Carbon Cycle Changes During the Triassic-Jurassic Transition

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Carbon cycle changes during the Triassic-Jurassic transition

Micha Ruhl Micha Ruhl

Palaeoecology Institute of Environmental Biology Laboratory of Palaeobotany and Palynology Utrecht University

Budapestlaan 4 3584 CD Utrecht the Netherlands

ISBN: 978-90-393-5270-0 NSG publication number: 20100126 LPP Contribution Series 28

Cover-design: Micha Ruhl Printed by GVO drukkers & vormgevers B.V. | Ponsen & Looijen, Ede Carbon cycle changes during the Triassic-Jurassic transition

Koolstofkringloop veranderingen gedurende de Trias-Jura overgang

(met een samenvatting in het Nederlands)

Proefschrift ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus, prof. dr. J.C. Stoof, ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op dinsdag 26 januari 2010 des ochtends te 10.30 uur

door Micha Ruhl

geboren op 16 april 1980 te Horn Promotor: Prof. dr. A.F. Lotter Co-promotor: Dr. W.M. Kürschner

The research reported in this thesis was funded by the High Potential program of Utrecht University. The printing of this thesis was financially supported by LAMERS TOOLING BV.

Contents

General Introduction and Synopsis 9

Chapter 1 Triassic-Jurassic organic carbon isotope stratigraphy of 15 key sections in the western Tethys realm (Austria) Ruhl, M., Kürschner, W.M., Krystyn, L. Earth and Planetary Science Letters 281 (2009) 169-187

Chapter 2 Climate change driven black shale deposition during the 31 end-Triassic in the western Tethys Bonis, N.R., Ruhl, M., Kürschner, W.M. Palaeogeography, Palaeoclimatology, Palaeoecology (in press)

Chapter 3 Sedimentary organic matter characterization of the 47 Triassic-Jurassic boundary GSSP at Kuhjoch (Austria) Ruhl, M., Veld, H., Kürschner, W.M. Earth and Planetary Science Letters (in review)

Chapter 4 Atmospheric methane injection caused end-Triassic mass 63 extinction Ruhl, M., Bonis, N.R., Reichart, G.-J., Sinninghe Damsté, J.S., Kürschner, W.M. (submitted)

Chapter 5 Astronomical constraints on the duration of the early 75 Jurassic Hettangian stage and recovery rates following the end-Triassic mass extinction (St. Audrie’s Bay/East Quantoxhead, UK) Ruhl, M., Deenen, M.H.L., Abels, H.A., Bonis, N.R., Krijgsman, W., Kürschner, W.M. Earth and Planetary Science Letters (in review)

Chapter 6 Multiple late Triassic carbon cycle perturbation observed 97 in continental and marine C-isotope records from the western Tethys (Austria) and NW European sections (UK and Germany) Ruhl, M., Kürschner, W.M. (submitted)

References 107

General Introduction and Synopsis in Dutch 121

Acknowledgements 129

Curriculum Vitae 133

Publications 137

Appendices 138

General Introduction

The cumulative anthropogenic release of up to 5000 Gt of carbon to the atmosphere and oceans in the coming centuries, may have a large influence on earths climate and biosphere (Caldeira and Wickett, 2003; Allen et al., 2009). The magnitude of projected future climate changes depends on often poorly constrained feedback mechanisms. Understanding boundary conditions for climate change in response to anthropogenic greenhouse gas emissions is necessary to ensure a relatively stable state of the Earth system (Rockström et al., 2009). Geological history is marked by multiple (major) carbon cycle perturbations, often in concurrence with climate change and biodiversity loss. In the past several thousands of years, mankind experienced only relatively minor environmental changes. Larger changes in climate did occur in the course of human evolution, during the Pleistocene (Hays et al., 1976). Time intervals with similar carbon emissions as today may however have only occurred tens to hundreds of million years ago. Understanding the potential causal relation between former climate change and massive carbon release, may allow for better predictions of future environmental changes. Studying these time intervals is of particular importance for understanding the mechanisms behind changes in climate and the carbon cycle and their effects on ecosystem evolution, species composition and the rate of biotic origination. Causes of extinction events have varied, but understanding of the underlying mechanisms may provide vital insight in the causes and effects of current (man-induced) biodiversity loss (Sala et al., 2000).

The study presented in this thesis is part of a multi-proxy project “Earth’s and Life’s History: From Core To Biosphere (CoBi)”, aiming to better constrain the causes, relative timing and mutual relation between changes in terrestrial and marine ecosystems and the global carbon cycle during the Triassic-Jurassic transition and especially the end- Triassic mass extinction interval (~201.5 Ma; Schaltegger et al., 2008).

The late Triassic has often been regarded as one of five major mass extinctions of the Phanerozoic (Raup and Sepkoski, 1982; Benton, 1995). In contrast to the sudden and catastrophic extinction event at the Cretaceous-Paleogene boundary, which is ascribed to a celestial bolide impact (Smit and Hertogen, 1980; Smit and ten Kate, 1982), late Triassic extinctions extended over several million years (Tanner et al., 2004; Kiessling et al., 2007; Kürschner and Herngreen, in press). Extinctions culminated in the end-Triassic, with marine and continental extinctions (e.g. ammonites (Guex et al., 2004), bivalves (McRoberts and Newton, 1995), radiolaria (Ward et al., 2001) and Theropod dinosaurs (Olsen et al., 2002)) and marine and terrestrial assemblage changes (e.g. dinoflagellates and foraminifera (Hesselbo et al.,

9 General Introduction and Synopsis

2002) and vegetation (Kürschner et al., 2007; Bonis et al., 2009, McElwain et al., 2009)). Although the end-Triassic mass extinction provides an eminent case history of global biosphere turnover, current concepts differ with respect to its cause (celestial versus terrestrial). A bolide impact was suggested after the discovery of an iridium anomaly in co-occurrence with a fern spike (Olsen et al., 2002). Supportive evidence such as shocked quartz grains and impact structures is however lacking (Tanner et al., 2004). The onset of massive volcanism and large-scale flood basalt outflow is often tentatively related to mass extinction intervals (Wignall, 2001; Courtillot and Renne, 2003). Large Igneous Province (LIP) emplacement in the Central Atlantic Magmatic Province (CAMP), likely related to the initial break up of Pangea (Olsen, 1997), possibly resulted in major influxes of CO2 and SO2 and consequent greenhouse warming, poisoning of ecosystems and marine anoxia (Beerling and Berner, 2002; Wignall et al., 2007; van de Schootbrugge et al., 2009). The timing and duration of CAMP eruptions are however still controversial (Marzoli et al., 2004; Marzoli et al., 2008; Whiteside et al., 2007; Whiteside et al., 2008). Fundamental questions about causes and causal relationships between end-Triassic global biotic turnovers, global changes in biogeochemical cycles and climate change are still debated.

GSSP for the base of the Jurassic System

In contrast to pre- and succeeding mass extinction events, attention for the end-Triassic extinction interval increased only more recently, when more boundary sections were discovered and available for study. The Triassic-Jurassic boundary is therefore one of the very last period boundaries to be allocated by the International Commission on Stratigraphy, to a Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic system. In the past few years and during the course of this research there has been ongoing discussion on appropriate criteria for the marker of the base of the Jurassic. A distinct negative Carbon Isotope Excursion (CIE) has now been extensively documented in the Eiberg Basin (chapter 1) and elsewhere and it can be regarded as a global phenomenon (chapter 4). It coincides with the extinction interval and was one of the proposed boundary markers. However, the first occurrence (FO) of the ammonite Psiloceras spelae was also proposed (Hillebrandt et al., 2007) and chosen as marker for the base of the Jurassic. Two subspecies of this ammonite, P. spelae spelae and P. spelae tirolicum (Hillebrandt and Krystyn, 2009), have their FO more or less simultaneously in New York Canyon (Panthalassic Ocean) and the Eiberg Basin (western Tethys Ocean), respectively. The Kuhjoch section in the Eiberg Basin was proposed (Hillebrandt et al., 2007) and ultimately accepted as GSSP for the base of the Jurassic. This section has been extensively studied during the course of this project (Bonis et al., 2009; Ruhl et al., 2009) and some of the data are discussed in chapters 1, 2, 3 and 4 of this thesis.

10 General Introduction and Synopsis

Synopsis

The end-Triassic extinction interval provides an eminent case-study for understanding potential causal relationships between carbon release, climate change and biodiversity loss/ecosystem changes. The study presented in this thesis mainly focuses on global carbon cycle changes at the Triassic-Jurassic transition. These reflect changes in flux sizes between the exogenic exchangeable carbon reservoirs (e.g. atmosphere, oceans, standing biota). In steady-state, the exogenic carbon pool is marked by constant flux and reservoir sizes and a fixed carbon retention time for each reservoir. Potential changes in these parameters may alter the relative abundance of 13C and 12C stable isotopes in each reservoir, which is reflected by marked perturbations in C-isotope proxy records. Carbon can also be transferred to the exogenic carbon pool from external reservoirs with a different isotopic signature (e.g. the mantle/crust). Both processes potentially caused global C-cycle changes at the T-J transition. This study aims to reconstruct the magnitude and nature of global carbon cycle changes in this time interval, to shed light on possible causes and consequences. It combines chemo- and biostratigraphy to reconstruct global carbon cycle perturbations in a high resolution biostratigraphic framework and explores the potential use of C-isotope proxy records for high resolution stratigraphic correlation in this time interval. Furthermore, it examines the relative timing of events coinciding with and after the end- Triassic biotic turnover and palaeoenvironmental changes.

Chapter 1: Triassic-Jurassic organic carbon isotope stratigraphy of key sections in the western Tethys realm (Austria), explores the potential use of C-isotope records as high resolution correlation proxy for the Triassic-Jurassic boundary interval. The T-J boundary interval is, in several marine basins in the world, marked by a distinct negative excursion in C-isotope records coincident with the end-Triassic mass extinction (Palfy et al., 2001; Hesselbo et al., 2002; Guex et al., 2004; Ward et al., 2004; Galli et al., 2005; Galli et al., 2007; Ward et al., 2007; Wignall et al., 2007; Williford et al., 2007). The magnitude of the observed excursions and their position relative to biostratigraphic markers, however, varies. In this chapter, we present eight new high resolution organic C-isotope records from the Eiberg Basin (Northern Calcareous Alps, Austria) including the GSSP for the base of the Jurassic. We show that these records are marked by a distinct negative Carbon Isotope Excursion (CIE) coincident with the extinction interval and a second negative shift at the base of the Jurassic. The data presented in this chapter suggest that high resolution C-isotope records are an excellent correlation proxy for the studied time interval in the Eiberg Basin.

Chapter 2: Climate change driven black shale deposition during the end- Triassic in the western Tethys, integrates high resolution geochemical and biological proxy data from several sections in the western Tethys Eiberg basin, including Kuhjoch, the GSSP for the base of the Jurassic. This chapter mainly focuses on an end-Triassic time interval coinciding with the negative CIE. We propose a model in which increased

11 General Introduction and Synopsis

terrestrial organic matter influx is related to an enhanced hydrological cycle and increased erosion of the hinterland. Reduced salinity of the surface waters possibly led to the mass occurrence of green algae. Stratification of the water column may have caused anoxic bottom water conditions and black shale deposition in concurrence with the end-Triassic negative CIE and environmental crisis.

Chapter 3: Sedimentary organic matter characterization of the Triassic- Jurassic boundary GSSP at Kuhjoch (Austria), focuses on end-Triassic black shale formation in the western Tethys Eiberg Basin. In this chapter we present integrated geochemical, stable isotope and palynological data. We show that the end-Triassic negative CIE is marked by only minor changes in kerogen type, which is mainly of 13 terrestrial origin. This suggests genuine changes in the δ CTOC composition reflecting true disturbances of the global C-cycle. We discuss potential palaeoenvironmental causes and mechanisms leading to end-Triassic black shale formation.

Some of the major unresolved questions regarding the end-Triassic extinction interval are related to its cause. In chapter 4: Atmospheric methane injection caused end- Triassic mass extinction, we investigate the reality of a global C-cycle turnover and potential causal relations to climate change, biotic extinctions and terrestrial ecosystem changes. The magnitude of the T-J carbon cycle perturbation, based on compound- specific carbon-isotope (δ13C) measurements of long-carbon-chain n-alkanes derived from epicuticular waxes of land plants, suggests that previous explanations based on enhanced volcanism no longer provide a feasible mechanism. The magnitude and rate of change in δ13C implies that 13C depleted carbon was most likely transferred from the methane-hydrate reservoir to the atmosphere and oceans. We show that the end-Triassic C-cycle perturbation coincides with a strong warming event and enhanced hydrological cycling. Hence, the data presented in this chapter may confirm the causal link between massive methane release, climate change and the extinction event at the T-J boundary interval.

An accurate chronology of events at the T-J transition is necessary for understanding mechanisms and causal relationships leading to the end-Triassic environmental crisis and subsequent early Jurassic origination events. In chapter 5: Astronomical constraints on the duration of the early Jurassic Hettangian stage and recovery rates following the end-Triassic mass extinction (St. Audrie’s Bay/East Quantoxhead, UK), we present high resolution physical and chemical proxy data and field observations, covering the uppermost Triassic and lower Jurassic. We construct a floating astronomical time-scale of ~2.5 Myr, based on recognition of ~100-kyr eccentricity cycles in limestone and black shale predominance and chemical proxy-records. Individual black shales are interpreted to reflect precession-controlled changes in monsoon intensity. On the basis of these findings, we constrain the duration of the Hettangian stage and Hettangian ammonite zones and the duration of the end-Triassic extinction and subsequent recovery interval. Cyclostratigraphic correlation to the astronomically tuned Geomagnetic Polarity Time-Scale of the continental Newark Basin (eastern USA), allows to locate the stratigraphic position of the T-J and Hettangian-Sinemurian boundary in the continental

12 General Introduction and Synopsis

13 realm. We discuss continuously low δ CTOC values throughout the Hettangian and early Sinemurian succeeding volcanic activity in the Central Atlantic Magmatic province, which may reflect long-term changes in earths global biogeochemical cycles.

Extinction levels did however not only increase in importance in the uppermost Rhaetian. The late Triassic (Carnian, Norian and Rhaetian stages) is already marked by enhanced biodiversity loss in both the marine and terrestrial realm. In order to explore potential causal relationships between C-cycle perturbations and biotic turnovers, we studied a Rhaetian time interval in sections from NW Europe and the western Tethys realm. In chapter 6: Multiple late Triassic carbon cycle perturbations observed in continental and marine C-isotope records from the western Tethys (Austria) and NW European sections (UK and Germany), we show that the end-Triassic negative CIE is preceded by two Rhaetian negative excursions in marine and continental 13 δ CTOC records from Germany and the Northern Calcareous Alps. A coinciding negative CIE in a δ13C leave-record suggests 13C depletion of the late Triassic atmosphere and oceans. Oxidation of organic carbon by subsurface thermal metamorphism of organic rich strata may be one potential mechanism to transfer isotopically light carbon to the exogenic carbon pool.

Concluding remarks The research presented in this thesis shows that the end- 13 Triassic negative perturbation in several δ CTOC records from the western Tethys Eiberg Basin occurs simultaneously, relative to biostratigraphic markers. Correlation of C-isotope records from different sedimentary basins suggests that this negative perturbation should be considered as a global event, representing changes in the global carbon cycle by release of 13C depleted carbon to the end-Triassic atmosphere. The large-scale release of carbon provoked a range of climatic and environmental changes, including greenhouse warming, changes in the hydrological cycle and stratification of the watercolumn in (at least) marginal basins. It is the likely direct and indirect cause of the end-Triassic mass extiction event in the marine realm and the ecosystem changes on the continents. Astronomical constraints on the duration of the mass extinction and subsequent recovery events suggest that increased volcanic activity is an unlikely sole cause of end-Triassic C-cycle changes. It probably only triggered the rapid and massive release of carbon from methane hydrates. This mechanisms better explains the observed changes in the global carbon cycle and causal relationships to the end-Triassic mass extinction event.

Future research Quantification of atmospheric-CO2 and absolute temperature changes are critical for understanding causal relationships between end-Triassic carbon release and global temperature evolution. It allows to study climate sensitivity changes under already high atmospheric-CO2 conditions. Terrestrial and marine biomarker studies potentially enable a range of palaeoenvironmental reconstructions (including marine anoxia), in relation to climate change and the end-Triassic mass extinction event. The study of continental and marine T-J boundary sections from different palaeolatitudes will provide better constraints on end-Triassic global climate change. Deeper marine sections potentially allow to reconstruct the effect of increased carbon release and subsequent climate change, on oceanographic conditions and global biogeochemical cycles.

13 14 Chapter 1

Triassic–Jurassic organic carbon isotope stratigraphy of key sections in the western Tethys realm (Austria)

The late Triassic period is recognized as one of the five major mass extinctions in the fossil record. All these important intervals in earth history are associated with excursions in C-isotope records thought to have been caused by perturbations in the global carbon cycle. The nature and causes of C-isotopic events across the Triassic–Jurassic (T–J) transition however, are poorly understood. We present several new high resolution organic C-isotope records from the Eiberg Basin, Austria, including the proposed Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic. The Triassic– Jurassic boundary interval in these records is characterized by the initial and main negative organic carbon isotope excursions (CIE) of up to 8‰. The initial and main CIEs are biostratigraphically constrained by first and last occurrences of boundary defining macro- and microfossils (e.g. ammonites). High resolution C-isotope records appear to be an excellent correlation proxy for this period in the Eiberg Basin. Pyrolysis analysis demonstrates increased Hydrogen Index (HI) values for organic matter coinciding with the initial CIE. Terrestrial organic matter influx and mass occurrences of green algae remains may have influenced the C-isotope composition of the sedimentary organic matter. This may have contributed to the extreme amplitude of the initial CIE in the Eiberg Basin.

