of the lowermost Cretaceous (Ryazanian – Barremian) of North East Greenland. Integrating geochemical data (87Sr/86Sr, δ13C) and biostratigraphy (calcareous nannofossils, ammonite), as well as correlation with the standard Tethyan zonations allowed for a refinement of the existing calcareous nannofossil zonation for the Boreal Lower Cretaceous. The new data permit the identification of the global environment perturbation in the late Valanginian stage (~135 - 132 Ma), the Weissert Event, in the studied section. A nannofossil response associated with the event, well known from the Tethys, is described for the first time in a section of the higher Boreal.

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Chapter 1

Chapter 3 is a manuscript that has been submitted to the journal Paleoceanography. It investigates the paleoceanographic changes associated with the Valanginian Weissert Event by studying the size evolution of three species of calcareous nannofossils. The size reductions of calcareous nannofossils during the Weissert Event are related to changes in the marine ecosystem caused by a humid late Valanginian climate, which are probably linked to volcanic CO2 outgassing. In the discussion of the nature of the event, the results are compared with similar data sets covering mid-Cretaceous Oceanic Anoxic Events.

In chapter 4, which has been published in Zeitschrift der Deutschen Geowissenschaftlichen Gesellschaft (Issue 165 (4), pp. 501-520, 2014), two synchronous successions of mid-Hauterivian sediments are correlated by nannofossil biostratigraphy. Nannofossil assemblages from a basin margin and a basin center setting of a marine epicontinental basin are analyzed. Nannofossil and geochemistry data are used for the reconstruction of nutrient concentrations and temperature trends related to mid-Hauterivian fluctuations in sea-level and climate. The oil bearing basin margin sequence is interpreted as a mass-flow deposit.

Chapter 5 summarizes the main findings of the thesis, discussing the implications of the three studies for Lower Cretaceous biostratigraphy, the reconstruction of environmental change during the Weissert Event, and Valanginian – Hauterivian paleoceanography of the Lower Saxony Basin (northern Germany). Additionally, perspectives for further research are discussed.

1.2. Calcareous nannofossils By definition, all calcareous fossils smaller than 30 µm belong to the calcareous nannofossils (e.g., Bown and Young, 1998). The most abundant fossils of this heterogenous group are calcite remains of single- celled algae of the division Haptophyta. Apart from these, remains of calcareous dinoflagellates, juvenile foraminifera and ascidians (sea squirts) are included in the calcareous nannofossil as well.

The coccolithophores are a group of haptophyte algae that are able to build an outer sphere consisting of numerous separate calcite platelets. These tiny oval calcite platelets, ~1 -20 µm in size, are called coccoliths. When they were first observed in chalks from the island of Rügen and in deep sea oozes of the North Atlantic, they were believed to be of inorganic origin (Ehrenberg, 1836, 1840, 1854; Huxley in Dayman, 1858). Later, spherical objects covered with coccoliths were observed floating in the surface waters of tropical oceans Wallich (1860, 1868). Lohmann (1902) summarized the observations of various researchers of the previous decades and concluded that coccolithophores are single-celled plants, whose cell-body is enclosed in a shell composed from coccoliths. He taxonomically assigned them to the

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Introduction chrysomonads based on the presence of flagella. These important first observations and publications were followed by numerous systematic biological studies and taxonomic descriptions of recent and fossil forms (eg. Arkhangelsky, 1912; Schiller, 1913; Kamptner, 1952; Deflandre, 1952, 1959; Braarud, 1954). Lohman (1902) was already aware of the worldwide distribution of the coccolithophores. Due to their small size and, as he assumed, low numbers he still considered them as a rather insignificant part of marine ecosystems. According to more recent estimates, however, coccolithophores are responsible for roughly half of the calcium carbonate production in the modern oceans (Milliman, 1993).

1.2.1. Biology The division Haptophyta includes almost solely marine, unicellular phytoplankton. In addition to two flagella, haptophytes in the motile stage possess a third appendage that is structurally quite different from the flagella – the haptonema (Inoue and Kawachi, 1994; Pienaar, 1994). The haptonema is used for attachment of the cell to a surface or in some cases for capturing and ingestion of particulate matter (Inoue and Kawachi, 1994; Pienaar, 1994; Billard and Inouye, 2004). A fundamental biological feature of the coccolithophores is their heteromorphic haplo-diploid life cycle (Fig. 1.1; DeVargas and Probert, 2004). In the haploid stage the cell nucleus contains only a single set of chromosomes, in the diploid stage it contains two copies of each chromosome. The cells alternate between the life-cycle phases by meiosis and syngamy, respectively. Asexual reproduction by binary fission can occur in both the diploid and haploid phase (Fig. 1.1; Billard and Inouye, 2004; Young et al., 2003). The life-cycle alternations are generally associated with changes from motility in the haploid phase, to non-motile cells in the diploid phase (Young et al., 2003; Hagino et al., 2016).

The modes of biomineralization differ between the two life cycle stages. Many coccolithophore calcify only in one of the life-cycle stages and some do not calcify at all (Fig. 1.1). The coccoliths of diploid cells, called heterococcoliths, are formed inside the cell. Heterococcolith formation takes place on organic scales that act as a base-plate or template for the nucleation and growth of calcite crystals (Young et al., 1999; Young and Henriksen, 2003). These organic scales are produced in vesicles derived from the Golgi body (Young and Henriksen, 2003; DeVargas and Probert, 2004). The fundamental building blocks are mineralized starting from a first basal ring of calcite crystals called proto-coccolith ring. Radially arranged, these building blocks form round or oval discs, the coccoliths. The crystallographic c-axes of the crystals of the proto-coccolith ring are alternately oriented radially and vertically relative to the base-plate scale (Westbroek et al., 1989; Young et al., 1992). The orientations of the initial calcite crystals are maintained in the two crystal-unit types which the heterococcolith consists of, which are consequently called R- and

3

Chapter 1

Figure 1.1 Coccolithophore life cycles. Left side: The hexagon of life in coccolithophores, from DeVargas and Probert (2004). It shows the life-cycle stages (2N = diploid; N=haploid) of coccolithophores and the cell covering that can be associated with the life stages life stages. Calcified: with either hetero- or holococcoliths; non-calcified: covered by organic scales or naked. Black arrows indicate the possible life cycle associations. Right side: SEM of a holococcolith coccosphere of Syracolithus quadriperforatus (a), SEM of a Calcidiscus leptoporus – Syracolithus quadriperforatus combination coccosphere with hetero- and holococcoliths (b), detail of the combination coccosphere (c), from Geisen et al. (2002).

V-units (Young et al., 1992, 1999). Heterococcoliths are divided into two fundamental morphological types: the placoliths with two horizontal shields connected by a central tube, and the muroliths characterized by a wall-like sub-vertical rim (Bown and Young, 1998).

When the intracellular formation is completed, heterococcoliths are transported to the cell surface. The interlocking coccoliths form an outer shell around the cell, the coccosphere. The formation of one coccolith of Coccolithus pelagicus takes about 2.5 to 4 hours (Taylor et al., 2007). In laboratory experiments, after having been decalcified, cells of Hymenomonmas carterae produced completely new coccospheres within 12 – 24 hours, depending on light availability (Ariovich and Pienaar, 1979). In some non-calcifying Prymnesiophyceae a cell cover is formed solely by organic scales.

A second type of coccoliths, the holococcoliths, are formed during the haploid phase. They are composed entirely of similar, minute (~0.1 µm) crystallites, predominantly euhedral rombohedra (Fig. 1.1; Young and Henriksen, 2003; Young et al., 2003). The process of holococcolith formation is distinctly different from the formation of heterococcoliths. It is very probable that holococcoliths are produced on organic scales outside of the cell membrane (Young and Henriksen, 2003). The arrangement patterns of the crystallites and the elaborate holococcolith morphologies suggest a highly regulated growth. The controlling mechanisms of holococcolith formation, however, are as yet poorly understood (Young and Henriksen,

4

Introduction

2003). Calcification might be regulated by a delicate skin enveloping the coccosphere. An alternative explanation is that holococcolith formation takes place just beneath the cell membrane, too rapid to be observed in cytological sections during culture experiments (Young and Henriksen, 2003).

The ~35 Ma delay between the first appearance of hetero- and holococcoliths in the fossil record suggests that the two different modes of coccolithophores biomineralization in the diploid and haploid life stage may have evolved separately (Young and Henriksen, 2003; DeVargas et al., 2007). This offset could alternatively be explained by preservation as holococcoliths are less robust than heterococcoliths. The secondary development of calcification in the haploid stage is supported, however, by molecular genetic analyses, that suggest that the basal coccolithophore clade consists of genera not calcifying in their haploid stage (Young and Henriksen, 2003; Sáez et al., 2004).

Documentation of life-cycle combinations of hetero- and holococcoliths has caused taxonomic changes. In most cases, species have originally been described from either hetero- or holococcolths and therefore had to be synonymized (Jordan et al., 2004). Coccospheres with both hetero- and holococcoliths, so-called combination coccospheres, document the transition from one phase of the life-cycle to the other (Fig. 1.1). These combination coccospheres revealed links between hetero- and holococcolith species that had formerly been assigned to different genera (e.g., Billard, 1994; Cros et al., 2000; Geisen et al., 2002; Jordan et al., 2004).

The function of coccoliths is being debated controversially. Protection against grazing and/or viruses has been proposed, but also control of sinking rate and light control - either to shield the cell from excessive sunlight/ harmful ultraviolet light, or on the contrary, a lense-like function for concentrating light towards the interior of the coccosphere. Biochemical benefits of calcification are under discussion as well, including carbon concentration for photosynthesis, phosphorous metabolism, and to balance between high external and low intracellular Ca concentration (Haq, 1978; Young, 1994; DeVargas et al., 2007). There might not be one single, universal function of coccoliths and coccolith formation. Instead, the benefits for the cell probably consist of a combination of effects. The broad variety of existing coccolith morphologies and sizes supports the assumption, that - depending on the habitat and ecologic strategy - some of the effects of coccoliths and/or coccolith formation are exploited by the coccolithophores, while others are minimized (Young, 1994).

Another aspect intensively discussed is the environmental control over coccolithophore calcification. The effects of parameters such as sea water pH, trace metal concentration, temperature, light availability, and dwelling depth are studied and discussed both in fossil and modern taxa. A link between haptophyte

5

Chapter 1

calcification and their habitat is demonstrated by the distribution pattern of recent coccolithophores. In modern oceans, the heavily calcified coccolithophores are found in oligotrophic pelagic settings, while coccolithophores populating coastal or neritic settings often produce small or poorly calcified coccoliths, and do not calcify in their haploid stages (DeVargas et al., 2007). The calcareous nannofossils interpreted as indicators for nutrient rich near-coast settings in the Cretaceous are accordingly small and delicate species (Mutterlose et al., 2005).

In view of the current anthropogenic rise of atmospheric CO2 concentrations and increasing ocean acidification, the effect of pH changes on biomineralization has become important. Culture experiments with several coccolithophore species (Emiliania huxleyi, Gephyrocapsa oceanica, Coccolithus pelagicus, Calcidiscus leptoporus) produced ambiguous results. Some studies report reduced calcite production, malformed coccoliths and incomplete coccospheres with declining pH (Riebesell et al., 2000; Bach et al., 2011). On the other hand, cultures of E. huxleyi can show significant increases in calcification and productivity under high CO2 conditions (Iglesias-Rodriguez et al., 2008). Responses to CO2 perturbations observed in laboratory experiments are not mirrored in the fossil record of glacial and preindustrial sediments, suggesting that the algae have the capacity to adapt their calcification mechanism (Langer et al., 2006). The reasons of the coccolithophore response to high CO2 concentration and low pH are still unclear. Modelling approaches suggest that the extra energetic costs of H+ extrusion in a lower pH are relatively small, compared, e.g., to the costs of photosynthetic carbon fixation (Monteiro et al., 2016).

Apart from CO2 concentrations, elevated concentrations of toxic trace metals have been suspected to inhibit coccolith formation and cause dwarfing during past episodes of strong submarine volcanism (Erba, 2004; Faucher et al., 2017a). Toxic trace metals can affect phytoplankton reproduction by competitively inhibiting the uptake and metabolism of trace nutrients (Brand et al., 1986; Sunda, 1989). Coccolithophores have been found to be particularly sensitive to Cadmium, which interferes with calcification (Brand et al., 1986; Brand, 1994). Recently, the negative effect of elevated trace metal concentrations on coccolith size and/or weight was verified in coccolithophore culture studies (Faucher et al., 2017b).

1.2.2. Nannoliths Nannoliths are a heterogenous group of calcareous nannofossils that includes taxa of uncertain systematic affinity. All biogenic calcareous structures in sizes of about 1-30 µm, but missing the characteristic features of hetero- or holococcoliths, are commonly assigned to this group (Haq, 1978; Young et al., 1999; DeVargas et al., 2007). The nannoliths include a number of fossil taxa that are significant in terms of abundance,

6

Introduction

Figure 1.2 SEM images of Nannoconus bucheri (A) and Nannoconus sp. (B) in a sample from the Hauterivian of northern Germany. The specimen in (B) is broken and the inner structure is visible. The scale bars equal 2 µm. distribution, diversity, and carbonate production. An important group of the Early Cretaceous are the nannoconids (Fig. 1.2), cylindrical structures composed of stacked calcite elements, which can be rock- forming in Tithonian to Barremian successions (Wieczorek, 1988; Bersezio et al., 2002; Mutterlose and Bottini, 2013).

By now, several recent nannolith species have been shown to belong to the calcifying haptophytes, either based on the observation of coccospheres combining both heterococcoliths and nannoliths, or by molecular phylogenetic studies (Alcober and Jordan, 1997; Sprengel and Young, 2000; Hagino et al., 2013). The production of heterococcoliths and nannoliths alternating with life-cycle stages have been observed in the genera Ceratolithus and Alisphaera (Alcober and Jordan, 1997; Cros and Fortuno, 2002; Young and Henriksen, 2003). Structure and morphology of these nannoliths neither resemble heterococcoliths nor holococcoliths. This strongly suggests that, similar to holococcoliths, these nannoliths represent a new haptophyte calcification strategy that evolved and a transfer of calcification from the diploid to the haploid stage (Young and Henriksen, 2003).

For the Braarudosphaeraceae, DNA sequencing confirmed the close affinities to the division Haptophyta (Takano et al., 2006). This is supported by the observation of haptonemae in cells of an extant member of the family (Hagino et al., 2016). The pentagonal plate-like nannoliths of the Braarudosphaeraceae, called pentaliths, first appear in the fossil record of the Upper Jurassic (Tithonian; Casellato, 2010). A pentalith is

7

Chapter 1

Figure 1.3 Microscope images of Braarudosphaera bigelowii from Hagino et al. (2013). (A) is a SEM image of a cell covered with pentaliths, (B) shows a single pentalith, and (C) is a detail of a pentalith showing the layers of stacked calcite crystals it is composed of. (D) – (F) are light microscope images of B. bigelowii cells. composed of five (rarely six) trapezoidal calcite elements with a laminar structure (Fig. 1.3). The pentaliths form pentagonal dodecahedra around the cells of the Braarudosphaeraceae. The few extant members of the Braarudosphaeraceae are limited to the genus Braarudosphaera, most prominent the type species of the family, B. bigelowii. In their detailed study of the morphology and crystallographic structure of B. bigelowii pentaliths, Hagino et al. (2016) conclude that calcification of B. bigelowii pentaliths occurs on the cell surface. During extensive studies of the species, incomplete pentaliths inside cells of B. bigelowii have never been observed, while the observation of cells containing incomplete heterococcoliths is common (Hagino et al., 2016). High Mg-contents compared to heterococcoliths supports the extracellular pentalith alifiatio. Further Hagio et al. osered a sustrate uderlig the petaliths ad thi orgai layers extending onto its surface, which they interpreted as a template for growth regulation.

The life-cycle of B. bigelowii has not been witnessed yet, but a molecular phylogenetic study suggests that the non-calcifying Chrysochromulina parkae represents a life-cycle stage of B. bigelowii (Hagino et al., 2013). Very likely the non-motile calcifying B. bigelowii represent the diploid life-cycle stage, and the motile C. parkae is haploid (Young et al., 2003; Hagino et al., 2016). If this is the case, the

8

Introduction

Braarudosphaeraceae evolved an extracellular calcification strategy in the diploid phase, thereby representing a new life-cycle combination of haptophytes (diploid phase: pentalith, haploid phase: non- calcifying; compare Fig. 1.1). It is likely that a number of nannoliths are closely related to the haptophytes, although particularly for fossil taxa without extant members, proof of this is not easily provided. Based on common morphological features (thin stacked calcite elements arranged with rotational symmetry and tangential c-axis orientations) and close origination dates in the late Jurassic, the Nannoconaceae were recently grouped with the Braarudosphaeraceae in the Braarudosphaerales (Lees and Bown, 2016).

1.2.3. Evolution and fossil record of calcareous nannofossils The oldest definite fossil coccoliths have been observed just below the Norian-Rhaetian boundary (upper Triassic, 209.5 Ma). Older Carnian nannofossil findings (~225 Ma) are limited to nannoliths of uncertain affinity and calcareous dinoflagellates (Janofske, 1992; Bown et al., 2004). The division Haptophyta, however, is considerably older, photosynthetic haptophytes are assumed to exist at least since the Neoproterozoic (1000-542 Ma; DeVargas et al., 2007). The appearance of coccoliths in the fossil record thus merely reflects the development of haptophyte biomineralization (DeVargas and Probert, 2004). Triassic nannoplankton assemblages are of low diversity and possibly restricted to low latitudes (Bown, 1992; Bown and Cooper, 1998; Bown et al., 2004). Most of these species did not survive the end-Triassic mass extinction (Bown, 1998; Bottini et al., 2016). The Early Jurassic is marked by an important radiation of calcareous nannoplankton, and the origination of nine of the 16 Mesozoic coccolithophores families (Bown et al., 2004). After the re-establishment of the surviving Triassic group (muroliths), a new coccolith morphology, the placoliths, evolved rapidly. By the end of the Early Jurassic they dominated the assemblages (Fig 1.4). Among the taxa that appeared during the Early Jurassic diversification event were two of the most important Mesozoic nannofossil families, the Watznaueriacea and the Biscutaceae (Bown and Cooper, 1998). The first holococcoliths are known from the Early Jurassic (Pliensbachian, 185 Ma; DeVargas et al., 2007), documenting the evolution of coccolithophore biomineralization strategies during that time. The nannofossil turnover across the Jurassic-Cretaceous boundary is marked by high rates of species extinctions and originations. Three important nannolith families, the Nannoconacea, Braarudosphaeraceae and Microrhabdulaceae, first appear in this interval (Bown et al., 2004). The first pelagic carbonates of significant thickness generated by nannofossils (e.g., the Italian Maiolica limestone formation) are of Late Jurassic age (Tithonian). These pelagic micrites are characteristic for the Lower

9

Chapter 1

Figure 1.4 Evolutionary history of coccolithophores, from Monteiro et al. (2016). (A) shows coccolithophores diversity (species richness of heterococcoliths and nannoliths, data from Bown et al., 2004). Q = Quaternary, N = Neogene, Pal=Paleogene, E/O = Eocene/ Oligocene glacial onset, PETM = Paleocene/Eocene thermal maximum, K/Pg = Cretaceous/Paleogene, OAE = Oceanic Anoxic Event, T-OAE = Toarcian Oceanic Anoxic Event, T/J = Triassic/Jurassic, P/T = Permian/Triassic; (B) shows some major innovations and appearance of morphogroups in the fossil record of coccolithophores.

Cretaceous of the Tethys, the Atlantic and Pacific Oceans (Wieczorek, 1988; Bersezio et al., 2002; Hay, 2008). They document the colonization of the open ocean by planktic carbonate producers (Hay, 2008). Calcareous nannofossils and planktic foraminifera were originally restricted to epicontinental seas, but spread to the open ocean during the Early Cretaceous (Roth, 1986). The main site of carbonate production shifted from reef dominated shallow water settings to the pelagic carbonates of the open ocean (Hay, 2008).

Calcareous nannofossil diversity reached its maximum in the Late Cretaceous (Campanian, ~ 80 Ma; Fig. 1.4), coinciding with generally large coccolith sizes (Bown et al., 2004; Falkowski et al., 2004). The Mesozoic

10

Introduction radiation of coccolithophores paralleled a long-term sea-level rise and expansion of flooded continental shelf areas, culminating in the Late Cretaceous (Fig. 1.5; Falkowski et al., 2004). The specific oceanographic and climatic conditions are reflected by the widespread deposition of chalks, a sediment unique unique for the late Cretaceous and Paleogene. Chalk consists nearly exclusively of calcareous tests of planktic organisms (calcareous nannofossils and foraminifera). The calcareous deep-sea oozes (Globigerina/aoplakto ooze of toda’s oeas are aalogous to of these halks. I otrast to the recent sediments, deposition of the massive chalk units took place in the epicontinental seas of the Cenomanian to Eocene (e.g., Hattin, 1988; Stanley et al., 2005; Linnert et al., 2016).

The Cretaceous/Paleogene boundary (K/Pg) is marked by a rapid breakdown of Cretaceous nannofossil abundance and diversity (e.g., Gardin and Monechi, 1998; Gardin, 2002). Only nine of 131 late Maastrichtian species survived the extinction event, none of them a common species of Late Cretaceous assemblages (Bramlette, 1965; Bown et al., 2004). Following the K/Pg event, small calcispheres dominated nannofossil assemblages (Gardin, 2002; Bown et al., 2004). During the Paleocene radiation, coccolithophores developed new morphologies very different from those of Mesozoic forms (Bown et al., 2004). By early Eocene, coccolithophore diversities had recovered (Bown et al., 2004; Falkowski et al., 2004). On the other hand, a long-term diversity decline commenced in the early Eocene that continues until today (Bown et al., 2004; Falkowski et al., 2004). Coccolithophores, as well as dinoflagellates, had dominated the warm Mesozoic oceans, which were characterized by sluggish circulation and low latitudinal temperature gradients. Coccolith diversity has been found to increase in phases of long-term stability of oligotrophic to mesotrophic water masses (Bown et al., 2004; DeVargas et al., 2007). The buildup of polar ice on Antarctica during the Eocene-Oligocene climate transition resulted in a more vigorous thermohaline circulation, increased wind speeds and upper ocean turbulence (Liu et al., 2009). These conditions favor diatoms, which seem to have started outcompeting coccolithophores and dinoflagellates from Late Eocene times on (Fig. 1.5; Falkowski et al., 2004).

1.2.4. Significance of coccolithophores for ocean chemistry and biogeochemical cycles Coccolithophores are part of the phytoplankton, which is responsible for more than 45% of the annual net primary production worldwide. They are, along with the dinoflagellates and diatoms, responsible for most of the export flux of organic matter to sediments (Falkowski et al., 2004). Coccolithophores account for about half of the calcium carbonate production in modern oceans (Milliman, 1993). Coccolithophore

11

Chapter 1

Figure 1.5 Comparison of eukaryotic phytoplankton species (red) and genus (blue) diversity curves with sea-level change (red), flooded continental areas (blue), and the evolution of grasses (Falkowski, 2004).

biomineralization thus plays an important role in the global carbon cycle. On the one hand, carbonate production is a source of CO2 to the surface ocean and the atmosphere (Fig. 1.6; Rost and Riebesell, 2004; DeVargas et al., 2007). On the other hand, coccolithophores are an important part of the organic carbon

12

Introduction

pump, which removes CO2 from the atmosphere (Rost and Riebesell, 2004; DeVargas et al., 2007).

Photosynthetic organisms consume dissolved CO2 in the photic zone to produce particulate organic carbon (POC) and oxygen (=primary production). Most of the POC is being recycled in the biological food web in the surface waters. Only roughly a fifth of the primary production reaches the lower boundary of the photic zone - this fraction is called the export production of carbon – and can form CO2 siks i the oea’s iterior and at the seafloor (Rullkötter, 1999; Honjo, 2008) Particulate organic matter on its own would not sink due to its low density. One of the major processes for POC export is the transport to the ocean interior by gravitational settling in aggregates of various origin, the so-called marine snow (Honjo et al., 2008). Here coccoliths are thought to play a major role, as they are considered the most suitable ballast particles, due to their small and uniform size, dissolution resistance, and direct supply from the euphotic zone (Honjo et al., 2008).

Furthermore, the proliferation of calcifying plankton in the Jurassic revolutionized the marine carbonate chemistry. In pre-Jurassic times, phases of extreme carbonate oversaturation of the oceans occurred repeatedly until the late Triassic, documented by - fro a oder poit of ie aoalousl - large quantities of marine cement in carbonate successions and abundant environmentally controlled carbonates such as inorganically precipitated sea-floor crusts (Grotzinger and Knoll, 1995; Ridgwell, 2005). Carbonate deposition in open oceanic settings created a substantial, new deep-sea carbonate sink that provides a negative feedback to carbonate over-saturation of the ocean (Ridgwell, 2005; Ridgwell and

Zeebe, 2005; DeVargas et al., 2007). During atmospheric CO2 perturbations, ocean chemistry is stabilized by changing the amount of preserved deep-sea carbonates (Ridgwell and Zeebe, 2005). To understand this buffering mechanism, a brief look at the carbonate system is needed.

Carbon dioxide exists in the ocean in three different inorganic forms, which are related by equilibrium

- 2- equations: aqueous carbon dioxide CO2(aq), bicarbonate HCO3 , and carbonate ion CO3 . The pH of seawater is a result of the relative proportions of these carbonate species. The concentration of CO2 in the ocean changes proportionally to variations of atmospheric CO2 (Zeebe and Wolf-Gladrow, 2001). If a large quantity of CO2 is removed from the atmosphere, e.g., stored in terrestrial biosphere due to increased

2- productivity, the carbonate equilibrium of sea-water shifts in favor of CO3 concentration and a higher pH. This increases the stability of carbonate, thereby enhancing carbonate precipitation. Counterintuitively, the formation of CaCO3 increases CO2 concentrations (e.g., Zeebe and Wolf-Gladrow, 2001). Higher rates

13

Chapter 1

Figure 1.6 Role of coccolithophores in biogeochemical cycles, from DeVargas et al. (2007). Coccolithophores are

thought to play an important role in the organic carbon pump (A) that removes CO2 from the atmosphere, as coccoliths are considered most suitable ballast particles for the export of organic matter to the deep ocean in aggregates (marine snow). Coccolithophores are also part of the carbonate counter pump (B), which is a short-term

source is a source of CO2 to the surface ocean and the atmosphere through carbonate precipitation. ACD=aragonite compensation depth, Lysocline=complete dissolution of planktic foraminifera, CCD=calcite compensation depth, DMS=Dimethyl sulphide, a secondary metabolite emitted to the atmosphere by phytoplankton.

of carbonate precipitation are thus driving more CO2 into the atmosphere, balancing the CO2 depletion of the atmosphere (Ridgwell and Zeebe, 2005). This calcite compensation buffering acts on time scales of 5- 10 ky (Ridgwell and Zeebe, 2005).

14

Introduction

1.2.5. Applications The worldwide distribution and their large numbers make calcareous nannofossils excellent tools for age assignment and correlation of sediment rock units with a high temporal resolution (e.g., Mutterlose et al., 2005). Intensive work on nannofossil biostratigraphy starting in the 1960s resulted in in the establishment of detailed biozonation schemes for the Mesozoic (e.g., Thierstein 1971; 1973; 1976; Sissingh, 1977; Roth, 1978; Mutterlose, 1992; Bown et al., 1998; Jeremiah, 2001) that are since being refined and amended.

Calcareous nannofossils are furthermore used as proxies for past environmental conditions, such as water temperature, nutrient concentrations, and productivity (e.g., Perch-Nielsen, 1985; Mutterlose et al., 2005). The abundance patterns and composition of modern coccolithophore assemblages reflect changing environmental conditions (e.g., Cortés et al., 2001). Based on the assumption that the basic parameters governing the distribution of nannoplankton in the Mesozoic were the same as in modern oceans (Lees et al., 2005), the composition and diversity of fossil assemblages are used for paleoceanographic reconstructions (e.g., Herrle et al., 2003; Gibbs et al., 2006). Environmental conditions influence the calcification behavior of coccolithophores (e.g., Mattioli et al. 2004; Bornemann & Mutterlose 2006; Bornemann et al. 2003; Linnert & Mutterlose 2013). Biometric analyses of coccoliths may thus give valuable insights into environmental changes.

Apart from studying calcareous nannofossil abundance, diversity and size distributions, the low-Mg calcite skeletons of calcareous nannofossils are also studied geochemically (e.g., Stoll and Schrag, 2000; Prentice et al., 2014). Coccolith calcite based geochemical proxies include Mg/Ca and oxygen isotope paleothermometry (Stoll et al., 2001), Sr/Ca ratios as a proxy for productivity (Rickaby et al., 2002; Stoll ad “hrag, ad aro isotope opositio as a easure of hages i δ13C of dissolved inorganic carbon (Stoll and Ziveri, 2004). However, as diagenetic overgrowth can selectively affect specific taxa, a thorough examination of potential diagenetic alteration and careful choice of the measured size fractions or specimens is crucial (Dedert et al., 2014).

Due to their small size, which makes selection and diagenetic screening of specimens for analysis a difficult procedure, coccolith calcite is not as well-established as an archive for stable isotope based paleoceanographic studies as the tests of foraminifera (Hermoso, 2014). In recent years, methods for measuring the elemental chemistry of single coccoliths or concentrating near monospecific assemblages have been developed (e.g., Stoll et al., 2007; Hermoso, 2014; Prentice et al., 2014). These methods exclude the falsifying effect of other calcite particles and also of coccolith species-specific isotope fractionation, which complicates analyzes of coccolith-dominated bulk calcite fraction from pelagic sediments.

15

Chapter 1

Still the problems regarding coccolith calcite isotope geochemistry related to vital effects are not solved completely. The assumption that isotopic fractionation during coccolith formation is a constant species- specific trait and that coccolith stable isotopes therefore reliably reflect environmental parameters has been challenged in recent studies (Hermoso, 2014). Alternatively, the environment dependent effect of coccolithophore physiology on the isotope composition of coccolith calcite has been proposed as a paleoenvironmental proxy (Hermoso, 2014). Further, geochemistry may be used to adae the lassial nannofossil paleoecology. Geochemical characterization of individual nannofossil taxa has been proposed to ascertain the paleoecological characteristics assigned to them (Lees et al., 2005).

1.3. The Early Cretaceous

1.3.1. Climate The Cretaceous Period is divided in an Early (145 – 100.5 Ma) and a Late (100.5 – 66 Ma) epoch. The Early Cretaceous climate was variable, characterized by alternating humid and arid phases (Hay, 1995; Föllmi, 2012). Large humid belts dominated by monsoonal climate and regional strong upwelling led to an uneven distribution of heat (Föllmi, 2012). Evidence for the presence of sea ice in higher latitudes is provided by large, exotic clasts found in Lower Cretaceous sediments from Australia, Alaska, Spitsbergen, and Siberia, that have been interpreted as ice rafted debris and glacial dropstones (Kemper, 1987; Frakes and Francis, 1988). Sedimentological, paleontological, and geochemical evidence indicates cooling episodes during the Early Cretaceous that interrupted the generally warm, equable Mesozoic climate (e.g., Weissert and Erba, 2004; Mutterlose et al., 2009; Price and Nunn, 2010).

The oxygen isotope composition of biogenic carbonates is a function of ambient water temperature and seaater δ18O (Urey, 1947). Oxygen isotope ratios (δ18O) of carbonate samples are therefore commonly used proxy for paleotemperature estimates (e.g., Huber et al., 1995; McArthur et al., 2004). Oxygen isotope data based on foraminifera, belemnites and bulk-rock carbonates show trends towards heavier values both in the upper Valanginian and upper Aptian, which have been interpreted as cooling episodes (e.g., Clarke and Jenkyns, 1999; Fassell and Bralower, 1999; McArthur et al., 2007; Meissner et al., 2015; Podlaha et al., 1998; Price and Mutterlose, 2004; Weissert and Erba, 2004). An icehouse interlude in the upper Aptian is supported by the abundance increase and biogeographic expansion of calcareous nannofossil taxa with assumed cool-water/ high latitudinal affinities in the Aptian-Albian (Mutterlose et al., 2009). Considerable latitudinal temperature gradients throughout the Valanginian to early Hauterivian times are supported by the bipolar distribution of the high-latitudinal nannofossil taxon Crucibiscutum

16

Introduction

salebrosum (Fig. 1.8; Mutterlose and Kessels, 2000). In the Valanginian calcareous nannofossils record, characteristic Tethyan and Boreal assemblages can be distinguished, with only rare overlap. This paleobiogeographic pattern is interpreted as largely isolated, temperature controlled high- and low- latitudinal assemblages, that document a cool Valanginian climate (Mutterlose and Kessels, 2000).

Glendonites frequently found in the Valanginian and Aptian/Albian strata of Spitsbergen, Siberia, and northern Alaska are seen as further evidence for cold climate interludes (Kemper and Schmitz, 1975; Kemper, 1987; Price and Nunn, 2010; Rogov and Zakharov, 2010; Schröder-Adams et al., 2014; Grasby et al., 2016). Glendonites are pseudomorphs of Ikaite, a carbonate mineral (Kemper and Schmitz, 1981; Brooks, 2016). Ikaite is only stable at low temperatures (< 7°C). The occurrence of glendonites in high latitude sediments has been interpreted as a document of a cold depositional environment (e.g., Kemper and Schmitz, 1981; Kemper, 1987; Grasby et al., 2017).

The evidence for a climate cooling during the Valanginian has Figure 1.7 Chronostratigraphic chart 18 of the Cretaceous, ICS International ee halleged, though. “eaater δ O is subject to large Commission on Stratigraphy 2016 regional variations, depending on evaporation and precipitation patterns (LeGrande and Schmidt, 2006; Roche et al., 2006; Brad et al., . A uifor δ18O value of - ‰ hih is geerall assued for Cretaeous sea ater for (e.g., Shackleton and Kenett, 1975; Podlaha et al., 1998) is therefore a simplification that may falsify the results of paleotemperature reconstructions. The positie tred i δ18O in the late Valanginian may be the result of a transition to a humid climate regime during which large volumes of water transferred to the continents, and not necessarily a cooling episode (Föllmi, 2012).