15 Triassic-Jurassic C-isotope stratigraphy

16 Chapter 1

1. Introduction

The late Triassic is recognized as a period of major mass extinction in both the marine and continental fossil record (Raup and Sepkoski, 1982; Benton, 1995). Major mass extinction events in the Phanerozoic are associated with distinct perturbations in marine C-isotope records. The nature and causes of the isotopic events however, are not always similar. The Permian–Triassic and Cretaceous–Tertiary extinction events are marked by pronounced negative shifts (Baud et al., 1989; D’Hondt et al., 1998) whereas the end-Devonian is marked by two distinct positive excursions (Joachimski et al., 2002). Initial studies on the Triassic–Jurassic (T–J) transition suggested that this mass extinction also coincides with a positive Carbon Isotope Excursion (CIE) (Morante and Hallam, 1996). Hesselbo et al. (2002) showed that the T–J transition in St. Audrie’s Bay (UK) is marked by a short “initial” negative CIE of 5‰, which is separated from the succeeding and longer “main” negative CIE, by a 3.5‰ positive excursion. The initial CIE in the UK coincides with a change from Triassic to Jurassic pollen assemblages and slightly precedes the last occurrence (LO) of Triassic conodonts. The onset of the main CIE slightly precedes the first occurrence (FO) of Jurassic ammonite species. The initial CIE is further demonstrated for the Bergamasc Alps sections in Italy (Galli et al., 2005; Galli et al., 2007), the Csõvár section in Hungary (Pálfy et al., 2001), Kennecott Point in British Columbia (Ward et al., 2004; Williford et al., 2007) and Williston Lake in British Columbia (Wignall et al., 2007). Muller Canyon (Nevada) (Guex et al., 2004; Ward et al., 2007) and the Tiefengraben section (Austria) (Kürschner et al., 2007) may show both the initial and main C-isotope excursion. The magnitude and stratigraphic position of these excursions relative to biotic proxies varies somewhat between sections, which may be due to different sample resolutions and possibly some reworking. Nonetheless, they have been used as global correlation markers. The negative CIEs at the T–J transition are believed to be related to changes in the major global exchangeable carbon reservoirs. Changes in isotopic composition of T–J carbon reservoirs may relate to volcanic CO2 outgassing during deposition of the Central Atlantic Magmatic Province (CAMP) and an additional release of methane from gas hydrates. Beerling and Berner (2002) estimate a required carbon flux of 8000 Gt and 5000 Gt, respectively. Isotopically light carbon may also be released by oxidation of methane gas generated by subsurface thermal metamorphism of organic-rich strata (Hesselbo et al., 2007). Synchrony of CAMP volcanism with the T–J mass extinction and isotopic events is supported by stomatal frequency data that suggest an up to fourfold increase of pCO2 across the boundary (McElwain et al., 1999). Distinct excursions in osmium and strontium isotope records resulting from increased volcanic activity and subsequent erosion of basalt deposits, coincide with the two major negative excursions in marine carbon records (Cohen and Coe, 2002, 2007). However, a direct relation between the negative C-isotope excursions and end-Triassic extinction events in relation to the onset of volcanism is still controversially discussed. Wherever CAMP lavas have been documented in the same sections as the T–J biotic transition, the CAMP lavas postdate the extinction events (Olsen et al., 2003; Whiteside et al., 2007). Recently, there has also been renewed debate on the actual nature of the C-isotope excursions at the transition from the Triassic to the Jurassic. Van de Schootbrugge et al. (2008)

17 Triassic-Jurassic C-isotope stratigraphy

10˚ 12˚ 14˚ 16˚

0 50 100 49˚ 49˚

Scheibelberg Vienna Munich Kammerkoehralm 48˚ Salzburg Restentalgraben 48˚ Eiberg quarry Kendlbachgraben Hochalplgraben Kuhjoch/ Ochsentaljoch 47˚ Schlossgraben 47˚

46˚ 46˚ 10˚ 12˚ 14˚ 16˚

Figure 1 Location of the Kuhjoch (47°29′02″N/11°31′50″E) and nearby Ochsental- joch (47°29′0″N/11°31′50″E), Hochalplgraben (47°28′20″N/11°24′42″E), Kendlbach- graben (47°41′15″N/13°21′30″E), Restentalgraben (47°50′27″N/14°32′21″E), Schloss- graben (47°28′32″N/11°28′55″E), Scheibelberg (47°37′44″N/12°34′21″E), Kammerköhralm (47°37′09″N/12°34′20″E) and Eiberg (47°33′00″N/12°10′07″E) outcrops in the Northern Cal- careous Alps, Austria. dispute the significance of the negative C-isotope excursions as global events. They suggest that variations in organic C-isotope values might be explained by changes in relative contribution of marine vs terrestrial organic matter. The initial negative CIE is observed in both the carbonate C-isotope record from the Val Adrara section (northern Italy) (Galli et al., 2007) and the organic C-isotope record from Kennecott Point (Williford et al., 2007). However, in contrast to other localities both sections fail to record the main negative C-isotope excursion in the lower Hettangian, instead a 4‰ positive excursion is observed (Williford et al., 2007; van de Schootbrugge et al., 2008). Uncertainties in nature, size and stratigraphic position of C-isotopic events at the Triassic–Jurassic boundary raise important questions about the significance of the observed excursions. We present several new, integrated high resolution C-isotope records from the Northern Calcareous Alps (Austria) (Figure 1) along with biostratigraphic data. These T–J transition sections were deposited in the shallow marine intra-platform Eiberg Basin in the western Tethys realm. The abundant macro- and microfossils and palynomorphs represent an excellent possibility for a strong biostratigraphical control and a good basis for multi-proxy studies. One of the sections, Kuhjoch, has now been proposed as the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic (Hillebrandt et al., 2007). The aim of the present study is to demonstrate the reproducibility of distinct C-isotope excursions in different sections within the same basin. Thereby, we aim to test whether high resolution C-isotope records are a reliable stratigraphic tool for regional and interregional correlation of different Triassic–Jurassic boundary sections.

18 Chapter 1

2. Geology and palaeogeography

During the late Triassic the Northern Calcareous Alps (NCA) together with the Southern Alps and the Dinarides formed an up to 300 km wide and approximately 500 km long shelf strip at the western end of the Tethys Ocean (Kürschner et al., 2007). Along this Tethyan passive margin extensive carbonate platforms developed, which were flanked by reefs rimming open shelf basins. At the very end of the Norian, the Kössen Basin formed as a result of extensional tectonics (Hetenyi, 2002). By Rhaetian time, spreading of the Kössen Fm over the Haupt-dolomite and prograding siliciclastic sedimentation strongly modified and reduced the carbonate shelf (Haas, 2002; Krystyn et al., 2005). During deposition of the late Rhaetian Eiberg Mb, which succeeds the Hochalm Mb at the top of the Kössen Fm, the intra-platform Eiberg Basin deepened between the newly growing carbonate platforms of the Oberrhaet Limestone (Golebiowski, 1990). All the studied sequences (Kuhjoch, Hochalplgraben, Schlossgraben, Scheibelberg, Kammerköhralm, Eiberg, Kendlbach) belong to the Eiberg Basin except for the Restentalgraben sequence, which was deposited on the northern side of the Oberrhaet limestones (Figure 2). Kuhjoch, Hochalplgraben and Schlossgraben are located within the western Eiberg Basin in the Karwendel syncline (Figure 1), an east–west trending, narrow geological subunit of the Lechtal nappe in the western Northern Calcareous Alps (Hillebrandt et al., 2008). These outcrops are located in the increasingly steep to overturned southern flank of the syncline. The classical Kendlbach section is located within the Osterhorn syncline of the eastern Eiberg Basin in the central part of the Northern Calcareous Alps (Figure 1). This flat-lying and nearly non-deformed regional subunit lies west of the Wolfgangsee in the Osterhorn Mountains within the Tirolic nappe (Hallam, 1990). Completeness of upper Triassic to lowermost Jurassic sedimentary sequences in the NCA depended on upper Triassic relief (Golebiowski, 1990). The Eiberg Basin underwent continuous subsidence during the late Rhaetian and as a result, deposition was less affected by the end-Triassic sea level lowering and fully marine conditions prevailed continuously in the deeper parts of the basin (Krystyn et al., 2005). Sedimentary and faunal characteristics suggest full marine basin facies for the Kössen Fm and shallow

NORTH Kuhjoch/ Ochsentaljoch SOUTH Hochalplgraben Kendlbachgraben Tiefengraben Restentalgraben Schlossgraben Eiberg Scheibelberg KammerKoehralm Jurassic Eiberg basin Oberrh. Oberrhaet Limestone Hallstatt basin Limest. Eiberg Mb Koessen Fm

Rhaetian Hochalm Mb

Triassic Hauptdolomite Fm Dachstein Norian

Figure 2 Palaeoenvironmental setting of the Kuhjoch/Ochsentaljoch, Hochalplgraben, Kend- lbachgraben, Tiefengraben, Schlossgraben, Eiberg, Scheibelberg and Kammerköhralm section in the Eiberg Basin and the Restentalgraben section north of the Oberrhaet limsetones (after Krystyn et al., 2005).

19 Triassic-Jurassic C-isotope stratigraphy

marine shelf conditions with progressive deepening for the subsequent Kendlbach Fm (Golebiowski, 1990). In addition, the shallow marine Restental locality was closest to the palaeo-coastline north of the Eiberg Basin at the northern side of the Oberrhaet limestone. Subsidence and tilting seems to have been highest in the north, as this locality obviously experienced the highest sedimentation rates. A distinct lithological change from limestones of the Eiberg Mb (Kössen Fm) to marly sediments of the Tiefengraben Mb (Kendlbach Fm) characterize the sedimentary sequences in the Eiberg Basin in the transition from the Triassic to the Jurassic (Figure 3). Well-bedded and variably thick limestones of the Kössen Fm alternate with thin marly inter-layers in Kuhjoch, Hochalplgraben and Restental. Continuous limestone deposition is observed for the top few metres of the Kössen Fm in Kendlbach. The variation in carbonate predominance in the Kössen Fm depends on a more marginal or distal setting within the basin (Kürschner et al., 2007). Several tens of centimetres up to a meter of grey–brown marls of the Tiefengraben Mb succeed the Kössen Fm. This interval is followed by reddish oxidized, clayey marls of the Schattwald beds. The thickness of the Schattwald beds varies between 200 cm in Kuhjoch and almost 800 cm in Restental. The time equivalent interval in the Kendlbach record is marked by similar but grey marly to silty sediments in the lower 250 cm of the Kendlbach Fm (Morante and Hallam, 1996). Different thicknesses of these beds are likely related to the proximal (e.g. Restental, Tiefengraben and Kendlbach) or distal (e.g. Kuhjoch and Hochalplgraben) setting during deposition. The Schattwald beds are succeeded by the main part of the Tiefengraben Mb with distinct Jurassic ammonite levels (Hallam, 1990; Krystyn et al., 2005; Hillebrandt et al., 2007). Limestone beds re-occur in the upper part of the Tiefengraben Mb just before the transition to the succeeding Breitenberg Mb.

3. Methods

Bulk stable C-isotope ratios were measured on sedimentary organic matter from (dark to light) grey and red marly to clayey sediments from several locations in the Eiberg Basin. Samples were collected from the top Rhaetian Eiberg Mb well into the Hettangian part of the subsequent Tiefengraben Mb. The Schlossgraben, Scheibelberg, Eiberg and Kammerköhralm outcrops were only sampled for a few tens of centimetres at the transition from the Kössen to Kendlbach Fm. Sample density in all records varied from centimeter-scale at the transition from the Eiberg to Tiefengraben Mb (where the initial CIE and a possible condensed interval was expected) up to a 20–40 cm resolution higher up in the sequence. A total of 305 samples were processed for bulk organic C-isotope measurements: Kuhjoch/Ochsentaljoch (101 samples), Hochalplgraben (70 samples), Kendlbach (46 samples), Restental (42 samples), Kammerköhralm (16 samples), Eiberg (12 samples), Scheibelberg (10 samples) and Schlossgraben (8 samples). Carbonate was removed by rinsing 0.9 g of powdered sediment twice with 15 ml of 1M HCl. To reach almost neutral pH values, the residue was additionally rinsed twice with 22.5 ml demi-water. After freeze drying, around 9 mg of homogenized de-carbonated sample residue was analyzed online for carbon content with a CNS-analyzer (NA 1500) following standard procedures. The total organic carbon (TOC) content of the sediment from Kuhjoch was obtained by pyrolysis measurements on a Rock-Eval VI apparatus

20 Chapter 1

using lab procedures as described in Behar et al. (2001). These measurements were performed at the integrated laboratory of the Faculty of Geosciences (Utrecht University) and The Netherlands Institute of Applied Geosciences (TNO-NITG). The total organic carbon content of the sediment from the other sections was obtained by multiplying the carbon content of the de-carbonated sample by the ratio between the weight of the de- 13 carbonated sample and the original weight of the sample. The δ Corg values were then measured on homogenized de-carbonated sample residue, containing 30 μg of carbon, by Elemental Analyzer Continuous Flow Isotope Ratio Mass Spectrometry using a Fisons 1500 CNS Elemental Analyzer coupled to a Finnigan Mat Delta Plus mass spectrometer at the Geochemistry group of the Department of Earth Sciences, Utrecht University. Isotope ratios are reported in standard delta notation relative to Vienna PDB. Analytical precision based on routine analysis of internal laboratory reference materials indicated a standard deviation <0.04‰ for the Kuhjoch, Restental and Hochalplgraben records and 13 <0.1‰ for the Kendlbach record. The δ Corg values for several samples from Kendlbach demonstrated a reproducibility with a standard deviation <0.24‰. Hydrogen index (HI) values for bulk sediments from Kuhjoch were obtained by pyrolysis measurements that were performed on a Rock-Eval VI apparatus using lab procedures as described in Behar et al. (2001).

4. Results

13 Significant fluctuations in δ Corg values of bulk sedimentary organic matter are observed in all T–J transition records within the Eiberg Basin. In the Kössen Fm these values vary between −25 to −28‰ in the Kuhjoch, Hochalplgraben and Restental sections (Figure 3). At the very top few centimetres of the limestones they start to shift towards more negative values of −28‰ in Kuhjoch and Hochalplgraben and −30‰ in Restental. The transition from the Eiberg to the Tiefengraben Mb is characterized by a continued shift to distinctly more negative values of −31‰ in the distal Kuhjoch and Hochalplgraben records, −33‰ in the proximal Kendlbach and Restentalgraben records and a successive shift back to less negative pre-excursion values. The most negative values of the initial CIE of 5 to 8‰ coincide with black clayey sediments at the very base of the Tiefengraben Mb. The initial CIE is in all sections succeeded by a return to rather constant pre-excursion C-isotope values of around −24‰ in Restental, −25‰ in Kuhjoch and Hochalplgraben and −26‰ in Kendlbach. The thickness of this interval ranges from 250 to 800 cm between sections and concurs with the reddish coloured sediments of the Schattwald beds. Just before the transition from the Schattwald beds to the grey Tiefengraben Mb a second negative shift occurs. This abrupt shift of 2‰ in Restental and Kuhjoch, 3‰ in Hochalplgraben and 4‰ in Kendlbach marks the onset of the main negative CIE. An additional gradual negative shift of 1‰ in Hochalplgraben and 2‰ in Kuhjoch persists through the lower Tiefengraben Mb. Small but significant positive excursions of 2.5‰ in Kuhjoch and 1.5‰ in Hochalplgraben are superimposed on the main C-isotope excursion in the Hettangian part of the Tiefengraben Mb. The first occurrence of the Jurassic Psiloceras spelae ammonite coincides with the first return to more positive values within the main CIE in Kuhjoch and Hochalplgraben (Figure 5). The upper part of the Tiefengraben Mb in the Kuhjoch section is sampled at the Ochsentaljoch

21 Triassic-Jurassic C-isotope stratigraphy 6 2 - CIE [‰]

8 2 - org C initial 0 Eiberg 3 13 - δ 2 3 0 - 0 0 5 - 5 8 2 -

[‰] 0 3 - org C 2 13 3 - δ 4 3 0 - 0 0 6 1 Kammerköhralm - 4 5 2 -

7 2 - [‰] 9 org 2 - C 1 13 3 - δ 3 3 - Scheibelberg 0 0 0 0 5 1 5 2 - [‰] 7

2 - org 9 C 2 - 13 1 δ 3 -

0 0 0

0 0 0 0 CIE main 3 3 2 1 Schlossgraben - 2 5 - 2

[‰] 7 - 2 org 9 C - 2 13 1 δ - 3 3 - 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 1 0 9 8 7 6 5 4 3 2 1 0

9 8 7 6 5 4 3 2 1 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9

2 2 1 1 1 1 1 1 1 1 1 1 - 1

depth in cm in depth

Eiberg Mb Eiberg Schattwald beds Schattwald grey Tiefengraben Mb Tiefengraben grey

gr Tg Mb

Rhaetian Restentalgraben Hettangian

CIE main 5 - 2 7 [‰]

- 2 9 org - 2 C 1 13 - 3 δ CIE 3 - 3 initial 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

8 7 6 5 4 3 2 1 depth in cm in depth - 1 - 2 - 3

Eiberg Mb Eiberg Tiefengraben Mb Tiefengraben

Hettangian Rhaetian

Kendlbachgraben CIE main 4 - 2

6 [‰] - 2 8 org - 2 C 0 13 - 3 δ 2 - 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 1 0 9 8 7 6 5 4 3 2 1 0

9 8 7 6 5 4 3 2 1 2 2 1 1 1 1 1 1 1 1 1 1 depth in cm in depth

Eiberg Mb Eiberg Schattwald beds Schattwald grey Tiefengraben Mb Tiefengraben grey

gr Tg Mb Hettangian Hochalplgraben Rhaetian

CIE main 3 - 2 5

- 2 [‰] 7 - 2 org 9 C - 2 13 Small shear zone Grey marly to silty sediments Red marly to silty sediments from the Schatwald beds Limestones 1 δ - 3 3 - 3 0 0

0 0

0 0 0 0 0 0 0 0 0 0 0 0 0

0 0

0 0 0 0 0 0 0 0 0 0 0

1 0

7 8 9 8 7 6 5 4 3 2 1 - 1 - 2 depth in cm in depth 1 1

Schattwald beds Schattwald grey Tiefengraben Mb Tiefengraben grey

Tiefengraben Mb Tiefengraben Mb Eiberg

grey Tg Mb

Kendlbach Fm Kendlbach Kössen Fm Kössen

Hettangian Rhaetian

Triassic Kuhjoch/ Ochsentaljoch Jurassic

22 Chapter 1

mountain pass and demonstrates rather stable isotope values of around −27‰ with some minor 1‰ negative excursions just below thin limestone beds. Relatively low total organic carbon (TOC) content of <1% is measured in all boundary records in the Eiberg Basin (Figure 4a). Dramatically increased TOC values of up to 9% in the more distal Kuhjoch and 7.5% in the more proximal Restental records are restricted to a small 2–10 cm interval coinciding with the lower half of the initial isotope excursion. This short-lived event with increased TOC values is recorded in dark-grey clayey sediments directly following the Kössen limestones (Figure 4a). TOC values in this interval are even higher in the Schlossgraben and Eiberg outcrops (8–9%) and the Hochalplgraben outcrop (up to 14.5%). Maximum TOC values coincide with stable 13 organic C-isotope values of up to −31‰ and precede even more negative δ Corg values by some centimetres in each record. The lower half of the initial CIE at Kuhjoch is marked by peak TOC values that coincide with significantly increased hydrogen index values of over 600 mg HC/g TOC (Figure 4b).

5. Bio- and C-isotope stratigraphy

Several marine fossil groups (ammonites, bivalves, brachiopods, echinoderms and conodonts) (Golebiowski, 1990 and references therein) have been used to establish a biostratigraphic framework for the upper Triassic Kössen Formation and the subsequent Kendlbach Fm in the NCA. Several sections in the Eiberg Basin are characterized by the LO of typical Triassic organisms and FO of typical Jurassic organisms. Choristoceras marshi along with conodonts have their last occurrence in the top of the Kössen Fm (Figure 5). The FO of the ammonite P. spelae has been proposed as marker event for the base of the Jurassic (Hillebrandt et al., 2007). The first appearance (FA) ofP. spelae n.ssp. in Kuhjoch and Hochalplgraben is regarded as synchronous basin wide (Hillebrandt pers. comm.). An almost simultaneous appearance in these two sections is confirmed by C-isotope (this study) and palynological data (Bonis et al., 2009-a, b). The Jurassic pollen Cerebropollenites thiergartii approximately co-occurs with the first Jurassic ammonites in the Eiberg Basin (Hillebrandt et al., 2007; Bonis et al., 2009-a, b) and St. Audrie’s Bay (Bonis et al., submitted). The initial CIE has been proposed as alternative marker for the T–J boundary (McRoberts et al., 2007) because it coincides with the marine extinction event in most boundary records. The great similarity between C-isotope records of Tiefengraben and St. Audrie’s Bay suggests a good correlation between the UK and Austria (Kürschner et al., 2007). The correlation of C-isotope records in New York Canyon (NYC) and European sections in relation to ammonite sequences is problematic. The first Jurassic ammonite P. spelae n.ssp. in the NCA (Austria) is separated from the American P. spelae on subspecies level. The two subspecies are considered as timely inseparable, but biogeograpically differentiated entities (Hillebrandt and Krystyn, 2009). P. spelae is defined as the nominate species of the first biohorizon ofthe P. tilmanni Subzone of the P. planorbis chronozone, i.e. the lowest Jurassic ammonite zone (Hillebrandt

13 Figure 3 High resolution δ Corg data of bulk sedimentary organic matter from the Kuhjoch/ Ochsentaljoch, Hochalplgraben, Kendlbach, Restentalgraben, Schlossgraben, Scheibelberg, Kam- merköhralm and Eiberg outcrops in the Northern Calcareous Alps, Austria. C-isotope values are in δ notation and relative to Vienna PDB. See Appendix 1

23 Triassic-Jurassic C-isotope stratigraphy

50 Figure 4a: Restental 50 Kendlbachgraben

40 -25 40 -25 30

30 δ δ

-27 13 -27 20 13 20 C C

o r

g -29 10 -29 r

g 10 [ [ ‰ ‰ ] 0 0 ] -31 -31 -10 -10 -33 -33 -33 -31 -29 -27 0 1 2 3 4 5 6 7 8 0 2 4 6 8 -33 -31 -29 -27 0 1 2 3 4 5 0 2 4 δ 13Corg [‰] TOC [%] TOC [%] δ 13Corg [‰] TOC [%] TOC [%] Scheibelberg Schlossgraben 60 -25 290 -24

-26 280 -25 40 -27 270 δ -26 13 -28 δ C 260 13

o -27 C

g -29 250 o

20 [

r ‰ -28 g [ ] -30 240 ‰ -29 ] 0 -31 230

-32 220 -30 -32 -30 -28 -26 0 1 2 3 0 1 2 3 δ 13Corg [‰] TOC [%] TOC [%] 210 -31 -31 -29 -27 -25 0 2 4 6 8 0 2 4 6 8 δ 13Corg [‰] TOC [%] TOC [%] Kammerkoehralm Hochalplgraben 60 -27 -25 -28 270 -26 δ -29 260 -27 13 δ 40 C

o 13

-30 r

C 250 -28 [

o ‰ -31 r g -29 ]

[ 240

20 ‰ -32 ] 230 -30 -33 -31 220 -31 -29 -27 0 2 4 6 8 10 12 14 0 4 8 12 0 -34 -34 -32 -30 -28 0 1 2 3 4 5 0 1 2 3 4 5 δ 13Corg [‰] TOC [%] TOC [%] δ 13Corg [‰] TOC [%] TOC [%]

Eiberg Figure 4b: Kuhjoch 20 -27 35 -28 δ -25

10 13

-29 C 25 δ 0 o r

-27 13 -30 g

[ 15 C ‰ -10 o

-31 r ] 5 -29 g [

-20 -32 ‰

-32 -30 -28 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 -5 ] δ 13Corg [‰] TOC [%] TOC [%] -31 -15

-25 -33 -32 -30 -28 -26 -24 0 2 4 6 8 0 200 400 600 0 2 4 6 δ 13Corg [‰] TOC [%] H.I. TOC [%] Limestones

Grey marly to silty sediments Darker grey marly to silty sediments Organic rich silty sediments

Figure 4 (A) The initial organic C-isotope excursion (CIE) and increased Total Organic Carbon (TOC) values at the transition from the Eiberg to Tiefengraben Mb in Restentalgraben, Kendl- bachgraben, Schlossgraben, Kammerköhralm, Eiberg quarry, Scheibelberg and Hochalplgraben. 13 Vertical scale is in centimetres. Open diamonds show δ Corg versus TOC values for the initial CIE, 13 and closed diamonds show δ Corg vs TOC values for the complete records. (B) The initial CIE, TOC and Hydrogen Index (HI) values at the Triassic–Jurassic transition in Kuhjoch. and Krystyn, 2009). In terms of Jurassic ammonite biostratigraphy the biohorizon is the smallest biochronological unit which in itself cannot be further subdivided and is therefore be treated as geologically instantaneous (Page, 2003). A negative CIE in the Muller Canyon Member of NYC and the initial CIE in St. Audrie’s Bay (UK) may both occur, in a sequence stratigraphic context, at the transition from a regressive to transgressive

24 Chapter 1

sea level (Wignall et al., 2007). However, a debris horizon with turbidite like deposits can be recognized at the uppermost top of the limestones of the Mount Hyatt Member in NYC. If ammonite appearance is synchronous in NYC and the Eiberg Basin, which experienced a similar palaeoenvironmental setting and sedimentary build-up, then a hiatus and unconformity may mark the top of the regression interval in NYC. Correlation of the negative CIE in NYC at the base of the Sunrise Formation to the main CIE in St. Audrie’s Bay as proposed by Guex et al. (2004) is equivocal. The negative CIE of the Muller Canyon Mb in NYC may just as well be time equivalent with the main negative CIE in the European sections. Alternatively, following the C-isotope correlations of NYC and St. Audrie’s Bay by Guex et al. (2004), the FO of P. spelae in New York Canyon may be up to 100 kyr older (based on astronomical pacing of T–J boundary proxy records from the UK (Ruhl et al., Chapter 5)) compared to European sections. Anyway, thermal alteration of the organic matter in NYC is due to contact-metamorphism with Cenozoic basalts and in contrast to the immature European sections, very high. Microscopic analysis revealed a major degradation of structural organic matter. Only black organic particles are preserved. Therefore it is impossible to estimate changes in the original composition of the organic matter, such as for example the proportion of marine vs terrestrial OM 13 which may have significantly influenced its originalδ Corg composition. Also it is virtually impossible to estimate the degree of alteration of the original C-isotope signal by thermal alteration which is on itself dependent on the composition of the original OM matter 13 too. While general trends might have been preserved in the δ Corg curve of NYC, it does not necessarily reflect the original signal. Although it has been tried to circumvent the problem of the significance of the NYC C-isotope record by statistical treatment of the original data, arguments on stratigraphic appearance of ammonites in NYC based on a C-isotope curve in relation to European sections are not valuable.

6. Discussion

The nature and origin of carbon isotopic events at the Triassic–Jurassic transition in Austria have been subject to ongoing debate. A distinct positive excursion in the organic C-isotope signature of the classical Kendlbach section was already described by Morante and Hallam (1996). New high resolution sampling at the same locality in the NCA now does show the initial CIE of up to 6‰ at the very base of the Tiefengraben Mb (Figure 3). The initial negative organic CIE has been described within (Pálfy et al., 2001; Galli et al., 2005, 2007; Kürschner et al., 2007) and outside the Tethys ocean (Hesselbo et al., 2002; Guex et al., 2004; Ward et al., 2004; Ward et al., 2007; Williford et al., 2007). The St. Audrie’s Bay and Tiefengraben C-isotope records also clearly demonstrate a main negative CIE (Hesselbo et al., 2002; Kürschner et al., 2007). The Kennecott Point and Val Adrara records do not show a main negative CIE for the lower Hettangian but in contrast record a 4‰ positive excursion, respectively in organic (Williford et al., 2007) and inorganic carbon (van de Schootbrugge et al., 2008). Both sections do record 1–2‰ more negative values for the upper Hettangian relative to Rhaetian values. Local effects may have contributed to a lower Hettangian positive excursion in the Kennecott Point record (Williford et al., 2007). However, additionally proposed mechanisms to explain a positive CIE, e.g. a biocalcification crisis related to increased pCO2 levels, are of global

25 Triassic-Jurassic C-isotope stratigraphy & neophyllites Caloceras ssp. Conodonts C. thiergartii P. sp. P. P. planorbis P. P. planorbis sp.cf. P. P. cf. erugatum P. └ ┌ └ └ └ └ └ 5 - 2 [‰] 7 org - 2 C 9 13 - 2 δ 1 - 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 St. Audrie’s Bay St. Audrie’s

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 depth in cm in depth ? P. calliphyllum P. A. varius & C. spp. P. minimus P. Heliosporites C. thiergartii C. marshi 4 < reissingeri < < └ ┌ Caloceras ssp. & └ - 2 5 - 2 6 - 2 7 [‰] - 2 8 - 2 9 org - 2 C 0 - 3 1 13 - 3 δ 2 - 3 3 Tiefengraben - 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9

9 8 7 6 5 4 3 2 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 depth in cm in depth < H. reissingeri Pinuspollenites Caloceras ssp. cf. pacificum P. C. thiergartii Acanthotriletes P. spelae n. ssp. P. 4 minimus < varius & Conbaculatisporitus spp. < └ └ └ & └ - 2 6 [‰] - 2 8 org - 2 C 0 13 - 3 δ 2 Hochalplgraben - 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

9 8 7 6 5 4 3 2 1 0 20 10 00 30

9 8 7 6 5 4 3 2 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 depth in cm in depth P. minimus P. Psiloceras Psiloceras Cerebropollenites Choristoceras Psiloceras < P. tilmanni P. ex gr. spelae n. ssp. thiergartii marshi └ └ └ ┌ cf. pacificum └ 4 - 2 6 [‰] - 2 8 org - 2 C 0 13 Increased abundance or mass occurence First occurence - 3 Last occurence δ 2 < Kuhjoch └ ┌ - 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

8 7 6 5 4 3 2 1 2 1 0

9 8 7 6 5 4 3 2 1 - 1 - 2 1 1 1 depth in cm in depth C. marshi 5 ┌ - 2 7 [‰] - 2 9 org - 2 C 1 13 - 3 δ

Kendlbach depth in cm in depth - 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 6 5 4 3 2 1 - 1 3 - 2 5 - 2 [‰] 7 - 2 org C 9 - 2 13 δ 1 - 3 3 Restentalgraben 0 - 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1

- 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 1 1 1 1 1 1 1 1 - 1 depth in cm in depth

26 Chapter 1

influence and complicate a direct link to a negative CIE in other sections. High resolution correlation of T–J boundary records can be difficult due to a lack of (bio-)stratigraphic markers. C-isotope stratigraphy has been suggested as a useful correlation tool. High resolution organic C-isotope records from the Eiberg Basin form an excellent test for the reproducibility of such curves across the Triassic–Jurassic boundary. All studied proximal and distal sections in the Eiberg Basin clearly show the initial CIE. Four of them are sufficiently long to also record the onset of the main CIE at the transition to the Jurassic, just preceding the FO of P. spelae n.ssp. The initial and main CIEs in the Eiberg Basin are stratigraphically confined between first and last occurrences of Triassic and Jurassic biostratigraphic marker species (e.g. the Triassic Choristoceras marshi and Jurassic P. spelae n.ssp. ammonite species and the Jurassic Cerebropollenites thiergartii pollen). The finding of distinct biological proxies just before and after both the CIEs in several records within and outside the Eiberg Basin confirm the relevance of these isotopic events as (inter-)regional correlation markers. In addition, second order variations in C-isotope records, superimposed on the main trend, can clearly be observed and correlated within the Eiberg Basin. These records can therefore function as a high resolution correlation proxy within this basin. Despite the similar isotopic trends in these sections, some differences are apparent especially for the main negative C-isotope excursion (Figure 3). The gradual main negative CIE of 4‰ in the Tiefengraben record corresponds to an abrupt shift in the newly studied Austrian sections. This shift coincides with a small shear horizon and suggests a minor hiatus (2–3 m) just before the transition from the Schattwald beds to the grey Tiefengraben Mb. In addition, the last Triassic palynological zone (TPo Zone) is lacking at this level in Hochalplgraben and Kuhjoch (Bonis et al., 2009-a, b). A new but similar outcrop only 10 m east of Kuhjoch, where no shear zone was apparent, presents a more gradual transition from the Schattwald beds to the grey Tiefengraben Mb. The studied interval in this section shows a continuous sedimentary sequence with a more gradual main negative CIE similar as in Tiefengraben. Carbon isotope values of both the initial and main CIE are 1–2‰ less depleted in 13C in the distal Kuhjoch and Hochalplgraben sections relative to the proximal Kendlbach and Tiefengraben sections. Isotopic fractionation of terrestrial primary producers depends on C-cycling processes. Modern terrestrial organic matter is associated with an about 13 7‰ depleted Corg composition relative to mean marine organic matter (Tyson, 1995; 13 Killops and Killops, 2005). Different δ Corg values for stratigraphically similar horizons in different sections in the Eiberg Basin may therefore be explained by a proximal or distal setting and subsequent influx of terrestrial organic matter. However, this isotopic relationship between marine and terrestrial organic matter may not be valid throughout geologic history. In the middle Jurassic (Hesselbo et al., 2003) and at the Permian–Triassic boundary (Grice et al., 2007), an increasingly marine proportion of the

Figure 5 Stratigraphic correlations of Triassic–Jurassic boundary sections from the Northern Cal- careous Alps and St. Audrie's Bay based on high resolution organic C-isotope records (this study) and biostratigraphic markers. Ammonite appearance in Austria from Hillebrandt et al. (2007), first occurrences of Jurassic pollen from Kürschner et al. (2007) and Bonis et al. (2009), Tiefen- graben C-isotope record from Kürschner et al. (2007) and St. Audrie's Bay C-isotope record from Hesselbo et al. (2002).

27 Triassic-Jurassic C-isotope stratigraphy

sedimentary organic matter pushed bulk organic C-isotopes to lighter values. This may be related to increased isotopic fractionation of marine algae under elevated atmospheric

CO2 concentrations. Alternatively, more depleted values in the proximal Tiefengraben and Kendlbach records may therefore suggest increased marine primary productivity in the shallower parts of the basin. The amplitude of the initial CIE in the Eiberg Basin (6–8‰) is up to 3‰ larger than demonstrated for any other record. Increased HI values of over 600 mg HC/g TOC coincide with increased TOC values during the first half of the initial CIE. Increased HI values generally suggest an algal or bacterial source for the organic matter (Wignall, 1994). However, increased HI values in this interval concur with an increasingly terrestrial origin of the SOM (Bonis et al., 2009-a, b; Ruhl et al., Chapter 3). The upper half of the initial CIE is characterized by dramatically increased green algae (the prasinophyte species: Cymatiosphaera spp.) abundance (Kürschner et al., 2007; Bonis et al., 2009-a, 13 b). Fossil and modern prasinophytes have a 7‰ depleted δ Corg composition relative to modern common marine primary producers and they are 3‰ depleted relative to Rhaetian base values in our records (Wong and Sackett, 1978; Prauss and Riegel,1989). A changing source of the organic matter, e.g. increased terrestrial organic matter influx followed by mass occurrence of green algae remains, may have influenced the amplitude of the initial CIE in the Eiberg Basin. Van de Schootbrugge et al. (2008) suggest that based on palynological studies, all organic C-isotope variations at the T–J transition are fully explained by changes in type of organic matter. Kürschner et al. (2007) demonstrate the close resemblance of the C-isotope curves of Tiefengraben and St. Audrie’s Bay. Different vegetation patterns in these sections in Austria and the UK (Orbell, 1973; Morbey, 1975; Schuurman, 1979; Hounslow et al., 2004; Kürschner et al., 2007; Bonis et al., submitted; Bonis et al., 2009-a, b) suggest different regional climatic conditions. Accordingly, it may be difficult to explain two very similar C-isotope signatures by changes in vegetation and source of the organic matter. New data from the UK show similarly shaped and sized initial and 13 main negative excursions in δ Ccarb-oyster records, as compared to the organic C-isotope 13 record (Korte et al., 2009). In addition, a 2–3‰ negative shift in bulk δ Ccarb records in the Bergamasc Alps in Italy (Galli et al., 2005) and the Scheibelberg record in the Eiberg Basin (Richoz et al., pers. comm.), coincides with the initial negative CIE. The changing isotopic composition of organic and carbonate matter at the Triassic–Jurassic transition suggests major changes in the global exchangeable carbon reservoirs. New data from the continental realm in Morocco and Austria also demonstrate distinct negative excursions 13 in bulk δ Corg records coinciding with the marine initial CIE (Deenen et al., submitted; Ruhl et al., Chapter 4) suggesting the release of 13C depleted carbon to the exogenic carbon pool.

7. Conclusions

High resolution organic C-isotope records from the Eiberg Basin (western Tethys margin), including the proposed GSSP for the base of the Jurassic, are marked by two negative CIEs. The initial and main CIEs are biostratigraphically constrained by first and last occurrences of T–J boundary defining macro- and microfossils (e.g. C. marshi, P.

28 Chapter 1

spelae n.ssp. and C. thiergartii). Good reproducibility of the CIEs with superimposed second order variations enable high resolution correlations within and outside the Tethys realm. Increased terrestrial organic matter influx into the basin and the mass occurrence of specific green algae (Cymatiosphaera spp.) coincide with the initial CIE and may have contributed to its extreme amplitude.

Acknowledgements

MR and WMK acknowledge funding from the high-potential stimulation program of Utrecht University. LK has been financially supported by the Austrian National Committee for IGCP (Project 458). We thank the Austrian Bundesforste for access to forest roads and A. van Dijk, H. Veld and K. Reimer (Int. Geoch. Lab., UU-NITG) for assisting with the C-isotope analysis and Rock-Eval VI pyrolysis. N.R. Bonis and M.H.L. Deenen are both thanked for supportive and constructive discussion and extensive field assistance. The manuscript has substantially benefitted from the constructive comments of Paul Wignall and two anonymous reviewers, for which they are gratefully thanked. This contribution has publication no 20090302 of the Netherlands Research School of Sedimentary Geology.

29 30 Chapter 2

Climate change driven black shale deposition during the end- Triassic in the western Tethys

Several new Triassic-Jurassic boundary sections from the Eiberg Basin (Northern Calcareous Alps, Austria) have been studied at high resolution. We present integrated geochemical and biological proxy data from this western Tethys shelf basin. High-resolution correlation of Kuhjoch, the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic, Hochalplgraben and Tiefengraben shows that the initial and main Carbon Isotope Excursions (CIE) are contemporaneous with first and last occurrences of boundary defining macro- and microfossils. We focus on the end-Triassic initial CIE at the transition from the limestones of the Kössen Formation to the marls of the Kendlbach Formation. This change coincides with a dramatically increased influx of conifer (Cheirolepidiaceae) pollen and increased Total Organic Carbon (TOC) values, succeeded by an acme of green algae (Cymatiosphaera). We present a model in which increased terrestrial organic matter influx is related to enhanced seasonality and increased erosion of the hinterland. Reduced salinity of the surface waters led to the mass occurrence of green algae. Stratification of the water column may have caused anoxic bottom water conditions and black shale deposition during the initial CIE at the base of the Kendlbach Formation.

31 Climate change driven black shale deposition

32 Chapter 2

1. Introduction

The Triassic-Jurassic (T-J) transition period is marked by major environmental changes (e.g. McElwain et al., 1999; Beerling, 2002). Marine and terrestrial extinction events and floral turnovers during the end-Triassic (Hallam, 2002; Tanner et al., 2004; Kiessling et al., 2007; Lucas and Tanner, 2008) coincide with possible perturbations of the global carbon cycle (Hesselbo et al., 2002; Hesselbo et al., 2004). End-Triassic climate and palaeoenvironmental changes (e.g. T and CO2 concentration; Cleveland et al., 2008) may be linked to the onset of volcanic activity of the Central Atlantic Magmatic Province (CAMP) that is related to the break-up of Pangaea. The T-J transition is characterized by two distinct negative organic Carbon Isotope Excursions (CIE) in many sections within and outside the Tethys Ocean (Pálfy et al., 2001; Hesselbo et al., 2002; Guex et al., 2004; Ward et al., 2004; Ward et al., 2007; Williford et al., 2007; Kürschner et al.,

2007; Ruhl et al., 2009). Negative excursions in Ccarb- and Coyster-isotope records (Galli et al., 2005, 2007; van de Schootbrugge et al., 2007; Korte et al., 2009) confirm the reality of global carbon cycle changes in the end-Triassic and transition to the Jurassic. The high resolution biological and organic geochemical proxy records of several well preserved sections including Kuhjoch, which is recently approved by the International Commission on Stratigraphy as the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic (Hillebrandt et al., 2007; Ogg et al., 2008), enable a good correlation within the Eiberg Basin. These records show several remarkable changes in the palaeoenvironment in the western Tethys realm at the transition from the Triassic to the Jurassic. We focus on the end-Triassic relatively short lived initial negative C-isotope excursion that precedes the main CIE at the base of the Jurassic. The initial CIE directly succeeds the transition from limestones of the Kössen Formation (Fm) to marls of the Kendlbach Fm and coincides with the deposition of organic rich, black and finely laminated sediments throughout the Eiberg Basin. Prasinophytes are often associated with black shale deposition throughout geological history (Riegel, 2008). The present study shows high resolution organic geochemical and palynological proxy records at the transition from the Kössen Fm to the Kendlbach Fm. We present a model to link the deposition of black shales to (regional) climate change.