The interpretation of biogeography in the earliest Cretaceous may be ambiguous as well. The Berriasian to Hauterivian was a time of significant geographic separation of the Boreal and Tethyan Realms. As a consequence of the Latest Jurassic – earliest Cretaceous sea level lowstand and the continent distribution in the early stages of the progressive breakup of Pangea, the two marine Realms were connected only by

17

Chapter 1

Figure 1.8 Paleogeography during Valanginian-Hauterivian times with distribution of the calcareous nannofossil Crucibiscutum salebrosum from Mutterlose and Kessels (2000). narrow seaways and small epicontinental basins. The provincialism of marine floras and faunas of the earliest Cretaceous may reflect this physical separation, instead of a pronounced temperature gradient (e.g., Remane, 1991; Mutterlose and Kessels, 2000; Wimbledon et al., 2011).

Recent studies link the occurrence of glendonites to submarine methane venting (Greinert and Derkachev, 2004; Morales et al., 2017). Transformation of Ikaite to glendonite has been shown to occur associated with anaerobic methane oxidation and methane-venting (Greinert and Derkachev, 2004; Morales et al., 2017). The phases of increased glendonite formation in the Toarcian (183 Ma), Valanginian (136 Ma), Aptian-Albian (126 – 100 Ma), and Paleocene-Eocene (56 Ma) each coincide with perturbations of the carbon cycle (Kemper and Schmitz, 1981; Spielhagen and Tripati, 2009). Thus, the glendonite occurrence in the sedimentary record may document increased methane release as well as climate cooling (Morales et al., 2017). For supposedly glacial dropstones alternatively a transport by driftwood or floating seaweed has been suggested (Price, 1999).

In contrast to Early Cretaceous, the Late Cretaceous was characterized by equable, warm conditions with episodically extreme temperatures until the global cooling in the Maastrichtian (e.g., Linnert et al., 2014). It has ee desried as a greehouse orld ith relatiel ar liate etedig up to polar latitudes

18

Introduction

(Jenkyns et al., 2004). Plant fossils document forests in high latitudes (>70° N/S) that required winter temperatures at or above freezing (Read and Francis, 1992; Herman and Spicer, 1996; Spicer et al., 2002). For the Cenomanian-Turonian, (100.5 – 93.9 Ma), peak temperatures have been reconstructed (e.g., Clarke and Jenkyns, 1999; Wilson et al., 2002; Puceat et al., 2003; Forster et al., 2007a,b). Throughout the Late Cretaceous, sea levels were high, reaching the maximum of ~240-250 m above present day mean sea level in the earliest Turonian (Haq, 2014). Due to the high sea level, large areas of the continental crust were flooded during the Late Cretaceous (Hay, 2017). The resulting expansive shelfs areas and epicontinental seas were the depositional environment of the characteristic white carbonate mudrocks, that provided the name for the whole time period – chalk (Hay, 2008).

1.3.2. Sea level and ocean circulation In the present-da iehouse orld hih as estalished i the Oligoee Ma, polar ie olue is a main control for sea level changes (Miller et al., 1987, 1991). Storage of large quantities of water during glacial times causes sea-level fall (glacio-eustasy), and depletes the ocean water reservoir in the light isotope 16O. Oxygen isotope fractionation during evaporation preferentially removes 16O from seawater, and the rain water condensating from water vapor is relatively enriched in 18O. With increasing distance from the site of evaporation, the water vapor becomes thus more and more depleted in 18O. Freshwater therefore has a relatiel light δ18O signature, and the precipitates in high latitudes, furthest removed from the low-latitudinal sites of bulk evaporation, show the most negative values. If these precipitates are preserved as ice sheets and thus permanently removed from the water cycle, the oxygen isotope opositio of seaater is haged. Maia i the δ18O of marine carbonates, coinciding with regression, are therefore commonly interpreted as glacial episodes (e.g., Shackleton, 1987; Miller et al., 2003). The late Valanginian – Early Hauterivian sea-level lowstand, in combination with a positive shift in carbonate δ18O, has been interpreted to document polar ice formation during a climate cooling (McArthur et al., 2007).

The presence of sufficient polar ice volumes to cause the rapid and large amplitude sea level changes during Cretaceous is controversial, though. The formation of large submarine basalt plateaus and high rates of ocean-crust production is an alternative model for explaining globally high sea levels in the mid- Cretaceous (Larson, 1991; Larson and Kincaid, 1996; Immenhauser, 2005). Higher-altitude perennial ice shields in high latitudes possibly contributed to the sea level changes (Immenhauser, 2005; Föllmi, 2012).

19

Chapter 1

Figure 1.9 Schematic diagram showing covariation of sea level and oxygen isotope records, illustrating similar patterns explained by opposite paleoclimate trends (warm, humid vs. cold climate with polar ice formation). Upper part modified from Föllmi (2012).

Even more important for Cretaceous sea level fluctuations probably were alternations between humid and arid climate modes, and the creation and freshwater filling of rift basins due to the break-up of Pangea (Föllmi, 2012). During warm greenhouse episodes increased water removal by evaporation and storage in continental freshwater reservoirs caused regression (Föllmi, 2012; Wendler and Wendler, 2016). Aquifer- eustasy has been proposed as the dominant force for sea-level changes during greenhouse climates (Wendler and Wendler, 2016). Continent configuration and major rifting in the Early Cretaceous probably created large capacity for water storage in continental basins (Föllmi, 2012). The low topography during this time produced extensive lowland areas with meandering rivers, swamps, and wetlands (Hay, 2017). The link between humid climate conditions and sealevel fall in the Cenomanian-Turonian is supported by evidence for intense chemical weathering (Wendler et al., 2016). The Cretaceous sea level minimum during the mid Valanginian (~75 m above present day mean sea level) coincides with evidence for humid conditions that prevailed since late Berriasian times and intensified during the Valanginian (Föllmi, 2012; Haq, 2014). Similar to the waxing and waning of polar ice, fluctuations in evaporation and continental water storage have an impact on the oxygen isotope composition of seawater. Alternative to the presence of ice-sheets, aquifer-eustasy is a potential explanation for sea-level variations during the Cretaceous that are paralleled by the marine oxygen isotope record (Fig. 1.9).

The irulatio of toda’s stratified oeas is haraterized a ostant heat transport from the equator to the high latitudes – the Global Conveyor Belt system (Stewart, 2008). Thermohaline circulation is driven

20

Introduction by dense water formation from two high-latitude sources, the North Atlantic (North Atlantic Deep Water), and the continental shelf of Antarctica (Antarctic Bottom Water; Warren, 1983; Dickson and Brown, 1994). Deep water is formed due to a combination of cooling and increasing salinity by sea ice formation and evaporation caused by cold wind moving over the ocean surface (evaporative cooling).

In the largely ice-free Cretaceous oceans, salinity gradients drove deep-water formation dependent on evaporation and precipitation patterns (Hay, 2008). Downwelling occurred to a large part in mid- to low- latitudes, temperature differences between surface and deep waters were relatively low (Hay, 1988; MacLeod et a., 2000. Copared to the struture of toda’s stratified oea, desit patters ere irregular (Hay, 2008). Marginal or epicontinental basins with high rates of evaporation and high salinity probably played an important role in Cretaceous deep water formation (Hay, 1988; 2008). Paleobathymetry and complex sea floor topography with subsea ridges and plateaus caused isolation of the large ocean basins. Each of these ocean basin (Tethys, Atlantic, Pacific) probably had its own source of deep water (Hay, 2008). Temperature and salinity of the deep waters differed substantially (MacLeod et al., 2000). Relatively warm polar regions require poleward heat transport by warm saline water masses. The occurrence of Tethyan belemnite taxa in the Valanginian-Hauterivian of North-East Greenland, for instance, implies the existence of a northward surface current bringing warm water from low latitudes to the Boreal sea (Alsen and Mutterlose, 2009).

1.3.3. Environmental change and Oceanic Anoxic Events The sedimentary record of the Jurassic, Cretaceous, and early Paleogene is punctuated by several organic rich intervals that coincide with excursions in the carbon isotope record (e.g., Jenkyns, 2010; Fig. 1.10). A result of the Deep Sea Drilling Project (DSDP) campaigns was the recognition of the widespread synchronous occurrence of black shales of Aptian/Albian and Cenomanian/Turonian age. The documentation of these black shales on a global scale led to the conclusion that they reflect global environment perturbations (Jenkyns, 1976; Jackson and Schlanger, 1976; Schlanger and Jenkyns, 1976). These were interpreted to be related to reduced ocean mixing and an expanding oxygen minimum zone; they were consequently termed Oceanic Anoxic Events (OAEs) (Jenkyns, 1976; Schlanger and Jenkyns, 1976). The causes and consequences of OAEs for climate and marine ecology have been a subject of intensive research ever since (e.g., Jenkyns, 1988; Weissert and Lini, 1991; Jenkyns and Clayton, 1997; Erba, 1994, 2004; Forster et al., 2007; Bottini et al., 2012; Pogge von Strandmann et al., 2013; Bodin et al., 2016).

21

Chapter 1

Figure 1.10 Left: Black shales of the Selli Level in the Vispi quarry section (Gubbio, Italy). Right: Carbon isotope record of the Aptian from the Piobicco core (Erba et al., 2015) showing the characteristic excursion of OAE1a.

The events of global significance, the Toarcian Event (T-OAE), the Aptian OAE1a, and the Cenomanian/Turonian OAE2 (Fig. 1.11), are all characterized by relatively abrupt climate warming induced by increased atmospheric CO2 of volcanogenic origin, possibly amplified by gas hydrate dissociation (e.g., Jenkyns, 2003; Forster et al., 2007; Bottini et al., 2015). Each of these events coincides with volcanic activity of large igneous provinces (LIPs; Karoo-Ferrar flood basalt province, Ontong Java Plateau, Kerguelen Plateau, Caribbean Plateau; Jones and Jenkyns, 2001; Bodin et al., 2016; Erba et al., 2015). High rates of continental weathering and run-off increased the nutrient input to marine ecosystems (Jenkyns, 1999; Cohen et al., 2004; Bottini et al., 2015). Fertilization may have been enhanced by the input of biolimiting metals due to submarine volcanic activity and changes in ocean circulation (Larson and Erba, 1999; Erba, 2004; Parente et al., 2008). Rapid changes in oceanography and climate, and the extreme conditions during the OAEs, had an impact on marine floral and faunal assemblages, documented, e.g., by high rates of species extinction of foraminifera (e.g., Parente et al., 2008).

High productivity during OAE1a and OAE2 is documented by radiolarian silica rich layers accompanying the black shales (Coccioni et al., 1992; Jenkyns, 1999; Premoli-Silva et al., 1999). The Aptian carbonate platform drowning paralleling the carbon isotope excursion (CIE) associated with OAE1a reflects the

22

Introduction

demise of the oligotrophic carbonate producing platform communities due to fertilization (Weissert et al., 1998). During OAE2, foraminifera communities experienced a turnover which resulted in the disappearance of oligotrophic taxa, documenting high nutrient concentrations of the surface waters (Parente et al., 2008).

The sediment successions corresponding to OAEs are in many cases marked by decreasing calcium carbonate contents (Premoli-Silva et al., 1999). Each of the events is marked by striking trends towards smaller, less massively calcifying nannofossil taxa and/or size decreases. During the T-OAE, the large calcite tests of Schizosphaerella spp. abruptly decrease in abundance as well as in size (Mattioli and Pittet, 2002; Erba, 2004; Tremolada et al., 2005; Suan et al., 2008). OAE1a is marked by a crisis of nannoconids, as well as a decrease in coccolith size of Biscutum constans and Zeugrhabdotus erectus (Erba, 1994; Erba and Tremolada, 2004; Erba et al., 2010; Lübke and Mutterlose, 2016). Dwarfism of B. constans has been observed also Figure 1.11 Timescale of the Jurassic, Cretaceous during OAE2 (Linnert and Mutterlose, 2013; Faucher et al., and part of the Paleogene from Jenkyns (2010), showing the stratigraphic position of the major 2017a). These biocalcification crises are thought to result Oceanic Anoxic Events and other environmental from nutrification events and high atmospheric CO2 perturbations. concentrations unfavourable for biocalcification (Premoli- Silva et al., 1999; Erba, 2004; Erba and Tremolada, 2004). The reduced calcification pf phytoplankton accounts for a marked decrease in the amount of nannofossil calcite contribution to the sediments (Erba and Tremolada, 2004).

In summary, the mechanisms behind OAEs thus involve warm climate and an accelerated hydrological cycle. Increased weathering and run-off caused increased nutrient transport to the oceans resulting in a eutrophication of ocean surface waters. This in turn increased primary productivity. Stagnation of ocean circulation and an expanding oxygen minimum zone led to preservation and burial of large amounts of

23

Chapter 1

organic matter (Jenkyns, 2003, Robinson et al., 2004; Fig. 1.12). High burial rates of marine organic matter hih is erihed i isotopiall light aro ireases the δ13C of atmospheric and marine carbon. This is documented by the positive excursion in the carbon isotope ratios of marine carbonates and organic matter, associated with OAEs (e.g., Jenkyns, 2010). The origin of the negative shifts preceding, interrupting, or locally replacing the positive CIEs of the T-OAEa and OAE1a is more problematic. Potential

13 soures of aro ith lo δ C are venting of volcanogenic CO2 and dissociation of gas hydrates (Hesselbo et al., 2000; Jenkyns, 2003; Kuroda et al., 2007). Glendonites related to methane oxidation accompanying the Mesozoic events supports the link between methane seepage and carbon cycle perturbations (Morales et al., 2017).

Mesozoic sediments also record periods of environment pertubations marked by carbon isotope excursions (Pliensbachian/Toarcian boundary event, Valanginian Weissert Event, Hauterivian Faraoni Event, OAE1b, OAE1d, Coniacian/Santonian OAE3; Fig. 1.11) which are not associated with global anoxia. Fölli oied the ter episodes of eiroetal hage (=EEC) for that includes all periods of oceanic perturbations. Some of these EECs can be recognized only regionally. The early Albian OAE1b has initially been described in the Vocontian Basin in southeast France, where the Niveau Paquier is developed. The OAE1b is also recorded from the North Atlantic and the Tethys, but it has not been observed in the Pacific Ocean (Robinson et al., 2004). Black shales of Coniacian - Santonian age (OAE3) are, with few exceptions, limited to the Atlantic Ocean (Wagner et al., 2004; Jenkyns, 2010). The patchy occurrence of organic rich sediment layers during these events is related to productivity levels which only locally outweighed oxidation of organic matter (Robinson et al., 2004).

The Paleocene/Eocene Thermal Maximum (PETM, ~56 Ma) has been proposed as the closest analogue of present day climate change, due to the rapid onset of the event – warming and carbon release occurred within a few thousand years (Kennett and Stott, 1991; Zachos et al., 2003; Sluijs et al., 2006). Massive carbon release to the atmosphere and oceans is documented by extensive dissolution of deep-sea carbonates caused by a sudden rise of the calcite compensation depth, a process termed ocean acidification (Zachos et al., 2005; Zeebe, 2012). Here the timescale of the event is a crucial factor. Studies modeling the response of surface ocean pH and carbonate saturation to atmospheric CO2 suggest that ocean acidification requires the output of large amounts of CO2 over a short period of time (Ridgwell and Schmidt, 2010). On longer time scales >10,000 years, ocean carbonate saturation will be buffered due to

24

Introduction

Figure 1.12 Diagram from Jenkyns (2003) illustrating possible relationships between volcanism, gashydrate dissociation, climate change, OAEs and assumed geochemical responses.

balancing of weathering and carbonate burial (Kump et al., 2009; Ridgwell and Schmidt, 2010; Zeebe, 2012).

Calcareous nannofossils experienced high rates of species extinction and origination during the PETM in response to environmental changes (Gibbs et al., 2006). The temperature rise of 5-10°C, depending on water depth and latitude, has been attributed a major role for the changes observed in calcareous

25

Chapter 1

nannofossils as well as foraminifera, while the effects of ocean acidification are thought to have been minor (Bown and Pearson, 2009; Gibbs et al., 2016). An even more important selective factor seems to be the fast rate of environmental change at the onset of the PETM (Gibbs et al., 2006).

1.4. Aims and objectives A pre-requisite for meaningful reconstructions of past environmental change is a high resolution stratigraphic framework. Reliable correlations are needed for understanding climate and oceanography on a global scale. In the lowermost Cretaceous, over-regional biostratigraphic correlations are difficult due to pronounced provincialism. A sea-level lowstand and the absence of sea-ways between ocean basins allowed only very limited floral and faunal exchange between ocean basins. Starting with the early subdivisions of the Lower Cretaceous (Koenen,1902, 1907a,b; Kilian, 1907-1913) until now, different zonation schemes have been used for the Tethys and the Boreal realm (e.g., Bown et al., 1998; Jeremiah, 2001). Even biostratigraphic correlations between the subbasins and seaways within the Boreal Realm face diffiulties due to edeiss ad iopleteess of the lassi setios Cru, , Mutterlose et al., 2014; Möller et al., 2015). Since the comprehensive work of Mutterlose (1992) on Lower Cretaceous calcareous nannofossils of Northern Germany, and the integration and refinement of the existing zonation schemes for the Boreal by Bown et al. (1998), new stratigraphic data has been accumulated (e.g., McArthur et al., 2004; Pauly et al., 2012; Mutterlose et al., 2014). This makes a renewed examination of the nannofossil biostratigraphy of northern Germany necessary. Geochemical tools for stratigraphic orrelatio δ13C, 86Sr/87Sr) can be a means to overcome the problem of geographically restricted index taxa.

One of the aims of the present study is to revise and refine the existing zonation schemes and the age assignments of lowermost Cretaceous sediment successions of the Boreal. This is achieved by studying the calcareous nannofossils of upper Berriasian to Hauterivian sections, and by integrating all available chemo- and biostratigraphic information.

Based on the stratigraphic work, this thesis further aims at a better understanding of the climate and oceanography of the Valanginian and Hauterivian. Climate proxy data of the Lower Cretaceous are in part ambiguous and climate reconstructions are discussed controversially. In the present study, particular focus lies on understanding the environmental causes behind the late Valanginian perturbation, the Weissert Event. The Oceanic Anoxic Events of the mid Cretaceous are accompanied by distinctive changes in the nannofossil record. By comparing published data from the Aptian and Cenomanian OAEs with own

26

Introduction observations on nannofossils from the Valanginian I want to contribute to a better understanding of the Weissert Event.

In the present thesis calcareous nannofossils and geochemistry (stable carbon and oxygen isotopes, strontium isotope ratios) are studied (a) to refine the existing stratigraphic zonations for the Boreal lowermost Cretaceous and to increase the accuracy of over-regional correlations, (b) to reconstruct Early Cretaceous climates and oceanography, (c) to understand the causes behind the environmental change during the Valanginian Weissert Event, and (d) to improve calcareous nannofossil proxies for paleoceanography.

1.5. References Alcober, J., and R. W. Jordan (1997), An interesting association between Neosphaera coccolithomorpha and Ceratolithus cristatus (Haptophyta), European Journal of Phycology, (32), 91–93. Alsen, P., and J. Mutterlose (2009), The Early Cretaceous of North-East Greenland: A crossroads of belemnite migration, Palaeogeography, Palaeoclimatology, Palaeoecology, 280(1–2), 168–182, doi:10.1016/j.palaeo.2009.06.011. Ariovich, D., and R. N. Pienaar (1979), The role of light in the incorporation and utilization of Ca++ ions by Hymenomonas carterae (Braarud et Fagerl.) Braarud (Prymnesiophyceae), British Phycological Journal, (14), 17–24. Arkhangelski, A. D. (1912), Upper Cretaceous deposits of east European Russia, Materialien zur Geologie Russlands, (25), 1–631. Bach, L. T., U. Riebesell, and K. G. Schulz (2011), Distinguishing between the effects of ocean acidification and ocean carbonation in the coccolithophore Emiliania huxleyi, Limnol. Oceanogr, 6(56), 2040–2050. Bersezio, R., E. Erba, M. Gorza, and A. Riva (2002), Berriasian–Aptian black shales of the Maiolica formation (Lombardian Basin, Southern Alps, Northern Italy): local to global events, Palaeogeography, Palaeoclimatology, Palaeoecology, 180(4), 253–275. Billard, C. (1994), Life cycles, in The Haptophyte Algae, edited by J.C. Green and B.S.C. Leadbeater, vol. 51, Clarendon Press, Oxford. Billard, C., and I. Inoue (2004), What is new in coccolithophore biology?, in Coccolithophores. From Moelcular processes to Global Impact, edited by Hans R. Thierstein and Jeremy R. Young, pp. 1–30, Springer, Berlin Heidelberg. Bodin, S., F.-N. Krencker, T. Kothe, R. Hoffmann, E. Mattioli, U. Heimhofer, and L. Kabiri (2016), Perturbation of the carbon cycle during the late Pliensbachian – early Toarcian: New insight from high-resolution carbon isotope records in Morocco, Journal of African Earth Sciences, 116, 89–104, doi:10.1016/j.jafrearsci.2015.12.018. Bornemann, A., and J. Mutterlose (2006), Size analyses of the coccolith species Biscutum constans and Watzaueria aresiae fro the Late Alia Nieau Breistroffer “E Frae: taooi ad palaeoecological implications, Geobios, 39(5), 599–615, doi:10.1016/j.geobios.2005.05.005.

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Bornemann, A., U. Aschwer, and J. Mutterlose (2003), The impact of calcareous nannofossils on the pelagic carbonate accumulation across the Jurassic–Cretaceous boundary, Palaeogeography, Palaeoclimatology, Palaeoecology, 199(3–4), 187–228, doi:10.1016/S0031-0182(03)00507-8. Bottini, C., A. S. Cohen, E. Erba, H. C. Jenkyns, and A. L. Coe (2012), Osmium-isotope evidence for volcanism, weathering, and ocean mixing during the early Aptian OAE 1a, Geology, 40(7), 583–586. Bottini, C., E. Erba, D. Tiraboschi, H. C. Jenkyns, S. Schouten, and J. S. Sinninghe Damsté (2015), Climate variability and ocean fertility during the Aptian Stage, Climate of the Past, 11(3), 383–402, doi:10.5194/cp-11-383-2015. Bottini, C., F. Jadoul, M. Rigo, M. Zaffani, C. Artoni, and E. Erba (2016), Calcareous Nannofossils at the Triassic/Jurassic Boundary: Stratigraphic and paleoceanographic characterization, Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy), 122(3). Bown, P., and P. Pearson (2009), Calcareous plankton evolution and the Paleocene/Eocene thermal maximum event: New evidence from Tanzania, Marine Micropaleontology, 71(1–2), 60–70, doi:10.1016/j.marmicro.2009.01.005. Bown, P. R. (1992), Late Triassic - Early Jurassic calcareous nannofossils of the QueenCharlotte Islands, British Columbia, Journal of Micropaleontology, (11), 177–188. Bown, P. R. (1998), Triassic, in Calcareous Nannofossil Biostratigraphy, edited by Paul R. Bown, Chapman & Hall, London. Bown, P. R., and M. K. E. Cooper (1998), Jurassic, in Calcareous Nannofossil Biostratigraphy, edited by Paul R. Bown, pp. 34–85, Chapman & Hall, London, UK. Bown, P. R., and J. R. Young (1998), Introduction, in Calcareous Nannofossil Biostratigraphy, edited by Paul R. Bown, Chapman & Hall, London. Bown, P. R., D. C. Rutledge, J. A. Crux, and L. T. Gallagher (1998), Lower Cretaceous, in Calcareous Nannofossil Biostratigraphy, edited by Paul R. Bown, Chapman & Hall, Londom, UK. Bown, P. R., J. A. Lees, and J. R. Young (2004), Calcareous nannoplankton evolution and diversity through time, in Coccolithophores. From Molecular Processes to Global Impact, edited by Hans R. Thierstein and Jeremy R. Young, pp. 481–508, Springer Verlag, Berlin Heidelberg. Braarud, T. (1954), Coccolith morphology and taxonomic position of Hymenomonas roseola Stein and Syracosphaera Braarud and Fagerland, Nytt Magasin foer Botanik, (3), 1–6. Bramlette, M. N. (1965), Massive extinctions in biota at the end of Mesozoic time, Science, 148(3678), 1696–1699. Brand, L. E. (1994), Physiological ecology of marine coccolithophores, in Coccolithophore, edited by Amos Winter and William G. Siesser, Cambridge University Press, Cambridge. Brand, L. E., W. G. Sunda, and R. R. Guillard (1986), Reduction of marine phytoplankton reproduction rates by copper and cadmium, Journal of Experimental Marine Biology and Ecology, 96(3), 225–250. Brand, U., J. Tazawa, H. Sano, K. Azmy, and X. Lee (2009), Is mid-late Paleozoic ocean-water chemistry coupled with epeiric seawater isotope records?, Geology, 37(9), 823–826. Brooks, K. (n.d.), Ikaite: enigmatic crystals of cold waters, Geology Today, 2(32), 75–78.

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2 Integrated stratigraphy of Lower Cretaceous sediments (Ryazanian- Hauterivian) from North-East Greenland

Carla Möllera, Jörg Mutterlosea, Peter Alsenb aRuhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany bGeological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-130 Copenhagen K, Denmark

(published 2015 in Palaeogeography, Palaeclimatology, Palaeoecology)

Abstract

The reconstruction of past climates and oceanography requires a solid stratigraphic framework ideally applicable on a global scale. The earliest Cretaceous, however, was a time of strong faunal provincialism, making supra-regional correlation of biostratigraphical zonations difficult. The step-by-step correlations between neighbouring provinces/subprovinces that are commonly utilized bear the risk of losing accuracy in every step.

87 86 13 18 Here we present Sr/ Sr- and stable isotope-data δ C, δ O) from belemnite rostra of the Rødryggen section in North-East Greenland. The integrated stratigraphy based on Sr-isotope ratios, ammonite and calcareous nannofossil biostratigraphy offers the opportunity for a direct comparison of the different

13 stratigraphi zoatios. These are opleeted δ Cbel-data recording the positive carbon isotope excursion of the Valanginian Weissert Event, which is a reliable stratigraphic event. The geochemical data furthermore allow a reliable correlation of Tethyan and Boreal strata.

The stratigraphic range of the Rødryggen section resulting from Sr-isotope stratigraphy (Ryazanian – Barremian) is in agreement with the biostratigraphic findings. Mismatches regarding stage/ substage boundaries demand a reconsideration of the nannofossil biostratigraphy of the Boreal Lower Cretaceous. Our findings suggest stratigraphic ranges for two nannofossil index species (Sollasites arcuatus, Micrantholithus speetonensis) different from published ranges. The new observations imply changes in the Boreal Ryazanian-Valanginian nannofossil zonation scheme. Specifically, the base of calcareous nannofossil zone BC3, originally defined as uppermost Ryazanian, is shifted to the lower Valanginian.

42

Integrated stratigraphy of Lower Cretaceous sediments from North-East Greenland

Based on these new stratigraphic interpretations a decrease in the abundance of nannoconids observed in the Rødryggen section can now be identified as the Valanginian nannoconid crises. This nannoconid decline has been observed in Tethyan sections along with the Weissert Event. A positive trend in the

18 δ Obel-data agrees with a late Valanginian cooling that has been postulated based on independent proxies from the Boreal Realm and the Tethys.

2.1. Introduction The earliest Cretaceous (Berriasian – Hauterivian) is an interval characterised by a distinctive provincialism of marine biota, causing the evolution of endemic floras and faunas in different parts of the world. The Indo-Pacific, the Tethys and the Boreal Realm show in parts geographically bound marine assemblages limited to these oceans (e.g. Remane, 1991; Wimbledon et al., 2011).

This situation applies for the Tethys (nowadays southern France, Switzerland, northern Italy) and the southern part of the Boreal Realm (northern Germany, Poland, North Sea, Great Britain). Both areas show close faunal links throughout the Early – Middle Jurassic and the Aptian – Campanian. A Late Jurassic – Early Cretaceous sea-level low-stand caused the closure of gateways, hampered thereby migration and resulted in biogeographic isolation (e. g. Haq et al., 1988; Michael, 1979; Scotese, 1991). This in turn led to the widespread evolution of endemic taxa. The biogeographic restrictions culminated in Tithonian – Berriasian times, an interval for which two different stage names are being used. The Berriasian stage, defined in the Tethys, corresponds to the upper Volgian and Ryazanian (Zakharov et al., 1996) in the northern parts of the Boreal Realm (Siberia, Greenland, Svalbard, in some cases also used in England). These biogeographic differences resulted in major problems for biostratigraphical correlations of the uppermost Jurassic and lowermost Cretaceous sedimentary sequences of both realms biostratigraphically (Remane, 1991; Zakharov et al., 1996). Discussions regarding these problems have been going on for nearly 100 years (Mazenot, 1939; Wimbledon et al., 2011) without finding a practicable solution yet.

The provincialism ultimately resulted in two different ammonite zonation schemes used for subdividing the Tithonian – Early Cretaceous succession of the northern Tethys (Kilian, 1907-1913) and the Boreal Realm (Koenen, 1902, 1907). Even in more recent biostratigraphic zonation schemes (e.g. Hoedemaeker, 1987, 1991; Rawson, 1995; Rawson et al., 1996; Rawson and Hoedemaeker et al., 1999; Thieuloy, 1977) the correlation of the two realms is limited to rare phases of faunal exchange. Further refinement of the correlations is therefore needed.

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Two different zonation schemes were established also for calcareous nannofossils, calibrated to the regional ammonite zonations. Most widely used for the Tethys are the nannofossil zonation schemes by Sissingh (1977, 1978) and Bralower et al. (1989). Two zonation schemes are available.for the Boreal. The LK zonation (LK standing for Lower and Kreide, German for Cretaceous) of Jeremiah (2001) is based mainly on boreholes from the Central North Sea Basin, England, the Netherlands and Germany. The BC (Boreal Cretaceous) zonation of Bown et al. (1998) compiles studies by Perch-Nielsen (1979), Jakubowski (1987), Crux (1989) and Mutterlose (1991). For the lowermost Cretaceous (Ryazanian – Hauterivian) the BC zonation is based on material from sections in northeast England, northwest Germany, North Sea cores (Moray Firth Basin, off northeast Scotland, offshore Norway) and the Barents Sea. The correlation with the Boreal ammonite zonation is provided by outcrops where both calcareous nannofossils and ammonites are available, particularly the Speeton section in northeast England and outcrops in northwest Germany.

Geochemical proxy data (87Sr/86“r, δ13C) can be used to overcome the stratigraphic problems caused by geographically restricted index taxa, provided that an influence of regional processes on the isotope signature can be ruled out. The Sr-isotope ratio (87Sr/86Sr) is an efficient stratigraphic tool for correlating marine sediments on a global scale due to the long residence time of Sr in seawater (e. g. Elderfield, 1986; Peterman et al., 1970; Veizer, 1989). The varying 87Sr/86Sr-signature of seawater as reflected in marine carbonates is not affected by fractionation during incorporation. It results from the input of heavy radiogenic Sr due to continental weathering, and the amount of light, non-radiogenic Sr released by hydrothermal activity associated with submarine volcanism (Allègre et al., 2010; Veizer, 1989).

Recently, Mutterlose et al. (2014) presented 87Sr/86Sr-curves for the lowermost Cretaceous (Berriasian - Barremian), compiling data measured on belemnites from Tethyan (Vocontian Basin, Bodin et al., 2009; McArthur et al., 2007) and Boreal sections (Speeton, McArthur et al., 2004). All belemnites have been collected bed-by-bed, thus allowing a calibration with the existing regional ammonite zonation scheme.

In the current study, 87Sr/86Sr-data are obtained from 28 belemnite specimens collected from the Lower Cretaceous (Ryazanian – Barremian) Rødryggen section on Wollaston Forland (North-East Greenland). The section has been studied with respect to its biostratigraphy. Alsen (2006) established an ammonite biostratigraphic zonation for the Valanginian of North-East Greenland. Pauly et al. (2012a) provided a detailed calcareous nannofossil zonation for Wollaston Forland. Using the Sr-isotope data a reliable correlation to the biostratigraphic zonation of the Tethys can be achieved. Further we present a high-

13 18 resolutio reord of Razaia to Hauteriia stale isotope ratios δ Cbel, δ Obel) of 102 belemnite

44

Integrated stratigraphy of Lower Cretaceous sediments from North-East Greenland specimens covering the positive carbon isotope excursion interval CIE of the Valagiia Weissert Event (Erba et al., 2004).

The Weissert Event is well established in the Tethys (Channell et al., 1993; Gréselle et al., 2011; Kujau et al., 2012; Lini et al., 1992; Weissert et al., 1998), but has also been documented from the western Atlantic and the Pacific (Bornemann and Mutterlose, 2008; Erba et al., 2004; Lini et al., 1992), and from the European and Russian parts of the Boreal Realm (Meissner et al., 2015; Nunn et al., 2010; Price and Mutterlose, 2004,). The stratigraphic position of the isotope anomaly is a well constrained isochronous event (Channell et al., 1993; Hennig et al., 1999; Lini et al., 1992; Weissert and Erba, 2004), which makes it a useful stratigraphic tool.

The CIE goes along with the drowning of carbonate platforms (Föllmi, 2012; Föllmi et al., 2006; Weissert et al., 1998; Wortmann and Weissert, 2000) and changes in calcareous nannofossil assemblages. Among these the dramatic decline of nannoconids is perhaps the most prominent (eg. Bersezio et al., 2002; Bornemann and Mutterlose, 2008; Channell et al., 1993; Erba and Tremolada, 2004; Barbarin et al., 2012).

2.2. Geological setting In the Early Cretaceous the Greenland-Norwegian Seaway was part of a gateway between the Tethys in the south and the Arctic Ocean in the north (Fig. 2.1). It formed during a rifting event that started in the late Bajocian (Middle Jurassic) and culminated in the latest Jurassic to earliest Cretaceous (Surlyk, 1978, 2003). The Upper Jurassic and Lower Cretaceous sediments in North-East Greenland are represented by up to three kilometres of siliciclastics. Conglomerates and pebbly sandstones are common in the near shore settings, and gradually finer grained sediments were deposited further off-shore (Pauly et al., 2012b; Surlyk, 1978, 2003). The fossiliferous mud- and marlstones of the Ryazanian - Hauterivian Albrechts Bugt Member and Rødryggen Member are the distal sediments of the late rifting phase. Due to a Ryazanian drowning event and a subsequent transgression they were deposited on top of the coarse clastics that represent the syn-rift deposits (Surlyk and Clemmensen, 1975; Surlyk, 1978, 2003).

2.3. Section The 138 samples analysed here were collected in the Rødryggen section (Pal4/2001, locality 5) in the northern part of the Wollaston Forland in North-East Greenland (N74°32'47.1'', W.19°50'35.5'') during field campaigns from 2000 to 2011. The interval considered here comprises 27 m of Lower Cretaceous sediments, which include 22 m of yellowish mudstones of the Albrechts Bugt Member in the lower part

45

Chapter 2

and 5 m claret-coloured silty mudstones of the Rødryggen Member in the upper part (Fig 2.2). For more detailed descriptions of the section see Alsen (2006), Alsen & Mutterlose (2009) and Pauly et al. (2012a, b). The ammonite biostratigraphy of the section has been established by Alsen (2006) and Alsen and Mutterlose (2009), assigning the entire succession to the upper Ryazanian to lower Hauterivian. A detailed calcareous nannofossil zonation has been published by Pauly et al. (2012a), dating the Albrechts Bugt and Rødryggen Members as early Ryazanian to late Hauterivian (Fig. 2.3).

Figure 2.1 Map of the Valanginian paleogeography, 2.4. Material and methods modified from Smith et al. (1994) showing the position of the Rødryggen section, Wollaston Forland, North-East A total of 138 belemnite rostra, collected bed Greenland. Indicated in grey are areas presumably above by bed throughout the section, have been sea-level in the Valanginian; GNS = Greenland-Norwegian Seaway. sampled for major and minor element analysis. Based on the results, 28 samples have been selected for 87Sr/ 86Sr isotope analysis. All 138 samples have been analysed for their stable

13 18 isotope composition (δ Cbel, δ Obel). Taxonomically the rostra have been assigned to the genera Pachyteuthis, Acroteuthis and Cylindroteuthis (table 1).

After having split the rostra in halves dorsoventrally, carbonate powder samples were obtained by hand- drilling under a stereomicroscope with a 0.3 mm drill-bit. For analyses, portions of clear calcite were selected. The margins, the apical line and the apex, which are most prone to alteration, were avoided.

Major and minor element analysis (Ca, Mg, Sr, Fe, Mn) was performed at the Ruhr-Universität Bochum on an ICP-OES (iCap 6500 Thermo Electron Corporation) on 1.5 mg of sample powder dissolved in 3 M HNO3. Element composition can indicate post-depositional alteration of the belemnite calcite (e.g. Rosales et al., 2004; Veizer and Fritz, 1976; Wierzbowski et al., 2013). Here belemnite samples with Mn-content >50

46

Integrated stratigraphy of Lower Cretaceous sediments from North-East Greenland ppm, Fe-content >200 ppm and/or Strontium contents <1000 ppm were considered diagenetically altered and excluded from further consideration.

Strontium isotope ratios (87Sr/86Sr) were determined using a 7-collector Thermal Ionisation Mass spectrometer (TIMS) MAT262 in 3-collector dynamic mode at the Ruhr-Universität Bochum. A detailed description of the sample preparation procedure is given by Meissner et al. (2015) and references therein. As standard reference material to test the repeatability of the measurements NIST NBS 987 and USGS EN- 1 were used. The average 87Sr/86Sr-alues of the stadards ere . ± . σ = ad . ± . σ =, respetiel. The preisio of the saple easureets as etter than . σ.

The stable isotope compositions (13C/12C, 18O/16O) were measured at the GeoZentrum Nordbayern, Friedrich-Alexander Universität Erlangen-Nürnberg. Reproducibility and accuracy is better than ± 0.07‰

13 18 for oth δ Cbel ad δ Obel. For details see Joachimski et al. (2001). The stable isotope data are given in per mil (‰) relative to V-PDB (Vienna Pee Dee Belemnite). The belemnite specimens are stored at the Ruhr- University Bochum.

2.5. Results 2.5.1. Element composition Of the belemnites analysed, 33 specimens have Mn-contents exceeding the threshold values of 50 ppm and have thus been excluded. Seventeen samples have Fe-concentrations above the threshold of 200 ppm, all but three of these also contain more than 50 ppm Mn. No belemnite specimen showed Sr-content below 1000 ppm. In total, 36 of the 138 belemnite samples were excluded from further consideration based on their element composition. The results of element composition and isotope analyses are listed in table 1, samples with element compositions beyond the thresholds are marked in grey.

2.5.2. Strontium isotopes The 87Sr/86Sr-data from Greenland presented here (n=28; Fig. 2.2) range from 0.707274 (sample GI- 123773; 0 m) in the lowermost part of the succession to 0.707486 (sample GI-123819; 27.1 m) in the uppermost part. The resulting curve (LOESS smoothed, factor 0.3) has a steady gradient over the larger part of the section (0-21.5 m). In the upper part (21. 5 - 24 m) it shows a break and a short interval of a more rapid increase of the Sr-isotope ratios. In the uppermost part (25 - 27 m) the Sr-curve comes back to the former gradient.

47

Chapter 2

48

Integrated stratigraphy of Lower Cretaceous sediments from North-East Greenland

2.5.3. Stable carbon and oxygen isotopes

13 The δ Cbel-data from the 102 belemnite samples considered can be best described dividing the studied interval in two parts (Fig. 2.2). The values from the lower part (0 – satter aroud a ea of .‰, in the upper part (12.7 – 27.1 m) they are more positie ith a ea of .‰. Statistical testing (t-test) shows that the difference between the data from the lower and upper part is significant with 95% confidence.

18 The δ Obel-data show a shift towards heavier values ~19 m above the base of the section (Fig. 2.2). The data from the lower part of the section (0-16 m) vary around a mean of -.‰. I the upper part -27.1 18 the ea alue is .‰. The statistial sigifiae of the differee etee the δ Obel-data differee of eas .‰ was checked with a t-test at the 95%-confidence level.

2.6. Discussion 2.6.1. The Ryazanian-Valanginian boundary The good match of the Sr-isotope ratios from Greenland with the Sr-curve based on data from southeast France, Spain and northeast England (Mutterlose et al., 2014) is encouraging regarding the potential of eleite alite to presere the gloal 87Sr/86Sr-ratio of Early Cretaceous seawater. The new Sr-data from Greenland help calibrating the different biostratigraphic zonation schemes of the lowermost Cretaceous. Our stratigraphic interpretation of the Sr-isotope curve agrees with the total range of the Rødryggen section suggested by biostratigraphy (Ryazanian - Barremian). A comparison of the Sr-, the calcareous nannofossil- and the ammonite stratigraphy of the Rødryggen section reveals, however, considerable discrepancies. Particularly the position of the Ryazanian / Valanginian boundary is not conclusive (Fig 2.2).

← Figure 2.2 Lithic log of the Rødryggen section (Pal-4/2001, locality 5) with ammonite zones (Alsen, 2006), calcareous nannofossil zonation (Pauly et al., 2012a), 87Sr/86Sr data (this study). Graphs on the right show 18 13 belemnite stable isotope data (δ Obel,δ Cbel) in permil V-PDB (this study) and absolute abundance data of Nannoconus spp. of Pauly et al. (2012b) from the same section given as 107 specimen per gram of sediment. In the stable isotope data three belemnite genera are distinguished (Acroteuthis, Pachyteuthis, Cylindroteuthis). The arrows at the top mark the average stable isotope ratio value of each genus. Black (Pachyteuthis & Acr./Pachy.) and grey lines (Acroteuthis & Cylindroteuthis) represent LOESS-smoothing (factor 0.4). Broken lines mark the 4m sampling gap, where no belemnite specimens were available.

49

Chapter 2

The new Sr-data presented here place the Ryazanian / Valanginian boundary ~2 m above the base of the Albrechts Bugt Member (~2 m above the base of the section). This is in agreement with the ammonite biostratigraphy, while nannofossil biostratigraphy defines the base of the Valanginian 6.4 m higher in the section (Fig. 2.2). This discrepancy of the ammonite and Sr-isotope based ages on one hand and the nannofossil findings on the other might be explained by a down-slope transport of the ammonites and belemnites. The Rødryggen section crops out in a low, gently sloping hillside exposed to precipitation, freezing and thawing. The fossils appear to weather out from the calcareous mudstones rather fast, and some downhill transport of macrofossils with solifluction at the hills surface can be expected. The nannofossil samples have been taken by digging a trench into the hillside to a depth considered unaffected by solifluction and weathering (Pauly et al., 2012a). The sequence of the macrofossils, which are lying in a sensible stratigraphic order, suggests them, however, to be lying at or close to their original stratigraphical level (Alsen, 2006).

Three calcareous nannofossil events, which occur shortly after each other (from bottom to top: last occurrence (=LO) Sollasites arcuatus, first occurrence (=FO) Triquetrorhabdulus shetlandensis, FO Micrantholithus speetonensis) have been observed in a number of localities in the North Sea and off Norway. These events define the Ryazanian / Valanginian boundary interval in the nannofossil zonations commonly used (Bown et al., 1998; Crux, 1989; Jakubowski, 1987; Jeremiah, 2001), with S. arcuatus confined to the uppermost Ryazanian and T. shetlandensis and M. speetonensis appearing in the lowermost Valanginian. All three nannofossil events have been observed in the Rødryggen section in this very sequence (Pauly et al., 2012a). It is therefore unlikely that they occur in North-East Greenland with a time-delay relative to the sites in the North Sea and Norwegian Sea. An explanation for the discrepancy regarding the position of the Ryazanian-Valanginian boundary has to be found elsewhere.

The correlation of the calcareous nannofossil zonation scheme commonly used for the Boreal lowermost Cretaceous (BC zonation of Bown et al. (1998), Ryazanian - lower Valanginian) is based virtually exclusively on the ammonite biostratigraphy of the Speeton section. The Speeton section covers most of the Lower Cretaceous from the Ryazanian to the Albian but is highly incomplete showing stratigraphic gaps and condensed intervals.

Based on "crushed fragments" of Platylenticeras found in the lower D4 beds (= Paratollia beds) by Doyle (Kemper, 1971; Kemper et al., 1981; see fig. 2.3), these beds have been correlated with the lowermost Valanginan Platylenticeras beds of Germany, the Pseudogarniera undulatoplicatilis zone of the Russian Platform and North-East Greenland and the Tirnovella pertransiens zone of the Tethys. These correlations

50

Integrated stratigraphy of Lower Cretaceous sediments from North-East Greenland are supported by the palynomorph Oligosphaeridium complex. O. complex makes its first appearance in the Tethys in the lower middle T. pertransiens zone (Leereveld, 1997), in northern Germany in the Platylenticeras heteropleurum subzone (Below, 1981), in Speeton in the lower/middle Paratollia beds (near boundary D5/D4, precise position unknown; Duxbury, 1977) and in Greenland in the upper P. undulatoplicatilis zone (Piasecki, pers. comm., Fig. 2.3).

Figure 2.3 Correlation of ammonite and calcareous nannofossil zonations and the first occurrence of the palynomorph Oligosphaeridium complex of the lowermost Cretaceous of northern Germany, Speeton (northeast England) and the Wollaston Forland (North-East Greenland) to the Tethyan ammonite biostratigraphy. Ammonite zonations are from Alsen (2006) and Mutterlose et al. (2014), calcareous nannofossil biostratigraphy from Crux (1989), Mutterlose (1991), Pauly (2012a), Möller and Mutterlose (2014), and palynomorph stratigraphy from Leereveld (1997), Below (1981), Duxbury (1977) and Piasecki (pers.comm.).

51

Chapter 2

In Speeton, S. arcuatus is limited to the upper Ryazanian D6I to D6A beds (Fig. 2.3). The overlying D5 and D4C beds are barren of nannofossils (Crux, 1989). The true stratigraphic range of S. arcuatus may therefore extend higher up in the section. According to the integrated stratigraphic data from nannofossils, ammonites, palynomorphs and Sr-isotopes presented here, the LO of S. arcuatus has to be placed in the lower Valanginian (fig. 2.3). This shifts the base of the Boreal nannofossil zone BC3 from uppermost Ryazanian into the lower Valanginian.

Accepting the position of the Ryazanian / Valanginian boundary in the Rødryggen section indicated by Sr- isotope data and ammonite biostratigraphy, the FO of S. arcuatus however seems to be diachronous. In Speeton it is present already in the Ryazanian P. albidum ammonite zone (D6I bed), while in the Rødryggen section it is first observed in the basal P. undulatoplicatilis zone (Pauly et al., 2012a, Fig. 2.3). The available Sr-isotope data support the diachroneity: Belemnite samples from the D7A and D6A beds of Speeton have an 87/86Sr of 0.707264 and 0.707265 (McArthur et al., 2004), respectively, corresponding to the late Berriasian (Mutterlose et al., 2014). In the Rødryggen section a belemnite (sample GI-123786) found directly below the FO of S. arcuatus gave a Sr-ratio of 0.707317, corresponding to an early Valanginian age. Preservation of the nannofossils as an explanation for the absence of S. arcuatus in the upper Ryazanian of the Rødryggen section can be ruled out. The entire upper Ryazanian and lower Valanginian are characterised by good to moderate preservation and comparatively high absolute nannofossil abundances (Pauly et al., 2012a,b).

2.6.2. The Weissert Event and the Valanginian nannoconid decline The ~1.5‰ positive carbon isotope excursion (CIE) of the Valanginian Weissert Event (Erba et al., 2004) is commonly used for stratigraphy and correlation. The CIE has been observed in marine bulk rock samples (Bornemann and Mutterlose, 2008; Channell et al., 1993; Gréselle et al., 2011; Lini et al., 1992; Weissert and Erba, 2004) and biogenic carbonates (Price and Mutterlose, 2004) as well as in terrestrial deposits (Gröcke et al., 2005; Nunn et al., 2010). The onset and maximum is recorded in the lowermost upper Valanginian, in the Tethyan Saynoceras verrucosum ammonite zone (Weissert and Erba, 2004).

13 The dataset from the Rødryggen section shows a large scatter of the δ Cbel values. A possible explanation lies in the origin of the data from different ontogenetic layers of different belemnite genera (Acroteuthis,

13 Pachyteuthis and Cylindroteuthis. Despite the large satter, a positie shift i the δ Cbel data can be clearly

52

Integrated stratigraphy of Lower Cretaceous sediments from North-East Greenland

Table 1 List of belemnite specimen with results from geochemical analyses. Samples with element compositions beyond threshold values for diagenetic alteration are marked in grey. original sample depth Ca Mg Sr Fe Mn 13C 18O sample identification δ δ 87Sr/86Sr no. [m] [ppm] [ppm] [ppm] [ppm] [ppm] no. [‰] [‰] GI-123773 W1 0.00 Pachyteuthis sp. 389460 2488 1445 80 34.9 -0.80 -0.03 GI-123773 W2 0.00 Acroteuthis sp. 386750 1910 1531 97 37.3 1.33 0.67 GI-123773 W3 0.00 Acroteuthis sp. 390240 1666 1612 73 14.2 0.93 -2.42 0.707274 GI-123774 W4 0.50 Pachyteuthis sp. 396330 553 1563 41 5.1 0.05 1.65 GI-123774 W5 (1) 0.50 Pachyteuthis sp. 397760 1424 1442 42 6.7 0.36 -0.18 0.707280 GI-123774 W5 (2) 0.50 Pachyteuthis sp. 0.46 -0.14 GI-123774 W6 0.50 Pachyteuthis sp. 395820 1199 1248 86 24.6 -0.46 0.44 GI-123775 W7 0.90 Pachyteuthis sp. 388290 3430 1454 96 52.4 -2.68 -1.08 GI-123775 W8 0.90 Pachyteuthis sp. 394140 1371 1437 70 24.5 1.26 -1.43 0.707278 GI-123775 W9 0.90 Pachyteuthis sp. 393710 1591 1453 89 12.5 -0.61 0.32 GI-123776 W10 (1) 1.50 Cylindroteuthis sp. 391930 1239 1656 65 5.7 0.41 0.55 GI-123776 W10 (2) 1.50 Cylindroteuthis sp. 0.46 0.64 GI-123776 W11 1.50 Cylindroteuthis sp. 395490 1284 1326 57 6.4 0.59 -1.39 0.707282 GI-123776 W12 1.50 Pachyteuthis sp. 387390 2524 1336 124 36.1 -1.08 0.62 GI-123777 W13 2.00 Pachyteuthis sp. 392780 1182 1455 61 22.2 -0.51 0.37 GI-123777 W14 2.00 Pachyteuthis sp. 389350 1736 1282 126 39.5 -0.11 0.28 0.707324 GI-123777 W15 (1) 2.00 Pachyteuthis sp. 389420 1489 1362 49 12.9 0.27 0.21 W15 (2) 2.00 Pachyteuthis sp. 0.32 0.22 GI-123778 W16 2.50 Pachyteuthis sp. 384010 2730 1788 80 42.6 -0.11 -0.72 GI-123778 W17 (1) 2.50 Pachyteuthis sp. 387880 2473 1293 103 25.3 -0.62 0.01 0.707292 W17 (2) 2.50 Pachyteuthis sp. -0.63 -0.04 GI-123778 W18 2.50 Pachyteuthis sp. 394010 915 1750 60 10.8 1.21 -1.63 GI-123779 W19 2.80 Pachyteuthis sp. 387500 2765 1764 176 97.6 0.65 -3.94 GI-123779 W20 2.80 Pachyteuthis sp. 384060 4073 1473 210 56.2 -2.41 -1.33 GI-123779 W21 2.80 Pachyteuthis sp. 392230 1596 1236 67 21.1 0.23 0.30 Acroteuthis/ GI-123780 W22 (1) 3.15 394150 1160 1380 87 22.4 -0.12 1.01 Pachyteuthis sp. Acroteuthis/ W22 (2) 3.15 -0.11 1.06 Pachyteuthis sp. Acroteuthis/ GI-123780 W23 3.15 389290 3717 1356 214 63.6 -2.12 -2.05 Pachytheutis sp. Acroteuthis/ GI-123780 W24 3.15 388260 3081 1404 105 70.8 -1.77 -0.24 Pachyteuthis sp. GI-123781 W25 3.40 Pachyteuthis sp. 380380 2766 1329 190 59.9 -1.64 -0.68 GI-123781 W26 3.40 Pachyteuthis sp. 391440 2579 1378 68 20.4 -1.39 -0.14 GI-123781 W27 (1) 3.40 Pachyteuthis sp. 394090 2048 1455 73 85.8 -0.70 -0.31 W27 (2) 3.40 Pachyteuthis sp. -0.65 -0.27 GI-123782 W28 3.70 Pachyteuthis sp. 388550 1427 1288 44 6.5 0.57 -2.11 GI-123782 W29 3.70 Acroteuthis sp. 390360 2119 1431 93 31.6 0.06 0.07 GI-123782 W30 3.70 Acroteuthis sp. 396950 980 1329 54 12.4 -0.87 0.51 0.707283 GI-123783 W31 4.00 Acroteuthis sp. 339830 753 1518 70 37.7 2.33 -2.57 0.707298 GI-123783 W32 (1) 4.00 Pachyteuthis sp. 393690 939 1620 49 7.1 0.28 0.11 W32 (2) 4.00 Pachyteuthis sp. 0.26 -0.09 GI-123783 W33 4.00 Pachyteuthis sp. 393710 1414 1496 39 27.8 -0.05 0.08 GI-123784 W34 4.40 Pachyteuthis sp. 386220 2241 1664 45 8.9 -0.30 0.02 GI-123784 W35 4.40 Pachyteuthis sp. 387590 2519 1538 63 22.8 0.07 -1.16 GI-123784 W36 4.40 Pachyteuthis sp. 389140 2530 1330 248 115 -1.79 0.22 GI-123785 W37 4.70 Pachyteuthis sp. 388780 2183 1482 60 11 -0.36 -0.70 GI-123785 W38 (1) 4.70 Pachyteuthis sp. 392250 1097 1371 135 61.2 -0.18 0.84 W38 (2) 4.70 Pachyteuthis sp. -0.04 0.83

53

Chapter 2

Table 1 (cont.)   original sample depth Ca Mg Sr Fe Mn 13C 18O sample identification δ δ 87Sr/86Sr no. [m] [ppm] [ppm] [ppm] [ppm] [ppm] no. [‰] [‰] GI-123785 W39 4.70 Pachyteuthis sp. 388910 1664 1371 113 52 -0.92 0.07 GI-123786 W40 4.90 Pachyteuthis sp. 390620 1260 1322 44 9.4 -0.31 -0.64 GI-123786 W41 4.90 Pachyteuthis sp. 383740 3851 1594 77 36.8 0.80 -1.33 GI-123786 W42 4.90 Pachyteuthis sp. 386520 2620 1473 75 18.1 0.28 -0.43 0.707317 GI-123787 W43 (1) 6.20 Pachyteuthis sp. 390700 905 1734 34 6.5 1.65 -0.49 W43 (2) 6.20 Pachyteuthis sp. 1.64 -0.49 GI-123787 W44 6.20 Pachyteuthis sp. 392590 1314 1206 40 5.9 -0.52 0.21 0.707314 GI-123787 W45 6.20 Pachyteuthis sp. 388100 1475 1295 110 32.8 -0.06 -1.15 GI-123788 W46 6.50 Pachyteuthis sp. 389380 2356 1518 151 28.4 0.39 -0.12 GI-123788 W47 6.50 Pachyteuthis sp. 396060 1968 1616 76 26.4 -0.24 0.81 GI-123788 W48 (1) 6.50 Pachyteuthis sp. 384570 3133 1838 237 118 -0.65 -4.39 W48 (2) 6.50 Pachyteuthis sp. -0.72 -4.36 GI-123789 W49 7.00 Pachyteuthis sp. 391440 1240 1458 87 21.6 -0.91 -0.16 GI-123789 W50 7.00 Pachyteuthis sp. 390770 1709 1455 43 13.2 -0.84 0.29 Cylindroteuthis GI-123789 W51 7.00 393150 1011 1753 40 5.3 1,18 -1,35 sp. Cylindroteuthis GI-123790 W52 7.30 388520 2227 1431 61 13.1 0.22 0.05 sp. Acroteuthis/ GI-123790 W53 (1) 7.30 394100 962 1472 57 7.2 0.98 0.47 Pachyteuthis sp. Acroteuthis/ W53 (2) 7.30 0.96 0.56 Pachyteuthis sp. Acroteuthis/ GI-123790 W54 7.30 381420 1407 1378 121 50.4 -1.08 0.58 Pachyteuthis sp. Acroteuthis/ GI-123791 W55 7.70 383610 1456 1312 61 25 0.26 0.18 Pachyteuthis sp. Acroteuthis/ GI-123791 W56 7.70 385680 958 1678 57 3.6 1.88 0.64 Pachyteuthis sp. Acroteuthis/ GI-123791 W57 7.70 384940 774 1370 43 2.7 -1.08 -0.97 0.707307 Pachyteuthis sp. Acroteuthis/ GI-123792 W58 (1) 8.00 378930 2032 1470 68 29 -0.84 -0.19 Pachyteuthis sp. Acroteuthis/ W58 (2) 8.00 -0.78 -0.06 Pachyteuthis sp. Acroteuthis/ GI-123792 W59 8.00 385530 809 1683 45 4.7 1.30 0.28 Pachyteuthis sp. Acroteuthis/ GI-123792 W60 8.00 383820 983 1503 48 11.6 2.62 -0.66 Pachyteuthis sp. Acroteuthis/ GI-123793 W61 8.50 384370 1249 1449 112 36.5 0.83 0.03 Pachyteuthis sp. Acroteuthis/ GI-123793 W62 8.50 381570 1976 1336 66 24.4 0.26 -0.01 Pachyteuthis sp. Acroteuthis/ GI-123793 W63 8.50 382510 1354 1309 71 12.5 -1.21 0.56 0.707327 Pachyteuthis sp. Acroteuthis/ GI-123794 W64 (1) 9.00 382820 1159 1349 58 32.6 -0.51 0.53 Pachyteuthis sp. Acroteuthis/ W64 (2) 9.00 -0.57 0.53 Pachyteuthis sp. Acroteuthis/ GI-123794 W65 9.00 374750 3322 1511 92 30.6 0.11 -0.67 0.707339 Pachyteuthis sp. GI-123794 W66 9.00 Pachyteuthis sp. 383040 1304 1301 47 10.9 -0.85 0.19 GI-123795 W67 9.50 Pachyteuthis sp. 384650 1631 1472 109 15.3 -0.33 -0.57 GI-123795 W68 9.50 Acroteuthis sp. 389370 709 1325 66 20.8 1.07 -0.21 0.707345 GI-123795 W69 (1) 9.50 Acroteuthis sp. 385750 2259 1479 215 119 -0.89 -0.96 W69 (2) 9.50 -0.82 -1.01 GI-123796 W70 10.00 Acroteuthis sp. 389740 2047 1274 136 32.7 0.38 -0.23 GI-123796 W71 10.00 Acroteuthis sp. 392100 1613 1226 52 11.6 0.32 0.21 0.707322 GI-123796 W72 10.00 Acroteuthis sp. 390510 1859 1481 95 37.2 0.25 -1.75 GI-123797 W73 11.00 Acroteuthis sp. 385600 2067 1205 130 72.7 -1.69 -0.88

54

Integrated stratigraphy of Lower Cretaceous sediments from North-East Greenland

Table 1 (cont.)   original sample depth Ca Mg Sr Fe Mn 13C 18O sample identification δ δ 87Sr/86Sr no. [m] [ppm] [ppm] [ppm] [ppm] [ppm] no. [‰] [‰] GI-123797 W74 (1) 11.00 Acroteuthis sp. 383390 1734 1654 80 31.3 -0.17 0.75 0.707329 W74 (2) 11.00 Acroteuthis sp. -0.20 0.76 GI-123798 W75 12.00 Acroteuthis sp. 394380 1117 1449 119 136 0.79 -0.39 GI-123799 W76 12.70 Acroteuthis sp. 389980 1029 1476 99 36.7 1.57 -0.52 0.707343

GI-123799 W77 12.70 Acroteuthis sp. 383790 1948 1341 203 202 0.43 -0.04

GI-123799 W78 12.70 Acroteuthis sp. 388870 824 1510 132 29.9 1.57 -0.12 Acroteuthis or GI-118554 CM8 13.10 Cylindroteuthis 388640 1185 1264 46 8.9 1.08 -0.02 sp. GI-123800 CM7 13.50 Acroteuthis sp. 388650 1007 1465 25 5.0 1.32 -0.66 GI-123800 W79 13.50 Acroteuthis sp. 391810 1662 1407 46 7.4 GI-118555 CM6 14.50 sp. indet. 392480 580 1414 25 4.4 1.18 0.06 ? Pachyteuthis GI-118558 CM5 18.50 393630 735 1374 15 3.1 -0.18 1.56 sp. GI-123801 CM4 19.00 Acroteuthis sp. 389960 1009 1705 24 2.2 3.77 -0.32 Cylindroteuthis GI-123801 W80 19.00 392690 1041 1250 56 7 1.66 0.56 0.707379 sp. Cylindroteuthis GI-123801 W81 19.00 396120 590 1234 73 112 -1.02 0.05 sp. Cylindroteuthis GI-123801 W82 (1) 19.00 395380 1380 1627 87 110 2.11 -2.72 sp. W82 (2) 19.00 2.12 -2.64 GI-123801 W83 19.00 Acroteuthis sp. 395770 481 1465 88 51.3 2.43 0.73 GI-123802 W84 20.00 Acroteuthis sp. 392600 1066 1143 118 45.5 1.06 1.19 Cylindroteuthis GI-123803 W85 20.80 394220 2010 1268 96 14.4 1.41 0.92 sp. Cylindroteuthis GI-123803 W86 20.80 394430 1379 1548 83 11.4 -0.13 0.54 sp. Cylindroteuthis GI-123803 W87 (1) 20.80 392750 2165 1120 85 14.7 -0.54 0.91 sp. Cylindroteuthis W87 (2) 20.80 -0.52 0.97 sp. GI-123803 W88 20.80 Acroteuthis sp. 381160 3022 1512 920 431 -1.56 -0.47 GI-123804 W89 21.30 Acroteuthis sp. 391590 1475 1441 228 27.2 0.95 0.62 GI-123804 W90 21.30 ? 394000 1079 1183 81 26.4 0.45 0.30 GI-123804 W91 21.30 Acroteuthis sp. 393430 2036 1223 56 4.9 0.60 0.18 0.707382 GI-123805 W92 (1) 21.70 Acroteuthis sp. 393020 1791 1287 59 5.6 0.52 1.30 0.707457 W92 (2) 21.70 Acroteuthis sp. 0.45 1.30 GI-123805 W93 21.70 Acroteuthis sp. 393690 1093 1734 56 8.3 2.13 0.94 0.707399 GI-123805 W94 21.70 Acroteuthis sp. 394800 1381 1194 118 82.8 0.80 -0.39 GI-123806 W95 22.00 Acroteuthis sp. 397400 791 1260 101 27.1 0.63 0.57 GI-123807 W96 22.70 Acroteuthis sp. 391000 2262 1133 272 91.5 -0.50 0.79 GI-123807 W97 (1) 22.70 Acroteuthis sp. 394660 1436 1266 106 5.5 1.09 1.36 W97 (2) 22.70 Acroteuthis sp. 1.06 1.32 GI-123807 W98 22.70 Acroteuthis sp. 390310 1791 1356 63 14.2 1.13 0.60 GI-123808 W99 23.30 Acroteuthis sp. 384590 2004 1319 176 18.4 0.20 0.88 GI-123808 W100 23.30 Acroteuthis sp. 385690 1820 1063 70 22.8 -0.35 1.07 GI-123808 W101 23.30 Acroteuthis sp. 392510 1491 1075 225 116 -0.14 0.78 GI-123809 W102 (1) 23.90 Acroteuthis sp. 388230 923 1580 49 7.8 0.56 1.06 W102 (2) 23.90 Acroteuthis sp. 0.44 0.92 GI-123809 W103 23.90 Acroteuthis sp. 385550 1802 1578 56 26.1 0.97 1.39 0.707445 GI-123809 W104 23.90 Acroteuthis sp. 382970 1359 1285 472 175 0.71 0.48 GI-123810 W105 24.40 Acroteuthis sp. 383000 1890 1143 67 6.2 1.16 1.00 0.707472 GI-123810 W106 24.40 Acroteuthis sp. 375900 3624 1201 106 136 -0.07 0.57

55

Chapter 2

Table 1 (cont.)   original sample depth Ca Mg Sr Fe Mn 13C 18O sample identification δ δ 87Sr/86Sr no. [m] [ppm] [ppm] [ppm] [ppm] [ppm] no. [‰] [‰] GI-123810 W107 (1) 24.40 Acroteuthis sp. 379400 2371 1126 542 327 -0.05 0.25 W107 (2) 24.40 Acroteuthis sp. 0.03 0.37 GI-123811 W108 24.70 Acroteuthis sp. 386260 907 1182 69 13.6 1.33 0.90 GI-123814 W109 25.00 Acroteuthis sp. 380280 1973 1146 87 10.1 0.83 0.69 0.707489 GI-123812 W110 25.00 Acroteuthis sp. 381370 2330 1086 162 47.3 -0.44 0.76 0.707463 GI-123813 W112 25.50 Acroteuthis sp. 389400 2302 1168 114 100 1.09 0.58 GI-123813 W113 (1) 25.50 Acroteuthis sp. 387540 2509 1238 76 20.1 0.04 1.01 0.707460 W113 (2) 25.50 0.06 1.01 GI-123814 W114 25.50 Acroteuthis sp. 390910 1425 1402 63 19.1 1.55 0.62 GI-123814 W115 25.90 Acroteuthis sp. 383510 2025 1129 1310 513 -0.14 0.38 GI-123815 W116 26.15 Acroteuthis sp. 386590 2482 1341 162 94.5 0.82 0.82 GI-123815 W117 26.15 Acroteuthis sp. 362120 2189 1127 482 315 -0.08 0.74 GI-123815 W118 (1) 26.15 Acroteuthis sp. 390850 1411 1425 64 4.9 3.02 -2.02 W118 (2) 26.15 2.95 -1.99 GI-123816 W119 26.30 Acroteuthis sp. 392130 2167 1156 568 16.8 1.04 0.71 GI-123816 W120 26.30 Acroteuthis sp. 393000 1794 1156 75 2.9 0.88 0.29 GI-123816 W121 26.30 Acroteuthis sp. 389340 1914 1124 49 4.6 0.47 0.71 GI-123817 W122 26.50 Acroteuthis sp. 391880 1409 1159 105 5.8 0.71 0.78 GI-123817 W123 (1) 26.50 Acroteuthis sp. 391960 1795 1276 59 3.4 1.06 0.46 0.707469 W123 (2) 26.50 1.01 0.39 GI-123817 W124 26.50 Acroteuthis sp. 391710 1801 1265 60 9.7 0.94 0.92 GI-123817 W125 26.50 Acroteuthis sp. 387520 1460 1122 215 45.8 0.68 0.89 GI-123818 W126 26.75 Acroteuthis sp. 387550 1616 1014 92 15.6 -0.50 0.72 GI-123818 W127 26.75 Acroteuthis sp. 388740 2272 1155 148 84.5 0.86 1.20 GI-123818 W128 (1) 26.75 Acroteuthis sp. 389740 2056 1099 181 55.8 0.34 0.70 W128 (2) 26.75 0.21 0.66 GI-123819 W129 27.10 Acroteuthis sp. 394410 910 1263 52 3.4 1.55 1.37 GI-123819 W130 (1) 27.10 Acroteuthis sp. 390950 2080 1207 55 5.5 0.707486 W130 (2) 390530 2093 1208 93 27.5 GI-123819 W131 27.10 385630 3470 1299 166 82.6 -0.57 0.31 GI-123819 W132 (1) 27.10 Acroteuthis sp. 387470 2365 1288 107 37.3 -0.08 0.25 W132 (2) 389370 2346 1288 128 48

distinguished (Fig. 2.3). The maximum of the positive carbon isotope excursion is, however, not clearly

13 reorded i the δ Cbel-data presented here, as only few belemnite specimens cover the CIE interval.