2. Material and methods

Detailed lithostratigraphic, palaeogeographical and geological descriptions of the studied sections were previously reported in Kürschner et al. (2007), Hillebrandt et al. (2007), Ruhl et al. (2009) and Hillebrandt and Krystyn (2009).

2.1 Geographical and geological setting The Northern Calcareous Alps (NCA) is one of few regions where continuous marine T-J boundary records are preserved. The Kuhjoch, Hochalplgraben and Tiefengraben outcrops are located in the Karwendel Syncline (Figure 1a). This is an east-west trending synclinal structure within the Lechtal Nappe in the western NCA (Hillebrandt et al., 2007). Hochalplgraben and Kuhjoch are situated in the increasingly steep to overturned western and south-western flank of the syncline. Kuhjoch is located at 47°29’02”N/11°31’50”E, Hochalplgraben at 47°28’20”N/11°24’42”E and Tiefengraben at 47°41’45’’N/13°21’00’’E.

33 Climate change driven black shale deposition

2.2 Palaeogeography In the late Triassic, the NCA together with the Southern Alps and the Dinarides formed an up to 300 km wide and approximately 500 km long shelf strip at the western end of the Tethys Ocean (Kürschner et al., 2007). Along this Tethyan passive margin extensive carbonate platforms developed, which were flanked by reefs rimming open shelf basins. At the very end of the Middle Norian, the Kössen Basin formed as a result of extensional tectonics (Hetenyi, 2002). By Rhaetian time, prograding siliciclastic sediments of the Kössen Fm over the Haupt-dolomite Fm strongly modified and reduced the carbonate shelf (Haas, 2002; Krystyn et al., 2005). During deposition of the late Rhaetian Eiberg Member (Mb), which succeeds the Hochalm Mb within the Kössen Fm, the Eiberg Basin

10˚ 12˚ 14˚ 16˚

km A 0 50 100 49˚ 49˚

Vienna Munich

48˚ Salzburg 48˚

Hochalplgraben Kuhjoch Tiefengraben 47˚ 47˚

46˚ 46˚ 10˚ 12˚ 14˚ 16˚

NORTH SOUTH c i Kuhjoch s

s Hochalplgraben B a

r Tiefengraben u Kendlbach Fm J

n Oberrh. Eiberg Basin a i t Limest. Oberrhaet Limestone Hallstatt Basin

e Eiberg Mb

a Kössen Fm c i h

s Hochalm Mb R s a i n r a T i r Hauptdolomite Fm Dachstein Fm o N

Figure 1 (A) Location of the Kuhjoch, Hochalplgraben and Tiefengraben sections, (B) North- South directed late Norian to Rhaetian facies cross-section of the north-western Tethys shelf margin with the position of Kuhjoch, Hochalplgraben and Tiefengraben in the Eiberg Basin.

34 Chapter 2

formed between the newly growing carbonate platforms of the Oberrhaet Limestone (Golebiowski, 1990). All three sections were deposited in the intra-platform Eiberg Basin (Krystyn et al., 2005) (Figure 1b). The Kuhjoch and Hochalplgraben sections are located in the deeper central part of the Eiberg Basin in the western NCA. The Tiefengraben section was deposited in a more restricted shallow environment at the eastern end of the basin. The Eiberg Basin underwent continuous subsidence and reached water depths of up to few hundred meters in the latest Rhaetian. As a result, deposition was less affected by the end-Triassic sea level fall and fully marine conditions prevailed continuously in the deeper parts of the basin. A distinct lithological transition from limestones of the Kössen Fm (Eiberg Mb) to marly sediments of the Kendlbach Fm (Tiefengraben Mb) characterizes the sedimentary sequences in the Eiberg Basin during the T-J transition. Dark brown to black sediments of 2-3 cm directly succeed the Kössen limestones in Kuhjoch and Hochalplgraben. On top of these beds follow the olive-grey marly to silty sediments of the Tiefengraben Mb. By contrast, the black sediments are missing in the Tiefengraben outcrop and olive-grey sediments directly follow the Kössen limestones. These sediments could be missing in the Tiefengraben section either due to a short depositional hiatus, possibly related to the sea level low-stand, or due to continued limestone deposition in the more proximal part of the basin and time equivalent with shale and marl deposition in the deeper central part of the Eiberg Basin. Reddish oxidized, silty marls of the Schattwald beds succeed the 30- 50 cm of grey Tiefengraben Mb sediments in Kuhjoch and Hochalplgraben, but are not developed in the Tiefengraben section.

2.3 Materials The transition from the Kössen Fm (Eiberg Mb) to the Kendlbach Fm (Tiefengraben Mb) was sampled on high resolution (2-10 cm) at three localities (Kuhjoch, Hochalplgraben and Tiefengraben) in the Northern Calcareous Alps, Austria. Bulk stable C-isotope ratios and total organic carbon (TOC) content were measured on sedimentary organic matter from marly to clayey sediments. A high resolution palynological study was performed on the same samples.

2.4 Methods: C-isotope and TOC measurements Carbonate was removed from the sediments by rinsing 0.9 g of powdered sediment twice with 15 ml of 1 M HCl. Neutral pH values were reached by rinsing the residue twice with 22.5 ml demineralized water. After freeze drying, around 9 mg of homogenized de- carbonated sample residue was analyzed online for carbon content with a CNS-analyzer (NA 1500) following standard procedures. The TOC content of the sediment from Hochalplgraben and Tiefengraben was obtained by multiplying the carbon content of the de-carbonated sample by the ratio between the weight of the de-carbonated sample and the original weight of the sample. TOC values from Kuhjoch were obtained by pyrolysis of bulk sediment on a Rock-Eval VI apparatus using lab procedures as described in Behar et al. (2001). Pyrolysis measurements were performed at the integrated laboratory of the Faculty of Geosciences (Utrecht University) and the Netherlands Institute of 13 Applied Geosciences (TNO-NITG). The δ Corg values were measured on homogenized

35 Climate change driven black shale deposition

cm Kuhjoch Hochalplgraben Tiefengraben

cm 500 2000

TPi cm 3000 5

4 TPi 0 1500 TPi cm 4

2500 1000

3 TH

1000 TH 2 TH TJB 2000 500 2 TPo

500 RPo RPo RPo

1500 1 0 1 Eiberg RL RL

-32 -30 -28 -26 -24 0 13 -32 -30 -28 -26 -24 δ Corg [‰] 13 δ Corg [‰]

5 1000 FO Parapsiloceras calliphyllum FO Ischyosporites variegatus 4 FO Psiloceras cf. pacificum Heliosporites reissingeri acme 3 FO Psiloceras ex gr. P. tilmanni Acanthotriletes varius acme RL 2 FO Psiloceras spelae tirolicum Conbaculatisporites spp. acme 1 LO Choristoceras marshi Pinuspollenites minimus acme

FO Cerebropollenites thiergartii Cymatiosphaera spp. acme 500

RL Rhaetipollis-Limbosporites zone RPo Rhaetipollis-Porcellispora zone TPo Trachysporites-Porcellispora zone TH Trachysporites-Heliosporites zone

TPi Trachysporites-Pinuspollenites zone 0 -34 -32 -30 -28 -26 -24 Fault 13 δ Corg [‰]

36 Chapter 2

de-carbonated sample residue, containing 25 µg of carbon, by Elemental Analyzer Continuous Flow Isotope Ratio Mass Spectrometry using a Fisons 1500 NCS Elemental Analyzer coupled to a Finnigan Mat Delta Plus mass spectrometer at the Geochemistry group of the Department of Earth Sciences, Utrecht University. Isotope ratios are reported in standard delta notation relative to Vienna PDB. Average analytical precision based on routine analysis of internal laboratory reference materials showed an error margin of 0.04‰ and lower.

2.5 Methods: palynological processing and analysis Between 10 and 20 g of sediment was crushed into small fragments and dried for 24 hours at 60 °C. A Lycopodium spore tablet was added to each sample. The samples were treated twice alternately with cold HCl (30%) and cold HF (40%) to remove the carbonates and silicates, respectively. The residue after chemical treatment was sieved with a 250 µm and a 15 µm mesh. Because of the large amount of mineral residue which still occurred in the samples after sieving, ZnCl2 was applied to separate the lighter organic material from the heavier mineral particles like pyrite. This lighter material was transferred from the test-tube and sieving was repeated with a 15 µm mesh. The remaining organic material was mounted on two slides per sample with glycerine jelly. The slides are stored in the collection of the Section Palaeoecology, Laboratory of Palaeobotany and Palynology, Utrecht University, The Netherlands. Pollen and spore identification was mainly based on Schulz (1967), Morbey (1975), Lund (1977) and Schuurman (1976, 1977, 1979). Around 300 terrestrial palynomorphs per sample were counted. Lycopodium spores were counted concomitantly, but they were excluded from the terrestrial palynomorph sum. The palynomorph concentrations (absolute number of palynomorphs per gram) were calculated based on the fossil palynomorphs counted, the Lycopodium spores counted, the dry weight of the sample, and the total number of Lycopodium spores added to the sample. Relative abundances were calculated and plotted using the Tilia and TgView computer programs (Grimm, 1991-2001).

3. Bio- and C-isotope stratigraphy of the Eiberg Basin

High-resolution correlation of several T-J boundary sections in the Eiberg Basin has been established by Bonis et al. (2009-a), Hillebrandt et al. (2007) and Ruhl et al. (2009), based on biological and geochemical proxies, respectively. Here we present an integrated framework for the transition of the late Rhaetian Kössen Fm limestones to the marls of the Tiefengraben Mb in Kuhjoch, Hochalplgraben and Tiefengraben (Figure 2). The onset of the initial and main negative C-isotope excursions of the Eiberg Basin are biostratigraphically confined by the last occurrence (LO) of the late Rhaetian ammonite Choristoceras marshi and the first occurrence (FO) of the Psiloceras spelae tirolicum ammonite. The latter is the marker for the base of the Jurassic (Hillebrandt et al., 2007;

Figure 2 Correlation of Kuhjoch, Hochalplgraben and Tiefengraben based on C-isotope stratigraphy, palynomorph assemblage zones and bio-events. The palynomorph assemblage zones are based on Kürschner et al. (2007) and Bonis et al. (2009). Dotted lines are correlation lines based on C-isotope stratigraphy from Ruhl et al. (2009). The shaded area represents the high resolution studied transition interval from the Kössen Fm to the Kendlbach Fm. The lithostratigraphy of these sections was given in Kürschner et al. (2007) and Hillebrandt et al. (2007).

37 Climate change driven black shale deposition drier s e 0 0 0 wetter 0 3 grey ) 0 0 Foraminiferal test linings Acritarchs Botryococcus sp. Prasinophyt Dinoflagellate cysts 0 0

. 0 s

g 0

s errestrial (

n 0

s T

& aquatic ( black )

l 1 c

t palynomorphs conc. [ppg]

o l

r 0

t 0 0

f 0

B 1 n 1

e m

y 0 0 0

o 8 8

p F

i s

t 0 0

a 6 6

6 s y r

h c

a 0 0

a i

l 4 4 r 4 Aquatic

e c

g A

f 0 0 0

o 2 2 2

n palynomorphs [%] i D 0 0 0 4 8 0 6 0 0 3 6 [%] 0 4 0 0 2 4 0 2 0 0 1 2 polypartita Cymatiosphaera 0 0 0 0 6 0 0 8 8 0 5 0 0 0 [%] 6 6 4 0 3 0 0 4 4 0 2 0 0 Classopollis 2 2 meyeriana 0 1 0 0 0 4 1 8 6 2 CIE 1 5 CIE 0 CIE 6 1 4 8 4 3 initial 6 initial OC [%] initial 2 T 4 2 1 2 0 0 0 4 5 5 2 2 - - 2 - ] 6 7 ‰ 2 [ 2 - -

7 g

2 r - 8

9 o 2 2 - - 9 2 0 1 - 3 3 - - δ 13C 2 3 1 3 3 3 - - - iefengraben T Kuhjoch Hochalplgraben 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 0 0 6 8 4 2 6 0 4 0 9 8 7 6 5 4 3 7 6 5 4 3 2 1 - - 5 4 5 5 6 6 7 7 3 2 2 2 2 2 2 2

(cm)

(cm) 1 1 1 1 1 1 1 1 Depth

(cm)

Depth Depth b M . E b M . E b M n e b a r g n e f e i T b M n e b a r g n e f e i T b M n e b a r g n e f e i T b M g r e b i E

m F h c a b l d n e K m F . K m F h c a b l d n e K m F n e s s ö K m F h c a b l d n e K m F . K

n a i t e a h R t s o m r e p p u n a i t e a h R t s o m r e p p u n a i t e a h R t s o m r e p p u Dark grey marl Black shale interval interval interval interval interval interval interval ? Spore interval cursion interval Light grey marl Red marl (Schattwald beds) Limestone Classopollis Classopollis pre-excursion interval pre-e x Classopollis post-excursion interval post-excursion interval post-excursion interval Cymatiosphaera Cymatiosphaera Cymatiosphaera Cymatiosphaera Lithological key

13 Figure 3 Lithology, δ Corg curve and total organic carbon (TOC) of bulk sedimentary organic matter across the Kössen Fm-Kendlbach Fm transition in Tiefengraben, Kuhjoch and Hochalplgraben. Also indicated are the relative abundance of Classopollis meyeriana and Cymatiosphaera spp. palynomorphs compared to all palynomorphs, the composition of the aquatic palynomorph fraction and the absolute palynomorph concentrations. The schematic humidity curve is based on statistical (PCA) analysis of palynological data (Chapter 4). See Appendix 2

38 Chapter 2

Hillebrandt and Krystyn, 2009). The established high resolution palynological zonation scheme for the Eiberg Basin (Kürschner et al., 2007; Bonis et al., 2009) together with the FO of macro- and microfossil species and acmes of marine and terrestrial palynomorphs, support the correlation between different section in the Eiberg Basin based on C-isotope stratigraphy (Ruhl et al., 2009). The FO of Cerebropollenites thiergartii is approximately contemporaneous with the FO of Psiloceras spelae tirolicum in the Eiberg Basin and is suggested as a useful palynological marker for the T-J boundary (Bonis et al., 2009- a). The very similar C-isotope record of the Tiefengraben and St. Audrie’s Bay (UK) sections enables correlation outside the Tethys Ocean (Kürschner et al., 2007). The FO of Cerebropollenites thiergartii pollen in Austria and the UK is time-equivalent relative to the C-isotope records. This further supports the recognition of the initial and main C-isotope excursions at the T-J transition interval in the Eiberg Basin and its correlation to the T-J boundary record of St. Audrie’s Bay.

4. Results

Dinoflagellate cysts (mostly Rhaetogonyaulax rhaetica) and foraminiferal test linings are the main constituents of the aquatic palynomorphs at the onset of the initial CIE (Figure 3). The lower half of the initial CIE directly follows at the top of the limestones and coincides with black shale deposits. This interval is characterized by 13 highly increased TOC values of up to 14% (Figure 3). The negative shift in the δ Corg signature and increased TOC values in Kuhjoch and Hochalplgraben co-occur with a peak abundance of up to 80% of Classopollis meyeriana relative to all palynomorphs. Terrestrial palynomorph concentrations from Kuhjoch show a dramatic increase to values of up to 30000 palynomorphs per gram (ppg) (Figure 3). In Tiefengraben, the lower half of the initial CIE, the highly increased TOC values and peak Classopollis meyeriana abundances are missing (Figure 3). A spore dominated interval (Acanthotriletes varius, Baculatisporites spp., Calamospora tener, Carnisporites anteriscus, Conbaculatisporites spp., Convolutispora microrugulata, Deltoidospora spp. and Todisporites spp.) directly succeeds the Classopollis meyeriana peak abundance at Kuhjoch. Maximum spore abundance increases to 55% (~2650 ppg) relative to terrestrial palynomorphs. The 13 spore interval coincides with relatively constant and extreme negative δ Corg values of -31‰. This interval is succeeded by a mass abundance of green algae, the prasinophyte Cymatiosphaera spp., of up to 80% relative to all palynomorphs (Figure 3 and Figure 4). Aquatic palynomorph concentrations during peak Cymatiosphaera abundance are higher than terrestrial palynomorph concentrations in Kuhjoch. In the post initial CIE interval, Cymatiosphaera %, Classopollis meyeriana % and TOC % return to relatively low pre- excursion values and dinoflagellate cysts become abundant again. Cymatiosphaera abundance increases again (to ~23%) in the post initial CIE interval at 1570 cm in the more shallow and restricted Tiefengraben section. Observed changes in aquatic palynomorphs are similar in Hochalplgraben and Kuhjoch. Although sampling resolution is much lower in Tiefengraben, changes in relative aquatic palynomorph abundance are similar to the sections in the centre of the basin.

39 Climate change driven black shale deposition

5. Discussion

The marine extinctions and (floral) turnovers during the end-Triassic and the transition to the Jurassic (Hallam, 2002; Tanner et al., 2004; Kiessling et al., 2007; McElwain et al., 2007; Lucas and Tanner, 2008) coincide with two marked negative C-isotope excursions of up to 7‰, in several records world-wide (Pálfy et al., 2001; Hesselbo et al., 2002; Guex et al., 2004; Ward et al., 2004; Galli et al., 2005; Galli et al., 2007; Kürschner et al., 2007; Ward et al., 2007; Williford et al., 2007; van de Schootbrugge, 2008; Ruhl et al., 2009). Major extinction events in the Phanerozoic are often contemporaneous with anoxic events and black shale deposition. Some examples are: a late Early Cambrian extinction event (Hallam and Wignall, 1999 and references therein), the Frasnian- Famennian mass extinction (Pujol et al., 2006; Bond and Wignall, 2008), the Devonian- Carboniferous Hangenberg mass extinction event (Caplan and Bustin, 1999; Hallam and Wignall, 1999) and the end-Permian extinction event (Takahashi et al., 2009). The early Toarcian Ocean Anoxic Event coincides with major marine extinctions (Wignall and Bond, 2008 and references therein) and distinct negative excursions in the C-isotope signature (Hesselbo et al., 2000; Kemp et al., 2005). Also the base of the Jurassic in NW Europe (Hallam, 1995) and Canada (Wignall et al., 2007) is marked by oxygen restricted facies and black shale deposition. Several new T-J boundary sections in the Eiberg Basin demonstrate high TOC values of up to 14% in the uppermost Rhaetian coinciding with the onset of the initial CIE (Ruhl et al., 2009). Finely laminated sediments in this interval suggest anoxic bottom water conditions. We propose a model to explain reduced mixing and anoxic conditions related to abrupt environmental changes in the end-Triassic Eiberg Basin.