A marked decline in the abundance of nannoconids, large and heavily calcified nannoliths of unknown taxonomic affiliation, preceeds the CIE in the Tethys (southeast France and northern Italy, Barbarin et al., 2012; Bersezio et al., 2002; Erba et al., 2004; Gréselle et al., 2011), central Atlantic (Bornemann and Mutterlose, 2008) and Pacific Ocean (ODP Hole 1149B, Erba et al., 2004). Pauly et al. (2012b) describe a decline of nannoconids in the lowermost Valanginian of the Rødryggen section. By using the re-calibrated Valanginian nannofossil zonation discussed here, this decline falls into the upper lower Valanginian. In

56

Integrated stratigraphy of Lower Cretaceous sediments from North-East Greenland agreement with the observations in low latitudinal settings, the decline of nannoconid abundance is just

13 preedig the δ Cbel shift towards higher mean values (Fig. 2.4).

2.6.3. The lower / upper Valanginian boundary The discrepancy of the ammonite and calcareous nannofossil biostratigraphy regarding the lower / upper Valanginian transition in the Rødryggen section can not be resolved by the 87Sr/86Sr dataset presented here, due to the low sample resolution in this interval (Fig. 2.2). The onset of the positive CIE has been dated as early late Valanginian in other sections. By extrapolating these observations to the Rødryggen section, the lower / upper Valanginian boundary is positioned between 11-13 m above the base of the Albrechts Bugt Member. This datum is in agreement with the ammonite zonation, but it conflicts with the LO of M. speetonensis (17 m above base of the section). In the Boreal LK and BC nannofossil zonation schemes, the LO of M. speetonensis marks the base of the upper Valanginian (Fig. 2.2).

For the Boreal Valanginian, few sections allow for correlation of nannofossil events to the ammonite zonation. One is the Speeton section, where the upper Valanginian is missing (Neale, 1962; Rawson, 1971). In the sections in northern Germany, the first abundant and consistent nannofossil floras occur in basal upper Valagiia Mutterlose, . I the Wąał setio i etral Poland M. speetonensis has been observed in only one sample belonging to the Prodichotomites hollwedensis ammonite zone (Mutterlose, 1993). Our observations imply, that the LO of M. speetonensis has been imprecisely correlated due to stratigraphic limitations of the outcrops. The integrated chemo- and biostratigraphic data from the Rødryggen section suggest that M. speetonensis ranges into the late Valanginian.

2.6.4. The Valanginian / Hauterivian boundary The position of the Valanginian / Hauterivian boundary established by Alsen (2006) and Alsen and Mutterlose (2009) based on ammonite biostratigraphy deviates by 6 m from the one suggested by calcareous nannofossils and Sr-isotope stratigraphy. By definition the base of the Hauterivian is drawn at the first occurrence of Acanthodiscus radiatus (Thieuloy, 1977; Mutterlose, 1996), an ammonite species common in the Tethys but also known from the Boreal Realm. In northwest Germany, A. radiatus first appears in the upper Endemoceras amblygonium zone (Kemper et al., 1981; Mutterlose, 1984, 1996). In Speeton this event is positioned even higher, in the Endemoceras regale zone (Rawson, 1971). The inclusion of the lower part of the E. amblygonium zone in the Valanginian, which has consequently been

57

Chapter 2 suggested (Kemper et al., 1981; Rawson, 1983; Rawson and Hoedemaeker et al., 1999), is supported by the Sr-isotope data of McArthur et al. (2007) and Mutterlose et al. (2014).

The nannofossil Eprolithus antiquus, which defines the base of nannofossil zone BC7 (Crux, 1989; Bown et al., 1998), consistently appears in northwest Germany in the E. amblygonium to Endemoceras noricum zone (Mutterlose, 1991), in Speeton in the upper E. amblygonium zone (Fig. 2.3). It is found also in the North Sea (Jeremiah, 2001) and in northeast Greenland (Pauly et al., 2012a). A short-lived earlier occurrence of E. antiquus has been observed in the upper Valanginian of the West Netherlands Basin and Lower Saxony Basin. Despite this scattered Valanginian occurrence, E. antiquus is regarded as a reliable nannofossil marker for the base of the Hauterivian.

In the Rødryggen section the lowermost Hauterivian is very condensed. This is reflected by a break in the Sr-isotope curve (Fig. 2.2). The closely spaced occurrences of the nannofossil marker species for nannofossil zones BC6 to BC8 document that the lowermost Hauterivian zones BC6 and BC7 are represented by 0.4 m of sediment at most.

Due to the condensed nature of the lowermost Hauterivian, E. antiquus was observed by Pauly et al. (2012a) in one sample only (sample 469464, 21.9 m above base of the Albrechts Bugt Member). The corresponding Sr-isotope values (0.707382, 21.3 m; 0.707399, 21.7 m) agree well with the Sr-isotope ratio of about 0.70739 given in the compiled Sr-curve of Mutterlose et al. (2014) for the Valanginian / Hauterivian boundary. Our Sr-data therefore clearly support the position of the base of the Hauterivian as suggested by nannofossil biostratigraphy. Based on ammonite fragments identified as Simbirskites sp., Alsen (2006) and Alsen and Mutterlose (2009) placed the base of the Hauterivian 6 m further down in the section. In contrast to the ammonite specimens found in the Rødryggen Member which can be clearly identified as Simbirskites, the ammonite fragments from the Albrechts Bugt Member are poorly preserved. Their identification as Simbirskites sp. did not unequivocally withstand re-examination.

2.6.5. Lowermost Cretaceous palaeotemperatures

18 The δ Obel-data presented here show an increase from average values of 0‰ i the upper Razaia and loer Valagiia to ~‰ i the upper Valagiian and lower Hauterivian (Fig. 2.2). A similar trend has

18 ee osered i the δ Obel-data from southeast France and Spain (McArthur et al., 2007), northern Germany (Podlaha et al., 1998), Western Siberia (Price and Mutterlose, 2004) and Arctic Svalbard (Price and Nunn, 2010). This increase is independently supported by oxygen isotope data from bulk rock

58

Integrated stratigraphy of Lower Cretaceous sediments from North-East Greenland carbonate (northern Italy; Weissert and Erba, 2004) and fish teeth from southeast France (Barbarin et al., 2012).

Proided that it has ot ee diageetiall altered, the δ18O of biogenic calcite is the result of ambient sea-water temperatures during calcification and the oxygen isotope composition of the water it preipitates fro. The δ18O of seawater is influenced by the volume of polar ice and the salinity, which in turn is the result of evaporation and freshwater input.

Clumped isotope data of eleite alite fro Wester “ieria suggest ireased δ18O of seawater and/or decreased precipitation and riverine input coincident with low late Valanginian temperatures (Price and Passey, 2013). Intervals of cool climate with at least seasonally low water temperatures in the earliest Cretaceous are supported by the occurrence of glendonites and dropstones in the upper lower and upper Valanginian (Frakes and Francis, 1988; Kemper and Schmitz, 1975; Price and Nunn, 2010). This late Valanginian cooling is reflected in the oxygen isotope data from Greenland presented here. Our data

18 douet a shift toards heaier =older δ Obel values, which postdates the onset and the peak of the CIE.

2.7. Conclusions

87 86 13 This study presents a correlation of strontium and carbon isotope ( Sr/ “r, δ Cbel) based stratigraphy within the framework of existing ammonite- and nannofossil zonations of the lowermost Cretaceous. The stratigraphic range of the Rødryggen section (Wollaston Forland, North-East Greenland) resulting from the Sr-isotope stratigraphy (Ryazanian - Barremian) agrees with the results from biostratigraphy. Mismatches regarding stage/ substage boundaries resulted in a reconsideration of the nannofossil biostratigraphy of the Boreal Lower Cretaceous. The correlation of the nannofossil zonation of this interval is based primarily on material from the Ryazanian - Hauterivian of Speeton (northern England), a section which is in part very condensed or incomplete.

13 The aerage irease of aout .‰ i the δ Cbel-data matches records of the carbon isotope excursion associated with the upper Valanginian Weissert Event from other areas of the world. The isotope anomaly is isochronous and well-established in stratigraphic correlation. Here it is a valuable datum for the determination of the lower / upper Valanginian boundary.

Based on the available stratigraphic data we conclude the following. a) The first occurrence (FO) of the nannofossil Sollasites arcuatus is probably diachronous. b) The last occurrence (LO) of S. arcuatus, which defines the base of nannofossil zone BC3 has been falsely assigned to the latest Ryazanian and is in fact

59

Chapter 2 early Valanginian of age. c) The LO of Micrantholithus speetonensis, marking the early / late Valanginian transition in Boreal nannofossil zonations, might actually be of late Valanginian age.

By using the re-calibration of the Valanginian nannofossil zonation discussed here, the marked decline in the abundance of Nannoconus spp. in the Rødryggen section falls into the upper lower Valanginian. In agreement with the observations on the nannoconid decline associated with the Weissert Event in the

13 Teths, this delie just preedes the shift toards higher ea δ Cbel. This makes the decrease in nannoconid abundance observed by Pauly et al. (2012b) the first documentation of the Valanginian nannoconid crisis in the Boreal Realm.

18 The oge isotope reord δ Obel preseted here shos a irease of ‰ durig the Valagiia. This agrees well with Lower Cretaceous oxygen isotope records from other areas of the Boreal Realm and the Tethys, as well as other geochemical and paleoecological proxies suggesting a late Valanginian cooling.

2.8. Acknowledgements We appreciate logistic support by the Geological Survey of Denmark and Greenland (GEUS, Copenhagen). Thank you to all Danish colleagues involved for assistance and the enjoyable field campaigns in North-East Greenland. We are grateful to the staff of the labs of the Friedrich-Alexander Universität Erlangen Nürnberg/ GeoZentrum Nordbayern and of the Ruhr-Universität Bochum for element composition analysis and measurements of C-, O- and Sr-isotopes. Financial support of the German Research foundation (DFG, MU 667/38-1) is gratefully acknowledged. We appreciate the effort and time two unknown reviewers spent on improving the manuscript.

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Weissert, H., and E. Erba (2004), Volcanism, CO2 and palaeoclimate: a Late Jurassic–Early Cretaceous carbon and oxygen isotope record, Journal of the Geological Society, 161(4), 695–702. Weissert, H., A. Lini, K. B. Föllmi, and O. Kuhn (1998), Correlation of Early Cretaceous carbon isotope stratigraphy and platform drowning events: a possible link?, Palaeogeography, Palaeoclimatology, Palaeoecology, 137(3–4), 189–203.

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Wimbledon, W. A. B., C. Casellato, D. Reháková, L. G. Bulot, E. Erba, S. Gardin, R. M. C. H. Verreussel, D. K. Munsterman, and C. O. Hunt (2011), Fixing a basal Berriasian and Jurassic/Cretaceous (J/K) boundary - is there perhaps some light at the end of the tunnel?, Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy), (117), 295–307. Wortmann, U. G., and H. Weissert (2000), Tying platform drowning to perturbations of the global carbon le ith a δCOrg-curve from the Valanginian of DSDP Site 416, Terra Nova, 12(6), 289–294. Zakharov, V. A., P. R. Bown, and P. F. Rawson (1996), The Berriasian stage and the Jurassic Cretaceous boundary, Bulleti de l’Istitut Royal des Scieces Natuelles de Belgiue, Scieces de la Tee, (66 (suppl.)), 7–10.

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Size changes of calcareous nannofossils and the nature of the Weissert Event

3 Size changes of calcareous nannofossils and the nature of the Weissert Event (Early Cretaceous)

Carla Möller1, André Bornemann2, Jörg Mutterlose1

1Ruhr-Universität Bochum, Institut für Geologie, Mineralogie & Geophysik, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany; [email protected]

2Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, 30655 Hannover, Germany

(Submitted 2017 to Paleoceanography)

Abstract

Strata of Valanginian age (Early Cretaceous, 139.8-132.9 Ma) reord a . ‰ positie aro isotope excursion (CIE), the Weissert Event. It coincides with volcanic activity of the Paraná-Etendeka large igneous province. Unlike the Mesozoic Oceanic Anoxic Events (OAEs), the few examples of organic-rich deposits associated with the CIE known from the Valanginian do not document a widespread perturbation of the carbon cycle. The nature of the Weissert Event, particularly in comparison with the Mesozoic OAEs, is thus still a subject of debate.

Recent biometric studies observed size reductions of certain calcareous nannofossil species during global environmental perturbations in the Cretaceous. Dwarfism has specifically been described for the mid Cretaceous (~125 - 90 Ma) OAE1a and OAE2. Our biometric analyzes of selected nannofossil taxa in samples from northern Germany and the Western Atlantic revealed an average size reduction of Biscutum constans throughout the late Valanginian, beginning at the climax of the Weissert Event. A humid climate in the late Valanginian, probably linked to volcanic CO2 outgassing, caused increased weathering and the transport of large amounts of detrital material into ocean basins. Due to light attenuation in the surface waters the smaller varieties of B. constans, adapted to lower light availability, had an advantage over the larger forms. The latter have been found to thrive in the clear waters of open ocean settings. The observed size redutio durig the Valagiia Weissert Eet reseles the darfig of B. constans documented from the early Aptian OAE1a and the Cenomanian/Turonian OAE2. All three events have been occurred during a phase of humid climate and intense weathering.

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3.1. Introduction Valagiia sediets reord a . ‰ positie aro isotope excursion (CIE) that has been detected worldwide in marine bulk rock and biogenic carbonates (Lini et al., 1992; Channell et al., 1993; Price and Mutterlose, 2004; Weissert and Erba, 2004; Bornemann and Mutterlose, 2008; Greselle et al., 2011; Meissner et al., 2015), organic matter (Lini et al., 1992; Wortmann and Weissert, 2000), and in terrestrial deposits (Gröcke et al., 2005; Nunn et al., 2010). Recent astrochronological data strongly support the original assumption of a link to the volcanic activity of the Paraná-Etendeka continental flood basalt province (Weissert et al., 1998; Weissert and Erba, 2004; Martinez et al. 2015). This so-called Weissert Event is considered the first of the Cretaceous Oceanic Anoxic Events (OAEs) by some authors (e.g., Erba et al., 2004; Jenkyns, 2010). So far only few occurrences of organic-rich sediments associated with the Weissert Event are known. Evidence for extremely high marine primary productivity and/or widespread anoxic conditions in the oceans, which would support the OAE scenario, has so far not been found (Westermann et al., 2010; Kujau et al., 2012). A well-known feature of the Valanginian nannofossil record is the decline of nannoconids, large nannoliths of unknown affinity. This decline coincides with the Weissert Event in a number of localities in the Tethys (Barbarin et al., 2012; Bersezio et al., 2002; Erba et al., 2004; Gréselle et al., 2011), the western North Atlantic (Bornemann and Mutterlose, 2008), the Pacific Ocean (Erba et al., 2004), and the Greenland Norwegian Seaway (Pauly et al., 2012; Möller et al., 2015). A similar, but more severe nannoconid crisis has been observed in association with the OAE1a (Weissert and Erba, 2004; Erba et al., 2010; Mutterlose and Bottini, 2013).

In present day oceans, a broad relationship between morphological types of coccoliths and coccospheres, and their distribution in different environments can be observed (Young, 1994; Monteiro et al., 2016). Biometry of recent calcareous nannoplankton species reveals links between the calcification process of coccolithophorids and seawater chemistry, nutrient availability, and surface water temperature (e.g., Knappertsbusch et al., 1997; Bollmann and Herrle, 2007; Langer et al., 2006, 2011). Biometric data of fossil coccoliths from the Jurassic and Cretaceous have been used for various purposes. In taxonomy they allow accurate species definitions (e.g. Mattioli et al., 2004; Bornemann and Mutterlose, 2006; Linnert and Mutterlose, 2009; Fraguas and Erba, 2010), nannofossil carbonate fluxes can be quantified (Bornemann et al., 2003; Erba and Tremolada, 2004), and in paleoceanography and paleoecology they serve as proxy data (e.g., Tremolada and Erba, 2002; Linnert and Mutterlose, 2013; Linnert et al., 2014). The calcareous nannofossil taxa Biscutum constans, Watznaueria barnesiae, and Zeugrhabdotus erectus are very common in the Lower Cretaceous. Despite the relatively large number of biometric studies dealing with B. constans, the environmental parameters chiefly responsible for size variations of B. constans are still poorly

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Size changes of calcareous nannofossils and the nature of the Weissert Event understood. Temperature (Bornemann and Mutterlose, 2006; Linnert et al., 2014; Lübke et al., 2015), acidity of the ocean water (Erba et al., 2010), toxic metal concentrations (Erba, 2004; Faucher et al., 2017), nutrient concentrations (Linnert and Mutterlose, 2013; Lübke et al, 2015), and light availability (Lübke et al., 2015) are potential factors which are controversially debated.

Size reductions of B. constans coccoliths have been documented both for the Aptian OAE1a and the Cenomanian/ Turonian OAE2 (Erba et al., 2010; Linnert and Mutterlose, 2013; Lübke and Mutterlose, 2016; Faucher et al., 2017). By providing a sound set of B. constans size data we test to what extent the Valanginian Weissert Event resembles the major OAEs of the Cretaceous. To assess the paleoceanographic changes during the Valanginian, three calcareous nannofossil taxa (B. constans, W. barnesiae and Z. erectus) were studied biometrically in 99 samples from two different marine settings. These include the geographically confined epicontinental Lower Saxony Basin (LSB) and the western North Atlantic, an open- oceanic setting. To compare the effect of environmental change on the different calcareous nannofossil groups, the biometry is combined with relative abundance data of Nannoconus spp. in the LSB (this study) and the western North Atlantic (from Bornemann and Mutterlose, 2008). A comparison with published independent proxy data (clay minerals, spore/pollen data) available for this interval supports the evaluation of the environmental factors recorded by calcareous nannofossils.

3.2. Study sites and stratigraphy 3.2.1. Lower Saxony Basin, Northern Germany Two cores from northern Germany, recovering Lower Cretaceous sediments, have been studied (Fig. 3.1). The core Scharrel 10 was drilled 20 km northwest of Hannover (52°30'29.7"N 9°33'14.1"E). It covers a 198 m thick succession of Lower Cretaceous claystones and silty claystones.

Core Wiedensahl 2, approximately 40 km west of Hannover, recovered 289 m of dark clayey siltstones with a low carbonate content (2 – 10 %). For a detailed description of this core see Keupp and Janofske (1988) and Janicke and Keupp (1988). Biostratigraphy based on ostracods and foraminifera provided a late Berriasian (Wealden 6) to early Hauterivian age (Niedziolka, 1988). The siliciclastic sediments in the Scharrel 10 and Wiedensahl 2 cores were deposited in the central part of the Lower Saxony Basin (LSB; Fig. 3.1). During the Early Cretaceous, the LSB formed the southern extension of the Proto-North Sea (36.66°N ± 3.97° according to the model of van Hinsbergen et al., 2015). It was bounded in the south by the Rhenish Massif, in the north by the Pompeckj Swell, in the west by the East Netherlands High, and in the east by the East Brandenburg High. Narrow seaways granted restricted marine connections to the neighboring

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Figure 3.1 Valanginian paleogeography modified after Kiel et al. (2014) showing the sample localities. Assumed land areas are indicated in grey, white represents areas covered by oceans, black lines show continent outlines. Map detail of the Lower Saxony Basin (LSB), northern Germany, after Möller and Mutterlose (2014). basins. The Early Cretaceous LSB can be characterized as a relatively small (400 km long, 100 km wide), epicontinental basin with high detrital input and high sedimentation rates (Mutterlose and Bornemann, 2000).

3.2.2. Blake Bahama Basin, western Atlantic Ocean DSDP Hole 534A was drilled in the Blake Bahama Basin off the eastern coast of Florida (28.34°N, 75.38°W; Fig. 3.1). An integrated stratigraphic framework of the section was provided by Bornemann and Mutterlose (2008). The interval studied here covers the upper Berriasian to lower Hauterivian (calcareous nannofossil subzones NK2a – NC4B, referring to the lower latitudinal NK nannofossil zonation of Bralower et al., 1989). Sediments comprise laminated calcareous nannofossil marls and chalks with interstratified bioturbated chalks, calcareous sand-/siltstones, and in the lower part claystones (Sheridan and Gradstein et al., 1983). The sediments represent an open oceanic setting with a paleolatitude of approximately 15°N according to Bornemann and Mutterlose (2008), based on paleogeographic reconstruction of Hay et al. (1999), and 23°N ± 5.08° following the model of van Hinsbergen et al. (2015).

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3.3. Material and methods 3.3.1. Nannofossil biostratigraphy A detailed biostratigraphic nannofossil zonation using the BC zones of Bown et al. (1998) was done for the Scharrel 10 core. A total of 79 smear slides were prepared and studied following the taxonomic concepts of Perch-Nielsen (1985) and Bown et al. (1998). The slides were analyzed by using an Olympus BH-2 light microscope with cross-polarized light at a magnification of x1250.

3.3.2. Counting Calcareous nannofossil counts were performed on 93 samples (80 samples for Scharrel 10, 13 samples for Wiedensahl 2). For DSDP Hole 534A the data of Bornemann and Mutterlose (2008) have been used. Microscope slides for counting were prepared following the random settling method of Geisen et al. (1999). To determine the composition of the calcareous nannofossil assemblages, at least 400 coccoliths were counted in each sample. Absolute and relative abundances of the taxa were calculated. For the interpretation, only the absolute and relative abundances of Nannoconus spp. are considered. The Shannon index was calculated as a measure of diversity of the nannofossil assemblages (heterogeneity Hs; Shannon and Weaver, 1949). The mode of preservation was checked by applying the visual criteria of Roth (1983) and Roth and Thierstein (1972). The visible degree of dissolution (etching, E) and overgrowth (O) is categorized as E1/O1 for minor, E2/O2 for moderate, and E3/O3 for major dissolution or overgrowth. Only well preserved samples (=E1/O1) were chosen for biometry.

3.3.3. Biometry The demarcation between the species B. constans and the morphologically closely related B. ellipticum is not unambiguously resolved. Brace and Watkins (2014) consider B. ellipticum as a synonym of B. constans. Biometric data supplied no significant criteria for differentiating between B. constans and B. ellipticum, therefore Bornemann and Mutterlose (2006) consider them as end-members of a morphological continuum. Similarly, W. barnesiae and W. fossacincta are considered morphotypes of the same species (Bornemann and Mutterlose, 2006). In this study, specimens for the morphometric analyses were selected without differentiating between these morphotypes. For simplification, only the terms B. constans and W. barnesiae are used.

Measurements of individual coccoliths widths and lengths were done for a total of 99 samples from the three sections using settling slides. The 27 samples analyzed from core Scharrel 10 and the 53 samples

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Size changes of calcareous nannofossils and the nature of the Weissert Event from DSDP Hole 534A cover the entire sections, the 19 samples studied from core Wiedensahl 2 cover an interval of 30 m. The Scharrel 10 samples were examined with a Leitz Laborlux 12 PolS microscope at a 1000x magnification, mounted with a QImaging MicroPublisher 5.0 RTV camera using the software Image Pro Plus 7.0. All samples of Wiedensahl 2 and the 28 samples from DSDP Hole 534A that were chosen for biometry of B. constans were analyzed with an Olympus BX53 microscope with a magnification of 1250x. An Olympus SC100 camera combined with the Olympus Stream Start 1.9.1 software was used. To obtain comparable data, the measurements were calibrated by measuring the same particle with each of the microscopes used. Coccoliths were randomly chosen along a transect of the slides and photographed, excluding etched, overgrown, or broken specimens. At least 50 specimens of B. constans and W. barnesiae were measured from each sample. In the Scharrel 10 samples, additionally at least 50 specimens of Zeugrhabdotus erectus were measured. Measurements were done with the software FIJI (Schindelin et al., 2012).

Size measurements of W. barnesiae were carried out on 53 samples from DSDP Hole 534A. Depending on the state of preservation between 80 and 100 specimens were measured per sample. For gaining biometric data, an image analysis system consisting of a CCD camera mounted on an OLYMPUS BH-2 light- microscope and an Apple MacIntosh PowerPC with a SCION LG-3 framegrabber card was used. The software package ScionImage 1.63. In a first step the specimens were captured electronically from live images with a macro routine and copied to a mosaic, which contains 50 specimens. In a second step the specimens were measured using macro routines documented in Young et al. (1996), which had been adjusted to our purposes. Measureets ield a preisio of ±. μ.

Calculation of mean values and 95% confidence intervals, as well as statistical testing of the morphometric data, were done using the software Past 3.0 (Hammer et al., 2001). To test the data for normal distribution, the Shapiro-Wilks and Anderson-Darling tests were applied. If the probability p(normal) is below the chosen alpha level 0.05, the sample data are not from a normally distributed population. To verify whether

← Figure 3.2 Data from Scharrel 10 and Wiedensahl 2 (northern Germany). From left to right: diversity of the nannofossil assemblage given as the Shannon index of heterogeneity (Shannon and Weaver, 1949), relative abundances of delicate, dissolution-prone nannofossil taxa (Stradnerlithus geometricus, S. silvaradius, Calciosolenia fossilis, Calculites sp., Discorhabdus ignotus), relative (black) and absolute (grey, in 106/ g sediment) abundances of Nannoconus spp. and coccolith mean lengths (black lines) and 95%-confidence intervals (orange, grey) of the calcareous nannofossil taxa Biscutum constans, Watznaueria and Zeugrhabdotus erectus. The carbon isotope record 13 (δ Corg) has been measured in the organic material of samples from Wiedensahl 2. For the nannofossil biostratigraphy of Scharrel 10 the BC zonation for the Boreal of Bown et al. (1998) was used. Correlation of the BC zones with ammonite zonation of northern Germany after Bown et al. (1998) and Möller et al. (2015). The ammonite zonation of Wiedensahl 2 is from Niedziolka (1988). Marked in darker blue is the interval of the B. constans size minimum, the light blue area corresponds to the long-term size decrease.

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observed variations in mean size of B. constans are significant, two different tests were performed on the datasets. To the normally distributed data sets with siilar ariaes, a ANOVA Tuke’s pairise post-hoc test was applied. Kruskal-Wallis Mann-Whitney pairwise post-hoc test was used to test for equal means of non-normally distributed datasets. The null-hypothesis of both methods is that the means of two data sets are equal. P(equal) < 0.0001 was chosen as threshold value for significantly different means.

13 Figure 3.3 Calcareous nannofossil zonation, bulk rock carbon isotope record (δ Ccarb), and relative abundances of Nannoconus spp. from DSDP Hole 534A from Bornemann and Mutterlose (2008), and mean coccolith lengths (black lines) with 95% confidence interval (colored) of the nannofossil taxa B. constans and Watznauria. TEX86–data from DSDP Hole 534A (grey) and Site 603 (white) are from Littler et al. (2011).

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3.3.4. Organic carbon isotopes A total of 123 bulk rock samples from the core Wiedensahl 2 have been processed for their carbon isotope

13 opositio of orgai atter δ Corg). Carbonate was first removed from the samples with 10% hydrochloric acid, then the samples were washed until pH 6 - 7 was reached, and dried at 50°C. Carbon isotopes have been measured at the GeoZentrum Nordbayern, Friedrich-Alexander Universität Erlangen- Nürnberg. To determine carbon isotope composition of organic matter, samples have been analyzed using a CE 1100 elemental analyzer coupled online via a Conflo III Interface to a ThermoFisher Delta Plus mass spectrometer. Organic compounds were oxidized at 1020° C by addition of O2 to CO2 and NOx. The gases were transferred in the He stream on a Cu reduction furnace (650° C) to reduce NOx to N2. After passing a chromatographic column, CO2 and N2 were transferred to the mass spectrometer. Repeated analysis of a laboratory standard (urea) were carried out to monitor the accuracy and reproducibility of the easureets. First stadard deiatio is ±. ‰ or etter. The aro isotope data are gie i per ill ‰ relatie to the V-PDB (Vienna Pee Dee Belemnite) standard. The bulk rock carbonate carbon

13 isotope reord δ Ccarb) of DSDP core 534A was adopted from Bornemann and Mutterlose (2008).

3.4. Results 3.4.1. Nannofossil biostratigraphy Calcareous nannofossil biostratigraphy provides an early Valanginian to early Hauterivian age for the Scharrel 10 core (Fig 3.2). Five nannofossil events were identified: the first occurrence (FO) of Micrantholithus speetonensis (193.55 m), the FO of Eiffelithus windii (169.4 m), the last occurrence (LO) of M. speetonensis (147,98 m), the FO of Conusphaera rothii (91.14 m), and the FO of Eprolithus antiquus (44.2 m). These events assign the core to the Boreal nannofossil zones BC4 - BC7 with the following modification. The lower/ upper Valanginian boundary does not equate the top of BC4, but is located in BC4; BC4 thus extends into the upper Valanginian (Möller et al., 2015).

3.4.2. Nannofossil abundances and preservation The upper lower Valanginian of the Scharrel 10 and the Wiedensahl 2 cores contains an interval in which calcareous nannofossils are very rare or completely missing (Scharrel 10 180-163 m; Wiedensahl 2 below 175 m). Excluding this interval, nannofossil preservation was found to meet the requirements for biometric analysis. A total of 91 species was identified. Average species richness above the barren interval is 36.9 in Scharrel 10, and 39.9 in Wiedensahl 2. Average values of the heterogeneity Hs are 2.64 (Scharrel 10, Fig.

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3.2) and 2.7 (Wiedensahl 2). Absolute abundances of calcareous nannofossils in Scharrel 10 vary from 92.5 to 1433.4*106 specimen/ g sediment, the mean absolute abundance above the barren interval is 566.7 *106 specimen/ g sediment (Fig. 3.2). In the counted samples of Wiedensahl 2 absolute abundances range from 113.6 to 728.1 *106 specimen/ g sediment with an average of 384.9 *106 specimen/ g sediment.

3.4.3. Absolute and relative abundances of Nannoconus spp. The abundances of Nannoconus spp. are highly variable throughout the Scharrel 10 core (Fig. 3.2). In the lower part (197.4 – 160.5 m) nannoconids are absent. The overlying interval (160.5 – 147.2 m) contains the highest abundances of nannoconids within the section with an average of 3.4 % and a maximum of 17.18 % at 150.3 m. The maximum absolute abundance (81.0 *106 specimen/ g) was observed at 149.8 m. From 147.2 – 135.4 m nannoconids are absent, they reappear in low abundances (average 0.7 %) at 133.4 m. In the upper part of the core (above 113 m) nannoconids are very rare or absent.

The average abundance of Nannoconus spp. in the Wiedensahl 2 core is 2 % (Fig. 3.2). The dataset shows two distinct abundance maxima with 5.4 % (168.4 m) and 7.6 % (163.0 m). Only one third of all specimens of Nannoconus found have been identified to the species level. The other speciemens could not be identified due to their orientation on the microscope slide or because they were fragmented. Seven species of Nannoconus were identified: N. steinmannii, N. kamptneri, N. bucheri, N. globulus, N. cornuta, N. oviformis, and N. minutus.

3.4.4. Biometry Biscutum constans

The mean sizes of B. constans are 3.56 µm length and 2.73 µm width (Scharrel 10, Fig. 3.2), 3.6 µm length and 2.78 µm width (Wiedensahl 2, Fig. 3.2), and 3.82 µm length and 2.99 µm width (DSDP Hole 534A, Fig. 3.3). Mean ellipticity is 1.33, 1.31, and 1.29, respectively. With mean standard deviations of 0.66 µm (Scharrel 10), 0.59 µm (Wiedensahl 2) and 0.60 µm (DSDP Hole 534A) of the measured lengths, the overall scatter of the data is large in all three cores.

Three samples from the lowermost 7 m of the Scharrel 10 core (194 – 181 m) document an average length increase from about 3.5 µm to 3.95 µm. The overlying 20 m (181 – 160 m) are nearly barren of calcareous nannofossils. The average lengths in the middle part of the core (160 - 67 m) is 3.49 µm, and 3.88 µm in the upper part (67 – 7 m). None of these data show a normal distribution. The means of the 160 – 67 m

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and the 67 – 7 m intervals differ significantly (Kruskal-Wallis test: p=8.963E-14, Mann-Whitney test: p=8.969E-14). In the interval 155.65 – 152.3 m, most Biscutum coccoliths (> 50%) are between 2 - 3 µm in lengths, the maximum is 4.6 µm. The smallest mean of 2.6 µm (152.3 m) also falls in this interval. In the samples above and below 155.65 – 152.3 m, the majority of specimens are in the size fraction between 3 - 4 µm length, and the largest coccolith has a length of 6.15 µm (Fig. 3.4).

Extremely small sized specimens of B. constans were also observed in the Wiedensahl 2 core, where the mean lengths decrease to an average of 2.98 µm in the interval 169.4 – 165.9 m. The averages for the underlying and overlying units are 3.84 µm and 3.91 µm, respectively. In both cores the mean lengths show a short timed decrease by about 1 µm, which represents a reduction of the average size by 25%.

In DSDP Hole 534A (Fig. 3.3) the average mean lengths of B. constans decrease from 4.01 µm (1260.97 – 1198.32 m) to 3.65 µm for the interval 1194.77 – 1146.29 m. They recover to 4.05 µm in the overlying sequence (1142.29 – 1116.79 m). The mean length data show three minima, 3.55 µm (1192.26 m), 3.46 µm (1166.37 m) and 3.5 µm (1150.04 µm; Fig. 3.4 and 3.5). The average size decrease in the interval 1194.77 – 1146.29 m is approximately 0.5 µm. Lengths data of B. constans are normally distributed. With a p(equal) of 8.761E- the ANOVA Tuke’s pairise post-hoc test indicates difference of means for the lengths data from 1194.77 – 1146.29 m compared to all samples below and above this interval.

Watznaueria

The mean length of all measured Watznaueria coccoliths from Scharrel 10 is 6.06 µm, mean width is 5.31 µm. The total mean of the samples from Wiedensahl 2 is 6.86 µm (length) and 5.97 µm (width). In both sections the sample with maximum mean length of Watznaueria coincides with the size decrease of B. constans. Maximum mean lengths values are 6.64 µm (Scharrel 10, 154.2 m) and 7.32 µm (Wiedensahl 2, 166.7 m). The total mean of length and width of Watznaueria in the samples from DSDP Core 534A is 4.92 µm, and 2.46 µm, respectively. The samples with maximum mean size (5.59 µm) are positioned at 1173.51 m, 1184.32 m and 1185.76 m; all lie within the B. constans size decrease interval.

Zeugrhabdotus erectus

Specimens of Z. erectus were measured only in samples from Scharrel 10. Average of all measured lengths is 3.20 µm, mean width is 2.18 µm. Maximum mean length is 3.34 µm (140.78 m), minimum is 3.05 µm (156.62 m). The average size of Z. erectus does not vary significantly throughout the section. With standard deviations between 0.26 – 0.43 the scatter of the length data of Z. erectus is relatively small.

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Figure 3.4 Size histogram showing the length distribution of B. constans in the studied samples from Scharrel 10. The black lines indicate the mean lengths of each sample, the blue line shows the total average lengths of all samples.

13 3.4.5. Organic carbon isotopes (δ Corg)

Stable carbon isotope data are presented in Fig. 3.2. The stable carbon isotope (Corg) values of the Wiedensahl 2 core range from -. ‰ iiu, to -. ‰ aiu, .5 m). In the lower

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Size changes of calcareous nannofossils and the nature of the Weissert Event

Figure 3.5 Size histogram showing the length distribution of B. constans in the studied samples from DSDP 534A. The black lines indicate the mean lengths of each sample, the blue line shows the total average lengths of all samples.

13 part of the setio the aerage δ Corg is -. ‰. Betee . ad . alues irease rapidl to -. ‰ o aerage. Aoe alues derease agai to a aerage of -. ‰.

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3.5. Discussion 3.5.1. Preservation Coccoliths are small delicate calcite structures and thus prone to dissolution. To obtain meaningful data, the preservation of the studied material used for morphometric analyzes has to be checked carefully. In our case coccolith preservation appears to be generally good with only minor dissolution or overgrowth according to the visual criteria of Roth (1983) and Roth and Thierstein (1972).

If the observed size decrease of B. constans was the result of dissolution, all smaller, more fragile nannofossil species (e.g. Stradnerlithus geometricus, Calciosolenia fossilis, Calculites sp., Discorhabdus ignotus) could be expected to show signs of dissolution, or even be partly fragmented. Consequently, small-sized B. constans should go along with lowered diversities of calcareous nannofossils. None of the studied sections shows a reduced diversity paralleling the size decrease, nor significantly reduced abundances of delicate nannofossil taxa (Fig. 3.2). Further evidence for a largely unbiased signal is provided by the fact that the small delicate coccoliths of Z. erectus do not decrease in size parallel to B. constans (Fig. 3.2, Scharrel 10). Watznaueria even shows maximum sizes coinciding with the smallest average lengths of B. constans (Figs. 3.2, 3.3).

3.5.2. Ocean acidification and toxic trace metals A darfig of B. constans has been described for the Aptian (Erba et al., 2010; Lübke and Mutterlose, 2016) and the Cenomanian/ Turonian (Linnert and Mutterlose, 2013; Faucher et al, 2017). In the Aptian nannoconid abundance declines simultaneously (Erba et al., 2010). These phenomena are related to the OAE1a and OAE2, which are marked by carbon isotope excursions and the deposition of black shales. Both OAEs can be linked to phases of high volcanic activity during the emplacement of the Ontong Java and Caribbean Plateaus. The environmental consequences of the substantial volcanic outgassing – high atmospheric pCO2, a change in the calcite saturation state and shallowing of the CCD – probably affected the biomineralization of marine calcifiers (e.g., Ridgwell and Schmidt, 2010; Bauer et al., 2017).

The Paraná-Etendeka Large Igneous Province (LIP) had a comparatively low output of CO2 gases over a

10 long time period (CO2 flux of 2.44 × 10 kg/y). The Ontong–Java LIP for comparison, associated with OAE-

2 11 1a, released a CO flux of 8.8 × 10 kg/y. The CO2 release of the Madagascar/ Caribbean LIPs (OAE2) is assessed to 4.5 to 17 x 1012 kg/y (Kuroda et al., 2007; Martinez et al., 2015). Studies modeling the response of surface ocean pH and carbonate saturation to atmospheric CO2 suggest that only the output of large

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amounts of CO2 over a short time period (< 10,000 years) would cause ocean acidification (Ridgwell and Schmidt, 2010). On time scales longer than 10,000 years, ocean carbonate saturation will be buffered due to balancing of weathering and carbonate burial (Kump et al., 2009; Ridgwell and Schmidt, 2010; Zeebe, 2011). It is therefore unlikely that ocean acidification affected calcifying phytoplankton during the

Weissert Event, as this was characterized by a relatively low CO2 output over a long period of time (Dodd et al., 2015; Martinez et al., 2015). Toxic trace metals can limit phytoplankton reproduction by competitively inhibiting the uptake and metabolism of trace nutrients (Brand et al., 1986; Sunda 1989). It has been argued that reduced coccolith calcification during OAE2 resulted from excess toxic metals introduced to the oceans by submarine volcanism (of hydrothermal origin) that affected the functioning of coccolithophores (Erba, 2004; Faucher et al., 2017). At the moment there is no indication of substantial submarine volcanism during the late Valanginian.

3.5.3. Temperature – the climate of the late Valanginian A irease i δ18O of bulk rock and belemnite calcite in the upper Valanginian has been interpreted as a cooling episode by several authors (e.g. Podlaha et al., 1998; Price and Mutterlose, 2004; Weissert and Erba, 2004; McArthur et al., 2007; Meissner et al., 2015). In the Arctic Boreal, a shift of δ18O measured from belemnite calcite from an average - . ‰ i the loer Valagiia to . ‰ i the upperost Valanginian implies a slight cooling (Price and Mutterlose, 2004). Tillites and glacial dropstones of late Valanginian age from paleolatitudes of 65 – 80° N/S (Sverdrup Channel, arctic Svalbard, Siberia, Alaska, Australia) give evidence for subfreezing temperatures at high latitudes (Kemper and Schmitz, 1975; Frakes and Francis, 1988). Further evidence for the accumulation of ice caps is provided by a reconstructed positie tred i δ18O of seawater in the late Valanginian (McArthur et al., 2007). A pause of the rising trend of the marine Sr isotope ratio in the late Valanginian is interpreted as reflecting lowered weathering rates (Bodin et al., . The rather isigifiat . ‰ positie shift i the loerost upper Valagiia (lower S. verrucosum zone) shown in the oposite Tetha δ18O record published by Meissner et al.

(2015) does not provide strong evidence for a cooling in the lower latitudes, though. TEX86 data from the proto North Atlantic do not indicate any significant temperature variation in the Valanginian either (Littler et al., 2011; Fig. 3.3).

Clay mineral data, palynology, and phosphorous accumulation rates (Fig. 3.6) point towards a humid, warm climate and enhanced weathering in the late early – late Valanginian of the northern Tethys (Van

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de Schootbrugge et al., 2003; Duchamp-Alphonse et al., 2011; Kujau et al., 2013; Westermann et al., 2015).

The warm conditions are attributed to increased atmospheric pCO2 due to volcanogenic outgassing of the Paraná-Etendeka LIP (Weissert et al., 1998; Martinez et al., 2015). Increased phosphorous burial and platform demise give evidence for enhanced continental weathering rates throughout the Weissert Event CIE (Föllmi, 1995; Föllmi et al., 2006; Westermann et al., 2010; Fig. 3.6). Carbonate platform drowning and the replacement of oligotrophic benthic communities by mesotrophic ones document a Valanginian eutrophication along river-influenced coasts and shelves in the Tethys (Föllmi et al., 1994; Weissert et al., . Likig the positie tred i δ18O to humidity rather than temperature, Föllmi (2012) interprets the late early and early late Valanginian (Busnardoites campylotoxus and Saynoceras verrucosum ammonite zones) as a time of generally warm and humid climate. Combining all evidence, it can be conjectured that if cooling occurred during the late Valanginian, it was probably restricted to higher latitudes (Price and Passey, 2013).

The size reduction of B. constans during the (early phase of the) Aptian OAE1a, probably coincided with a time of global warming most pronounced during the onset of the event (Erba et al., 2015; Lübke and Mutterlose, 2016; Ando et al., 2008; Mutterlose et al., 2010; Keller et al., 2011). Paleotemperature estimates for the Late Cenomanian-Early Turonian indicate, that OAE2 coincided with the warmest climate of the Late Cretaceous (e.g., Jenkyns et al., 2004; Forster et al., 2007; Friedrich et al., 2012). This adds to the conclusion that B. constans did not reduce the size of its coccoliths as a response to cool surface water temperatures. Similar to the late Valanginian, the early phase of the OAE1a is thought to be characterized by increased rates of weathering, evidenced by an increase in radiogenic osmium derived from continental run-off and a negative shift in the Lithium isotope ratio (Bottini et al., 2012; Lechler et al., 2015). The siliciclastic input into marginal marine seas like the LSB and the Proto-North Sea was high as well (Mutterlose and Bottini, 2013; Lübke and Mutterlose, 2016). Increased humidity and hydrolytic weathering during OAE2 is supported by Li- and Ca-isotope shifts (Blättler et al., 2011; Pogge von Strandmann et al., 2013). While temperature trends seem to be disparate, an increase in weathering and continental run-off is a common feature of the Valanginian, the Aptian and the latest Cenomanian phases of B. constans size decrease.

3.5.4. Loss of ecological niches In their study on biometry of B. constans, Lübke et al. (2015) found a large range of sizes and larger mean sizes in low latitudinal open ocean settings (Tethys, Mid-Pacific). In the samples from smaller, more

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Size changes of calcareous nannofossils and the nature of the Weissert Event confined ocean basins of the southern Boreal Realm (North Sea, LSB) sizes were on average smaller and the large sizes (>5 µm, > 4.5 µm respectively) absent. Based on this size distribution, Lübke et al. (2015) proposed that varieties of B. constans producing smaller coccoliths were adapted to lower light availability and/or elevated nutrient levels in marine settings dominated by continent derived detritus. They designed a model, stating that in open ocean settings where conditions were advantageous for morphospecies with larger coccoliths, the smaller varieties were confined to deeper parts of the photic zone. Alternatively, the observations may be explained by the production of smaller coccoliths in response to the environmental stress of light attenuation for photoautotrophic organisms.

The observations of Lübke et al. (2015) can be interpreted to the effect, that any environmental changes that bring about light attenuation in the photic zone may be reflected in the size spectrum of B. constans. A short, pronounced phase of high humidity in the early late Valanginian has been inferred based on spore and pollen data from the Vocontian Basin (southeast France) and the Mid Polish Trough (Poland) (Kujau et al., 2013; Fig. 3.6). Clay mineral data from southeast France support this view, indicating intense hydrolytic weathering and increased terrigenous input to the Vocontian Basin (Duchamp-Alphonse et al., 2011; Westermann et al., 2015). Correlation with eccentricity cycle reconstructions based on cyclostratigraphy of rhythmic marl/limestone alternations of the Italian Maiolica Formation suggest that the humid climate phase occurred during an eccentricity maximum (Sprovieri et al., 2006; Kujau et al., 2013). Eccentricity modulates precessional cycles which are responsible for variations in summer insolation (Short et al., 1991; Zachos et al., 2001). It is well established that glacial maxima are associated with eccentricity minima (Hays et al., 1976; Zachos et al., 2001). Likewise, being affected by the intensity of summer insolation and the degree of seasonal temperature changes, monsoonal precipitation is influenced by orbital forcing (e.g. Fleitmann et al., 2003; Kutzbach et al., 2008).

The humid phase corresponds stratigraphically to the middle part of the Tethyan Saynoceras verrucosum ammonite zone and coincides with the initial phase of the Weissert Event CIE (Kujau et al., 2013; Duchamp- Alphonse et al., 2011). The Tethyan S. verrucosum zone is correlated to the upper part of the Prodichotomites hollwedensis ammonite zone of northern Germany (Mutterlose et al., 2014) and to the upper part of the Boreal nannofossil zone BC4 (Möller et al., 2015). The onset and peak of the Weissert Event CIE in the LSB corresponds to nannofossil zone BC4 (boreal Dichotomites ammonite zones). Morphometric data from both LSB cores show a size minimum for B. constans in the upper BC4 nannofossil zone, with the average coccolith size reduced by about 25 % of the original mean (Fig. 3.2). Biostratigraphy suggests that the B. constans size minimum phase of high humidity occurred synchronously.

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A humid climate with intense weathering would have had a strong effect on the small, almost completely landlocked epicontinental LSB. Large amounts of detrital material transported to the basin would have increased the turbidity of the water as well as nutrient concentrations. According to Lübke et al. (2015), this scenario is disadvantageous for the large cryptic species of B. constans which are adapted to clear waters and high light availability. The smaller, deeper dwelling forms were adapted to reduced light availability. They compensated for the higher turbidity by shifting their habitat to shallower depths.

A minimum in the average size of B. constans during the initial phase of the Weissert Event, though of lower magnitude, can be observed in the dataset from the western Atlantic Ocean as well (Fig. 3.3). With mean sizes reduced by 0.48 µm (12 %) compared to the averages before and after the event, this size minimum is not as pronounced as in the LSB. In this open ocean setting, far from direct river influx, the humid phase did not increase turbidity and nutrient levels in the photic zone that severely. This is reflected by the size composition of the B. constans species group. Compared to the narrow size range (2 – 3.5 µm, Fig 3.4) of the B. constans size minimum in the LSB, the size data from the Atlantic Ocean remain more evenly distributed (Fig. 3.5). This suggests an ecological advantage for the smaller cryptic species of B. constans, but not the coplete loss of the larger ariet’s ihe.

Apart from the distinctive size minimum in the initial phase of the Weissert Event, our data document that B. constans coccoliths are on average smaller during the entire Weissert Event, compared to the under- and overlying intervals. Both in the Scharrel 10 core and in DSDP Hole 534A this reduction of mean size by . µ ad . µ, respetiel, preails util the δ13C curve approaches pre-event values in the lower Hauterivian (Fig. 3.2, Fig. 3.3). This may be explained by the accelerated continental weathering and runoff, and the late Valanginian marine eutrophication (discussed in 3.5.3), which caused increased nutrient concentrations also in pelagic settings (Fig. 3.6). In DSDP Hole 534A, fertility indicating taxa constitute around 40 % of the nannofossil assemblage in the CIE interval (Bornemann and Mutterlose, 2008). Higher productivity and large amounts of organic matter in the photic zone may have caused increased water turbidity and competition of phytoplankton, advantageous for the smaller varieties of B. constans. The long-term 0.4 µm B. constans size decrease observed in two different localities is the expression of a relatively long phase of increased humidity and weathering, impacting marine ecology.

Chages of the paraeters otrollig the Earth’s liate sste, like a irease i atospheri CO2, can ifluee the sste’s sesitiit to orital forig Zachos et al., 2001). During the initial phase of the Weissert Event the combined impact of maximum eccentricity and the Paraná-Etendeka volcanism produced a short phase of extremely humid climate with intense hydrolytic weathering (Duchamp-

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Size changes of calcareous nannofossils and the nature of the Weissert Event

Alphonse et al., 2011; Kujau et al., 2013). The next eccentricity maximum at the Valanginian - Hauterivian boundary is not accompanied by a humid phase as intense as that of the early late Valanginian (Sprovieri et al., 2006; Duchamp-Alphonse et al., 2011; Kujau et al., 2013; Fig. 3.6). Consequently, no B. constans size minimum has been observed in the latest Valanginian of the LSB (Fig. 3.2). Alternatively, leaving orbital forcing effects aside, the size minimum may imply a high initial rate of volcanic outgassing at the Paraná- Etendeka LIP, which was not maintained throughout.

3.5.5. The Valanginian nannoconid decline The observation that nannoconid abundances are low in clay-rich sediments, and high in pelagic carbonates has led to the conclusion that clay and nutrient input is one of the factors controlling nannoconid distribution (e.g. Busson and Noël, 1991; Bersezio et al., 2002; Barbarin et al., 2012; Mutterlose and Bottini, 2013). The large, heavily calcified nannoconids have been interpreted as deep- dwellers analogous to the modern Florisphaera profunda (Erba, 1994; Herrle, 2002). F. profunda occupies depths between 100 and 200 m at temperatures above 10°C and its abundance depends on the depth of the nutricline (Okada and Honjo, 1973; Molfino and McIntyre, 1990; Haidar and Thierstein, 2001). High abundances of F. profunda are associated with a deep nutricline, low abundances with a shallow nutricline (Molfino and McIntyre, 1990). If the analogy is valid, high turbidity during phases of increased terrigenous input, possibly combined with a collapse of water stratification and a shift of the nutricline, may have disturbed the niche occupied by Nannoconus spp., causing a decline.

The distribution of nannoconids in the Lower Cretaceous supports this view. They are most abundant in Lower Cretaceous sediments from low to mid latitudinal tropical shelf seas with low sedimentation rates (Wyton et al., 2007). In Valanginian limestones and marls from Romania, Nannoconus spp. constitutes 20 – 40 % of the nannofossil assemblage (Melinte and Mutterlose, 2001), in Italian pelagic limestones even 25 - 50 % (Erba and Tremolada, 2004). In the epicontinental Vocontian Basin at the northwestern margin of the Tethys, nannoconids make up only 2 -11 % of the nannofossil assemblage (Duchamp-Alphonse et al., 2007). In the Boreal Valanginian, nannoconids seem to be generally rare, the nannofossil assemblage of the Wollaston Forland (North-East Greenland) contains 0.3 – 4 % Nannoconus spp. (Pauly et al., 2012), in the LSB the average abundance is 3.4 % (this study). The thickness of the Lower Cretaceous in the LSB reflects excessive siliciclastic input and high sedimentation rates. The muddy, nutrient rich waters of the LSB were unfavorable for nannoconids, documented by their low abundance.

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In the lower upper Valanginian of Romania (S. verrucosum zone) the abundance of nannoconids decreases to < 10%. At the same time the shallower epicontinental sedimentation changes from limestones to claystones (Melinte and Mutterlose, 2001). In the pelagic sections of the Tethys, chert layers occur in this interval (radiolarian-rich layers, chert nodules, lenses and beds; Erba and Tremolada, 2004), coinciding with the nannoconid decline and the Weissert CIE (Melinte and Mutterlose, 2001; Erba and Tremolada, 2004). Platform drowning observed worldwide in the Valanginian and the change from oligotrophic to mesotrophic platform communities document the change in ecologic conditions of the marine realm, which have been linked to riverine nutrient input (Föllmi et al., 1994; Weissert et al., 1998; Wortmann and Weissert, 2000). In the Vocontian Basin lithology changes from marl-limestone alternations of the lower Valanginian to marl dominated succession with fewer limestone beds in the upper Valanginian (Bulot and Thieuloy, 1995). These marl dominated sediments record the positive CIE, during which nannoconid abundances decrease to 2 – 6 % (Duchamp-Alphonse et al., 2007).

In the LSB a nannoconid decline to < 1% coincides with the B. constans size minimum in the initial phase of the Weissert Eet, siultaeous ith peak δ13C values. Subsequently, nannoconid abundance briefly rises to abundances as high as 17.18, but in the rest of the section Scharrel 10, except for a few samples, abundances remain < 1% (Fig. 3.2). The abundance pattern of Nannoconus spp. in the western Atlantic Ocean bears some striking similarities. In the initial phase of the Weissert CIE, abundances rise above 10%, decrease and come back briefly, to remain < 4% during the rest of the Weissert Event. Contrary to the LSB, in the western Atlantic nannoconid abundances increase again after the event in the lower Hauterivian.

Overall, there is a considerable amount of evidence supporting a link between nannoconid abundance and turbidity/ nutrient content. There are clear parallels of the abundance pattern of Nannoconus spp. and the size trends of B. constans, supporting our interpretation of a phase of high humidity and intense weathering.

3.5.6. Implications for the interpretation of the Weissert Event The nature of the Weissert Event is still a subject of debate. During the Mesozoic events of global significance - the Toarcian T-OAE, the early Aptian OAE1a and the Cenomanian-Turonian OAE2 - volcanogenic outgassing of CO2 is believed to have created the preconditions for the OAEs (Jenkyns, 2010). These include global warming and accelerated continental weathering, which in turn led to an increased productivity in the oceans (Jones and Jenkyns, 2001; Jenkyns, 2010). The positive shifts in the carbon isotope records are generally attributed to the increased burial of organic matter, which preferentially

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Size changes of calcareous nannofossils and the nature of the Weissert Event

Figure 3.6 Synthesis of proxy data relevant for paleoclimate and –oceanography of the Valanginian – lower 13 Hauterivian, including carbon isotope records from northern Germany (δ Corg; this study) and from the Western 13 Atlantic Ocean (δ Ccarb; Bornemann and Mutterlose, 2008), onset (black) and duration (red) of volcanic activity of the Paraná-Etendeka large igneous province (Martinez et al., 2015), weathering index based on clay mineral data (Duchamp-Alphonse et al., 2011), palynofacies data (Kujau et al., 2013), relative abundance of high productivity indicating calcareous nannofossil taxa (B. constans, D. ignotus, Z.erectus) and other main constituents of the nannofossil assemblage of DSDP 534A, Western Atlantic (Bornemann and Mutterlose, 2008), northern Tethyan carbonate platform evolution (Föllmi et al., 2006), and evolution of average size of B. constans coccoliths. consists of isotopically light carbon, thus, relatively enriching the ocean in the heavy carbon isotope (Scholle and Arthur, 1980; Jones and Jenkyns, 2001).

Although a distitie positie aro isotope eursio of . ‰ has ee osered orldide, ol fe occurrences of organic-rich sediments associated with the Weissert Event are known. In the Valanginian of DSDP Holes 534A and 603B, organic carbon-rich layers have been discovered (Bornemann and Mutterlose, Littler et al., 2014). These have probably been displaced from near shore-settings affected by an extended oxygen minimum zone (Applegate et al., 1989; Bornemann and Mutterlose, 2008). If these TOC-rich sediments have been deposited all along the shelf areas of the western North Atlantic, they would account for a considerable amount of organic carbon burial. The origin of the organic matter content is at least partly terrestrial (Littler et al., 2014). Examples for rare Valanginian TOC-rich units, where the accumulated organic matter clearly derives from marine productivity are the Barrande layers in the

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Vocontian Basin (Reboulet et al., 2003), which predate the onset of the CIE, and organic matter rich sediments in the Pacific recovered during ODP Leg 198 on Shatsky Rise (Gröcke et al., 2005; Brassell, 2009). In most cases the provenience of the organic matter in TOC-rich Valanginian sediments does not suggest extremely high marine primary productivity, nor is there evidence for widespread dysaerobic/anaerobic conditions in the oceans (Claypool and Baysinger, 1980; Gröcke et al., 2005; Westermann et al., 2010; Kujau et al., 2012).

High rates of marine carbon burial therefore do not seem to be the main cause for the pronounced orldide δ13C excursion in the Valanginian. Possible causes for the perturbation during the Weissert Event are the observed decrease in shallow marine carbonate production, and the burial of large amounts of organic matter in continental deposits (Weissert et al., 1998; Wortmann and Weissert, 2000; Westermann et al., 2010). Of these, only the latter seems to be a reasonable explanation. The drowning of carbonate platforms in the late Valanginian is mainly a Tethyan event. Furthermore, carbon isotope fractionation during biogenic formation of carbonate is minor compared to the fractionation during organic carbon fixation (Bickert, 2006). The fractionation effects can both act to increase and to decrease δ13C of biogenic carbonates. Photosynthesis effects cause enrichment in 13C in biogenic carbonates, while kinetic discrimination against 13C results in depletion in the heavy carbon isotope (McConnaughey et al., 1997). A potential storage of large amounts of organic matter on the continents during the Valanginian on the other hand remains to be proven. In general, the Early Cretaceous is one of the major periods of coal deposition (Budyko et al., 1987; Westermann et al., 2010). With a high humidity, boosting vegetation, and a cool climate in the higher latitudes facilitating low decay rates of organic material, the late Valanginian may well have been a particularly favorable time for coal formation (McCabe and Totmann Parrish, 1992).

Considering that there is no evidence for widespread anoxic conditions in the oceans, the Weissert Event cannot be called an anoxic event. Föllmi (2012) proposed a more differentiated view, defining the Weissert Event as one of the Cretaceous episodes of environmental change of which OAEs are one specific case among others. In the nannofossil record, however, the Weissert Event bears a substantial similarity to OAEa ad OAE. The size derease osered here reseles the darfig of B. constans during the Aptian OAE1a and the Cenomanian/ Turonian OAE2. The same applies for the decline in nannoconid abundance during OAE1a. For all three intervals, the mid Valanginian, the OAE1a and the OAE 2, there is evidence for increased humidity and chemical weathering (Blättler et al., 2011; Bottini et al., 2012; Mutterlose and Bottini, 2013; Pogge von Strandmann et al., 2013; Lechler et al., 2015; Lübke and

Mutterlose, 2016). In all three cases the weathering regime is linked to high atmospheric CO2

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CO2 flux to the atmosphere has been estimated to be one to two orders of magnitude lower than the respective volcanic emissions during OAE1a and OAE2 (Martinez et al., 2015). The nevertheless existing commonalities between the events are in favor of the approach of Föllmi (2012), suggesting a broader view of the events of environmental perturbation that punctuate the Mesozoic.

3.6. Conclusions Biometric analyzes reveal an average size reduction of the calcareous nannofossil taxon Biscutum constans by 0.4 µm (10 %) throughout the late Valanginian. This phase of size reduction coincides with a positive δ13C excursion, the Weissert Event. During a short B. constans size minimum in the initial phase of the Weissert Event, coccolith lengths are reduced by 1 µm on average (25 % size reduction) at a mid-latitude site (Lower Saxony Basin, northern Germany). In the Western Atlantic this size minimum is less pronounced albeit a general smaller size of B. constans has been observed throughout δ13C excursion interval.

A phase of humid climate in the late Valanginian, probably linked to CO2 outgassing of the Paraná-Etendeka volcanism, caused increased weathering. This in turn transported large amounts of detrital material into the ocean basins. Siliciclastic input and eutrophication increased the ocean water turbidity and caused light attenuation in the surface waters. In the resulting competition of phytoplankton, the smaller varieties of B. constans, adapted to lower light availability, had an advantage over the larger forms, thriving in the clear waters of open ocean settings. Intense humidity prevailing during the initial phase of the event, coinciding with the B. constans size minimum, may result either from the combined impact of maximum eccentricity and volcanic activity of the Paraná-Etendeka Large Igneous Province, or signify a high initial rate of volcanic outgassing, which was not maintained throughout.

The size redutio durig the Valagiia Weissert Eet is siilar to the darfig of Biscutum constans during the Aptian OAE1a and the Cenomanian/Turonian OAE2. All three events seem to have been accompanied by humid climate and intense weathering.

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3.7. Acknowledgements The authors would like to thank Prof. E. Erba for discussions and support during a two-months research stay of C. Möller at the Università degli Studi di Milano. The financial support for this stay by the Research School Plus program of the Ruhr-Universität Bochum is gratefully acknowledged. Dr. C. Bottini, Dr. C. Casellato, and Dr. G. Faucher are thanked for discussions and general support, both regarding microscope work and getting along in Milan. We further thank Dr. C. Linnert and K. Stevens for discussions and helpful suggestions. We are grateful to the staff of the labs of the Ruhr-Universität Bochum and the Friedrich- Alexander Universität Erlangen Nürnberg/GeoZentrum Nordbayern for processing the samples and measurements of carbon isotopy. The Wilhelm and Günter Esser-Stiftung is thanked for financial support during the completion of this project. Permission to use the paleogeographic map of northern Germany was kindly given by Schweizerbart Science Publishers (www.schweizerbart.de/journals/zdgg). Finally, we thank the Bundesanstalt für Geowissenschaften & Rohstoffe and Niedersächsische Landesamt für Bergbau, Energie und Geologie for granting access to the Scharrel 10 and Wiedensahl 2 drill cores. The biometric data used in this study are available from the authors upon request ([email protected]).

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Meissner, P., J. Mutterlose, and S. Bodin (2015), Latitudinal temperature trends in the northern hemisphere during the Early Cretaceous (Valanginian–Hauterivian), Palaeogeography, Palaeoclimatology, Palaeoecology, 424, 17–39, doi:10.1016/j.palaeo.2015.02.003. Melite, M., ad J. Mutterlose , A Valagiia Earl Cretaeousoreal aoplakto eursioi setios fro Roaia, Marine Micropaleontology, 43(1), 1–25. Molfino, B., and A. McIntyre (1990), Precessional forcing of nutricline dynamics in the Equatorial Atlantic., Science(Washington), 249(4970), 766–769. Möller, C., and J. Mutterlose (2014), Middle Hauterivian biostratigraphy and palaeoceanography of the Lower Saxony Basin (Northwest Germany), Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, doi:10.1127/1860-1804/2014/0084. Möller, C., J. Mutterlose, and P. Alsen (2015), Integrated stratigraphy of Lower Cretaceous sediments (Ryazanian–Hauterivian) from North-East Greenland, Palaeogeography, Palaeoclimatology, Palaeoecology, 437, 85–97, doi:10.1016/j.palaeo.2015.07.014. Monteiro, F. M. et al. (2016), Why marine phytoplankton calcify, Science Advances, 2(7), e1501822– e1501822, doi:10.1126/sciadv.1501822. Mutterlose, J., and C. Bottini (2013), Early Cretaceous chalks from the North Sea giving evidence for global change, Nature Communications, 4, 1686, doi:10.1038/ncomms2698. Mutterlose, J., M. Malkoc, S. Schouten, J. S. Sinninghe Damsté, and A. Forster (2010), TEX86 and stable δO paleotheroetr of earl Cretaeous sediets: Ipliatios for eleite eolog ad paleotemperature proxy application, Earth and Planetary Science Letters, 298(3–4), 286–298, doi:10.1016/j.epsl.2010.07.043. Mutterlose, J., S. Bodin, and L. Fähnrich (2014), Strontium-isotope stratigraphy of the Early Cretaceous (Valanginian–Barremian): Implications for Boreal–Tethys correlation and paleoclimate, Cretaceous Research, 50, 252–263, doi:10.1016/j.cretres.2014.03.027. Niedzolka, K. (1988), Die Mikrofauna im Valangin-Hauterive-Grenzbereich des zentralen Niedersächsischen Beckens (Pollhagen, Wiedensahl 2), in Die Valangin-Hauterive-Grenze im zentralen Niedersächsischen Becken, edited by Helmut Keupp and Dorothea Janofske, vol. 94, pp. 89– 173. Nunn, E. V., G. D. Price, D. R. Gröcke, E. Y. Baraboshkin, M. J. Leng, and M. B. Hart (2010), The Valanginian positive carbon isotope event in Arctic Russia: Evidence from terrestrial and marine isotope records and implications for global carbon cycling, Cretaceous Research, 31(6), 577–592, doi:10.1016/j.cretres.2010.07.007. Okada, H., and S. Honjo (1973), The distribution of oceanic coccolithophorids in the Pacific, Deep-Sea Research, 20, 355–374. Pauly, S., J. Mutterlose, and P. Alsen (2012), Early Cretaceous palaeoceanography of the Greenland– Norwegian Seaway evidenced by calcareous nannofossils, Marine Micropaleontology, 90–91, 72–85, doi:10.1016/j.marmicro.2012.04.004.

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Price, G. D., and J. Mutterlose (2004), Isotopic signals from late Jurassic–early Cretaceous (Volgian– Valanginian) sub-Arctic belemnites, Yatria River, Western Siberia, Journal of the Geological Society, 161(6), 959–968. Reboulet, S., E. Mattioli, B. Pittet, F. Baudin, D. Olivero, and O. Proux (2003), Ammonoid and nannoplankton abundance in Valanginian (early Cretaceous) limestone–marl successions from the southeast France Basin: carbonate dilution or productivity?, Palaeogeography, Palaeoclimatology, Palaeoecology, 201(1–2), 113–139, doi:10.1016/S0031-0182(03)00541-8. Ridgwell, A., and D. N. Schmidt (2010), Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release, Nature Geoscience, 3(3), 196–200, doi:10.1038/ngeo755. Roth, P. H. (1983), Jurassic and Lower Cretaceous calacareous nannofossils in the Western North Atlantic (Site 534): Biostratigraphy, preservation, and some observations on biogeography and paleoceanography, Initial Reports of the Deep Sea Drilling Project, (76), 517–546. Roth, P. H., and H. R. Thierstein (1972), Calcareous Nannoplankton: Leg 14 of the Deep Sea Drilling Project, Initial Reports of the Deep Sea Drilling Project, 14, 421–485. Schindelin, J. et al. (2012), Fiji: an open-source platform for biological-image analysis, Nature Methods, 9(7), 676–682, doi:10.1038/nmeth.2019. Scholle, P. A., and M. Arthur (1980), Carbon isotope fluctuations in Cretaceous pelagic limestones: potential stratigraphic and petroleum exploration tool, The American Association of Petroleum Geology Bulletin, 1(64), 67–87. van de Schootbrugge, B., O. Kuhn, T. Adatte, P. Steinmann, and K. Föllmi (2003), Decoupling of P- and Corg- burial following Early Cretaceous (Valanginian–Hauterivian) platform drowning along the NW Tethyan margin, Palaeogeography, Palaeoclimatology, Palaeoecology, 199(3–4), 315–331, doi:10.1016/S0031-0182(03)00540-6. Shannon, C. E., and W. Weaver (1949), The mathematical theory of communication, University of Illinois Press, Champaign, IL. Sheridan, R., F. Gradstein, and Shipboard Scientific Party (1983), Site 534: Blake-Bahama Basin, Initial Reports of the Deep Sea Drilling Project(76), 141–340. Short, D. A., J. G. Mengel, T. J. Crowley, W. T. Hyde, and G. R. North (1991), Filtering of Milankovitch cycles Earth’s geograph, Quaternary Research, 35(2), 157–173. Sprovieri, M., R. Coccioni, F. Lirer, N. Pelosi, and F. Lozar (2006), Orbital tuning of a lower Cretaceous composite record (Maiolica Formation, central Italy): LOWER CRETACEOUS ORBITAL TUNING, Paleoceanography, 21(4), n/a-n/a, doi:10.1029/2005PA001224.