5.1 Fresh-water influx and regional climate change in the Eiberg Basin Our high resolution geochemical and palynological study across the initial CIE at the T-J transition interval in the Eiberg Basin shows dramatic changes in the relative abundance of certain marine and terrestrial palynomorphs. Abundant Classopollis meyeriana pollen at the base of the studied section suggest warm and dry regional climatic conditions (Vakhrameev, 1981; Vakhrameev, 1987). A sudden and dramatic twentyfold increase in terrestrial pollen and spore concentrations of up to 30000 ppg marks the onset of the initial CIE. Classopollis meyeriana represent up to 90% of the palynomorphs in this interval. Increased pollen influx into the basin can be explained by an abrupt increase in seasonality in a semi-arid region. Classopollis meyeriana and amorphous organic matter bearing soils are washed into the Eiberg Basin, causing strongly increased TOC values. Additionally, the breakdown of carbonate production caused a condensed interval and therefore an increase in concentration of terrestrial organic material. A spore-dominated zone indicating wetter conditions directly follows the peak TOC values in Kuhjoch. Subsequent dramatically increased Cymatiosphaera abundance of up to 80% (relative to all palynomorphs) and increased absolute marine palynomorph concentrations suggest a basin-wide acme of this particular prasinophyte species. These green algae are known to prefer brackish to fresh water conditions as well as increased nutrient availability (Prauss and Riegel, 1989; Mudie, 1992; Guy- Ohlson, 1996 and references therein; Prebble et al., 2006;). The prasinophyte acme

40 Chapter 2

in the Eiberg Basin coincides with the absence of foraminifera (Kürschner et al. 2007). Prasinophyte abundance appears sensitive to grazing, which may explain an additionally increased abundance when foraminifera are absent (Metaxas and Scheibling, 1996). The (almost) absence of foraminiferal linings and a decreasing number of foraminifera species (Hillebrandt et al., 2007) directly following the Kössen limestones may thus be an alternative explanation for part of the prasinophyte mass occurrence (Kürschner et al., 2007). However, prasinophytes may be considered as disaster species that are highly successful in adapting to changing environments (Guy-Ohlson, 1996) as they survive widespread extinctions in the middle Palaeozoic (Tappan, 1980). The decrease in foraminifera may be caused by the calcification crisis resulting from acidification of the atmosphere and oceans by volcanic activity and methane release. In the Eiberg Basin, the initial CIE concurs with the prasinophyte acme and the absence of foraminifera which underlines the acidification hypothesis and consequent calcification crisis. A prasinophyte peak at the T-J boundary interval corresponding to the δ13C negative excursion is also reported from the Csővár Basin in Hungary (Götz et al., 2009) supporting the possibility of an interregional signal. Recently, van de Schootbrugge et al. (2007) suggested that green algal phytoplankton blooms may be symptomatic of elevated carbon dioxide levels in the atmosphere and oceans.

25 μm a 25 μm b 25 μm c

Figure 4 (A) Cymatiosphaera sp. with a fine wall structure (Hochalplgraben), (B)Cymatiosphaera sp. with a coarse wall structure (Kuhjoch), (C) both Cymatiosphaera types from the peak abundance interval (Hoch-alplgraben). See Appendix 3

A relatively wetter climate concurrent with the initial CIE is inferred from multivariate statistical analysis of palynological data from Hochalplgraben and Kuhjoch (Chapter 4). This is reflected by an increased spore abundance at the transition from the limestones of the Kössen Fm to the marls of the Kendlbach Fm in palynomorph records from the Eiberg Basin (Karle, 1984; Bonis et al., 2009-a). Increased humidity led to increased run-off, enhanced erosion and increased supply of nutrients and terrestrial organic matter into the basin. Although the Kössen Fm represents a full marine basinal facies (Kuss, 1983; Golebiowski and Braunstein, 1988; Golebiowski, 1990), increased run-off and decreased salinity of the surface waters likely led to the formation of a fresh-water lens in the semi-restricted Eiberg Basin. This is reflected in the aquatic palynomorph abundance by an increase in prasinophytes and a decrease in dinoflagellate cysts (Figure 3). The reduced salinity of the surface waters possibly led to stratification of the water column and anoxic bottom water conditions concurring with the initial CIE. This is

41 Climate change driven black shale deposition

supported by millimetre scale organic rich finely laminated sediments that are present throughout the Eiberg Basin at the base of the Tiefengraben Mb (Figure 5). The sea level lowstand coinciding with the initial CIE possibly caused a semi- but not complete closure of the Eiberg Basin that further enhanced a strongly reduced circulation. Furthermore, the onset of the transgression during the T-J boundary interval could have caused the spreading of oxygen-deficient bottom waters (Hallam, 1990; Hallam, 1995) which may have contributed to increased preservation in shallower settings. Increased prasinophyte abundances through geological time are often related to temperate and cool waters, e.g., higher palaeolatitudes or in concurrence with major global glaciation episodes (Prauss, 2007). However, the lack of major glaciations in the late Triassic (Frakes et al., 1992; Satterley, 1996; Hallam and Wignall, 1999) and the relatively low palaeolatitude of the Eiberg Basin favour a decreased salinity and increased nutrient availability rather than lower sea surface temperature. Several short-term end-Triassic climate changes with CO2 values of up to 3000 ppmv based on pedogenic carbonate nodules have been reported for the Rhaetian (Cleveland et al., 2008). A fourfold increase of atmospheric CO2 and global warming across the T-J boundary is also suggested from stomatal frequency values (McElwain et al., 1999). Whether these climate changes are caused by the onset of CAMP volcanism (Nomade et al., 2007) or mainly linked to the release of methane hydrates is still subject to debate. Possible end-Triassic global warming may have caused a pole ward expansion of the Hadley cells and a subsequent shift in climate belts. Modelling studies support a monsoonal climate in the upper Triassic western Tethys Ocean (Sellwood and Valdes, 2007). The relatively low palaeolatitude of the Eiberg Basin during this period (Kent and Tauxe, 2005) could have caused an increased sensitivity for enhanced monsoonal activity in this region. Alternatively, global warming could have led to an enhanced hydrological cycle which resulted into increased precipitation in the western Tethys realm.

5.2 Mesozoic black shale deposition and climate change During geological history prasinophyte mass occurrences are often linked to black shale deposition (Riegel, 2008) which suggests a climatological and/or oceanographic control (Prauss and Riegel, 1989). Generally, deposition of black shales is explained either by the stagnation/preservation model or by the upwelling/enhanced marine productivity model (e.g. Heimhofer et al., 2006; Meyers, 2006; Negri et al., 2009). A combination of both mechanisms is also possible, with an increased freshwater and nutrient input via river runoff leading to stratification and increased productivity (Negri et al., 2009). The onset and main phase of black shale deposition in the Eiberg Basin resulted from increased terrestrial organic matter influx from the hinterland with enhanced preservation caused by a stagnant water column. The end of black shale deposition is marked by increased primary productivity of green algae as a result of less saline surface waters with increased nutrient conditions. Black shale events in the Mesozoic, particularly in the Cretaceous often resulted from changes in climate and the hydrological regime, with a similar mechanism as we propose for the T-J transition period in the Eiberg Basin. A causal relationship between enhanced volcanism, gas-hydrate dissociation and climate change possibly led to Oceanic Anoxic Events (Jenkyns, 2003). The early Toarcian

OAE is marked by a warming climate trend, which was probably related to increased CO2

42 Chapter 2 values (Hesselbo et al., 2000) and that was 14mm coupled to an enhanced hydrological cycle and riverine input, causing less saline surface waters, stratification and anoxic bottom water conditions in most NW European epicontinental basins (Mailliot et al., 2009). During the early Cretaceous Valanginian Weissert OAE, volcanism of a large igneous province was presumably responsible for an increase of CO2, triggering a climate change and accelerated hydrological cycling (Erba et al., 2004). Semi-arid conditions at the Jurassic- Cretaceous boundary in Dorset (UK), partly inferred from a Classopollis dominated vegetation, are succeeded by more humid conditions in the middle Berriasian (Schnyder et al., 2009). An increasingly wetter climate led to enhanced freshwater influx from the hinterland and organic- matter enrichment (with TOC values of up to 8.5%) of littoral sediments in an evaporitic and semi-closed environment. An increased spore content was documented during Figure 5 Thin-section of finely laminated organic this transition from a semi-arid to a semi- rich sediments at the base of the Tiefengraben Mb humid phase that was furthermore marked in the Eiberg Basin (sample from Schlossgraben, for description and lithostratigraphy of this section by acmes of various algal types (Schnyder see Chapter 1). See Appendix 4 et al., 2009). Enhanced terrestrial organic matter influx and preservation is thus linked to a climate-driven changing hydrological regime in the coastal area. Also mid-Cretaceous episodes of black shale deposition coincide with times of wetter climate (e.g. Meyers, 2006). A greenhouse climate was present due to increased rates of seafloor spreading and the evolution of associated volcanism-derived CO2. This warmer climate caused increased sea surface evaporation and subsequently a wetter climate and enhanced hydrological cycle (Meyers, 2006). Increased continental runoff would have delivered more soil derived nutrients to the coastal ocean and increased thermohaline stratification. This is a strikingly similar model as we propose for the end-Triassic. During the Cretaceous Barremian-Early Aptian, finely laminated black shales (e.g. Blätterton horizons, Fischschiefer) with TOC contents of up to 7% have been deposited in the Lower Saxony Basin (Mutterlose et al., 2009). Comparable with our palynomorph record from the Eiberg Basin, the laminated sediments show a strong influx of terrestrial organic matter, a low abundance of dinoflagellate cysts andan enrichment of prasinophytes. Although the main prasinophyte constituents are different (Pterospermella, Leiosphaera), this group is interpreted as an indicator for reduced salinity of surface waters (Below and Kirsch, 1997). Strong terrigenous influx with a

43 Climate change driven black shale deposition

subsequent weaker marine signal caused reduced salinity of the surface waters. This set the right conditions for laminated sediment deposition in the late Barremian (Mutterlose et al., 2009). Salinity driven stratification of the water column during more humid periods was caused by significant freshwater runoff. Seasonally increased runoff from the hinterland caused also an increased surface water primary productivity (Mutterlose et al., 2009). A final example of black shale deposition related to enhanced continental runoff occurred in the late Aptian Vocontian Basin (western Tethys Ocean) (Heimhofer et al., 2006). This so-called ‘Niveau Jacob’ is characterized by enriched TOC values, a laminated sedimentary texture and strongly increased terrestrial palynomorph abundances. The increased fern spore abundance in these sediments probably indicates warmer and more humid conditions in the hinterland. Increased runoff caused stratification of the water column, anoxic bottom water conditions and increased preservation of the (largely terrestrial) sedimentary organic matter. In addition, the strongly enhanced input of land plant-derived organic matter also may have led to increasing oxygen-deficient conditions in the bottom waters (Heimhofer et al., 2006). Oxidation of the highly increased (sedimentary) organic matter content in the Eiberg Basin at the T-J transition could have further enhanced dysoxic conditions in the bottom waters during black shale formation.

6. Conclusions

High-resolution correlation of Triassic-Jurassic boundary sections (Kuhjoch, Hochalplgraben and Tiefengraben) in the Eiberg Basin, based on biological and geochemical proxies, shows several remarkable changes in the palaeoenvironment. One particular event is the transition from the limestones of the Kössen Fm to the marls of the Kendlbach Fm. This transition is accompanied by the deposition of black shales that are present throughout the Eiberg Basin at the base of the Tiefengraben Mb. The lower half of the initial negative carbon isotope excursion coincides with increased TOC values, highly increased terrestrial palynomorph concentrations and peak Classopollis meyeriana abundance. This is interpreted as organic soils being washed into the basin caused by increased seasonality. We propose a model in which increased humidity (supported by the higher abundance of spores) may have led to increased runoff, enhanced erosion and increased supply of nutrients and terrestrial organic matter into the basin. Increased runoff and decreased salinity of the surface waters led to the formation of a freshwater lens in the semi-restricted Eiberg Basin. This is reflected by the highly increased Cymatiosphaera abundance. Increased absolute marine palynomorph concentrations suggest a basin-wide acme of this particular prasinophyte species. The reduced salinity of the surface waters probably led to stratification of the water column and anoxic bottom water conditions coinciding with the initial CIE. Also in other Mesozoic time periods, changes in climate (e.g. CO2 increase) and an enhanced hydrological cycle were main drivers of enhanced organic matter preservation.

44 Chapter 2

Acknowledgements

The authors acknowledge funding from the High-Potential stimulation program of Utrecht University. We thank J. van Tongeren and N. Welters for assistance in the laboratory and A. van Dijk (Int. Geoch. Lab., UU-NITG) for performing the C-isotope analyses. We thank S. Hesselbo and an anonymous reviewer for their constructive reviews of the manuscript.

45 46 Chapter 3

Sedimentary organic matter characterization of the Triassic-Jurassic boundary GSSP at Kuhjoch (Austria)

The Triassic-Jurassic (T-J) boundary interval coincides with enhanced extinction rates in the marine realm and pronounced changes on the continents. It is further marked by distinct 13 13 negative excursions in the δ Corg and δ Ccarb signature that may represent strong perturbations of the global carbon cycle. In the Eiberg Basin in the western Tethys realm, this important interval in Earth history is marked by the formation of black shales. We present integrated geochemical, stable isotope and palynological data from the Kuhjoch section, the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic (Northern Calcareous Alps, Austria). We show that the initial Carbon Isotope Excursion (CIE) is marked by only minor changes in kerogen type, which is mainly of terrestrial origin. Increased Total Organic Carbon (TOC) concentrations of 9% at the first half of the initial CIE coincide with Hydrogen Index values of over 600 mg HC/g TOC. The high correlation (with R2 = 0.93) between HI values and terrestrial Cheirolepidiaceae conifer pollen suggests a terrestrial source for the hydrogen enriched organic compounds. The lack of major changes in the origin of the sedimentary organic matter suggests that 13 changes in the δ Corg composition are genuine and represent true disturbances of the global C-cycle. The sudden decrease in Total Inorganic Carbon (TIC) concentrations coincides with 13 a 4.5‰ negative drop in δ Corg values and may correspond to the beginning of CAMP related volcanic activity and represents the onset of the biocalcification crisis. The second half of the initial CIE is marked by the dramatic increase of green algae remains in the sediment. The simultaneous increase of the

Corg/Ntot ratio suggests increased marine primary production at the final stage of black shale formation. The acme of green 13 algae may have prolonged the initial bulk δ Corg negative CIE when atmospheric 13C values already returned to pre-excursion levels.

47 End-Triassic black shale formation

48 Chapter 3

1. Introduction

Large fluctuations in Mesozoic and Palaeozoic climate are often linked to widespread deposition of organic carbon rich sediments along continental margins (Negri et al., 2009). The deposition of black shales at the T-J boundary interval has been reported from the Panthalassic and Tethys Ocean (Hallam, 1995; Wignall et al., 2007; Bonis et al., in press). This important interval in Earth history is marked by elevated extinction rates in the marine realm (Raup and Sepkoski, 1982) and marked changes in continental ecosystems (McElwain et al., 1999; Olsen et al., 2002; Tanner et al., 2004; Bonis et al., 2009). Two distinct negative carbon isotope excursions (CIEs) at the T-J boundary interval have been attributed to major disturbance of the global carbon cycle (Hesselbo et al., 2002) that may be linked to the onset of Central Atlantic Magmatic Province (CAMP) volcanism (Marzoli et al., 1999 and 2004). Negative CIEs at the T-J transition interval have been documented in both the marine (e.g. Hesselbo et al., 2002; Ward et al., 2004; Pálfy et al., 2007; Ruhl et al., 2009) and terrestrial realm (McElwain et al, 1999; Hesselbo et al., 2002). The short-lived “initial” CIE concurs with the major end- Triassic biotic turnover and is separated from the longer-lived “main” CIE by a return to Rhaetian base values (Hesselbo et al., 2002). The onset of the main CIE coincides with the base of the Jurassic, which is defined by the first occurrence of thePsiloceras spelae ammonite species (Hillebrandt et al., 2007; Ruhl et al., 2009). Mass extinction events in the Phanerozoic are often associated with distinct perturbations in the C-isotope signature which are reflected in the carbon isotope records. At the T-J transition, however, it has been recently argued that changes in the bulk C-isotope composition of the sedimentary organic matter (SOM) are largely controlled by changes in type of organic matter (van de Schootbrugge et al., 2008). We present an integrated geochemical, stable-isotope and palynological study from the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic at Kuhjoch (Austria). In this study, we assess the implications of C-burial events and possible changes in kerogen at the T-J boundary interval, for the size and nature of the 13 δ Corg negative excursions. Combined high resolution Rock-Eval VI and palynological data are used to constrain the source of sedimentary organic matter and the associated history of environmental changes. We further discuss the stratigraphic relationship between the onset of a biocalcification crisis with the beginning of the CAMP volcanism, and events during the T-J transition.

2. Material & methods

Characterization of the bulk organic matter from the Triassic-Jurassic boundary section at Kuhjoch was performed by Rock-Eval (RE) and total carbon (TC) measurements, respectively on a Rock-Eval VI plus TOC (Total Organic Carbon) module and a Leco SC-632 at the laboratory of TNO Built Environment and Geosciences (TNO-NITG, Utrecht, the Netherlands). The analytical procedure is based on the laboratory’s internal standard operating procedure GL-WV 204 for Rock-Eval analysis. The measurements were performed on a set of 74 marly to clayey samples from an almost 14 m thick interval spanning the transition from the Eiberg to the Tiefengraben Mb (Kössen and Kendlbach Fm). Sediments from Kuhjoch and other nearby T-J boundary sections were

49 End-Triassic black shale formation

1200 [a] [b] [c] [d] 1100 > 1000

900

800

700 Hettangian Jurassic

600

500 Rhaetian Triassic

400 main CIE grey Tiefengraben Mb grey Tiefengraben

300 >

200 CIE initial Tiefengraben Mb Tiefengraben Schattwald beds 100 Kendlbach Fm

grey Tg Mb >

0 >

-100 Eiberg Mb -200 Kössen Fm -32 -30 -28 -26 -24 0 2 4 6 8 0 2 4 6 8 10 0 200 400 600

Limestones 13 Corg [‰] TOC [%] TIC [%] H.I. Calcaroues rich marls

Marls Organic rich marls Organic rich shales Organic poor red marls

Figure 1 Geochemical proxy records of environmental change across the T-J boundary, in the Kuhjoch section (Austria). (A) The organic C-isotope signature [‰], (B) Total Organic Carbon content [%], (C) Total Inorganic Carbon content [%] and (D) Hydrogen Index values [mg HC/g TOC]. White diamonds in the TOC and HI records show samples with values too low for a reliable S2 determination. deposited in the intra-platform Eiberg Basin in the western Tethys realm. A detailed (palaeo-) geographical and geological description of this section is reported in Hillebrandt et al. (2007) and Ruhl et al. (2009). Quality control was provided by analyzing one ISE

921 standard for every 10 sediment samples (S2-SD: 0.3; Tmax-SD: 2.32). After freeze drying, the TC content of 0.2-0.3 g of homogenized sample residue was determined by total combustion at 1350 °C at the Leco SC. To thermally extract the amount of free hydrocarbons (HC) (S1 peak), Rock-Eval VI measurements were performed by heating approximately 65 mg of homogenized sample at 300 °C. The pyrolysable amount of hydrocarbons (S2 peak) is measured by heating the sample in an inert atmosphere from 300 °C to 650 °C at a rate of 25 °C per minute. S1 and S2 are given in mg HC/g sample. TOC is determined by the sum of the carbon in the pyrolysate and the carbon from the residual oxidized organic matter. Total Inorganic Carbon (TIC) is the sum of inorganic carbon measured during pyrolysis and oxidation. The Hydrogen Index (HI) is defined as the amount of pyrolysed hydrocarbons normalized to the TOC [(S2*100)/TOC]. The Tmax value is the temperature with maximum pyrolysed hydrocarbon production (S2). This value functions as a thermal maturity indicator. The parameters described by the Rock- Eval VI method are reported in Behar et al. (2001). High resolution organic C-isotope records were further established for several other nearby T-J boundary sections in the Eiberg Basin (Ruhl et al., 2009). Sample preparation procedures and results are

50 Chapter 3

published in Ruhl et al. (2009). Twelve samples from the initial CIE interval from Kuhjoch were prepared for palynological study. Detailed description of the processing method is given in Kürschner et al. (2007) and Bonis et al. (2009).