Sunda, W. G. (1989), Trace metal interactions with marine phytoplankton, Biological Oceanography, 6(5– 6), 411–442. Weissert, H., and E. Erba (2004), Volcanism, CO2 and palaeoclimate: a Late Jurassic–Early Cretaceous carbon and oxygen isotope record, Journal of the Geological Society, 161(4), 695–702.

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Weissert, H., A. Lini, K. B. Föllmi, and O. Kuhn (1998), Correlation of Early Cretaceous carbon isotope stratigraphy and platform drowning events: a possible link?, Palaeogeography, Palaeoclimatology, Palaeoecology, 137(3–4), 189–203. Weissert, H., A. Lini, K. B. Föllmi, and O. Kuhn (n.d.), Correlation of Early Cretaceous carbon isotope stratigraphy and platform drowning events: a possible link?, Westermann, S., K. B. Föllmi, T. Adatte, V. Matera, J. Schnyder, D. Fleitmann, N. Fiet, I. Ploch, and S. Duchamp-Alphose , The Valagiia δC eursio a ot e a epressio of a gloal oceanic anoxic event, Earth and Planetary Science Letters, 290(1–2), 118–131, doi:10.1016/j.epsl.2009.12.011. Westermann, S., S. Duchamp-Alphonse, N. Fiet, D. Fleitmann, V. Matera, T. Adatte, and K. B. Föllmi (2013), Paleoenvironmental changes during the Valanginian: New insights from variations in phosphorus contents and bulk- and clay mineralogies in the western Tethys, Palaeogeography, Palaeoclimatology, Palaeoecology, 392, 196–208, doi:10.1016/j.palaeo.2013.09.017. Wortmann, U. G., and H. Weissert (2000), Tying platform drowning to perturbations of the global carbon le ith a δCOrg-curve from the Valanginian of DSDP Site 416, Terra Nova, 12(6), 289–294. Wyton, J., P. R. Bown, and H. Bailey (2007), Palaeoecological trends in Turonian-Coniacian (Late Cretaceous) calcareous nannofossils from Chalk Group sections, SE England, J. Nannoplankton Res, 29(1), 31–37. Young, J. R. (1994), Functions of coccoliths, in Coccolithophores, edited by Amos Winter and William G. Siesser, pp. 63–82, Cambridge University Press, Cambridge. Young, J. R., M. Kucera, and H.-W. Chung (1996), Automated biometrics on captured light microscope images of coccoliths of Emiliania huxleyi, in Microfossils and oceanic environments, pp. 261–277, Aberystwyth Press, Aberystwyth. Zachos, J., M. Pagani, L. Sloan, E. Thomas, and K. Billups (2001), Trends, Rythms, and Aberrations in Global Climate 65 Ma to Present, Science, 292, 686–693.

Zeebe, R. E. (2012), History of Seawater Carbonate Chemistry, Atmospheric CO 2 , and Ocean Acidification, Annual Review of Earth and Planetary Sciences, 40(1), 141–165, doi:10.1146/annurev-earth-042711- 105521.

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4 Middle Hauterivian biostratigraphy and paleoceanography of the Lower Saxony Basin (northwest Germany)

Carla Möller*, Jörg Mutterlose*

*Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany

(published 2014 in Zeitschrift der Deutschen Gesellschaft für Geowissenschaften [German Journal of Geosciences])

Abstract In the Early Cretaceous an epicontinental sea covered most of what is nowadays northwest Germany. Sediments accumulated in a synsedimentary subsiding basin, the Lower Saxony Basin (=LSB), which formed the southern extension of the proto North Sea. Two sedimentary successions of mid Hauterivian age (calcareous nannofossil zones BC 8 – 9) were correlated by means of coccolith biostratigraphy. The sections represent a) a marginal marine environment, <10 km distance from the former coastline, dominated by sandy deposits (Emlichheim), and b) the basin centre, about 50 km off-shore, with clay dominated sedimentation (Resse). Our study aims at reconstructing the palaeoceanography of the LSB in the mid Hauterivian and at comparing the nannofossil assemblages of the two different settings.

In the Emlichheim area (German – Dutch borderland) the Gildehaus Sandstone is represented by coarse siliciclastics and intercalated mudstone intervals. The mud dominated matrix contains rich and diverse calcareous nannofossil assemblages, which in combination with lithology allow for a sequence stratigraphic interpretation of the Gildehaus Sandstone. The mudstones of the Resse section (basin centre) contain a rich nannoflora and an abundant ammonite fauna. The latter shows an alternation of endemic, Tethyan and Boreal taxa, which shed light on the palaeoceanographic conditions of the LSB in the mid Hauterivian.

Quantitative analyses of the calcareous nannofossil assemblages show an offset between the abundances of the fertility indicators Zeugrhabdotus erectus and Biscutum constans. In Emlichheim, Z. erectus is present in higher abundances than B. constans, in Resse B. constans is dominating. These results confirm previous ideas regarding the palaeoecological preferences of the two species. At the same time, they indicate palaeoceanographic differences between the both sections.

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In Resse, calcareous nannofossils show a pronounced increase in abundance that coincides with the

18 diversification of the ammonite fauna. The combined nannofossil-, aoite ad δ Obel-datasets suggest, that the changes in the biota of the mid Hauterivian (calcareous nannofossil zone BC8) are related to an increase in surface water fertility that goes along with fluctuations of relative sea-level and a moderate warming.

Kurzfassung Marine Sedimente der Unterkreide haben heute in Nordwestdeutschland eine weite Verbreitung. In der frühen Kreide bildete dieser Raum einen epikontinental-marin geprägten Sedimentationsbereich, der auch als Niedersächsisches Becken bezeichnet wird und die südliche Fortsetzung der Proto-Nordsee darstellt. Zwei Profile, die ein hauterivezeitliches Alter haben (Nannofossil Zonen BC 8 – 9) wurden mittels Coccolithenbiostratigraphie korreliert. Diese Profile repräsentieren zwei unterschiedliche Ablagerungsräume im NB. Ein randlich-mariner Ablagerungsbereich mit einer Küstenentfernung von < 10 km wird geprägt von sandigen Sedimenten (Emlichheim), das Profil des Beckenzentrums, > 50 km Küstenentfernung, hingegen durch Tone und Siltsteine (Resse). Ziel dieser Arbeit war die Rekonstruktion der paläoozeanographischen Verhältnisse im Niedersächsischen Becken während des mittleren Hauterive. Zu diesem Zweck wurden die zeitgleichen Nannofossilassoziationen des Rand- und Beckenprofils analysiert, interpretiert und palökologisch gedeutet.

Im Raum Emlichheim (6 km südöstlich der Deutsch-Niederländischen Grenze) ist der Gildehaus Sandstein mit groben Siliziklastika und Tonsteineinschaltungen entwickelt. Die tonige Matrix führt eine diverse Nannofossil-Vergesellschaftung, die in Kombination mit der Lithologie eine sequenzstratigraphische Interpretation des Gildehaus Sandsteins ermöglicht. Die Ton- und Siltsteine des Beckenprofils (Resse) sind neben den Nannofloren durch reiche Ammonitenfaunen gekennzeichnet. Letztere zeigen innerhalb des Profils deutliche Änderungen in ihrer provinziellen Herkunft; endemische, tethyale und boreale Taxa schliessen sich in ihrer vertikalen Verbreitung aus.

Die quantitative Analyse der kalkigen Nannofloren ergab, dass die relative Häufigkeit der Nährstoff- Indikatoren Zeugrhabdotus erectus und Biscutum constans der beiden Lokalitäten gegensätzlich ist. In Emlichheim ist Z. erectus häufiger als B. constans, während in Resse B. constans dominiert. Dies unterstützt die Annahme, dass die beiden Taxa sich in ihren ökologischen Präferenzen unterscheiden und dass der limitierende Parameter die Höhe des Nährstoffgehalts ist. Damit spiegelt sich in den beiden Profilen ein unterschiedlicher Nährstoffeintrag wider.

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Korrespondierend mit dem Wechsel der Ammonitenfauna von endemischen zu kosmopolitischen Formen zeigen die kalkigen Nannofossilien in Resse einen starken Anstieg der absoluten Häufigkeiten. Die

18 Nannofossil-, Ammoniten- und δ Obel-Daten sowie die Lithologie der bearbeiteten Profile dokumentieren einen Anstieg des Nährstoffgehalts, eine Regression und eine schwache Erwärmung.

4.1. Introduction I the Earl Cretaeous orthest Gera as oered a epiotietal sea ith ater depths ot eeedig . The palaeogeographi positio of the Loer “ao Basi =L“B, forig a gatea etee the Boreal Real i the orth ad the Teths i the south, ade it eeptioall sesitie to hages i sea leel, liate ad palaeogeograph. These shifts are doueted arig opositios of arie floras ad fauas. Presual ar periods ad sea-leel highs are haraterised the iigratio of Tetha eleets, ooler phases ad sea-leel los o the other had are arked taa of Boreal proeae e.g. Mihael, ; Keper et al., ; Mutterlose, a,. Aog other palaeotologial groups foraiifera, aoites, eleites alareous aofossils hae supplied iportat iforatio for uderstadig these eiroetal hages, alloig for a detailed palaeoeaographi reostrutio of speifi iterals of the Earl Cretaeous. During the Valanginian - Albian interval siliciclastic sedimentation dominated throughout the LSB, showing a differentiation of a coarser grained basin margin facies and a finer grained basin centre facies. The western margin of the basin (Ochtrup – Emsland area) is characterised by several marine sandstone horizons including, among others, the Bentheim Sandstone (lower Valanginian), the Dichotomiten Sandstone (upper Valanginian), the Gildehaus Sandstone (Hauterivian) and the Rothenberg Sandstone (Aptian/Albian). Along the southern margin (Teutoburger Wald) up to 1000m of coarse clastics (Osning Sandstone, Valanginian – Aptian) represent a former near-shore coastal environment. At the same time up to 2000m of clay- and siltstones accumulated in the basin centre (Minden – Hannover – Braunschweig area) further north (e.g. Schott et al., 1969; Kemper, 1979; Mutterlose, 1992a; Mutterlose and Bornemann, 2000).

The mid Hauterivian (Aegocrioceras Beds, Simbirskites staffi ammonite zone) is an interval which specifically shows rapid vertical changes of endemic, tethyan and boreal ammonite taxa, suggesting short termed environmental variations. These changes of ammonite abundances have been observed both along the western basin margin in the coarse clastics of the Bentheim – Emsland area and in the expanded sequences of the basin centre, suggesting that these faunal shifts occurred basin wide (Michael, 1979;

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Kemper et al., 1987; Mutterlose, 1992). Precise and biostratigraphically well dated findings are, however, rare for the mid Hauterivian, consequently integrated palaeoceanographic interpretations are unknown for this interval. Cored material, recently made available from the western margin (Emlicheim area), in combination with a well dated outcrop succession of the basin centre (Resse section, Hannover) now offered for the first time the chance for a detailed biostratigraphic and palaeoecologic analyses of the sequence under discussion.

The aim of this study is to provide a detailed biostratigraphic framework and a correlation of siliciclastic successions from the basin margin and the basin centre by using calcareous nannofossils. Based on this high resolution zonation scheme a palaeoceanographic analyses will provide clues for the understanding of the depositional environments of the two settings, for which different turbidity and nutrient levels of the surface waters are likely. By comparing the data from the margin and the basin we want to understand to which extent the different environmental conditions affected the composition of the calcareous

18 aofossil asselages. I additio, e at to test hether palaeoliati pro data δ Obel) and ammonite findings from Resse can be used for interpreting the mid Hauterivian succession in the entire LSB in a palaeoclimatic context.

4.2. Geological Setting The Lower Saxony Basin, which formed the southernmost extension of the proto North Sea Basin in the Early Cretaceous, extended over about 400 km in west – east direction and 100 km in north – south direction. It was bounded to the north by the Pompeckj Swell, to the south by the Rhenish Massif, to the west by the East Netherlands High and to the east by the East Brandenburg High (Fig. 4.1). Differential subsidence of the LSB started in the Late Jurassic (Kimmeridgian) due to divergent dextral shear movements, related to contemporaneous rifting in the Central North Sea Graben (Ziegler 1990). Throughout the Kimmeridgian to Albian, sedimentation patterns were controlled by tectonic movements along northwest - southeast trending faults. These resulted in an asymmetric trough, bound to the north and south by synsedimentary faults with sedimentation rates highest in the north. Local tectonics were caused by salt diapirs mainly in the eastern part of the basin and along the western, southern and eastern margins. More detailed descriptions of the evolution of the basin have been given by Schott et al. (1967/69), Michael (1974; 1979), Kemper (1979), Betz et al. (1987), Mutterlose (1992), Baldschuhn and Kockel (1996) and Mutterlose and Bornemann (2000).

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Figure 4.1 Palaeogeographic map of the Hauterivian of Northwest Europe after Schott et al. (1969) and Diener (1966), showing the locations of the studied successions of Hauterivian sediments (Emlichheim, Resse) in the Lower Saxony Basin (= LSB).

Along the margin of the LSB, coarse grained clastics, including sandstones and conglomerates were deposited. Towards the central part of the basin, these coarse clastics are replaced by finer grained siliciclastics. The central parts of the basin were characterised by high subsidence, high sedimentation rates and oxygen depletion of bottom waters throughout the Early Cretaceous. Sediments of the basin centre are lithologically characterised by dark grey clays that are poor in calcium carbonate and contain sideritic nodules.

The mid Hauterivian sandstones and conglomerates of the Bentheim – Emsland area originated from a nearby landmass in the west (Wilsum High, northwestern edge of the East Netherlands High), which supplied clastic material (Schott et al., 1967/69, Kemper, 1992). These marginal marine siliciclastics of the Gildehaus Sandstone are well known from outcrops of the Bentheim – Losser area, where they provided ammonites (Aegocrioceras, Spitidiscus, Simbriskites) suggesting a mid Hauterivian age (Aegocrioceras Beds, Simbirskites staffi ammonite zone). Data from the subsurface are based on oil wells, coring the

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Figure 4.2 Hauterivian biostratigraphy with ammonite zonations after Mutterlose et al. (2014) and calcareous nannofossil BC zones and events for the Boreal after Bown et al. (1998). On the left side, the lithologies of the western margin and the basin centre of the Lower Saxony Basin and the stratigraphic ranges of the sections studied here.

Gildehaus Sandstone in the Emlichheim, the Rühlermoor and other oil fields. The Gildehaus Sandstone, which is also rich in benthic fossil communities in the outcrop area (Vries, 2002), has been interpreted as an oxygen rich shallow water setting (Kemper, 1992).

About 200 km east of Emlichheim sediments of mid Hauterivian age are exposed in the Resse clay-pit north of Hannover. The clays and siltstones mined here correspond to the basin centre facies (e.g. Mutterlose and Wiedenroth, 2009). Based on commonly occurring ammonites the Resse section was stratigraphically assigned to the Aegocrioceras beds and the Simbirskites staffi zone (Fig. 4.2). The ammonite faunas of the Resse pit show rapid changes of endemic, Tethyan and Boreal taxa, suggesting short termed climatic variations.

4.3. Studied sections and stratigraphy 4.3.1. Emlichheim section The Emlichheim field, which produces oil mainly from the Valanginian Bentheim Sandstone, is located 8 km east of the Dutch border. The Lower Cretaceous succession in the subsurface has been penetrated in

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Middle Hauterivian biostratigraphy and paleoceanography of the Lower Saxony Basin the past 50 years by many wells. For the present study a 20 m thick interval which cored the entire mid Hauterivian Gildehaus Sandstone has been analysed. The 18 m thick Gildehaus Sandstone is represented by 5.5 m of fine grained sandstones, 9 m of coarser grained conglomerates, which are embedded in a fine grained carbonate rich mud matrix, and 3.3 m claystones. Several thin claystone layers occur within the coarse siliciclastics. Based on observations both from outcrops and wells, Kemper (1992) subdivided the Gildehaus Sandstone into a lower and an upper unit (lower GHS, upper GHS), separated by a clay rich interval (Fig. 4.3). Outcrop findings document the presence of the ammonite genus Aegocrioceras in the lower GHS (Breyer and Lögters, 1949) and of the ammonite genera Crioceratites, Spitidiscus and Simbirskites in the upper GHS (Kemper 1992). These ammonites assign the Gildehaus Sandstone to the Simbirskites inversum and Simbirskites staffi ammonite zones of the mid Hauterivian (Fig. 4.2). The correlation of outcrop data and the subsurface findings of the Emlichheim section is based on lithological observations, and needs biostratigraphic verification. A total of 50 samples have been examined from the

Emlichheim section with respect to calcareous nannofossils and CaCO3 content.

4.3.2. Resse section The Resse clay-pit is situated 10 km north of Hannover (52°28.794N, 9°38.116E; Fig. 4.1). A 24 m thick sequence of silty claystones and intercalated calcareous concretions is exposed (Fig. 4.3). Based on the common occurrence of the ammonite taxa Aegocrioceras spp. and Simbirskites staffi the succession has been assigned to the Aegocrioceras beds (= S. inversum zone) and the S. staffi ammonite zone. For a detailed description of the succession see Mutterlose and Wiedenroth (2009). A total of 56 samples have been studied for calcareous nannofossils and CaCO3 content, 91 rostra of the belemnite species Hibolithes jaculoides hae ee aalsed for stale isotopes δ18O, δ13C) and element composition.

4.4. Material and methods 4.4.1. Calcareous nannofossils Simple smear slides of 106 samples from the two sections were prepared for biostratigraphic examination and to evaluate the state of preservation of the calcareous nannofossils. Following this a total of 82 settling slides were examined from the two sections, for preparation techniques see Geisen et al. (1999). The slides were studied with an OLYMPUS BH-2 light microscope under cross polarized light at a magnification of

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Figure 4.3 Correlation of the Emlichheim section (left) and the Resse section (right) based on calcareous nannofossil biostratigraphy, presented with their positions in a schematic east‒west transect of the Lower Saxony Basin. In the middle relative abundances of the calcareous nannofossil taxon Cyclagelosphaera margerelii are shown. Ammonite biostratigraphy of Resse from Mutterlose & Wiedenroth (2009). x1250. For biostratigraphy at least three transects of each slide were examined. Preservation of the specimens has been judged by applying the visual criteria of Roth (1983) and Roth and Thierstein (1972), regarding the visible degree of dissolution (etching, E) and calcite overgrowth (O), in the categories E1/O1 = minor, E2/O2 = moderate and E3/O3 = major etching/ overgrowth. At least 300, in most cases more than 400 nannofossil specimens were counted on each settling slide. Absolute and relative abundances of the calcareous nannofossils are considered.

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To support the palaeoecological interpretation of the different taxa, a correlation matrix was calculated. Changes in fertility were quantified using a modified version of the the nutrient index (NI) of Herrle et al. (2003), that was already successfully used by other authors (e.g. Tiraboschi et al., 2009; Pauly et al., 2012; Bottini et al., 2014): NI (modified) = [Biscutum constans + Discorhabdus ignotus + Zeugrhabdotus erectus] / [B. constans + D. ignotus + Z. erectus + Watznaueria spp.] x 100. The taxonomy follows the taxonomic concept of Perch-Nielsen (1985) and Bown (1998). A full list of taxa mentioned in text, figures and tables is given in the Appendix.

4.4.2. Geochemistry

Bulk rock CaCO3-content was determined by usig a aroate o Müller ad Gastner, 1971). The carbonate content of 106 samples was measured.

A total of 91 belemnite rostra, collected bed-by-bed in the Resse pit, have been sampled for geochemical analyses (trace elements, δ18O, δ13C). All rostra have been assigned to Hibolithes jaculoides. After having split the rostra in halves carbonate powder samples were obtained by hand-drilling under a stereomicroscope with a 0.3 mm drill-bit. For sampling, portions of clear calcite were selected. The margins, the apical line and the apex, which are most prone to alteration, were avoided.

Major and minor element analysis (Ca, Mg, Sr, Fe, Mn) was performed at the Ruhr-Universität Bochum on an ICP-OES (iCap 6500 Thermo Electron Corporation) on 1.5 mg of sample powder, after having been

13 18 dissolved in 3 M HNO3. The stale isotope opositio δ C, δ O) were measured at the GeoZentrum Nordbayern, Friedrich-Alexander Universität Erlangen-Nürnberg. Reproducibility and accuracy is better than ± . for δ13C ad . for δ18O. For details see Joachimski et al. (2001). The isotope data are given in per mil (‰) relative to V-PDB (Vienna Pee Dee Belemnite). The belemnite specimens are stored at the Ruhr-University Bochum.

4.5. Results

4.5.1. Calcareous nannofossil biostratigraphy Based on the stratigraphic zonations of Mutterlose (1991) and Bown et al. (1998) the Hauterivian can be subdivided into 6 nannofossil zones (Fig. 4.2). These are from bottom to top the BC6, the BC7, the BC8,

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Middle Hauterivian biostratigraphy and paleoceanography of the Lower Saxony Basin the BC9, the BC10 and the BC11 zones (Boreal Cretaceous). The mid Hauterivian is covered by the BC8 and BC9 nannofossil zones. The boundaries of these two zones are defined by the first occurrences (FO) or last occurrences (LO) of specific index taxa. The base of BC8 is defined by the FO of Tegumentum octiformis, the base of BC9 by the FO of Tegulalithus septentrionalis. The BC8 zone can further be subdivided into the

BCa, BCb and BCc subzones (from bottom to top). The boundaries of these subzones are marked by the following nannofossil events: Base BC8a – LO of Eprolithus antiquus and FO of T. octiformis, Base BC8b – end of the acme of Cyclagelosphaera margerelii, base BC8c – FO of Perissocyclus plethotretus and Zeugrhabdotus scutula (Fig. 4.2).

Emlichheim

The lower part of the Emlichheim section (0 – 10.5 m) can be assigned to nannofossil zone BC8, based on the presence of T. octiformis (0.7 m, sample EM71). The top of BC 8 is marked by the FO of T. septentrionalis (11.2 m, sample EM49) (Fig. 4.3). High abundances of C. margerelii (0.7 m, sample EM71, 24%) were observed in the clay sequence below the first sandstone horizon followed by an abrupt decrease in abundance (1.6 m, sample EM68, 0.5%). This corresponds to the renewed peak abundances of C. margerelii in the lower Aegocrioceras beds (BC8b) that were described by Mutterlose (1991) in the close-by Moorberg section, and that have been also observed in the Resse section (this study, see below). The base of subzone BC 8c is indicated by the FO of P. plethotretus (8.53 m, sample EM58). The FO of T. septentrionalis (11.2 m, sample EM49) marks the base of the middle upper Hauterivian nannofossil zone BC 9. The presence of Eiffelithus striatus throughout the entire sequence suggests a stratigraphic age not younger than BC 9. The uppermost ~2 m are barren, therefore a biostratigraphic age assignment is not possible. A selection of common and/or biostratigraphically important calcareous nannofossils from the Emlichheim section is shown in Fig. 4.4.

← Figure 4.4 Calcareous nannofossil micrographs and SEM pictures from the Emlichheim section (mid-Hauterivian BC8–9); scale bars represent 2 μm. (a) Perissocyclus plethotretus (sample EM42); (b) Retecapsa angustiforata (sample EM40); (c) Cretarhabdus conicus (sample EM2); (d) Cretarhabdus inaequalis (sample EM35); (e) Diloma galiciense (sample EM44); (f) Eiffelithus striatus (sample EM 41); (g) Tegumentum octiformis (sample EM36); (h) Zeugrhabdotus erectus (sample EM32); (i) Staurolithites quadriarcullus (sample EM34); (j) Conusphaera rothii (sample EM8); (k) Percivalia fenestra (sample EM32); (l) Tegulalithes septentrionalis (sample EM43); (m) Crucibiscutum salebrosum (sample EM37); (n) Biscutum constans (sample EM25); (o) Watznaueria barnesiae (sample EM15); (p) Watznaueria fossacincta (sample EM32); (q) Rhagodiscus asper proximal view (SEM picture; sample EM35); (r) Staurolithites sp. (SEM picture; sample EM 42); (s) Rotelapillus laffittei (SEM picture; sample EM40); (t) Watznaueria fossacincta (SEM picture; sample EM51); (u) Cyclagelosphaera app. C. rotaclypeata (SEM picture; sample EM35); (v) Watznaueria barnesiae (SEM picture; sample EM40); (w) Perissocyclus sp. distal view (SEM picture; sample EM40); (x) Staurolithites quadriarcullus (SEM picture; sample EM32).

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Resse

The lower part of the Resse section (0 – 18.6 m) has a BC8 zone age based on the presence of T. octiformis (0 m, sample Resse 81/1) and the absence of E. antiquus (Fig. 4.3). C. margerelii is present in high abundances at the base of the section (sample 81/1, 6.5%). Abundances decrease in the upper part of bed 81 (1 m, sample 81/2, 0.7%). Peak abundances of C. margerelii occur at 4.1 m height above base (sample

83/1, 25.8%), 11.3 m (sample 93/1, 4.2%), 15.3 m (sample 97/4, 9.9%) and 16.4 m (99/3, 6.5%). The base of subzone BC 8c is marked by the FO of Z. scutula and P. plethotretus, the top by the FO of T. septentrionalis (19.38 m, sample 103/2). The youngest beds (103-108) can be assigned to BC 9 (Eiffelithus striatus nannofossil zone) based on the consistent occurrence of E. striatus, the LO of which defines the top of the zone (Bown et al. 1998). See Fig. 4.5 for micrographs and SEM pictures of selected calcareous nannofossils from the Resse section.

4.5.2. Nannofossil preservation, diversity and abundance The calcareous nannofossils of Emlichheim are moderately well preserved, with preservational modes varying between E1-E3, O1–O2 (Fig. 4.6). A total of 70 species were recognized, the species richness of the individual samples varies from 23 – 37, with an average of 30. The absolute abundances range from 7.4 – 397.3 x 106 specimen/g sediment, on average 46.1 x 106 specimen/ g sediment in the sand-/siltstones and granular samples, and 270.4 x 106 specimen/ g sediment in the clay dominated samples. In the claystones at the top of the Emlichheim section the absolute abundances increase to a maximum of 397.3 x 106 specimen/g sediment.

In Resse the preservation is varying between well preserved and moderately etched/ overgrown, the preservational modes are E1-E2, O1–O2. From base to top a trend towards better preservation has been

← Figure 4.5 Calcareous nannofossil micrographs and SEM pictures from the Resse section (mid-Hauterivian BC8– 9); scale bars represent 2 μm. (a) Cretarhabdus conicus (sample Resse 95/2); (b) Retecapsa angustiforata (sample Resse 99/1); (c) Pickelhaube furtiva (sample Resse 99/1); (d) Pickelhaube furtiva (sample Resse 83/1); (e) Hemipodorhabdus gorkae (sample Resse 99/3); (f) Clepsilithus maculosus (sample Resse 99/1); (g) Crucibiscutum ryazanicum (sample Resse 92/1); (h) Crucibiscutum ryazanicum (sample Resse 93/3); (i) Eiffelithus windii (sample Resse 99/1); (j) Eiffelithus striatus (sample Resse 97/1); (k) Tegumentum octiformis (sample Resse 99/3) (l) Zeugrhabdotus scutula (sample Resse 97/2); (m) Staurolithites mutterlosei (sample Resse 93/3); (n) Staurolithites mutterlosei (sample Resse 93/3); (o) Rhagodiscus asper (sample Resse 97/2); (p) Bukrylithus ambiguus (sample Resse 92/1); (q) Rotelapillus laffittei (sample Resse 93/3); (r) Stradnerlithus geometricus (sample Resse 99/1); (s) Cyclagelosphaera margerelii (sample Resse 93/1); (t) Cyclagelosphaera margerelii (sample EM 99/3); (u) Diazomatolitus lehmannii (sample Resse 99/1); (v) Tegulalithus septentrionalis (sample Resse 103/1); (w) Rhagodiscus asper distal view (SEM picture; sample Resse 103/1); (x) Rotelapillus laffitei (SEM picture; sample Resse 102/1). 111

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observed, the samples with the best preservation belong to zone BC 8c (14 – 19 m above base, Fig. 4.7). A total of 65 species have been recognized, the number of species (species richness S) observed in a single sample varies from 21 – 35, the average is 29. The absolute abundances range from 17.7 – 1051.12 x 106/g sediment, with an average of 359.1 x 106 /g sediment. On average, absolute abundances, heterogeneity and evenness show an increase throughout BC8. The bigger part of BC9 in Resse is barren and in the topmost samples absolute abundances to not recover to the peak values of top BC8c.

4.5.3. Calcareous nannofossil ecology – relative abundances of selected species Emlichheim

The dominant species in both sections are Watznaueria barnesiae/ fossacincta and Rhagodiscus asper. In Emlichheim, the two taxa constitute on average 60.7% of the assemblage. W. barnesiae/ fossacincta ranges between 15.2 – 71.6% with an average of 41.6%, without showing any trend. The relative abundances of R. asper vary around an average of 18.4%. The average relative abundances C. salebrosum decrease between BC 8 and BC 9 (3.2 to1.5%). The average relative abundances of B. constans are lower in BC 8 (2.2%) than in BC 9 (3.3%). In BC 9 abundances increase to a maximum of 11.7% in the uppermost sample of the section. Z. erectus and D. ignotus both show a trend towards higher abundances from BC 8 (on average 3.8% and 0.5%, respectively) to BC 9 (averages 6.3% and 3.01%, respectively).

Following its FO T. septentrionalis is present in elevated abundances of 4.0 – 6.6% throughout the lowermost BC9. Upwards abundances decrease to an average of 0.4%. This acme event has not been observed in the samples from the Resse section.

Resse

In Resse W. barnesiae/ fossacincta and R. asper on average make up for 49.0%. The average abundances of W. barnesiae/ fossacincta decrease from 44.9 % to 28.3 % in BC 8b and further to 15.5 % in BC 8c, and increase again in BC 9 (average 25.6 %). Both R. asper and C. salebrosum increase steadily in relative abundance over the studied section (16.0 – 27.0 % and 1.0 -15.9%, respectively). The maximum relative abundance of R. asper of 45% is reached at the base of BC 9, of C. salebrosum in BC 9 at the very top of the section with 20.1%. B. constans is present in very low abundances in the lower part of BC 8b (average 2.5 %). Abundances increase in the upper part of BC 8b (average 5.2 %), and peak in BC 8c (8.1%), in BC 9 the average abundance is 3.7%. The abundance patterns of Z. erectus, with averages of 2.1 – 3.4 % in BC 8b, 3.8 % in BC 8c and 1.9 % in BC9, and of D. ignotus with averages of 0.2 – 3.3 % in BC 8b, 3.7 % in BC 8c

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Figure 4.6 Lithologic log of the Emlichheim section, calcareous nannofossil biostratigraphy (BC zonation for the Boreal of Bown et al.1998), carbonate contents (%), absolute abundances of calcareous nannofossils (specimen/g sediment) and relative abundances of palaeoecologically relevant calcareous nannofossil taxa (%). and 0.1 % in BC 9, show similar trends. C. margerelii has an overall average relative abundance of 2.6 %, which is punctuated by short-lived abundance peaks of 6.5 % and 25.8 % in the lower part of BC 8b and a phase of high abundances (2.2 – 9.9 %, average 6.3 %) in BC 9 (Fig. 4.3).

Relative abundances of selected species of Emlichheim and Resse are shown in figures 4.6 and 4.7. In both sections, trends in relative abundances generally match the absolute abundances.

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Figure 4.7 Lithologic log of the Resse section, calcareous nannofossil biostratigraphy (BC zonation for the Boreal of Bown et al. 1998), carbonate contents (%), absolute abundances of calcareous nannofossils (specimen/g sediment) and relative abundances of palaeoecologically relevant calcareous nannofossil taxa. Double data points represent multiple counts of samples from the same bed.

Statistical analyses

Statistical correlation of the abundances of two taxa suggests response to the same ecological factor. Correlatio is assued here statistial sigifiae is % or etter ρ=.. The orrelatio aalsis doe here for the Emlichheim and Resse material reveals an absence of strong correlation patterns.

Principal component analysis (PCA) was applied separately for Emlichheim and Resse to percentages of the most abundant and palaeoecological important nannofossil taxa (table 1). Positive loadings of Z. erectus, B. constans and D. ignotus and negative loadings of the other nannofossil species considered in the PCA (Emlicheim, PC2), and negative loadings of Z. erectus, B. constans and D. ignotus contrasting the

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Table 1 Loadings PC1-4 from principal component analysis (R-mode) Emlichheim PC1 PC2 PC3 PC4 W. barnesiae/ fossacincta 0.93 -0.02 0.14 0.24 R. asper -0.24 -0.72 0.50 0.31 C. salebrosum -0.05 -0.12 -0.29 0.09 C. margerelii -0.10 -0.10 -0.69 0.58 Zeugrhabdotus spp. -0.19 0.54 0.33 0.37 Z. erectus -0.14 0.40 0.21 0.35 B. constans -0.04 0.06 -0.12 -0.46 D. ignotus -0.09 0.10 0.07 -0.19 Variance percent 66.5 15.48 10.10 4.20

Resse PC 1 PC 2 PC 3 PC 4 W. barnesiae/ fossacincta -0.79 0.49 0.16 0.02 R. asper 0.59 0.75 0.16 0.11 C. salebrosum 0.07 -0.32 0.87 0.14 C. margerelii 0.00 -0.14 -0.34 0.83 Zeughrabdotus spp. 0.05 -0.18 0.01 -0.01 Z. erectus 0.02 -0.08 -0.05 -0.08 B. constans/ B. Ellipticum 0.11 -0.19 -0.11 -0.27 D. ignotus 0.06 -0.04 -0.23 -0.45 Variance percent 62.33 19.56 8.02 4.81

positive loadings of the other species (Resse, PC3 and PC4) corroborate the assumption of similar ecological affinities of these taxa. Thus the results of the PCA support the use of the nutrient index of Herrle et al. (2003) in the modified version. Pearson correlation of the principal components' scores with the nutrient index reveals significant correlation (p < 0.05) with a correlation coefficient ρ = 0.48 between

PC2EM and NIEM, and with ρ = -0.33 between PC4Resse and NIResse.

4.5.4. Geochemistry The average carbonate content in the Emlichheim section varies from <1 % (sample EM10) to 27.8 % (sample EM60), in Resse from <1 % (sample 81/1) to 16.5 % (sample 108/1; Figs. 4.6 and 4.7). Twenty- eight belemnite samples show Sr concentrations lower than 1000 ppm, and/or Fe and Mn concentrations higher than 500 ppm and 50 ppm, these were excluded from further consideration. In table 1 the complete

13 18 geoheial dataset δ Cbel, δ Obel and element composition) is given, with the samples outside the limits for non-altered belemnite calcite marked in grey.

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13 The δ Cbel values from Resse vary considerably from -0.25 – .‰, ith a ea alue of .‰. The

18 δ Obel data in the lower part of BC 8b range between -1‰ saple B to 1.12‰ saple Re, ad shift towards more negative values in the upper part of BC 8b and in BC 9, varying from -0.84 (sample Re to .‰ saple Re.

Where available, multiple specimens from the same horizon were measured. Following Mutterlose et al.

18 , the large satter of the δ Obel alues > ‰ i speies fro the sae horizo see tale may be due to pronounced seasonal temperature fluctuations in the Boreal Realm.

4.6. Discussion 4.6.1. Biostratigraphy The two successions can be correlated stratigraphically based on the FOs of P. plethotretus and T. septentrionalis (Fig. 4.3). The lower/upper Hauterivian boundary is defined in the Tethys by the FO of the ammonite Subsaynella sayni which equates the upper part of the S. inversum zone in the Boreal Realm (Mutterlose et al. 2014), and the upper BC8, respectively (Bown et al., 1998). In the Boreal Realm a specific marker for the boundary is missing. According to the correlation published by Mutterlose et al. (2014), the base of the lower/upper Hauterivian boundary falls in the upper S. inversum zone. This corresponds to the upper part of calcareous nannofossil zone BC8 (uppermost BC8b to BC8c). The basal part of the Gildehaus Sandstone thus is of late early Hauterivian age, thereby modifying older biostratigraphic age assignments by Breyer and Figure 4.8 Relative abundances of Zeugrhabdotus erectus and Biscutum constans in a marginal setting (left; Lögters (1949) and Kemper (1992). Emlichheim) and in the basin centre (right; Resse).

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4.6.2. Palaeoecology The marginal marine environment of Emlichheim is characterised by sandy deposits, while the Resse section of the basin centre is clay dominated. The main source of both the clastic material and the nutrients in a small basin like the LSB is riverine influx from the nearby hinterland. A reduction of water turbidity and a decrease of fertility of the surface waters with increasing distance from the coast is likely. This should be reflected by differences in the composition of the calcareous nannofossil assemblages, as well as by abundance and diversity changes from near shore to basin centre settings. In our example, however, the percentages of the high-nutrient taxa B. constans, Z. erectus and D. ignotus are similar in Emlichheim and in Resse. Given the different lithologies, the absolute abundances from the two sections cannot be compared, but the diversity of the assemblages do not differ substantially. This implies, that the two depositional settings discussed here, though lithologically quite different, did not differ significantly in terms of nutrients and ecology.

In contrast to the Gildehaus Sandstone of the Bentheim region, a shallow marine sandstone with abundant echinoderms and bivalves (Kemper, 1992; Vries, 2002), barren of calcareous nannofossils, the Gildehaus Sandstone in Emlichheim contains a diverse nannoflora. This suggests a rather pelagic depositional setting, where the coarse siliciclastics have to be interpreted as a mass flow originating from a hinterland in the southwest. The lithology in the basin centre (Resse) is likewise dominated by siliciclastics with low percentages of biogenic material. The current model where near shore settings are characterised by nutrient input and high productivity and off shore settings by low nutrient concentrations has been described for the mid Cretaceous North Atlantic (Roth, 1981; Roth and Bowdler, 1981). This scenario valid for an open ocean may not be applicable to an epicontinental basin like the LSB.

The current datasets shed, however, light on the ecological affinities of the high-fertility indicators Z. erectus and B. constans. In the marginal setting (Emlichheim) Z. erectus is more abundant than B. constans, while these proportions are reversed in the basin centre (Resse; Fig. 4.8). Although both taxa are associated with elevated nutrient levels, the ecological preferences of the two species are thought to differ slightly (Erba, 1992; Fisher and Hay, 1999; Kessels et al., 2003; Lees et al., 2005). Erba (1992) assumed that B. constans is indicative of higher fertility in a mesotrophic environment, while Z. erectus preferred elevated nutrient levels in a eutrophic setting. The higher nutrient level of the coastal Emlichheim section is expressed by the dominance of Z. erectus. The reversal of the abundance ratio of Z. erectus and B. constans close to the top of the Emlichheim section (Fig. 4.6), corresponds to the clay dominated interval

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with peak absolute abundances of calcareous nannofossils. This interval seems to represent ecological conditions similar to the basin centre, with lower nutrient levels and more pelagic sedimentation.

4.6.3. Palaeotemperatures

18 The δ Obel data from Resse reflect rather stable values with a slight negative shift in BC 8b. In terms of palaeotemperature, the data suggest a slight warming trend (about 2°C) from BC8b to BC8c.

A distinctive change in the ammonite faunas took place in the upper BC 8 (upper Aegocrioceras beds) (Fig. 4.9) of the Resse section. The ammonite fauna of nannofossil zone BC 8b only consists of the heteromorph ammonite genus Aegocrioceras. This genus, which is endemic to the southern part of the Boreal Realm, abruptly disappears in the uppermost BC 8b zone, the upper part of the section is characterized by Boreal (Simbirskites) and Tethyan (Crioceratites, Spitidiscus) genera. Endemic, boreal and tethyan taxa exclude each other (Mutterlose and Wiedenroth, 2009). The boreal ammonite genus Simbirskites occurs in Speeton (northeast England) at the base of the Simbirskites inversum zone (Rawson, 1971), in the western part of the LSB in the lower Aegocrioceras beds. This suggests a gradual spreading of Simbirskites spp. towards the south into the LSB from the North Sea Basin via the area of toda’s Netherlads Mutterlose and Wiedenroth, 2009).

A climatically induced southward migration of Simbirskites spp. as proposed by Mutterlose and

18 Wiederoth is ot ofired the δ Obel-based palaeotemperature reconstruction, which rather

18 idiate stale oditios. The δ Obel data are in better agreement with the occurrence of the tethyan Crioceratites ammonites. It is doubtful, though, whether a warming of only 2°C alone can account for the migration of ammonites from the Tethys into the LSB. Changes in palaeogeography cannot explain the appearance of the boreal and tethyan ammonite taxa in LSB. Both the Carpathian Seaway and the connections to the proto North Sea are believed to have been open throughout the Hauterivian (Michael, 1979; Mutterlose, 1992; Michalik, 1995; Melinte and Mutterlose, 2001). The results of this study rather suggest, that a moderate warming and an increase in surface water fertility in combination with fluctuations of relative sea-level in the upper BC8 zone may have caused a change in the marine ecosystem of the LSB. Endemic faunas thriving under restricted conditions were replaced by more diverse and abundant biota (Fig. 4.9).

18 The δ Obel decrease towards more negative values in the upper BC 8b zone goes along with an abundance increase of R. asper. In Resse two maxima (beds 97 and 101) of R. asper co-occur with the tethyan

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Table 2 Isotope and trace element data of belemnite samples from Resse 13 18 sample height δ C δ O Mg/Ca Mg Sr Fe Mn zone [permil [ppm [m] [mM/M] [ppm] [ppm] [ppm] V- [permil V- ] PDB] PDB]

Re 34 23.85 0.93 -0.52 11.78 2783 1314 134 29.0 BC 9/ S. staffi

Re 35 23.85 0.82 0.29 8.62 2042 1216 328 34.6 BC 9/ S. staffi

Re 37 23.85 0.08 -0.68 10.52 2512 1336 404 68.4 BC 9/ S. staffi

Re 38 23.85 -0.12 0.49 9.43 2258 1449 46 19.0 BC 9/ S. staffi

Re 39 23.85 0.68 -0.06 7.94 1869 1573 418 70.0 BC 9/ S. staffi

Re 40 23.85 0.69 0.07 11.95 2783 1205 246 37.9 BC 9/ S. staffi

Re 26 22.50 0.85 -0.06 8.28 1959 1420 3061 52.9 BC 9/ S. staffi

Re 27 22.38 1.16 0.17 9.39 2251 1619 56 4.9 BC 9/ S. staffi

Re 28 22.38 1.75 -0.45 9.28 2100 1764 2534 11.7 BC 9/ S. staffi

Re 46 22.08 1.52 -0.23 7.88 1844 1427 106 14.1 BC 9/ S. staffi

Re 47 22.08 0.18 -0.47 9.19 2153 1468 122 28.9 BC 9/ S. staffi

Re 25 20.85 1.09 -0.11 10.83 2588 1637 35 4.9 BC 9/ S. staffi

Re 22 20.68 -0.17 0.31 9.11 2181 1530 68 8.8 BC 9/ S. staffi

Re 18 20.68 0.68 -0.54 9.67 2113 1625 3650 8.3 BC 9/ S. staffi

Re 23 20.58 1.11 -0.76 9.98 2399 1595 482 60.5 BC 9/ S. staffi

Re 24 20.58 0.83 0.64 9.75 2336 1736 74 7.0 BC 9/ S. staffi

Re 20 20.48 1.90 0.19 8.64 2002 1397 34 6.7 BC 9/ S. staffi

Re 21 20.48 0.22 -0.43 7.91 1874 1588 71 5.4 BC 9/ S. staffi

Re 19 20.48 0.79 -0.01 7.90 1859 1567 119 19.6 BC 9/ S. staffi

Re 17 19.48 0.82 -0.13 12.28 2853 1276 407 16.9 BC 9/ S. staffi

Re 8 19.38 0.78 0.64 8.82 2062 1434 219 36.9 BC 9/ S. staffi

Re 9 19.38 -1.63 -9.82 14.66 3329 1091 7559 392.0 BC 9/ S. staffi

Re 31 19.00 0.69 0.09 13.18 3132 1614 72 18.1 BC 9/ S. staffi

Re 32 19.00 1.07 0.61 7.69 1843 1377 55 7.9 BC 9/ S. staffi

Re 33 19.00 0.62 0.38 9.61 2299 1545 53 30.5 BC 9/ S. staffi

Re 41 18.08 0.54 -0.44 7.42 1741 1283 241 50.3 BC 8c/ S. staffi

Re 7 18.00 1.19 -0.02 12.20 2814 1364 2627 36.8 BC 8c/ S. staffi

Re 42 17.60 -3.22 -7.17 18.28 3430 853 34800 780.0 BC 8c/ S. staffi

Re 29 17.50 0.81 -0.20 11.46 2714 1724 688 124.0 BC 8c/ S. staffi

Re30 17.50 -3.38 -7.84 11.42 2390 992 634 93.0 BC 8c/ S. staffi

Re 16 16.70 1.94 -0.55 11.77 2735 1426 95 15.7 BC 8c/ S. staffi

Re54 15.00 1.16 -0.13 8.46 1968 1404 105 15.0 BC 8b/ S. concinnus

Re55 15.00 0.86 -0.23 7.54 1757 1410 853 38.7 BC 8b/ S. concinnus

Re56 15.00 1.86 0.26 8.13 1897 1514 153 26.6 BC 8b/ S. concinnus

Re57 15.00 1.97 0.44 7.28 1701 1511 71 9.6 BC 8b/ S. concinnus

Re58 15.00 0.97 -1.36 13.91 3206 1261 595 49.0 BC 8b/ S. concinnus

Re59 15.00 0.99 -0.84 11.83 2746 1278 419 35.5 BC 8b/ S. concinnus BC 8b/ Aegocrioceras Re 44 14.70 -2.90 -8.52 14.86 3324 1102 18260 966.0 beds BC 8b/ Aegocrioceras Re 4 13.40 1.61 0.43 8.26 1955 1433 279 21.7 beds

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Table 2 (continued) Isotope and trace element data of belemnite samples from Resse

sample height δ13C δ18O Mg/Ca Mg Sr Fe Mn zone [permil [m] V- [permil V- [mM/M] [ppm] [ppm] [ppm] [ppm] PDB] PDB]

Re 5 13.40 0.26 -0.07 9.33 2223 1451 68 39.1 BC 8b/ Aegocrioceras beds

Re 1 13.20 1.72 0.01 7.35 1736 1497 265 19.1 BC 8b/ Aegocrioceras beds

Re 2 13.20 0.46 -2.40 8.61 2037 1262 126 24.6 BC 8b/ Aegocrioceras beds

Re 3 13.20 0.53 0.04 8.49 2008 1208 160 22.1 BC 8b/ Aegocrioceras beds

Re 15 13.10 -0.25 0.17 10.66 2483 1277 116 32.2 BC 8b/ Aegocrioceras beds

Re 12 12.70 0.74 0.29 8.49 1993 1327 178 21.6 BC 8b/ Aegocrioceras beds

Re 10 12.60 0.84 0.09 8.21 1922 1423 63 7.8 BC 8b/ Aegocrioceras beds

Re 11 12.60 0.26 0.10 9.90 2319 1303 75 10.9 BC 8b/ Aegocrioceras beds

Re 45 12.30 1.41 0.45 7.45 1745 1412 1638 23.2 BC 8b/ Aegocrioceras beds

Re 50 11.35 1.39 0.38 7.25 1676 1444 422 9.4 BC 8b/ Aegocrioceras beds

Re 48 11.20 1.19 0.20 8.20 1924 1606 102 21.5 BC 8b/ Aegocrioceras beds

Re 52 11.10 1.11 0.03 10.05 2343 1479 302 42.7 BC 8b/ Aegocrioceras beds

Re 49 11.00 0.74 -0.38 6.83 1608 1474 188 32.1 BC 8b/ Aegocrioceras beds

Re 51 10.90 1.56 0.46 9.18 2142 1537 51 8.9 BC 8b/ Aegocrioceras beds

Re 43 10.75 -2.19 -10.31 15.57 3593 1116 4836 389.0 BC 8b/ Aegocrioceras beds

B35 9.50 0.09 -0.08 8.16 1943 1316 321.00 57.20 BC 8b/ Aegocrioceras beds

B34 9.45 1.34 0.08 8.59 2045 1651 265.10 59.90 BC 8b/ Aegocrioceras beds

B33 9.30 1.37 0.21 8.16 1947 1438 137.40 27.60 BC 8b/ Aegocrioceras beds

B32 8.80 1.03 0.20 10.17 2425 1697 234.60 49.10 BC 8b/ Aegocrioceras beds

B31 8.70 0.99 0.65 8.18 1955 1291 227.50 12.30 BC 8b/ Aegocrioceras beds

B30 8.70 0.68 -0.53 9.97 2360 1510 293.90 57.10 BC 8b/ Aegocrioceras beds

B29 8.50 1.86 0.43 7.02 1663 1484 204.00 28.10 BC 8b/ Aegocrioceras beds

Re 13 8.10 1.53 1.12 9.39 2185 1659 176 8.3 BC 8b/ Aegocrioceras beds

Re 14 8.10 1.07 0.26 8.79 2052 1697 51 10.0 BC 8b/ Aegocrioceras beds

B28 7.70 1.37 0.30 8.95 2120 1668 196.30 47.30 BC 8b/ Aegocrioceras beds

B27 7.70 0.50 0.19 10.33 2447 1630 177.00 40.00 BC 8b/ Aegocrioceras beds

B26 7.45 1.22 0.41 8.95 2106 1410 732.5 131 BC 8b/ Aegocrioceras beds

B25 7.45 0.88 0.30 9.94 2329 1413 3416 142 BC 8b/ Aegocrioceras beds

B24 7.40 2.22 0.34 7.74 1845 1550 121.80 23.40 BC 8b/ Aegocrioceras beds

B23 7.30 1.20 0.46 9.49 2255 1594 241.20 50.30 BC 8b/ Aegocrioceras beds

B22 7.30 1.18 0.10 9.04 2144 1411 126.40 29.40 BC 8b/ Aegocrioceras beds

B21 7.30 2.04 0.63 7.91 1873 1677 201.40 46.90 BC 8b/ Aegocrioceras beds

B20 7.30 1.69 -0.50 10.33 2428 1824 207.80 45.50 BC 8b/ Aegocrioceras beds

B19 7.30 2.10 0.31 8.35 1997 1669 120.60 23.20 BC 8b/ Aegocrioceras beds

B18 7.30 0.64 0.77 8.66 2061 1497 264.80 69.90 BC 8b/ Aegocrioceras beds

B17 7.30 1.21 -0.67 11.44 2697 1572 498.20 91.40 BC 8b/ Aegocrioceras beds

B16 7.30 1.22 0.38 8.37 2013 1620 239.20 51.00 BC 8b/ Aegocrioceras beds

B15 7.30 0.89 -0.99 10.02 2354 1857 101.30 24.10 BC 8b/ Aegocrioceras beds

B14 7.30 1.09 0.55 8.67 2069 1610 246.50 50.90 BC 8b/ Aegocrioceras beds

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Table 2 (continued) Isotope and trace element data of belemnite samples from Resse

sample height δ13C δ18O Mg/Ca Mg Sr Fe Mn zone

[m] [permil [permil [mM/M] [ppm] [ppm] [ppm] [ppm] V-PDB] V-PDB]

B13 7.30 1.07 -1.00 10.94 2589 1717 96.12 18.60 BC 8b/ Aegocrioceras beds

B12 7.30 1.53 -0.09 9.58 2276 1604 263.50 54.10 BC 8b/ Aegocrioceras beds

B11 7.30 2.03 0.26 8.47 1999 1721 101.50 19.10 BC 8b/ Aegocrioceras beds

B10 7.30 1.32 0.76 9.33 2211 1642 178.80 41.00 BC 8b/ Aegocrioceras beds

B9 7.30 1.17 -0.35 7.69 1834 1450 263.60 49.80 BC 8b/ Aegocrioceras beds

B8 6.70 0.28 0.17 8.85 2103 1482 132.10 24.80 BC 8b/ Aegocrioceras beds

B7 6.50 1.50 0.17 8.34 1982 1483 85.87 16.50 BC 8b/ Aegocrioceras beds

B6 6.20 1.82 1.11 9.34 2213 1684 163.30 44.60 BC 8b/ Aegocrioceras beds

B5 5.90 0.92 0.03 9.68 2294 1497 153.30 28.10 BC 8b/ Aegocrioceras beds

B4 5.10 0.95 0.00 8.83 2102 1534 222.70 30.00 BC 8b/ Aegocrioceras beds

B3 5.70 1.65 0.69 9.71 2311 1648 109.00 23.00 BC 8b/ Aegocrioceras beds

B2 4.10 1.50 0.42 7.62 1827 1671 80.00 15.70 BC 8b/ Aegocrioceras beds

B1 4.00 0.63 0.11 9.61 2279 1497 52.00 19.90 BC 8b/ Aegocrioceras beds

ammonite Crioceratites. These findings go along with rare nannoconids, a decline of C. salebrosum and the appearance of Simbirskites spp. (Fig. 4.9). These correlations support the assumption, that nannoconids as well as R. asper were associated with warm water temperatures, whereas C. salebrosum is a high latitudinal taxon indicating cooler temperatures (Roth an Krumbach, 1986; Erba et al., 1992; Mutterlose and Kessels, 2000).

4.6.4. Palaeoceanography and sequence stratigraphy The studied interval can be subdivided into three main ecological phases (Fig. 4.9):

In phase 1 (BC 8b) ecological conditions were unfavourable for coccolithophores in both localities, based on the low absolute abundances and the low nutrient index of both sections. The ammonite fauna is dominated by the endemic heteromorph Aegocrioceras spp. Following Hoedemaeker and Herngreen (2003) the lower Gildehaus Sandstone represents the top part of a highstand systems tract. The change towards coarse, granular deposits is interpreted as abrupt shift of the facies' towards the basin representing the sequence boundary.

In Resse, phase 2 (upper BC 8b to lowermost BC 9) is characterised by diversification and increased

18 audaes of alareous aofossils. The shift i aerage δ Obel (from 0.32 to -0.01‰) and the

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composition of the calcareous nannofossil assemblages (high abundances of R. asper) indicate a warming. Conditions more favourable for calcareous nannofossils and higher nutrient levels are reflected by increased absolute abundances and high nutrient indices. Simultaneously the ammonite- and microfaunas diversified and the carbonate content increased in the centre of the LSB (Kemper et al., 1987; Mutterlose and Wiedenroth, 2009).

In contrast to Resse the coarse grained, gravel-rich deposits (BC 8C) of Emlichheim are barren of calcareous nannofossils (Fig. 4.6). The coarsening of the deposits and the decline of the nannofloras in Emlichheim are here interpreted as the basinward movement of the coastline during a sea-level fall (falling stage systems tract). This corresponds to the major sea-level fall recorded in the prograding coastal sediments of the Hauterivian in the southern North Sea and Moray Firth Basin, culminating over the upper/ lower Hauterivian boundary (Jeremiah et al., 2010). The fall of sea-level, a basinward shift of the coastline and presumably an increase of weathering in BC 8 places Emlichheim in a very marginal position. At the same time these conditions allow for more nutrients in the central parts of the basin (e.g. Resse). Phase 2 ends with a decline of nannofossil absolute abundances and fertility. In the lower BC 9 zone nannoflora abundances in Emlichheim recover slightly (sea-level rise, beginning of transgressive systems tract). The transgressive surface, corresponding to the transition from coastal progradation to retrogradation, and thus the level of the most seaward position of the shoreline, is located in the coarse, barren interval below. In the lower BC9 (samples 103/1 – 105/2), the sediments from Resse are nearly or completely barren of calcareous nannofossils, corresponding to low carbonate values (< 5% CaCO3). This may indicate a primary reduction of carbonate shelled organisms in this interval due to unsuitable conditions linked to reduced nutrient availability.

In phase 3 (upper BC 9) absolute abundances of calcareous nannofossils increase in Emlichheim, connected to high nutrient indices. Also in Resse the nannoflora recovers in the upmost samples. In Emlichheim, fine grained sediments and the recovery of calcareous nannofossils indicate a landward shift of the shoreline due to a sea-level rise. This corresponds to the retrograding basal transgressive systems tract of the upper part of the Gildehaus Sandstone Member (Hoedemaeker and Herngreen, 2003). The peak nannofossil abundances mark the maximum flooding surface (MFS; see Fig. 4.9). Calcareous

→ Figure 4.9 Synthesis of the results with the sequence stratigraphical interpretation of the data and curve of relative water depth/distance to the coastline, lithology of the Emlichheim section, the absolute abundances of calcareous nannofossils in Resse and Emlichheim given in 106 specimen/g of sediment, the calcareous nannofossil nutrient index, δ18O-data from belemnites from Resse, relative abundances of the warm-water taxon Rhagodiscus asper and the cold-water taxon Crucibiscutum salebrosum (%) in Emlichheim and Resse, stratigraphic ranges of ammonite taxa in Resse and lithology of the Resse section, correlated with calcareous nannofossil biostratigraphy (BC zones 8‒9). 122

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nannofossils and oxygen isotopes suggest a warming in agreement with the occurrence of the tethyan ammonite Spitidiscus rotula.

4.7. Conclusions 1.) A detailed biostratigraphical zonation of the two studied sections (Emlichheim, Resse) has been established. Based on the marker species both sections were assigned to the boreal calcareous nannofossil zones BC 8 and BC 9 of the mid Hauterivian.

2.) Based on the calcareous nannofossil assemblages we assume that the Gildehaus Sandstone in Emlichheim was deposited in a rather pelagic position, with an input of coarse siliciclastics as discharge from shallower positions. An exception is the coarser grained interval barren of calcareous nannofossils (BC 8c), that reflects the basinward movement of the coastline during a period of sea-level fall.

3.) The relative abundances of the fertility indicators Zeugrhabdotus erectus and Biscutum constans indicate differences between the two settings. In the marginal setting (Emlichheim) Z. erectus is present in higher abundances than B. constans, in the basin centre (Resse) B. constans is more common.

18 4.) The δ Obel palaeotemperature estimates indicate an overall warming trend (increase of 0.5‰ over 18 zones BC8b and BC9 (pars)). The combined data set of calcareous nannofossils, δ Obel, ammonites suggests several short termed phases of warming and cooling.

5.) The results of this study suggest that a slight warming and an increase in surface water fertility in the upper BC8 caused a change in the marine ecosystem of the LSB. Endemic faunas thriving under restricted conditions were replaced by diverse and abundant biota.

4.8. Acknowledgements Material from the Emlichheim oilfield was kindly supplied by the Wintershall Holding GmbH and ExxonMobil Production Deutschland GmbH. We thank the staff of the labs of the Friedrich-Alexander Universität Erlangen Nürnberg/ GeoZentrum Nordbayern and of the Ruhr-Universität Bochum for the stable isotope measurements and element composition analysis. We are grateful to Martin Hiss and an anonymous reviewer for their their useful comments. Stefano Dellepiane, Bastian Köhrer, Christian Linnert, Kevin Stevens and Dominik Weiel are thanked for their useful comments.

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4.9. References Baldschuhn, R., and F. Kockel (1996), Geotektonischer Atlas von NW-Deutschland, in Geotektonischer Atlas von NW-Deutschland, edited by Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover.

Betz, D., F. Führer, G. Greiner, and E. Plein (1987), Evolution of the Lower Saxony basin, Tectonophysics, 137(1–4), 127145149155165–142146151159170.

Bottini, C., E. Erba, D. Tiraboschi, H. C. Jenkyns, S. Schouten, and J. S. Sinninghe Damsté (2015), Climate variability and ocean fertility during the Aptian Stage, Climate of the Past, 11(3), 383–402, doi:10.5194/cp-11-383-2015.

Bown, P. R., D. C. Rutledge, J. A. Crux, and L. T. Gallagher (1998), Lower Cretaceous, in Calcareous Nannofossil Biostratigraphy, edited by Paul R. Bown, Chapman & Hall, Londom, UK.

Bown, Paul R. (1998), Calcareous Nannofossil Biostratigraphy, Chapman & Hall, London, UK.

Breyer, F., and H. Lögters (n.d.), Georgsdorf, ein Ölfeld im Emsland, in Erdöl und Tektonik in Nordwestdeutschland, pp. 257–275, Hannover, Celle.

Diener, I. (n.d.), Stratigraphisches Korrelationsschema für die Kreide der Deutschen Demokratischen Republik und angrenzender Gebiete, Abhandlungen der Zentralen Geologischen Instituts, (5), 1–137.

Erba, E. (n.d.), Middle Cretaceous calcareous nannofossils from the western Pacific (ODP Leg 129): Evidence for paleoequatorial crossings, Procedings of the Ocean Drilling Program Scientific Results, (129), 189–201. Erba, E., D. Castradori, G. Guasti, and M. Ripepe (1992), Calcareous nannofossils and Milankovitch cycles: the example of the Albian Gault Clay Formation (southern England), Palaeogeography, Palaeoclimatology, Palaeoecology, 93(1–2), 47–69.

Fisher, C., and W. W. Hay (n.d.), Calcareous nannofossils as indicators of mid-Cretaceous paleofertility along an ocean front, U.S. western interior, in Evolution of the Cretaceous ocean–climate system, edited by E. Barrera and C.C. Johnson, pp. 161–180, Madison, Wisconsin.

Geisen, M., Herrle, J.O., Mutterlose, J., and Young, J.R. (1999), Calibration of the random settling technique for calculation of absolute abundances of calcareous nannoplankton, Micropalaeontology, 45, 123– 138.

Hoedemaeker, P. J., and G. . Waldemar Herngreen (2003), Correlation of Tethyan and Boreal Berriasian – Barremian strata with emphasis on strata in the subsurface of the Netherlands, Cretaceous Research, 24(3), 253–275, doi:10.1016/S0195-6671(03)00044-2.

Jeremiah, J. M., S. Duxbury, and P. Rawson (2010), Lower Cretaceous of the southern North Sea Basins: reservoir distribution within a sequence stratigraphic framework, Netherlands Journal of Geosciences, 89(3–4), 203–237, doi:10.1017/S0016774600000706. Joachimski, M., C. Ostertag-Henning, R. D. Pancost, H. Strauss, K. H. Freeman, R. Littke, J. S. Sinninghe Damsté, and G. Racki (2001), Water column anoxia, enhanced productivity and concomitant changes

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i δC ad δ“ aross the Frasia-Famennian boundary (Kowala – Holy Cross Mountains/ Poland), Chemical Geology, (175), 109–237. Kemper, E. (1992), Die tiefe Unter-Kreide im Vechte-Dinkel Gebiet, Losser.

Kemper, E., P. Rawson, and J.-P. Thieuloy (1981), Ammonites of Tethyan ancestry in the early Lower Cretaceous of north-west Europe, Palaeontology, (24), 251–311.

Kemper, E., J. Mutterlose, and K. Wiedenroth (n.d.), Die Grenze Unter-/Ober-Hauterive in Nordwestdeutschland, Beispiel eines stratigraphisch zu nutzenden Klima-Umschwungs, Geologisches Jahrbuch A, (96), 209–218. Kemper, W. (n.d.), Die Unterkreide Nordwestdeutschlands. Ein Überblick, in Aspekte der Kreide Europas, edited by J. Wiedmann, pp. 1–9. Kessels, K., J. Mutterlose, and A. Ruffell (2003), Calcareous nannofossils from late Jurassic sediments of the Volga Basin (Russian Platform): evidence for productivity-controlled black shale deposition, International Journal of Earth Sciences, 92(5), 743–757, doi:10.1007/s00531-003-0343-x.

Lees, J. A., P. R. Bown, and E. Mattioli (2005), Problems with proxies? Cautionary tales of calcareous nannofossil paleoenvironmental indicators, Micropaleontology, 51(4), 333–343.

Melite, M., ad J. Mutterlose , A Valagiia Earl Cretaeousoreal aoplakto eursioi setios fro Roaia, Marine Micropaleontology, 43(1), 1–25.

Michael, E. (1974), Zur Palökologie und Faunenführung des norddeutschen Unterkreide-Meeres, Geologisches Jahrbuch A, (19), 1–68.

Michael, E. (n.d.), Mediterrane Fauneneinflüsse in den borealen Unterkreide-Becken Europas, besonders Nordwestdeutschlands, in Aspekte der Kreide Europas, edited by J. Wiedmann, vol. 6.

Michalik, J. (1995), Lower Cretaceous stratigraphy, facies, faunas and Tethyan/Boreal influences in the Western Carpathians, Cretaceous Research, (16), 229–310.

Mutterlose, J. (1992a), Migration and evolution patterns of floras and faunas in marine Early Cretaceous sediments of NW Europe, Palaeogeography, Palaeoclimatology, Palaeoecology, (94), 261–282.

Mutterlose, J. (1992), Biostratigraphy and palaeobiogeography of Early Cretaceous calcareous nannofossils, Cretaceous Research, 13(2), 167–189.

Mutterlose, J. (n.d.), Das Verteilungs- und Migrationsmuster des kalkigen Nannoplanktons in der Unterkreide (Valangin–Apt) NW-Deutschlands, Palaeontographica Abteilung B, (221), 27–152.

Mutterlose, J., and A. Bornemann (2000), Distribution and facies patterns of Lower Cretaceous sediments in northern Germany: a review, Cretaceous Research, 21(6), 733–759, doi:10.1006/cres.2000.0232.

Mutterlose, J., and K. Kessels (2000), Early Cretaceous calcareous nannofossils from high latitudes: implications for palaeobiogeography and palaeoclimate, Palaeogeography, Palaeoclimatology, Palaeoecology, 160(3), 347–372.

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Mutterlose, J., and K. Wiedenroth (2009), Neue Tagesaufschlüsse der Unter-Kreide (Hauterive–Unter-Apt) im Gro\s sraum Hannover–Braunschweig: Stratigraphie und Faunenführung, Berliner paläobiologische Abhandlungen, 10, 257–288.

Mutterlose, J., M. Mecklenbeck, and S. Rückheim (2001), Die Floren- und Faunenverteilung im Unter- Hauterive (Unter-Kreide) der Tongrube Heisterholz, Geologie und Paläontologie von Westfalen, (58), 5–31.

Mutterlose, J., S. Bodin, and L. Fähnrich (2014), Strontium-isotope stratigraphy of the Early Cretaceous (Valanginian–Barremian): Implications for Boreal–Tethys correlation and paleoclimate, Cretaceous Research, 50, 252–263, doi:10.1016/j.cretres.2014.03.027.

Pauly, S., J. Mutterlose, and P. Alsen (2012), Early Cretaceous palaeoceanography of the Greenland– Norwegian Seaway evidenced by calcareous nannofossils, Marine Micropaleontology, 90–91, 72–85, doi:10.1016/j.marmicro.2012.04.004.

Perch-Nielsen, K. (1985), Mesozoic calcareous nannofossils, in Plankton stratigraphy, edited by H.M. Bolli, J.B. Saunders and K. Perch-Nielsen, pp. 329–426, Cambridge University Press, Cambridge.

Rawson, P. (1971), The Hauterivian (Lower Cretaceous) biostratigraphy of the Speeton Clay of Yorkshire, England, Newsletters on Stratigraphy, 4(1), 61–76.