3. Results

High resolution Rock-Eval VI measurements on sediments across the Triassic- Jurassic boundary at Kuhjoch show relatively low TOC values of less than 1% for most of the section (Figure 1-B). Peak TOC values of up to 9% (Figure 1-B and 2-C) coincide with the onset and first half of the rapid initial negative CIE at the very base ofthe Tiefengraben Mb (Figure 1-A and 2-A). Hydrogen index values are generally low, but peak HI values of over 600 mg HC/g TOC exactly coincide with increased TOC values in the lower half of the initial CIE (Figure 1-D and 2-D). An earlier but smaller peak in HI values (at ~-150 m) also coincides with increased TOC and more negative organic carbon isotope values. An increased TIC content of ~10% is reported from occasional marly sedimentary horizons between the limestones of the Eiberg Mb. The TIC content decreases to less than 1% in the marls at the base of the Tiefengraben Mb (Figure 2-B). Values increase again to 2-4% in the main part of the Tiefengraben Mb succeeding the Schattwald beds (Figure 1-C). The S1 and S2 peak values vary around 0.03 (Figure 4-A) and 0.1 mg HC/g sediment respectively (Figure 4-B), with peak values of about 0.45 and 35 mg HC/g sediment concurring with increased TOC values and the onset of the initial CIE at a stratigraphic position of ~0 m in the lithological column (Figure 4-A and B). However, TOC and S2 values are very low in the Schattwald beds from 20-230 cm in the Kuhjoch section (Figure 4-B). Low S2 values complicate a reliable determination of the position of the

S2 peak in these samples (Figure 4-C) and therefore Tmax (Figure 4-D). The reliability of other parameters, e.g. TOC and HI may therefore be hard to define for this interval.

Tmax values in the rest of the samples are typically between 430-440 °C (Figure 4-D) and correspond to vitrinite reflectance values of about 0.8%. 13 The bulk δ Corg values in the Kuhjoch section show a negative correlation with HI values (with R2 = 0.60), but only when five samples with increased HI values or not considered (black trendline Figure 3-A). However, when these samples from the onset of the initial CIE (light grey diamonds) are taken into account then the correlation 13 2 between δ Corg and HI values is far less good (with R = 0.25, Figure 3-A). A pseudo

Van Krevelen diagram in which HI values are plotted against Tmax, characterizes these five samples as typically Type II and Type II+III organic matter (Figure 3-B).The sedimentary organic matter in the remaining samples, including five samples from the second half of the initial CIE (dark grey diamonds, Figure 3-B), is characterized as of Type III terrestrial organic matter. Palynological study on the same samples shows highly increased terrestrial and aquatic palynomorph concentrations, of ~30000 ppg and 8000 ppg respectively, coinciding with the initial CIE (Figure 2-E). Peak terrestrial palynomorph concentrations co-occur with absolute concentrations (~30000 ppg) and relative abundance (~85%) of Classopollis meyeriana conifer pollen (Figure 2-F). Total sulphur concentrations are generally low (below the detection limit of 0.05%) but slightly increased values (0.09%, Figure 2-H) occur together with peak TOC and HI values and

51 End-Triassic black shale formation 9 0 . 0 0 2 1

[h] 6 tot 0 . 0 N 0 [%] 8

/ -ratio tot org 3 S 0 0 C . 4 0 0 0 0 0 0 6 6 [g] 0 0 0 0 4 4 0 spp. [%] 0 0 0 2 2 conc. [ppg] spp. conc. Cymatiosphaera Cymatiosphaera 0 0 0 8 3 [f] 0 *10 6 2 0 3 Calcaroues rich marls Organic rich marls Organic rich shales Organic poor red marls Limestones Marls 4 *10 1 0 Classopollis 2 Classopollis meyeriana [%] 0 0 conc. [ppg] meyeriana conc. 3 3 [e] *10 *10 2 2 3 3 0 *10 *1 conc. [ppg] 1 1 conc. [ppg] Terr. palynom. Terr. Aq. palynom. 0 0 0 0 6 [d] 0 0 4 H.I. 0 0 2 [mg HC/ g TOC] 0 8 [c] 6 4 TOC [%] 2 0 0 1 [b] 8 6 TIC [%] 4 CIE 2 initial 0 4 2 - ] 6 ‰ 2 [ -

g r

8 o 2 C - 13

0 3 δ [a] - 2

Schattwald beds Schattwald

Tiefengraben Mb Tiefengraben Eiberg Mb Eiberg

Kössen Fm Kössen Kendlbach Fm Kendlbach

Rhaetian uppermost 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 8 6 4 2 8 6 4 2 0 8 6 4 2

- - - -

1 1 1 1 1 1 tratigraphic position (cm) position tratigraphic s - - - - -

52 Chapter 3

increased terrestrial palynomorph concentrations. Increased Stot values are succeeded by increased Corg/ Ntot ratio values (Figure 2-H) that coincide with the onset of the green algae Cymatiosphaera spp. mass occurrence (with absolute concentrations of ~6000 ppg and relative abundance of ~70%, Figure 2-G). The initial CIE is marked by a good correlation between the absolute terrestrial palynomorph concentration and HI values (with R2 = 0.91, Figure 3-D). The correlation between the absolute concentration of Classopollis meyeriana conifer pollen and HI values is even better with R2 values of 0.93 (Figure 3-C). However, the correlation between HI and TOC values is less good (with R2 = 0.52, Figure 3-F). HI values show no correlation to absolute and relative Cymatiosphaera spp. green algae abundance, with R2 values of 0.002 and 0.06, respectively (Figure 3-E).

4. Discussion

The Triassic-Jurassic boundary interval is at several locations around the world, 13 13 marked by two negative excursions of 2-7‰ in the bulk δ Corg and δ Ccarb signature (Palfy et al., 2001; Hesselbo et al., 2002; Guex et al., 2004; Ward et al., 2004; Kürschner et al., 2007; Ward et al., 2007; Williford et al., 2007; Ruhl et al., 2009) and 3‰ (Galli et al., 2005; Galli et al., 2007; van de Schootbrugge et al., 2007, Korte et al., 2009), respectively. The rapid initial negative CIE coincides with a strong reduction in marine invertebrate diversity (Raup and Sepkoski, 1982; Kiessling et al., 2007) and marked changes in continental ecosystems (McElwain et al., 1999; Olsen et al., 2002; Kürschner et al., 2007; Bonis et al., 2009; Götz et al., 2009) that are possibly related to the onset of major volcanic activity and increased CO2 levels (Huynh & Poulsen, 2005). The onset of the long-lasting main negative CIE coincides with the T-J system boundary, which is defined by the first occurrence (FO) of the Jurassic ammonitePsiloceras spelae tirolicum (Hillebrandt and Krystyn, 2009).

Major climate changes, carbon cycle perturbations, increased CO2 levels and extinction events in the Phanerozoic often coincide with episodes of significant black shale formation (Berner, 1994; Negri et al., 2009). Marine organic rich strata in the Palaeozoic and Mesozoic result from enhanced sedimentary organic matter preservation together with either major basin influx of terrestrial organic matter or highly increased marine primary productivity, which are ultimately related to changes in the palaeoclimate. Enhanced preservation of organic matter in fine-laminated sediments at the T-J boundary in the Eiberg basin is suggested by increased TOC values (Ruhl et al., 2009; Bonis et al., in press). Palynological data from the same samples suggest a shift to wetter palaeoenvironmental conditions with increased precipitation and erosion co-occurring with the initial CIE (Bonis et al, in press). Less saline and nutrient-rich surface water conditions then caused enhanced marine green algae production. Increased preservation of the sedimentary organic matter in the Eiberg basin resulted from salinity stratification and anoxic bottom waters conditions (Bonis et al., in press). Götz et al. (2009) described

13 Figure 2 High resolution records of the initial CIE interval. (A) δ Corg values [‰], (B) Total Inorganic Carbon content [%], (C) Total Organic Carbon content [%], (D) Hydrogen Index values [mg HC/g TOC], (E) Terrestrial and aquatic palynomorph concentration [ppg] in the sediment, (F) Classopollis meyeriana absolute concentration [ppg] in the sediment and relative [%] to all palynomoprhs, (G) Cymatiosphaera spp. absolute concentration [ppg] in the sediment and

relative [%] to all palynomoprhs, (H) Corg/Ntot ratio and Stot abundance [%] in the sediment. See Appendix 5

53 End-Triassic black shale formation Classopollis meyeriana Terrestrial palynomorphs [ppg] -24 900 100 30000 100 30000 90 90 [a] [b] [%] [c] [d] 25000 R2 = 0.14 25000 80 R2 = 0.88 80 800 -25 70 70 20000 20000 60 60 TYPE I 50 15000 50 15000 ] 700

-26 C 40 40

O 10000 10000

T 30 30 R2 = 0.91 g

2 [ppg] 600 20 R = 0.92 20 /

5000 5000

] -27 C 10 10 H ‰ TYPE II Classopollis meyeriana

0 0 palynomorphs [%] Terrestrial 0 0 [

g 500 g

r 0 200 400 600 0 200 400 600

[m o

-28 x C H.I. H.I. e d 13 Cymatiosphaera spp. [ppg]

n 400 i δ 100 7000 10

n TYPE II+III

-29 e 90 9 g [e] 6000 [f] o

r 300 80 8 d

y 70 5000 7 H -30 TYPE III 60 6 R2 = 0.52 200 4000 50 5 40 3000 4 TOC [%] TOC -31 100 30 2000 3 2 2 R = 0.25 20 R2 = 0.06 2 R = 0.60 2 1000 10 R = 0.002 1 -32 0 Cymatiosphaera spp. [%] 0 0 0 0 100 200 300 400 500 600 420 440 460 480 0 200 400 600 0 200 400 600 H.I. Tmax [°C] H.I. H.I.

13 Figure 3 (A) δ Corg [‰] versus HI values [mg HC/g TOC], (B) HI versus [mg HC/g TOC]

Tmax values [°C], (C) Classopollis meyeriana absolute concentration [ppg] and relative abundance [%] versus HI values [mg HC/g TOC], (D) Terrestrial palynomorph absolute concentration [ppg] and relative abundance [%] versus HI values [mg HC/g TOC], (E) Cymatiosphaera spp. absolute concentration [ppg] and relative abundance [%] versus HI values [mg HC/g TOC] and (F) TOC content [%] versus HI values [mg HC/g TOC]. similar prasinophyte green algae blooms in the Csővár section coinciding with the initial CIE. This may suggest a supra-regional change in climate and the palaeoenvironment at the T-J boundary interval, with enhanced organic C burial possibly also in other continental shelf basins in the western Tethys realm.

4.1 Depositional conditions and origin of the sedimentary organic matter High resolution Rock-Eval VI measurements of T-J boundary sediments from Kuhjoch show that the sedimentary organic matter in most of the samples throughout the section typically consists of Type III kerogen (Figure 3-B). This kerogen type is characterized by low H/C values and relatively high O/C values for which woody organic matter or vascular plant remains are thought to be the main contributing sources (Wignall, 1994; Killops and Killops, 2005). Several samples coinciding with the initial CIE at the base of the Tiefengraben Mb and one sample in the Eiberg Mb, however, are marked by increased HI values of up to ~600 mg HC/g TOC. Four of these samples typically consist of Type II kerogen (Figure 3-B). This type of kerogen generally suggests an algal or bacterial source for the organic matter, lipid remains of leaf waxes could however be an alternative source (Wignall, 1994; Tyson, 1995; Killops and Killops, 2005). The mass occurrence of green algae remains mainly concurs with the upper part of the initial CIE. The low correlation between green algae abundance and HI values further suggests a different source for the hydrogen enriched molecules in the SOM in this interval (Figure 3-E). Good correlation between terrestrial palynomorphs and HI values may suggest a terrestrial origin of these molecules (Figure 3-D). A high correlation between Classopollis meyeriana pollen and HI values (R2 = 0.93) suggests that hydrogen enriched molecules originate from this thermophilic Mesozoic conifer species. However, palynomorphs constitute only a small fraction of the sedimentary organic matter and do not necessarily correspond with the

54 Chapter 3

composition of the palynofacies, which also influence the HI values. A molecular based study of the same samples from Kuhjoch shows a high abundance of n-alkanes with a distinctly odd over even predominance, suggesting that terrestrial higher plant organic matter strongly contributes to the sedimentary organic matter (Chapter 4). Additionally, highly increased terrestrial relative to marine palynomorph concentrations (Figure 2-E), also suggest increased terrestrial organic matter input rather than marine primary productivity as a source for the increased TOC content of the SOM. Slightly increased TOC and HI values of almost 2% and 200 mg HC/g TOC respectively, suggest that increased marine primary productivity contributes mainly to the final part of the organic matter enriched interval. Palaeo-oceanographic and climatic conditions during Mediterranean sapropel and Cretaceous black shale formation are often similar and marked by an increased hydrological cycle, increased river run-off, a stagnant water column and an increased organic matter flux to the basin floor (Meyers, 2006). Similar mechanisms and conditions may have led to black shale formation in the Eiberg Basin (Bonis et al., in press). The concurrent increase in Stot and TOC concentrations in the studied interval may, similar to the early Aptian Oceanic Anoxic Event at Shatsky Rise (Dumitrescu and Brassell, 2006), reflect decreased oxygen levels at the sea floor. Increased TOC concentrations and terrestrial organic matter influx in the Eiberg Basin correspond to enhanced precipitation and a more stratified water-column (Bonis et al., in press) that possibly led to more anoxic bottom water conditions. In Mediterranean Pliocene sapropels, total nitrogen

(Ntot) is commonly used, as in this study, as proxy for organic nitrogen content (Arnaboldi and Meyers, 2006). In the Neogene (late Miocene to Pliocene), enhanced ocean surface productivity commonly relates to TOC enriched sediments and increased Corg/ Ntot values due to preferential re-mineralization of nitrogen relative to carbon (Twichell et al., 2002). Ward et al. (2001) suggest a sudden productivity collapse based on a negative CIE and a sudden turnover in radiolarian assemblages (Carter and Hori, 2005) from the T-J transition interval at the Queen Charlotte Islands (British Columbia, Canada). Our high resolution Corg/ Ntot record does increase dramatically in concordance with the onset of the green algae mass occurrence. The simultaneous increase suggests an increased marine primary productivity as organic matter source at the final stage of black shale formation. Differences in palaeoproductivity records are likely to be attributed to differences in local environmental conditions between the Panthalassa and Tethys oceans.

13 4.2 Origin of sedimentary organic matter and the δ Corg signature Carbon isotopic events, especially at the T-J system boundary, are often discussed as representing (global) carbon cycle turnovers (Hesselbo et al., 2002). However, some authors argue that changes in the C-isotope composition of the Sedimentary Organic Matter (SOM) at this boundary interval are largely controlled by changes in type of organic matter (van de Schootbrugge et al., 2008). To constrain isotopic changes of the globally exchangeable carbon reservoirs, it is essential to understand the nature and size of the negative CIEs. Characterizing the type and origin of the SOM is potentially useful to estimate the influence of possible changes on the C-isotope signature. Low HI values for most of the samples in the T-J boundary section of Kuhjoch suggest that most of the SOM is terrestrial in origin. Sedimentary organic matter with peak HI values

55 End-Triassic black shale formation 0 0 6 0 0 5 C) 0 ( ° 0 4 ma x T 0 0 3 [d] 0 0 2 0 2 1 3 3

S S 3

C C S C 50° 50° 0 6 6 50° 8 6 2 2

S S 0 3 1 4 2 6 8 Time in minutes Time C C C ° ° ° 0 0 0 ample ample ample 0 0 0 1 1 1

3 3 3 S S S S S S 0 [c] 0 4 1 6 0 3 0 ample 2 3 . S 0 0 1 [b] 0 0 0 0 0 0 0 0 0 0 2 1 2 2 1 . - - 8 0 3 2 S 2 mg HC/ g ample S 1 . 0 ample S 0 . 0 5 . 0 4 . 0 3 . 0 2 . 0 1 . 0 0 . 0 0 0 0 8 0 0 1 8 0 0 0 0 6 0 1 2 2 1 . - - 0 3 2 [a] ample 6 ample S 0 . S 0 ample S 4 0 . S 1 mg HC/ g 0 2 0 . 0 0 0 . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

2 0 2 2 8 6 4

- 1 1 Stratigraphic position (cm) position Stratigraphic

56 Chapter 3

of over 600 mg HC/g TOC, which are generally associated with increased green algae production (Killops and Killops, 2005), is in this case interpreted as terrestrial in origin (see section 4.1). The acme of green algae coinciding with the second half of the initial CIE is marked by only slightly enhanced HI values (Figure 2-D). This suggests that the sedimentary organic matter consists of a mixture of marine primary produced organic matter (green algae palynomorphs) and possibly terrestrial amorphous organic matter. Our geochemical and palynological data suggest that the upper half of the initial CIE is the only interval with a possibly significant contribution of marine organic C, causing a change in origin from mainly terrestrial to a marine-terrestrial mixture. This green algae 13 acme could potentially have influenced the bulk δ Corg signature as fossil and modern 13 prasinophytes have a 7‰ depleted δ Corg composition of -28‰, relative to modern common marine primary producers (Wong and Sackett, 1978; Prauss and Riegel, 1989). A change in predominant terrestrial plant species in the catchment area of the Eiberg Basin could potentially have influenced the C-isotope composition of the total terrestrial biomass carbon reservoir. Large differences in carbon fractionation and internal carbon cycling processes between species (e.g. C3/ C4 plant species), however had not evolved until much later in Earth History (Cerling et al., 1993). Furthermore, large changes in vegetation from a predominantly fern to a conifer dominated vegetation, do not occur simultaneously in different basins. In the Austrian T-J boundary sections, pollen-producing plants are gradually succeeded by spore producing plants from the initial CIE onwards into the Hettangian (Kürschner et al., 2007; Bonis et al., 2009). In the St. Audrie’s Bay palynological record (UK), the prevailing Rhaetian fern assemblages are succeeded by a turnover to conifer dominated vegetation from the initial CIE onwards into the Hettangian (Hounslow et al., 2004; Bonis et al., in review). Despite the clear differences in vegetation history at both sites, the C-isotope record is remarkably similar (Kürschner et al., 2007; Ruhl et al., 2009). Changes in the terrestrial vegetation composition may therefore only have a minor influence on the organic C-isotope signature. Consequently, the initial negative CIE may represent true changes in the atmospheric C-isotope composition. The mass occurrence of green algae remains in the sediments of the Eiberg Basin then only caused a delayed return to end-Rhaetian base values (Figure 5). The sudden and dramatic decrease in C-isotope composition and the subsequent return to pre-excursion values in mainly Type III terrestrial kerogen closely resembles similar isotopic trends at the Cretaceous-Palaeogene boundary (D’Hondt et al., 1998) and the Palaeocene-Eocene Thermal Maximum (Bains et al., 1999). Extreme negative C-isotope excursions at these boundaries are related to sudden changes in global exchangeable carbon reservoirs and accompanied by climatic and palaeo-environmental changes. New high resolution molecular compound-specific C-isotope data do show a 13 13 considerable δ Cn-alkane negative excursion coinciding with the initial CIE in bulk δ Corg records (Chapter 4), suggesting a depletion of atmospheric δ13C and major disturbance of the global carbon cycle.

Figure 4 (A) The free hydrocarbon (S1) content [mg HC/g], (B) the pyrolysable hydrocarbon (S2) content [mg HC/g], (C) thermal maturation diagrams (S1, S2, S3) for samples 8, 23 and

61, (D) Tmax values [°C]: white diamonds show samples with to low S2 values for reliable Tmax determination.

57 End-Triassic black shale formation

100

20 Reduced surface water salinity; green algae acme 13 and delayed return to pre-excursion δ Corg values 0 Increased precipitation; increased TOC content; influx of conifer pollen (cm) Onset of biocalcification crisis; beginning of major volcanic activity, methane release? -20 Onset of oceanic and atmospheric 13C depletion

-40

-60

-80 Stratigraphic position -100

-120

-140

-160

-180 -32 -30 -28 -26 -24 13 δ Corg [‰]

13 Figure 5 The uppermost Rhaetian δ Corg [‰] record of Kuhjoch (Eiberg Basin) with the initial CIE.

4.3 Volcanism and black shale deposition at the T-J boundary in the Eiberg basin A causal relationship is suggested between enhanced volcanic activity, with the deposition of the Central Atlantic Magmatic Province (CAMP) basalts, and climatic and biotic crisis at the T-J boundary (Marzoli et al., 1999; Marzoli et al., 2004). In the Phanerozoic, mass extinctions are often related to the formation of large igneous provinces (Wignall, 2001). During the Early Cretaceous Late Barremian-Early Aptian transition, intense volcanic degassing and extremely rapid release of methane hydrates added large amounts of carbon to the ocean and atmosphere, causing highly increased

CO2 levels (Wissler et al., 2003). The reduced marine calcium carbonate oversaturation and calcification potential of benthic and planktonic organisms resulted in a biocalcification crisis that culminated during the Aptian methane event (Wissler et al., 2003). Volcanic outgassing of CAMP and a subsequent release of 13C depleted methane clathrates probably added large amounts of CO2 to the global oceans and atmosphere

(McElwain et al., 1999; Beerling and Berner, 2002). Increased CO2 levels (up to ~2500 ppm) probably had a profound influence on ocean water chemistry. Acidification of the oceans with lower pH values (Caldeira and Wickett, 2003) may have largely reduced the survival potential of calcifying organisms and their communities at the T-J transition (Hautmann et al., 2008). This led to the end of widespread carbonate production in the western Tethys realm (Hillebrandt et al., 2007). In the Eiberg basin this may be represented by a lithological change from limestones of the Eiberg Mb (Kössen Fm) to

58 Chapter 3

marls of the Tiefengraben Mb (Kendlbach Fm) and diminished foraminiferal communities (Hillebrandt et al., 2007; Bonis et al., in press). The large and sudden reduction of TIC at the onset of the initial CIE (Figure 1-C and 2-B) corresponds to a ~4.5‰ negative 13 shift in the δ Corg signature (Figure 2-A) and may reflect the beginning of the calcification crisis in Kuhjoch. Alternatively, the calcification crisis can, like at the Toarcian OAE, also be regarded as an indirect consequence of high atmospheric CO2 values (Mailliot et al., 2009). Related climatic effects may then have caused environmental stress and the collapse of marine productivity.

4.4 Carbon burial at the T-J boundary Anoxic depositional conditions inferred from trace metal redox indicators and finely laminated shales mark the T-J boundary interval in deeper water sections in British Columbia (Canada) (Wignall et al., 2007). Together with possible anoxic conditions in shallower settings in north-western Europe (Hallam et al., 1995) and the western Tethys Ocean (Bonis et al., in press) this could suggest marine anoxia in marginal marine settings, at the T-J boundary. A major ocean anoxic (OAE) event at the mid-Cretaceous Cenomanian/Turonian boundary (OAE-2) was triggered by massive magmatic activity (Kuroda et al., 2007; Turgeon and Creaser, 2008) that led to increased primary production and the burial of large amounts of organic carbon on the ocean floor. Volcanic activity at the T-J boundary, which led to deposition of CAMP basalts (Marzoli et al, 1999; Marzoli et al., 2004), increased CO2 values (McElwain, et al., 1999) and a possible biocalcification crisis (Hautmann et al., 2008), potentially caused similar marine anoxia as in the mid- Cretaceous. However, the early Cretaceous Valanginian Weissert OAE (Erba et al., 2004) and the middle Cretaceous Mid-Cenomanian Event (MCE) (Coccioni and Galeotti, 2003) and OAE-2 (Coccioni and Galeotti, 2003; Turgeon and Creaser, 2008) are marked by increased marine primary productivity and preservation of large amounts of organic carbon in marine sedimentary reservoirs. Enhanced burial of 12C enriched OM then creates a positive shift in the δ13C composition of the oceanic reservoir (Dumitrescu and Brassell, 2006). The Cretaceous OAEs are indeed marked by a positive excursion in the δ13C signature of the sedimentary organic matter. Also at the T-J boundary, increased storage of carbon on the continental shelf or in the deep sea may have had a significant influence on the C-isotope composition of globally exchangeable carbon reservoirs. The observed δ13C negative excursions at the T-J boundary however, suggest that (i) carbon burial at the ocean floor was much smaller with the deep oceans likely not being anoxic, or (ii) the increased sedimentary organic matter is mainly terrestrial in origin with fertilization of the oceans being too small for a major increase in primary productivity, or (iii) the actual amplitude of the negative excursion in the atmosphere and ocean δ13C reservoirs is larger than registered in bulk δ13C records. The regression that culminates at about the initial CIE (Guex et al., 2004; Hesselbo et al., 2004; Wignall et al., 2007; Wignall and Bond, 2008) makes spreading of anoxic deeper waters in formerly well aerated shallower shelf environments unlikely. Instead a continentally driven environmental change with intensified runoff and an increased terrestrial organic matter and nutrient flux, likely caused (regional) organic-C burial and primary productivity in shelf settings. To examine possible large scale organic carbon burial at the T-J boundary both shallow but also deeper water sections should be (further) studied.

59 End-Triassic black shale formation

5. Conclusions

The initial CIE at the T-J boundary GSSP of Kuhjoch is marked by only minor changes in kerogen. Most of the samples preceding, concurring and succeeding the initial CIE are of Type III kerogen, suggesting a distinctly terrestrial origin. The first half of the initial CIE is marked by black shale formation. Increased TOC concentrations of 9% coincide with HI values of over 600 mg HC/g TOC. The high correlation (with R2 = 0.93) between HI values and terrestrial Cheirolepidiaceae conifer pollen suggests a terrestrial origin for the hydrogen enriched organic compounds in the sediment. The lack of major changes 13 in the origin of the sedimentary organic matter suggests that the changes in the δ Corg composition are genuine and represent true disturbances of the global C-cycle. The 13 sudden decrease in TIC concentrations coincides with a 4.5 ‰ negative drop in δ Corg values and may reflect the beginning of CAMP related volcanic activity and the onset of a biocalcification crisis. The second half of the initial CIE is marked by the dramatic increase of green algae remains in the sediment. The simultaneous increase of the Corg/

Ntot-ratio suggests an increased marine primary production and a subsequent increased contribution to the SOM at the final stage of black shale formation. The mass occurrence 13 of green algae may have prolonged the initial bulk δ Corg negative CIE when atmospheric 13C values already returned to pre-excursion levels.

Acknowledgements MR and WMK acknowledge funding from the high-potential stimulation program of Utrecht University. We thank A. van Dijk and K. Reimer (Integrated Geochemical Laboratory, UU-NITG) for laboratory assistance. N.R. Bonis and M.H.L. Deenen are both thanked for supportive and constructive discussion and extensive field assistance.

60 Chapter 3

61 62 Chapter 4

Atmospheric methane injection caused end-Triassic mass extinction

The end-Triassic mass extinction (~201.5 Ma), marked by major terrestrial ecosystem changes and 50% marine biodiversity loss, has been attributed to a major volcanic episode during the break-up of Pangaea. Here, we present C-isotope data of long-chain n-alkanes derived from epicuticular waxes of land plants. Our data show a 5-6‰ negative excursion in compound specific C-isotope records, coincident with the extinction interval. This suggests strong 13C depletion of the end-Triassic atmosphere, within 5-10 kyr. The magnitude and rate of C-cycle disruption suggest the injection of ~7-8x103 Gt of isotopically light carbon from the methane-hydrate reservoir. Concurrent vegetation changes reflect a strong warming event and an enhanced hydrological cycle. Hence, our data, for the first time, link the end-Triassic events to massive carbon release and associated climate change.

63 Methane-driven climate change and mass extinction

The end-Triassic mass extinction (~201.5 Ma; Schaltegger et al., 2008), one of the five major extinction events of the Phanerozoic (Raup and Sepkoski, 1982), is marked by up to 50% of marine biodiversity loss and terrestrial ecosystem changes (Raup and Sepkoski, 1982; Sepkoski, 1996; Olsen et al., 2002; McElwain et al., 2009). This event 13 closely matches a distinct negative excursion in δ CTOC (CIE) records (Hesselbo et al.,

2002; Ruhl et al., 2009) and a potential fourfold increase in atmospheric CO2 concentrations (McElwain et al., 1999). The end-Triassic C-cycle perturbation has been attributed to large-scale carbon release, caused by a major volcanic episode with deposition of the Central Atlantic Magmatic Province (CAMP) during the break-up of Pangaea. However, deposition of this large igneous province continued for ~610 kyr (Whiteside et al., 2007), much longer than the ~20 to 40 kyr duration of the end-Triassic extinction event. The magnitude of the negative CIE also varies significantly between different geological basins, possibly due to changes in the source of the sedimentary organic matter. These observations question the reality of an end-Triassic global carbon cycle turnover and causal relationships to the mass extinction event (van de Schootbrugge et al., 2008; van de Schootbrugge et al., 2009). Here we present compound specific C-isotope records from the western Tethys Ocean (including the Global Stratotype Section and Point (GSSP) for the base of the Jurassic), which span the end-Triassic mass extinction interval. Changes in the carbon isotopic composition of long chain n-alkanes, derived from epicuticular plant waxes, directly reflect changes in atmospheric-13C values since the carbon in these compounds is incorporated from atmospheric CO2. Furthermore, preservation of these organic molecules is unaffected by diagenetic alteration of the organic matter (Pancost and Boot, 2004). Hence, this allows for the first accurate reconstruction of the end- Triassic C-cycle perturbation, in a biostratigraphically well-constrained framework. Sediments for this study come from a 60 cm upper Rhaetian (latest Triassic) interval in the Kuhjoch and Hochalplgraben outcrops (Ruhl et al., 2009). These sediments were deposited in the intra-platform Eiberg Basin at the continental margin of the western Tethys Ocean (Hillebrandt et al., 2007). The studied interval in both sections directly succeeds the transition from limestones of the Kössen Formation (Fm) to marls of the Kendlbach Fm and coincides with marine extinctions and assemblage changes (Figure 1). Organic compounds derived from plant waxes, are preserved in these over 200 Million year old, but immature sediments. Analyses of the chemical structure and carbon isotopic composition of the isolated n-alkane fractions, show a ~6‰ negative excursion from Rhaetian base values of ~-29‰, which is 2-3‰ larger than previously assumed (Beerling and Berner, 2002) (Figure 2). This negative excursion in compound specific C-isotope records represents the first convincing evidence for end-Triassic atmospheric- 13C depletion. The onset of the negative CIE probably transpired within ~5-10 kyr, based on the astronomically constrained ~20-40 kyr duration of the complete event. This suggests that large amounts of isotopically light carbon were rapidly released to the end-Triassic atmosphere. Major vegetation changes at the studied time interval potentially modified the magnitude of the negative CIE in the terrestrial higher plant C-isotope records, due to differential carbon isotopic fractionation among plant groups. Although this is not suggested by changes in the Average Chain Length (ACL) of n-alkanes (Supplementary Information Figure 2-E & F), Cheirolepidiaceaen conifer abundance strongly increases in

64 Chapter 4

Kuhjoch, Austria

1200 Organic rich shales Organic poor shales 1100 Limestones LO Triassic organisms FO Jurassic organisms 1000 Assemblage changes

900 UK Bay, St. Audrie’s

800 Newark supergroup basins, USA Queen Charlotte Islands, Canada

700 Ammonites Jurassic Hettangian

600

500 Triassic Rhaetian

400 Pollen/ spores Molluscs Echinoidea Foraminifera Ostracodes

Stratigraphic position (cm) 300

200 CAMP volcanism CAMP 100 Tiefengraben Mb Tiefengraben Kendlbach Fm 0 Methane event Triassic pollen/ spores Triassic -100 Eiberg Mb Kössen Fm Palynology

-200 Foraminifera Dinoflagellates Ammonites -32 -31 -30 -29 -28 -27 -26 -25 -24 Ostracodes LO Conodonts

13 Radiolarian turnover bulk δ CTOC Bivalve extinction Theropod dinosaur turnover

13 Figure 1 End-Triassic δ CTOC negative excursion in concurrence with mass extinction 13 event The δ CTOC record of Kuhjoch (Ruhl et al., 2009), the GSSP for the base of the Jurassic, with the end-Triassic negative CIE closely matching continental and marine assemblage changes (Ward et al., 2001; Hesselbo et al., 2002; Olsen et al., 2002; Hillebrandt et al., 2007). See Ap- pendix 6 concurrence with the negative CIE (Bonis et al., 2009). Modern conifer derived n-alkanes are relatively enriched in 13C, which is caused by lower stomatal conductance relative to other plant groups (Pedentchouk et al., 2008). A rapid transition from a mixed angiosperm- conifer flora to a purely angiosperm flora at the Paleocene-Eocene Thermal Maximum amplified the observed negative CIE by 1 to 2‰ (Schouten et al., 2007; Smithet

65 Methane-driven climate change and mass extinction

δ13C n-alkanes al., 2007). Assuming similar -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 40 physiological mechanisms in Mesozoic conifers as today, 30 the observed end‑Triassic 20 higher plant n-alkane δ13C excursion is even dampened 10 relative to atmospheric 0 values. The actual magnitude

-10 Extinction interval of the end-Triassic C-cycle Stratigraphic position (cm) disruption may thus be even -20

Onset of biocalcification crisis larger than observed. Kuhjoch ~ 5‰ -30 The end-Triassic negative -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 - Temperature + - Humidity + 13 13 CIE in δ C records was, δ CTOC TOC based on model calculations, δ13C n-alkanes previously ascribed to the -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 280 ~ 6‰ release of ~8000-9000 Gt ~ 5‰ 270 carbon from volcanogenic

gaseous CO2 in the Central 260 Atlantic Magmatic Province,

250 Onset of biocal- which also destabilized cification crisis ~5000 Gt carbon from the 240

Extinction interval methane hydrate reservoir 230

Stratigraphic position (cm) (Beerling and Berner, 2002).

220 However, the modeled Hochalplgraben ~ 5‰ release of carbon from these 210 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 - Temperature + - Humidity + two reservoirs would result 13 δ CTOC in a ~3‰ depletion of the 13 δ CTOC exogenic carbon pool only. 13 δ C-[C25-C27-C29-C31-C33-C35] 13 The ~6‰ magnitude and the δ C-[C17-C18-C19-C20-C21-C22-C23] short (~20-40 kyr) duration Figure 2 N-alkane biomarker C-isotope and climate of the observed negative CIE records The combined n-C25 to n-C35 odd-chain-length (green) and n-C to n-C (blue) δ13C signature from 17 23 n-alkane do therefore not match with the end-Triassic mass extinction interval in Kuhjoch and Hochalplgraben. The onset of the 5-6‰ negative CIE co- CAMP related CO2 release. incides with strong relative warming and enhanced hydro- A simple mass balance logical cycling based on statistical analysis of palynological data. See Appendix 7 calculation, using end- Triassic boundary conditions (Beerling and Berner, 2002), shows that 5-6‰ atmospheric-13C depletion is be best explained by the release of ~6900-8200 Gt carbon as methane (with δ13C values of -60‰). Combustion of subsurface organic rich strata, associated with flood basalt lavas, has also been proposed to have contributed to the magnitude of the end-Triassic C-cycle perturbation (van de Schootbrugge et al., 2009). Carbon release purely from this source (with δ13C values of ~-25‰), would involve an input at least two times larger than for methane, possibly as much as 23000 Gt. The injection of 6900-23000 Gt of carbon during the end-Triassic likely had a profound impact on global climate. Statistical analyses of palynological data spanning

66 Chapter 4

this time interval (Supplementary Information) show a strong warming event and enhanced hydrological cycle, directly coinciding with the onset of the negative CIE (Figure 2). This suggests a strong causal relationship between massive carbon release, associated climate change and terrestrial ecosystem turnover. Massive carbon release to the atmosphere and subsequently the ocean, results in strong ocean acidification (Caldeira and Wickett, 2003; Zachos et al., 2005). In the end-Triassic, this likely caused major carbonate dissolution and stressed marine ecosystems and marine extinctions (Hautmann, 2004; Hautmann et al., 2008). Similar events of rapid carbon release to the atmosphere (e.g. at the Palaeocene- Eocene Thermal Maximum (Zachos et al., 2005) and the in early Toarcian (Kemp et al., 2005), suggest a ~100 kyr duration for δ13C recovery of the exchangeable carbon reservoirs. This is in line with the residence time of carbon in the exogenic carbon pool (Dickens, 2003), but longer than the suggested ~20-40 kyr duration of the observed end-Triassic C-cycle perturbation. Dilution of the exchangeable carbon reservoirs with 13 C enriched carbon from dissolving end-Triassic carbonate ramps under high CO2 conditions (Hautmann, 2004; Hautmann et al., 2008) can explain the rapid return of the atmospheric-δ13C signal to pre-excursion values. Enhanced surface ocean productivity and increased preservation of carbon in organic rich black-shales coinciding with the negative CIE (Bonis et al., 2009), likely contributed to the rapid recovery of the δ13C signal. This may be further enhanced by diminished background release of isotopically light carbon caused by changes in the gas-hydrate capacitor (Dickens, 2003). A delay in the recovery of the mixed terrestrial and aquatic (possibly algae; Han and Calvin, 1969) short-chain n-alkane (n-C17 to n-C23) C-isotope records, relative to terrestrial long-chain C-isotope records (Figure 2), suggests a more sluggish exchange between ocean and atmosphere. Such a partitioning between isotopically distinct carbon reservoirs could be due to a more stratified water column, with enhanced storage of 13C depleted carbon in the deeper parts of the ocean (Schouten et al., 2000). The end-Triassic mass extinction interval with rapid and large-scale carbon release, may now be regarded as a natural deep-time analogue similar to today’s anthropogenic carbon emissions. The present cumulative anthropogenic carbon release of over 5000 Gt (Caldeira and Wickett, 2003) will likely enhance greenhouse warming by several degrees (Allen et al., 2009) and substantially lower oceanic pH values (Caldeira and Wickett, 2003). Earths biosphere is also projected to experience major disruption of ecosystems, with associated loss of biodiversity (Sala et al., 2000). The direct link between massive carbon release and the end-Triassic mass extinction, strongly suggests that modern day ecosystems will experience a further loss of biodiversity, not only by habitat reduction but also by carbon release driven rapid climate changes.

Acknowledgements

We thank laboratory technician G. Nobbe, who assisted with most of the stable-isotope measurements presented in this paper and H. Visscher and A. Sluijs for suggestions and corrections during the drafting of this paper. M. Deenen is gratefully acknowledged for discussion on events at the T-J transition. MR, NB and WK acknowledge funding from the High Potential program of Utrecht University.