Roth, P. H. (1981), Mid-Cretaceous calcareous nannoplankton from the Central Pacific: implications for paleoceanography, Initial Reports of the Deep Sea Drilling Project, (62), 471–489.

Roth, P. H. (1983), Jurassic and Lower Cretaceous calcareous nannofossils in the western North Atlantic (Site 534): biostratigraphy, preservation, and some observations on biogeography and palaeoceanography, Initial Reports of the Deep Sea Drilling Project, (76), 587–621. Roth, P. H., and J. L. Bowdler (1981), Middle Cretaceous calcareous nannoplankton biogeography and oceanography of the Atlantic Ocean, SEPM Special Publications, (32), 517–546. Roth, P. H., and K. R. Krumbach (1986), Middle Cretaceous calcareous nannofossils biostratigraphy and preservation in the Atlantic and Indian oceans: implications for Paleoceanography, Marine Micropaleontology, (10), 235–266.

Roth, P. H., and H. R. Thierstein (1972), Calcareous nannoplankton: Leg 14 of the Deep Sea Drilling Project, Initial Reports of the Deep Sea Drilling Project, (14), 421–485.

Schott, W., W. Jaritz, F. Kockel, C. W. Sames, V. Stackelberg, J. Stets, D. Stoppel, R. Baldschuhn, and K. D. Krampe (n.d.), Paläogeographischer Atlas der Unterkreide von Nordwestdeutschland mit einer Übersichtsdarstellung des nördlichen Mitteleuropa, Hannover.

Tiraboschi, D., E. Erba, and H. C. Jenkyns (2009), Origin of rhythmic Albian black shales (Piobbico core, central Italy): Calcareous nannofossil quantitative and statistical analyses and paleoceanographic reconstructions: ORIGIN OF RHYTHMIC ALBIAN BLACK SHALES, Paleoceanography, 24(2), n/a-n/a, doi:10.1029/2008PA001670.

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Vries, J. de (2002), Bivalvia from the Gildehaus Sandstone (Hauterivian; Lower Cretaceous) of Losser, Twente; the Netherlands, Stichting Staring Monument.

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5 Conclusions and perspectives

5.1. Conclusions This thesis presents data on calcareous nannofossil assemblage composition and abundance patterns, biometry of three coccolith species, and geochemical data from Lower Cretaceous sediments (Berriasian – Hauterivian). The results of the studies illustrate the value of calcareous nannofossils for reconstructions of paleoclimate and paleoceanography. Combined with sedimentological data, nannofossil data can trace changes in marine environments and can be used to characterize depositional environments as well as ecological conditions.

5.1.1. Stratigraphy Integrated stratigraphy (87Sr/86“r, δ13C, ammonite biostratigraphy, calcareous nannofossil biostratigraphy) results in a revision of the stratigraphic interpretation of Lower Cretaceous sediments (Ryazanian – Hauterivian) of North-East Greenland (Möller et al., 2015). The outcome of this are extended stratigraphic ranges of two calcareous nannofossil index species (Sollasites arcuatus, Micrantholithus speetonensis), implying changes for the standard nannofossil zonation of the Boreal Lower Cretaceous.

Using the modified zonation scheme, the decline in abundance of the calcareous nannofossil genus Nannoconus in North-East Greenland documented by Pauly et al. (2012), is of early late Valanginian age and thus correlates with the global late Valanginian environmental perturbation, the Weissert Event. This nannoconid crisis, well known from the Tethys, had previously not been observed in the Boreal Realm. This first documentation of the Valanginian decline of Nannoconus spp. as far north as Greenland makes it a global event, not only limited to the Tethys. This finding illustrates necessity of a reliable integrated stratigraphic framework for paleoceanographic reconstructions.

Two coeval sediment successions of mid-Hauterivian age were dated based on calcareous nannofossils. The correlation made a paleoecological comparison of a marginal setting of the Lower Saxony Basin (LSB) and the basin center possible. Furthermore, previous biostratigraphic age assignments for the Gildehaus Sandstone Formation based on ammonites (Breyer and Lögters 1949; Kemper 1992) are modified based on the nannofossil data. Nannofossil biostratigraphy of the Emlichheim drill core suggests a late early Hauterivian age for the base of the formation (Möller and Mutterlose, 2014). The new biostratigraphic

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data verified the correlation of observations from outcrops of the Gildehaus sandstone with the subsurface findings from the Emlichheim drill core, previously solely based on lithological observations.

5.1.2. A model for environmental change during the Valanginian Weissert Event A decrease in size of Biscutum constans coccoliths was detected in the Valanginian paralleling the Weissert Event, an episode of environmental perturbation marked by a carbon isotope excursion. Similar darfig of B. constans has been observed during the Aptian Oceanic Anoxic Event 1a (OAE1a) and the Cenomanian/ Turonian Oceanic Anoxic Event 2 (OAE2; Fig. 5.1; Erba et al., 2010; Lübke and Mutterlose, 2016; Faucher et al., 2017). Each of these events coincides with a phase of intensive volcanism and is accompanied by a carbon isotope excursion. The potential causes for the B. constans size decreases currently under discussion, are (a) ocean acidification, (b) the injection of toxic trace metals into the ocean that affected phytoplankton productivity and inhibited coccolith formation, and (c) reduced light availability in the surface waters due to high rates of detrital input (Erba, 2004; Erba et al., 2010; Lübke et al., 2015; Lübke and Mutterlose, 2016; Faucher et al., 2017a, b; Möller et al., subm.). These repeated occurrences of small B. constans during episodes of environmental perturbation are striking. A model to explain the Valanginian B. constans size decrease should ideally be applicable to all three events.

In the case of the Valanginian environmental perturbation, ocean acidification is unlikely. The estimated

10 CO2 output rate of 2.5 x 10 kg/year of the coeval Paraná-Etendeka Large Igneous Province (LIP) is by one, respectively two orders of magnitude lower than the CO2 output during OAE1a and OAE2 (Dodd et al., 2015; Martinez et al., 2015). Modelling approaches suggest that ocean acidification occurs only when large amounts of CO2 are emitted in a short time period, probably <10,000 years (Ridgwell and Schmidt, 2010). High concentrations of hydrothermally derived toxic trace metals in the oceans during the Valanginian are also improbable. In contrast to the massive volcanic activity coinciding with OAE1a and OAE2 which formed gigantic submarine plateaus (Erba et al., 2015), there is no indication of substantial submarine volcanism during the Valanginian. The Paraná-Etendeka large igneous province, which was active during the Valanginian, is a continental flood basalt province.

For all three intervals under discussion, the mid-Valanginian, the OAE1a, and the OAE 2, there is evidence for increased humidity and chemical weathering (Blättler et al., 2011; Bottini et al., 2012; Mutterlose and Bottini, 2013; Pogge von Strandmann et al., 2013; Lechler et al., 2015; Lübke and Mutterlose, 2016). During all three intervals, the weathering regime is linked to high atmospheric CO2 concentrations due to volcanic

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Figure 5.1 Size variation of B. constans, Z. erectus and W. barnesiae during the Valanginian Weissert Event (Möller et al., subm.), the Aptian OAE 1a (Lübke et al., 2015), and the Cenomanian/ Turonian OAE 2 (Faucher et al., 2017).

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Figure 5.2 Box model of depth distribution of the calcareous nannofossil taxa Biscutum constans and Nannoconus spp., modified and extended after Lübke et al. (2015). (A) represents arid climate regime with relatively clear waters, stable stratification and a deep nutricline. These are favorable conditions for the deep dwelling nannoconids. In (B) climate is humid and weathering increased. High run-off transports large amounts of detrital material and nutrients into the ocean. These conditions resulted in high turbidity, a shallow nutricline, and break-down of water stratification, destroying the niche of Nannoconus spp. Reduced light availability was unfavorable for the large varieties of B. constans, while the small could adapt by shifting their habitat upwards in the water column. LP = lower euphotic zone, UP = upper euphotic zone. atiit. The redued light aailailitit-model of Lübke et al. (2015) thus potentially applies for all three events.

Both during the Weissert Event and the Aptian OAE1a, declining abundances of nannoconids coincide with the size decrease of B. constans (Erba et al., 2010; Möller et al., subm.). It can be conjectured that the nannoconid crisis and the dwarfing of B. constans are part of the same disruption of marine ecosystems. Nannoconids have been interpreted as deep-dwellers analogous to the modern Florisphaera profunda (Erba, 1994; Herrle, 2002). F. profunda is a modern nannolith species that is restricted to the lower euphotic zone (~150 to 200 m; Okada and Honjo, 1973), thriving in the oligotrophic stable conditions of open ocean settings, with high water transparenty, stable stratification, and a deep nutricline (e.g. Molfino and McIntyre, 1990; Ahagon et al., 1993; Andruleit and Rogalla, 2002; Malinverno et al., 2009; Grelaud et 132

Conclusions and perspectives al., 2012). The correlation of Lower Cretaceous nannoconid distribution and sedimentation patterns suggests ecologic preferences similar to those of F. profunda. In general, high relative abundances of Nannoconus spp. are found in pelagic limestones. Abundances are comparatively low in siliciclastic dominated sequences of epicontinental seas that were characterized by high detrital input (Möller et al., 2015; Möller et al., submit.). This distribution pattern supports the view that the success of nannoconids depended on clear waters and a stable deep nutricline (Mutterlose and Bottini, 2013; Möller et al., subm.).

Based on the redued light aailailitit-model, a scenario for environmental changes during the Valanginian can be developed that incorporates the nannoconid crisis and the dwarfing of B. constans (Fig. 5.2). When the Valanginian climate shifted towards increasingly humid conditions, a high rate of terrigenous input and increasing water turbidity made conditions unfavorable for the large morphological types of B. constans. The smaller varieties were adapted to lower light availability in deeper parts of the photic zone (Lübke et al., 2015). They persisted by shifting their habitat to shallower water depths, while the large morphotypes of B. constans were reduced in abundance. In the small epicontinental LSB, where rates of detrital input must have been extremely high, the larger B. constans vanished nearly completely during the onset of the Weissert Event (Möller et al., subm.). The high turbidity, possibly combined with a collapse of water stratification and increased nutrient concentration, nearly eliminated the niche occupied by Nannoconus spp., causing a decline of these species.

5.1.3. Paleoceanography of the Lower Saxony Basin in the Valanginian – Hauterivian The B. constans size minimum observed in the LSB reflects the important role of continent derived siliciclastic sedimentation for nearly completely landlocked epicontinental basins. High sedimentation rates are documented by up to 2000 m of marine clay- and siltstones of Early Cretaceous age in the LSB (Mutterlose and Bornemann, 2000). After brackish and fresh water conditions prevailing in the Berriasian, widespread transgressions in the early and in the early late Valanginian established permanently marine conditions (Mutterlose and Bornemann, 2000). This development is documented by the appearance and diversification of calcareous nannofossils. Calcareous nannofossils first appear in the LSB in the upper lower Valanginian, but their abundances and diversities remain very low up to the base of the upper Valanginian (Mutterlose, 1991; Möller et al., subm.).

Following the re-establishment of marine conditions, the LSB formed one of the few seaways between the Boreal Realm in the north and the Tethys in the south. The late Valanginian transgression was accompanied by an influx of Tethyan faunas and nannofloras (Mutterlose and Ruffel, 1999; Mutterlose 133

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and Bornemann, 2000). By the end of this transgressive phase in the early Hauterivian, however, the ammonite fauna was dominated by the endemic heteromorph genus Aegocrioceras (Mutterlose and Wiedenroth, 2009). Low abundances document unfavorable conditions for coccolithophores in the LSB during this time (Möller and Mutterlose, 2014).

The mid-Hauterivian is marked by the rapid replacement of the endemic ammonite fauna by Tethyan and Boreal taxa (Mutterlose and Wiedenroth, 2009). Warm humid conditions likely characterized this time, along with a basin-wide regression, during which the sandstone units of the Gildehaus Formation were deposited at the western margin of the LSB (Kemper, 1992; Mutterlose and Bornemann, 2000; Möller et al., 2014). The presence of nannofossils suggests a relatively pelagic depositional setting of the Gildehaus Sandstone, where the coarse siliciclastic probably represent a mass-flow deposit.

During the sea level lowstand at the lower/upper Hauterivian transition, nannofossils are very rare or absent in the marginal setting, indicating the basinward shift of the coastline. Nannofossil abundances in the corresponding clays of the basin center are high, probably corresponding to high nutrient concentrations. The presence of nannoconids, which are otherwise absent in the mid-Hauterivian of the LSB, indicates stable water stratification (Mutterlose, 1991; Möller and Mutterlose, 2014).

5.2. Perspectives Further investigations will provide a better understanding of the late Valanginian global environmental perturbation. The recognition of specific ecological factors which control the size of calcareous nannofossils may ultimately establish a new climate proxy.

To confirm that the B. constans size decrease is a global nannofossil event related to the Valanginian environmental perturbation, additional biometric data should be collected. The ecological implementations of global climate change depend on the latitude and the regional geographic as well as oceanographic situation. To be able to distinguish between global trends and regional factors, the sample localities should ideally cover a wide spectrum of marine settings, extending from coastal to open-oceanic, covering all latitudes.

Further research needs to test the role of environmental parameters which regulate the size evolution of calcareous nannofossils. To test the proposed light attenuation model, independent evaluation of humidity, weathering rate and detrital influx, productivity, and nutrient concentration is needed in correlation with biometric data. On the other hand, the feasibility of the alternative model based on toxic

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Conclusions and perspectives metals (Erba, 2004; Faucher et al, 2017a,b) should be tested as well. In the following, proxies that can provide information on these environment parameters are briefly discussed.

Composition of calcareous nannofossil assemblages

In pelagic settings the effect of weathering, runoff and detrital input is smaller than in nearshore settings, shelf settings, and epicontinental basins like the Vocontian Basin and the LSB. The B. constans size decrease in the north Atlantic open marine setting (Möller et al., subm.) may result from eutrophication, as suggested by high abundances of fertility-indicating nannofossil taxa. Quantitative analyses of calcareous nannofossil assemblages in addition to the biometric analyses can supply information about productivity levels related to higher nutrient concentration.

Phosphorous accumulation

As continental weathering is the main source of phosphorous for the ocean, phosphorous accumulation is a proxy for variations in weathering rates (Mackenzie et al., 1993; Föllmi, 1995). Phosphorous flux rates to the ocean can be estimated based on sedimentation rates and measured phosphorous contents (Föllmi, 1995). A rapid increase in phosphorous burial has been reconstructed for the Valanginian (Föllmi, 1995).

Clay mineralogy

Increases in moisture and/or temperature intensify weathering and leaching processes. Weathering is at a minimum where climate is either cold or dry (Weaver, 1989). The amount as well as the type of clay minerals formed is related to precipitation rates. Clay mineral analyses of the Valanginian of the Vocontian Basin document intensified hydrolytic weathering and an increase of detrital input in the late Valanginian (Duchamp-Alphonse et al., 2011). Obtaining clay mineral data along with nannofossil biometry could give evidence for a connection between size trends and input of detrital material.

Spore/ pollen data

Data on spore and pollen assemblages in marine sediments can be used to reconstruct continental vegetation structures and thus trace climate changes. Spore and pollen data from Poland and France 135

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document a trend towards a humid climate in the Valanginian (Kujau et al., 2013). Obtaining additional data sets could reveal latitudinal differences and answer, whether this humid climate phase is of regional, trans-regional, or global significance.

Trace metal concentrations

Enhanced submarine volcanism is thought to have changed ocean chemistry during the mid-Cretaceous (e.g., Vogt, 1989; Larson and Erba, 1999). Minor and trace element concentrations of whole rock samples might reveal enrichment in trace metals associated with hydrothermal activity. Normalization to Zr concentrations can be used to remove the effect of variations in terrigenous input (Snow et al., 2005). Metal abundance anomalies can give evidence for an influence of ocean chemistry on marine phytoplankton (Faucher et al., 2017a).

5.3. References Ahagon, N., Y. Tanaka, and H. Ujiie (1993), Florisphaera profunda, a possible nannoplankton indicator of late Quaternary changes in sea-water turbidity at the northwestern margin of the Pacific, Marine Micropaleontology, 22(3), 255–273. Andruleit, H., and U. Rogalla (2002), Coccolithophores in surface sediments of the Arabian Sea in relation to environmental gradients in surface waters, Marine Geology, 186(3), 505–526. Blättler, C. L., H. C. Jenkyns, L. M. Reynard, and G. M. Henderson (2011), Significant increases in global weathering during Oceanic Anoxic Events 1a and 2 indicated by calcium isotopes, Earth and Planetary Science Letters, 309(1–2), 77–88, doi:10.1016/j.epsl.2011.06.029. Bottini, C., A. S. Cohen, E. Erba, H. C. Jenkyns, and A. L. Coe (2012), Osmium-isotope evidence for volcanism, weathering, and ocean mixing during the early Aptian OAE 1a, Geology, 40(7), 583–586. Breyer, F., and H. Lögters (1949), Georgsdorf, ein Ölfeld im Emsland, in Erdöl und Tektonik in Nordwestdeutschland, pp. 257–275, Hannover, Celle. Duchamp-Alphonse, S., N. Fiet, T. Adatte, and M. Pagel (2011), Climate and sea-level variations along the northwestern Tethyan margin during the Valanginian C-isotope excursion: Mineralogical evidence from the Vocontian Basin (SE France), Palaeogeography, Palaeoclimatology, Palaeoecology, 302(3– 4), 243–254, doi:10.1016/j.palaeo.2011.01.015. Era, E. , Naofossils ad superplues: The Earl Aptia aooid risis, Paleoceanography, 9(3), 483–501, doi:10.1029/94PA00258. Erba, E. (2004), Calcareous nannofossils and Mesozoic oceanic anoxic events, Marine Micropaleontology, 52(1–4), 85–106, doi:10.1016/j.marmicro.2004.04.007.

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Erba, E., C. Bottini, H. J. Weissert, and C. E. Keller (2010), Calcareous Nannoplankton Response to Surface- Water Acidification Around Oceanic Anoxic Event 1a, Science, 329(5990), 428–432, doi:10.1126/science.1188886. Erba, E., R. A. Duncan, C. Bottini, D. Tiraboschi, H. Weissert, H. C. Jenkyns, and A. Malinverno (2015), Environmental consequences of Ontong Java Plateau and Kerguelen Plateau volcanism, in Geological Society of America Special Papers, vol. 511, pp. 271–303, Geological Society of America. Faucher, G., E. Erba, C. Bottini, and G. Gambacorta (2017a), Calcareous nannoplankton response to the latest Cenomanian Oceanic Anoxic Event 2 perturbation, Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy), 123(1). Faucher, G., L. Hoffmann, L. T. Bach, C. Bottini, E. Erba, and U. Riebesell (2017b), Impact of trace metal concentrations on coccolithophore growth and morphology: laboratory simulations of Cretaceous stress, Biogeosciences Discussions, 1–24, doi:10.5194/bg-2017-138. Föllmi, K. B. (1995), 160 m.y. record of marine sedimentary phosphorus burial: Coupling of climate and continental weathering under greenhouse and icehouse conditions, Geology, 9(23), 859–862. Grelaud, M., G. Marino, P. Ziveri, and E. J. Rohling (2012), Abrupt shoaling of the nutricline in response to massive freshwater flooding at the onset of the last interglacial sapropel event: SHOALING OF THE NUTRICLINE DURING S5, Paleoceanography, 27(3), n/a-n/a, doi:10.1029/2012PA002288. Herrle, J. O. (2003), Reconstructing nutricline dynamics of mid-Cretaceous oceans: evidence from calcareous nannofossils from the Niveau Paquier black shale (SE France), Marine Micropaleontology, 47(3), 307–321. Kemper, E. (1992), Die tiefe Unter-Kreide im Vechte-Dinkel Gebiet, Losser. Kujau, A., U. Heimhofer, P. A. Hochuli, S. Pauly, C. Morales, T. Adatte, K. Föllmi, I. Ploch, and J. Mutterlose (2013), Reconstructing Valanginian (Early Cretaceous) mid-latitude vegetation and climate dynamics based on spore–pollen assemblages, Review of Palaeobotany and Palynology, 197, 50–69, doi:10.1016/j.revpalbo.2013.05.003. Larson, R. L., and E. Erba (1999), Onset of the mid-Cretaceous greenhouse in the Barremian-Aptian: Igneous events and biological, sedimentary, and geochemical responses, Paleoceanography, 6(14), 663–678. Lechler, M., P. A. E. Pogge von Strandmann, H. C. Jenkyns, G. Prosser, and M. Parente (2015), Lithium- isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event), Earth and Planetary Science Letters, 432, 210–222, doi:10.1016/j.epsl.2015.09.052. Lübke, N., and J. Mutterlose (2016), The impact of OAE 1a on marine biota deciphered by size variations of coccoliths, Cretaceous Research, 61, 169–179, doi:10.1016/j.cretres.2016.01.006. Lübke, N., J. Mutterlose, and C. Bottini (2015), Size variations of coccoliths in Cretaceous oceans — A result of preservation, genetics and ecology?, Marine Micropaleontology, 117, 25–39, doi:10.1016/j.marmicro.2015.03.002. Mackenzie, F. T., L. M. Ver, C. Sabine, M. Lane, and A. Lerman (1993), C,N,P,S global biogeochemical cycles and modeling of global change, in Interactions of C,N,P and S biogeochemical cycles and global change, edited by Rland Wollast, Fred T. Mackenzi and Lei Chou, pp. 1–61, Springer Verlag, Berlin.

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Malinverno, E., M. V. Triantaphyllou, S. Stavrakakis, P. Ziveri, and V. Lykousis (2009), Seasonal and spatial variability of coccolithophore export production at the South-Western margin of Crete (Eastern Mediterranean), Marine Micropaleontology, 71(3–4), 131–147, doi:10.1016/j.marmicro.2009.02.002. Molfino, B., and A. McIntyre (1990), Precessional forcing of nutricline dynamics in the Equatorial Atlantic., Science(Washington), 249(4970), 766–769. Möller, C., and J. Mutterlose (2014), Middle Hauterivian biostratigraphy and palaeoceanography of the Lower Saxony Basin (Northwest Germany), Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, doi:10.1127/1860-1804/2014/0084. Möller, C., A. Bornemann, and J. Mutterlose (submitted to Paleoceanography), Size changes of calcareous nannofossils and the nature of the Weissert Event (Early Cretaceous), Möller, C., J. Mutterlose, and P. Alsen (2015), Integrated stratigraphy of Lower Cretaceous sediments (Ryazanian–Hauterivian) from North-East Greenland, Palaeogeography, Palaeoclimatology, Palaeoecology, 437, 85–97, doi:10.1016/j.palaeo.2015.07.014. Mutterlose, J. (1991), Das Verteilungs- und Migrationsmuster des kalkigen Nannoplanktons in der Unterkreide (Valangin–Apt) NW-Deutschlands, Palaeontographica Abteilung B, (221), 27–152. Mutterlose, J., and A. Bornemann (2000), Distribution and facies patterns of Lower Cretaceous sediments in northern Germany: a review, Cretaceous Research, 21(6), 733–759, doi:10.1006/cres.2000.0232. Mutterlose, J., and C. Bottini (2013), Early Cretaceous chalks from the North Sea giving evidence for global change, Nature Communications, 4, 1686, doi:10.1038/ncomms2698.

Mutterlose, J., and A. Ruffell (1999), Milankovitch-scale palaeoclimate changes in pale–dark bedding rhythms from the Early Cretaceous (Hauterivian and Barremian) of eastern England and northern Germany, Palaeogeography, Palaeoclimatology, Palaeoecology, 154(3), 133–160. Mutterlose, J., and K. Wiedenroth (2009), Neue Tagesaufschlüsse der Unter-Kreide (Hauterive–Unter-Apt) im Gro\s sraum Hannover–Braunschweig: Stratigraphie und Faunenführung, Berliner paläobiologische Abhandlungen, 10, 257–288. Okada, H., and S. Honjo (1973), The distribution of oceanic coccolithophorids in the Pacific, Deep-Sea Research, 20, 355–374. Pauly, S., J. Mutterlose, and P. Alsen (2012), Early Cretaceous palaeoceanography of the Greenland– Norwegian Seaway evidenced by calcareous nannofossils, Marine Micropaleontology, 90–91, 72–85, doi:10.1016/j.marmicro.2012.04.004. Pogge von Strandmann, P. A. E., H. C. Jenkyns, and R. G. Woodfine (2013), Lithium isotope evidence for enhanced weathering during Oceanic Anoxic Event 2, Nature Geoscience, 6(8), 668–672, doi:10.1038/ngeo1875. Ridgwell, A., and D. N. Schmidt (2010), Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release, Nature Geoscience, 3(3), 196–200, doi:10.1038/ngeo755. Snow, L. J., R. A. Duncan, and T. J. Bralower (2005), Trace element abundances in the Rock Canyon Anticline, Pueblo, Colorado, marine sedimentary section and their relationship to Caribbean plateau construction and oxygen anoxic event 2: OAE2 LINKED TO HYDROTHERMAL ACTIVITY, Paleoceanography, 20(3), n/a-n/a, doi:10.1029/2004PA001093.

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Vogt, P. R. (1989), Volcanogenic upwelling of anoxic, nutrient-rich water: A possible factor in carbonate- bank/reef demise and benthic faunal extinctions?, Geological Society of America Bulletin, 101(10), 1225–1245. Weaver, C. E. (1989), Clays, Muds and Shales, Elsevier, Amsterdam.

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6 Taxonomic Index

Calcareous nannoplankton

Alisphaera Heimdal 1973

Biscutum constans (Górka 1957) Black in Black and Barnes 1959

Braarudosphaera Deflandre 1947

Braarudosphaera bigelowii (Gran and Braarud 1935) Deflandre 1947

Bukrylithus ambiguus Black 1971a

Calcidiscus leptoporus (Murray and Blackman 1898) Loeblich and Tappan 1978

Calciosolenia Gran 1912

Calculites Prins and Sissingh in Sissingh 1977

Ceratolithus Kamptner 1950

Clepsilithus maculosus Rutledge and Bown 1996

Coccolithus Schwarz 1894

Coccolithus pelagicus (Wallich 1877) Schiller 1930

Conusphaera rothii (Thierstein, 1971) Jakubowski 1986

Cretarhabdus Bramlette and Martini 1964

Cretarhabdus conicus Bramlette and Martini 1964

Cretarhabdus inaequalis Crux 1987

Crucibiscutum Jakubowski 1986

Crucibiscutum salebrosum (Black 1971a) Jakubowski 1986

Crucibiscutum ryazanicum Jeremiah, 2001

Cruciellipsis cuvillieri (Manivit 1966) Thierstein 1971

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Taxonomic Index

Chrysochromulina parkae Green and Leadbeater 1972

Cyclagelosphaera Noёl 1965

Cyclagelosphaera margerelii Noël 1965

Cyclagelosphaera rotaclypeata Bukry 1969

Diazomatolithus lehmannii Noël 1965

Diloma galiciense Bergen 1994

Discorhabdus ignotus (Górka 1957) Perch-Nielsen 1968

Eiffellithus striatus (Black 1971a) Applegate and Bergen 1988

Eiffellithus windii Applegate and Bergen 1988

Emiliania huxleyi (Lohmann 1902) Hay and Mohler, in Hay et al. 1967

Eprolithus antiquus Perch-Nielsen 1979a

Florisphaera profunda Okada and Honjo 1973

Gephyrocapsa oceanica Kamptner 1943

Hemipodorhabdus gorkae (Reinhardt 1969) Grün in Grün and Allemann 1975

Hymenomonmas carterae (Braarud and Fagerland) Braarud 1954

Micrantholithus speetonensis Perch-Nielsen 1987

Nannoconus Kamptner 1931

Nannoconus bucheri Brönnimann 1955

Percivalia fenestrata (Worsley 1971) Wise 1983

Perissocyclus Black 1971a

Perissocyclus plethotretus, Crux 1989

Perissocyclus tayloriae Crux 1989

Pickelhaube furtiva (Roth 1983) Applegate et al. in Covington and Wise 1987

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Repagulum parvidentatum (Deflandre & Fert 1954) Forchheimer 1972

Retecapsa angustiforata Black 1971

Retecapsa surirella (Deflandre and Fert 1954) Grün in Grün and Allemann 1975

Rhagodiscus asper (Stradner 1963) Reinhardt 1967

Rotelapillus laffittei Noël 1973

Schizosphaerella Deflandre and Dangeard 1938

Sollasites arcuatus Black 1971a

Staurolitithes Caratini 1963

Staurolitithes mutterlosei Crux 1989

Staurolitithes quadriarcullus (Noël 1965) Wilcoxon 1972

Stradnerlithus geometricus (Górka 1957) Bown and Cooper 1989a

Stradnerlithus silvaradius Filewicz et al. in Wind and Wise 1977

Syracolithus quadriperforatus (Kamptner 1937) Gaarder in Heimdal and Gaarder 1980

Tegulalithus septentrionalis (Stradner 1963) Crux 1986

Tegumentum octiformis (Köthe 1981) Crux 1989

Triquetrorhabdulus shetlandensis Perch-Nielsen 1988

Watznaueria Reinhardt 1964

Watznaueria barnesiae (Black 1959) Perch-Nielsen 1968

Watznaueria fasciata Wind and Cepek 1979

Watznaueria fossacincta (Black 1971) Bown in Bown and Cooper 1989

Zeugrhabdotus Reinhardt 1965

Zeugrhabdotus erectus (Deflandre in Deflandre and Fert 1954) Reinhardt 1965

Zeugrhabdotus scutula (Bergen 1994) Rutledge and Bown 1996

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Taxonomic Index

Palynomorphs/ Dinoflagellate cysts

Oligosphaeridium complex (White 1842) Davey and Williams 1966

Foraminifera

Globigerina d’Orig

Ammonites

Acanthodiscus Uhlig 1905

Acanthodiscus radiatus (Buguière 1789)

Aegocrioceras Spath 1924

Aegocrioceras capricornu (Roemer, 1841)

Busnardoites campylotoxus

Crioceratites Léveillé 1837

Dichotomites Koenen 1909

Dichotomites crassus, Kemper 1978

Endemoceras Thiermann 1963

Endemoceras amblygonium (Neumayr & Uhlig 1881)

Endemoceras noricum (Roemer 1836)

Endemoceras regale (Pavlow 1892)

Paratollia Casey 1973

Peregrinoceras Sazonova 1971

Peregrinoceras albidum Casey 1973

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Platylenticeras Hyatt 1900

Polyptychites Pavlow 1892

Polyptychites michalskii (Bogoslowsky 1902)

Saynoceras Munier-Chalmas 1894

Saynoceras verrucosum (D'Orbigny 1841)

Simbirskites Pavlow 1892

Simbirskites (Milanowskia) concinnus (Phillips 1829)

Simbirskites (Craspedodiscus) gottschei Koenen 1904

Simbirskites (Speetoniceras) inversum (Pavlow 1886)

Simbirskites marginatus (Phillips 1829)

Simbirskites (Milanowskia) speetonensis (Young & Bird 1828)

Simbirskites (Milanowskia) staffi Wedekind 1910

Simbirskites variabilis Rawson 1971

Spitidiscus Kilian 1910

Subsaynella sayni (Paquier 1900)

Tirnovella pertransiens (Sayn 1901)

Belemnites

Acrotheutis Stolley 1911

Cylindrotheutis Bayle 1878

Hibolithes Montfort 1808

Hibolithes jaculoides Swinnerton 1936

Pachytheutis Bayle 1878

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Curriculum vitae

7 Curriculum Vitae

Carla Möller

Born on June 1, 1986 in Dortmund

Education

June 2017 Completion of the PhD

Since 2013 PhD student and member of the scientific staff in the working group paleontology of

Prof. Jörg Mutterlose, Faculty of Geosciences, Ruhr-Universität Bochum

2006 - 2012 Studies of geosciences at the Ruhr-Universität Bochum

Graduation as Bachelor and Master of Science

Master thesis „The Aptia-Albian Sediments of the Agadir Basin (SW Morocco): “edietolog, Biostratigraph ad Geoheistr

Bahelor thesis: Metastaile Vorläuferphase ei der )eolith-“these

1996 – 2005 Secondary school (Käthe Kollwitz Gymnasium, Dortmund) 1992 -1996 Primary school (St. Franziskus Grundschule, Dortmund)

Publications

Möller, C., Bornemann, A., Mutterlose, J., submitted. Size changes of calcareous nannofossils and the nature of the Weissert Event (Early Cretaceous).

Möller, C., Mutterlose, J., Alsen, P., 2015. Integrated stratigraphy of Lower Cretaceous sediments (Ryazanian-Hauterivian) from North-East Greenland. Palaeogeography, Palaeoclimatology, Palaeoecology 437, 85-97.

Möller, C., Mutterlose, J., 2014. Middle Hauterivian biostratigraphy and palaeoceanography of the Lower Saxony Basin (Northwest Germany). Zeitschrift der Deutschen Gesellschaft für Geowissenschaften (German Journal of Geosciences) 165, 501-520.

Conference contributions

Möller C., Heimhofer, U., Mutterlose, J., 2016. Calcareous nannofossil response to ecosystem changes during the Valanginian Event. Jahrestagung der Palaontologischen Gesellschaft 2016, Dresden. 145

Möller, C., Mutterlose, J., Alsen, P., 2015: Integrated stratigraphy of Lower Cretaceous sediments (Ryazanian - Hauterivian) from North-East Greenland: Refining the calcareous nannofossil zonation for the Boreal. 2nd International Congress on Stratigraphy 2015, Graz, Austria.

Möller C., Mutterlose, J., Heimhofer, U., 2015. Calcareous nannofossil response to the Valanginian Weissert event in a Boreal epicontinental sea. 15th International nannoplankton Association Meeting 2015, Bohol Island, Philippines.

Möller, C., Mutterlose, J., 2014. Paleoceanographic reconstruction of an Early Cretaceous (Hauterivian) basin - „proial ersus „distal alareous aofossil asselages. GeoFrakfurt , Frakfurt.

Möller, C., Mutterlose, J., 2014. Paleoceanographic reconstruction of an Hauterivian basin - „proial ersus „distal alareous aofossil asselages. The Micropaleontological Society spring meeting 2014, Texel, Netherlands.

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