67 Methane-driven climate change and mass extinction

Chapter 4

Supplementary Information

Materials

Two Triassic-Jurassic boundary sections in the Northern Calcareous Alps (Kuhjoch and 13 Hochalplgraben), where studied for the δ C composition of long-chain n-alkanes. This study focuses on a 60 cm sedimentary interval at the very base of the Tiefengraben Mb (Kendlbach Fm) that succeeds the Eiberg Mb (Kössen Fm) in the uppermost Rhaetian, in the Eiberg Basin. This intra-platform shelf basin was situated on the continental margin of the western Tethys Ocean. The basin extended over several hundred kilometers from east to west and was located in between upper Triassic Oberrhät reef systems (Hillebrandt et al., 2007; Ruhl et al., 2009). Eight samples from Kuhjoch and nine samples from the Hochalplgraben section were processed for this study. The same samples were previously 13 studied for its δ CTOC composition (Ruhl et al., 2009). Eleven samples from Kuhjoch and ten samples from Hochalplgraben were previously studied for palynomorph composition (Bonis et al., 2009).

13 Methods: δ Cn-alkane measurements Between 10-20 g of fresh sediment of each sample was freeze dried and subsequently powdered. Organic compounds were extracted from the sediment, with a Dionex 200 Accelerated Solvent Extraction (ASE) equipment and a dichlo-romethane-methanol (9:1) solution. The total lipid extracts were rinsed over a Na2SO4 column and separated in polar and a-polar compound classes with a hexane/dichloromethane (1/1) and hexane/ dichloromethane (9/1) mixture, respectively. Elemental sulfur was removed from the a-polar fraction with activated copper. Copper fragments were activated with 2M HCl and subsequently rinsed with demi-water, methanol and dichloromethane. Straight chain n-alkanes were isolated from the a-polar fraction using the urea-adduction method. For this, the dry residue was dissolved in a 200 μl methanol/urea (~10%, H2NCONH2, Merck) solution. Subsequently, 200 μl acetone and 200 μl hexane were added to the solution and than frozen and dried under nitrogen flow. Then -alkane compounds were captured during formation of the urea crystals, which were subsequently washed with hexane to remove non-adductable branched and cyclic alkanes. Urea crystals, containing the adductable normal alkanes were then dissolved in 500 μl methanol and 500 μl distilled water. These compounds were subsequently extracted from the solution with hexane. This process was repeated 2-3 times to eliminate non-adductable alkanes from the residue. The n-alkanes were identified through mass spectra, molecular ion mass and retention time using a Thermo-Finnigan Trace Gas Chromatograph (GC) Mass Spectrometer (Thermo-Finnigan Trace DSQ). The δ13C composition of individual n-alkanes (Supplementary Information Figure 2-A & B and Table 1) was measured by injection of the a-polar adductable fraction on a HP 6890N Gas Chromatograph (GC) coupled to a Thermo-Finnigan Combustion III and Thermo-Finnigan Delta Plus XP Isotope Ratio Mass Spectrometer (GC-IRMS) at the Molecular Biogeochemistry laboratory at the department of Earth

68 Chapter 4

Sciences, Utrecht University. C25

The GC temperature was C27 A programmed to increase 20°C per minute from 70-130°C and 5°C per minute from 130- 320°C. Based on standard C29 analyses the accuracy was better than 0.2 and 1.6‰ C31

(depending on standard, Relative abundace with the latter based on the C33 squalane standard with a δ13C composition of -19.54‰). Only relatively small amounts Time (min) of the n-alkane fraction were recovered from most samples B in the studied time interval, leading to only few duplicate C25 sample measurements. C27 Standard deviations on duplicate sample measurements are reported C29

in Table 1 (Supplementary Relative abundace

Information). C31

C33 Methods: Multivariate statistical analysis on palynological data Time (min)

The relative pollen and Supplementary Information Figure 1 Total-ion chro- spore abundance of Kuhjoch matogram from the a-polar adductable fraction of sediments from (A) the first half of the negative carbon iso- and Hochalplgraben was tope excursion (CIE) at Kuhjoch (sample S-3; 0.5 cm) summarised using a linear and (B) the second half of the negative CIE at Hoch- alplgraben (sample Hin-6; 252 cm). The labeled long- ordination method, Principal chain odd-carbon numbered n-alkanes are used to calcu- Components Analysis (PCA), late Average Chain Length (Supplementary Information Figure 2E & F). as the gradient lengths of the datasets did not exceed 3 standard deviations (Leps and Smilauer, 2003) (SD). All analyses were performed with a square-root transformation of the species data. The two main ordination axes explain the largest variance in a multi-dimensional species composition dataset. The first axis of the Kuhjoch dataset represents 44.8% of the variance (38.7% in the Hochalplgraben dataset), and 22.7% of the variance is represented along the second axis (24.9% in the Hochalplgraben dataset) (Supplementary Information Figure 3). The two main axes are interpreted as climatic gradient control on the dataset. Based on ecological preferences of the palynomorph producing plants, the two main ordination axes are interpreted to reflect temperature and humidity changes through time (Main Text Figure 2).

69 Methane-driven climate change and mass extinction

13 13 δ Cn-alkanes δ Cn-alkanes -40-39 -38-37-36 -35 -34-33-32 -31-30-29-28-27 -26-25-24 -38 -37-36 -35 -34 -33-32 -31 -30-29 -28 -27-26 -25 -24 280 40 n-C25 n-C25 n-C 270 27 30 n-C27 n-C29 n-C29 n-C 260 31 20 n-C31 n-C33 n-C33 n-C35 n-C35 250 13 10 13 δ CTOC δ CTOC

240 0

230 -10 Stratigraphic position (cm)

220 -20 A B 210 -30 -40-39 -38-37-36 -35-34-33 -32-31-30 -29-28-27 -26-25-24 -38 -37-36 -35 -34-33 -32 -31-30 -29 -28-27 -26-25 -24 13 13 δ CTOC δ CTOC 13 13 δ Cn-alkanes δ Cn-alkanes -40-39 -38-37-36 -35 -34-33-32 -31-30-29-28-27 -26-25-24 -38 -37-36 -35-34 -33-32 -31 -30-29 -28 -27-26 -25 -24 280 40 13 n-C19 δ CTOC n-C17 n-C21 270 n-C20 30 n-C18 n-C22 n-C21 n-C19 n-C23 13 260 n-C22 20 n-C20 δ CTOC n-C23 250 10

240 0

230 -10 Stratigraphic position (cm) 220 -20 C D 210 -30 -40-39 -38-37-36 -35-34-33 -32-31-30 -29-28-27 -26-25-24 -38 -37-36 -35 -34-33 -32 -31-30 -29 -28-27 -26-25 -24 13 13 δ CTOC δ CTOC CPI CPI 0 1 2 3 4 5 0 1 2 3 280 40

270 30

260 20

250 10

240 0

230 -10 Stratigraphic position (cm) 220 -20 E F 210 -30 26 27 28 29 30 26 27 28 29

ACLC25-C33 ACLC25-C33

-25 -26 -27 -28 -29 -30 -31 -32

-33 -34

C n -alkanes per sample -36 -35 13 δ -38 -37 G H -40 -39 17 19 21 23 25 27 29 31 33 35 17 19 21 23 25 27 29 31 33 35 n-alkane c-chainlength n-alkane c-chainlength

Hin-9, 273 cm Hin-5, 245 cm S-9, 20 cm S-6, 7 cm Hin-8, 266 cm hin-4, 242 cm S-8, 15 cm S-5, 6 cm Hin-6, 252 cm Hin-2, 235 cm S-1, -4 cm S-2, -1 cm HinA-7, 259 cm Hin-1A, 230 cm S-7, 8 cm S-3, 0.5 cm HinB-4, 229 cm

70 Chapter 4

Results & Discussion

The a-polar residue of each sample mainly comprises middle (C17-C23) to long (C25-C35) n-alkanes, with the latter demonstrating a distinctly odd over even predominance in chain length distribution (Supplementary Information Figure 1). The individual n-alkane C-isotope records of both sections, demonstrate distinct negative excursions of ~6‰ (n-

C25 to n-C35) and ~5‰ (n-C17 to n-C23) (Supplementary Information Figure 2-A, B, C & D). The δ13C composition of individual n-alkane compounds per sample is relatively constant with increasing chain length in the Kuhjoch record (Supplementary Information Figure 2-H). However, the C-isotope composition slightly increases with increasing chain length in the Hochalplgraben record (Supplementary Information Figure 2-G). The influence of potential vegetation changes on the n-alkane chain length distribution was studied by reconstruction of the Average Chain Length (ACL) per sample. The maturity of the long- carbon-chain n-alkane fraction and the possible influence of migrated hydrocarbons on the n-alkane biomarker C-isotope records are studied by reconstruction of the relative abundance of odd versus even numbered n-alkanes (carbon preference index (CPI)). The ACL and CPI are calculated using the following formulae (Smith et al., 2007):

(1) ACL = (25A25+27A27+29A29+31A31+33A33)/(A25+A27+A29+A31+A33)

(2) CPI = (((A25+A27+A29+A31+A33)/(A24+A26+A28+A30+A32)) +

((A25+A27+A29+A31+A33)/(A26+A28+A30+A32+A34))) * 0.5

A is the area under the chromatogram peak for every individual n-alkane biomarker (Supplementary Information Figure 1). The Average Chain Length decreases from 28 to 27 in the Kuhjoch dataset, but independent of changes in the C-isotope composition of the longer-chain n-alkanes (Supplementary Information Figure 2-F). The Hochalplgraben dataset is marked by a similar decrease from 29 to 28, but with lower values down to 27, in between (Supplementary Information Figure 2-E). Although lower ACL values in the Hochalplgraben record coincide with the negative excursion in the combined long-chain n-alkane C-isotope record (Supplementary Information Figure 2-E), there is no statistically significant relation. CPI values for the studied interval at Kuhjoch and Hochalplgraben are relatively constant at ~1.5 and ~2 respectively. The CPI value of mainly one sample (at 242 cm) from the latter section increases in concurrence with the negative shift in n-alkane C-isotope records. CPI values of subsequent samples are however significantly lower even though long-carbon-chain n-alkanes remain relatively depleted in 13C. There is no significant relationship between the n-alkane C-isotope record and CPI values.

Supplementary Information Figure 2 Individual high molecular weight odd-carbon numbered 13 13 δ Cn-alkane signatures and δ CTOC signatures (in grey) from (A) Hochalplgraben and (B) Kuhjoch. 13 13 Individual low to middle molecular weight odd-carbon numbered δ Cn-alkane signatures and δ CTOC signatures (in grey) from (C) Hochalplgraben and (D) Kuhjoch. The calculated Average Chain Length (ACL) compared to Carbon Preference Index (CPI) values from (E) Hochalplgraben and (F) Kuhjoch. The C-isotope composition of individual n-alkanes per sample from (G) Hochalplgraben and (H) Kuhjoch. See Appendix 8

71 Methane-driven climate change and mass extinction

Conbaculatisporites spp. (F) A Baculatisporites spp. (F)

2.4

+ Calamospora spp. (H) Acanthotriletes varius (CM)

d Carnisporites e 1.2 anteriscus (CM) Classopollis n

i meyeriana (Ch) a

l Todisporites spp. (F) p x e r e u

t Polypodiisporites a % polymicroforatus (F) r 7 e

. 0.0 p

2 Ricciisporites m 2 tuberculatus (L) † e , * Araucariacites t

2 Polypodiisporites australis (C) s

i ipsviciensis (F) Vitreisporites x Trachysporites a pallidus (S) -1.2 fuscus (F) A Vitreisporites Deltoidospora spp. (F) C bjuvensis (S) P

- Classopollis torosus (Ch) -2.4 Tsugaepollenites pseudomassulae (C) * Sporesindet † Rhaetipollis Ovalipollis germanicus (G) pseudoalatus (G) -3.6 -4.5 -3.0 -1.5 0.0 1.5 3.0 4.5 + PCA axis 1, 44.8% explained - humidity

3.0 Classopollis torosus (Ch) B

- Tsugaepollenites pseudomassulae (C) 1.5 Classopollissp. (Ch)

d Classopollis e meyeriana (Ch) n i a l p x

e 0.0 y % t i 9 d . i 4

m Baculatisporitesspp. (F) 2 u , h 2 s i Concavisporitesspp. (F)

x -1.5 Ricciisporites a Deltoidospora spp. (F) tuberculatus (L) A C P +

-3.0

Vitreisporites spp. (S) Polypodiisporites polymicroforatus (F)

-4.5 -5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 + - PCA axis 1, 38.7% explained temperature

Supplementary Information Figure 3 Principal Components Analy- sis (PCA) ordination diagram of pollen and spore taxa in (A) Kuhjoch and (B) Hochalplgraben. Abbreviations are of the parent plant group. C: conifer, Ch: Cheirolepidiacean conifer, CM: club mosses, H: horse- tails, F: ferns, L: liverworts, G: gymnosperms, S: seed ferns.

72 Chapter 4 3 3 C

- 3

3 L 3 3 8 5 6 8 9 8 5 ...... 2 C C 7 8 7 7 7 7 6 7

- C A 2 2 2 2 2 2 2 2

L 2 0 6 2 8 0 7 2 1 5 ...... 2 C 7 9 7 7 7 7 8 8 9 C A 2 2 2 2 2 2 2 2 2 8 6 8 6 4 . . . . . 0 8 1 0 3 35 3 2 3 3 3 C - - - - - 8 0 0 9 1 5 4 2 ...... 5 9 5 6 0 5 8 9 7 5 3 . 0 6 9 6 6 2 2 2 3 2 2 2 2 . . . . . C - 1 ------4 2 8 2 0 3 3 3 2 3 3 3 C - - - - - 8 5 0 3 4 . . . . . 4 8 6 7 9 8 7 6 5 7 1 6 0 3 ...... 3 2 2 3 2 3 1 6 1 8 5 0 3 7 C - - - - - 3 . 3 2 3 2 3 3 3 C ------3 - 1 8 4 7 5 1 0 9 9 ...... 1 6 5 9 5 4 3 ...... 7 5 8 5 3 9 1 6 7 4 2 3 . 3 0 2 0 4 3 6 2 2 2 2 3 2 3 2 2 3 . C 0 ------3 3 3 3 3 3 C - - - - - 1 - 0 0 4 1 2 6 7 6 4 3 9 2 7 6 5 6 5 ...... 2 1 1 8 0 4 8 7 4 7 2 1 1 0 0 3 9 2 3 3 7 1 3 3 . . . 2 3 3 2 2 3 2 3 3 3 3 3 3 2 3 3 3 C 1 C - - 1 ------1 - - - 0 4 0 8 0 1 3 4 ...... 9 8 4 9 4 8 2 8 4 0 ...... 4 8 8 2 0 4 2 3 9 7 1 3 . . 6 0 6 3 2 0 9 9 0 3 3 2 2 3 3 3 3 3 3 . C 1 ------0 - - 2 3 2 3 3 3 2 2 3 C 0 ------8 7 1 2 3 7 7 5 ...... 9 4 6 1 8 3 6 4 6 8 3 7 7 3 0 3 1 3 4 6 2 ...... 0 3 2 2 3 3 3 3 3 7 4 7 4 2 0 0 1 1 1 C 0 ------0 - - 3 . 2 3 2 3 3 3 3 3 3 C 0 ------8 2 3 3 4 9 7 6 ...... 8 2 8 8 3 0 3 2 3 6 7 2 . . 3 0 9 2 2 1 5 2 0 3 2 2 3 3 3 3 3 ...... C 1 ------0 - - 9 7 3 6 4 0 2 8 1 0 9 2 . 2 3 2 3 3 3 2 3 3 C 0 ------8 1 8 4 0 5 2 4 ...... 7 2 8 8 3 2 4 3 4 6 5 2 . . 3 2 2 3 3 3 3 3 8 0 2 9 7 1 3 7 4 C 0 ------0 - - ...... 8 8 6 8 3 0 1 9 2 1 5 2 . 2 3 2 3 3 3 2 3 3 3 9 3 0 3 7 9 2 C 1 ------...... 6 2 8 8 3 1 4 2 4 7 5 2 . . 3 2 2 3 3 3 3 3 C 0 ------0 - - 7 1 4 7 9 6 1 5 9 ...... 7 8 5 8 5 0 1 9 3 0 6 2 3 1 8 1 6 6 0 6 . 2 3 2 3 3 3 2 3 . . 3 ...... 5 C 0 ------2 8 8 4 2 5 4 4 0 6 2 . . 3 2 2 3 3 3 3 3 C 0 ------0 - - 1 8 0 6 7 1 8 9 5 ...... 6 0 4 5 7 7 4 5 7 9 3 9 5 0 1 9 2 1 1 2 ...... 4 2 3 2 3 3 3 2 3 3 2 8 8 4 1 5 4 4 3 2 C 1 - - 2 ------. . 3 2 -alkanes -alkanes per sample. Standard deviations are given for samples that are measured in duplicate. 2 3 3 3 3 3 C 0 ------0 - - n 0 9 5 4 1 8 6 0 4 ...... 7 1 8 0 2 0 9 7 5 ...... 9 3 8 6 2 1 8 4 0 3 1 2 2 8 9 7 5 7 . 6 5 0 4 2 2 3 2 3 3 3 2 3 3 . . -alkanes. 3 2 2 3 3 3 C - - 0 3 - - 3 - - - - - C 0 ------0 - - n

33 9 6 8 2 9 7 7 1 9 4 5 0 8 1 3 ...... 2 4 1 0 5 1 5 5 4 3 -C 3 0 4 9 7 0 1 5 1 8 2 2 . . . 3 3 3 3 3 3 3 3 3 2 3 n 3 3 3 3 C - - - - - 0 - 0 - C - - 0 ------to 4 0 3 7 0 1 7 ...... 1 8 1 6 0 4 4 3 1 25 ...... 9 6 3 6 6 4 1 9 6 2 3 . . 0 7 9 9 3 2 8 1 3 2 3 3 3 3 3 3 2 . C - - -C - - 0 - 0 - - 3 3 2 3 3 3 3 3 C - - 0 ------n 3 1 0 2 7 . . . . . 0 6 6 6 4 1 6 8 3 0 6 1 5 9 2 ...... 3 3 3 3 3 2 C - - 1 6 2 - 7 1 2 - 5 - 0 2 composition of individual 3 3 3 3 3 3 C ------4 2 6 . . . e 9 -alkane 5 7 3 1 1 n n . 9 9 8 1 3 3 3 3 . . . . . a C - - 4 - C 1 e 6 6 1 7 1 k 2 l n 13 3 3 3 3 3 a C - - - - - a 7 5 - . . k 8 l 5 3 n 1 a 3 3 - 5 4 6 6 8 C - - . . . . . C 0 The δ 3 n 5 5 1 6 2 2 1 3 3 3 3 3 1 8 C δ - . - - - - . C 7 3 4 3 1 1 3 3 C δ - -

) c i m h c ( ) p

c a i n m r h c o g i ( p i

t t i a n a r s 3 5 6 2 9 5 0 2 9 r o g t o i 7 4 6 4 5 3 3 5 2 i t t p 2 S 2 2 2 2 2 2 2 2 i a s r 5 t o 0 5 . 1 4 p 2 S 6 1 8 0 7 - - ) e n g e . ) ) a b r e e D a . e r g g . . v S a a g

l r r a

D D

( h . . p e e

e l e c A l v v l S S 4 4 7 a -

- - - o a a p

p j 9 5 8 4 2 1 6 h ( (

- - B - - A - - - B

h c m m 9 5 8 7 3 6 3 6 2 1 n n n n n n n n n n u o i i i - a i i - - i i - - i i - i - - - - a K S S S S S S S S S S S H H S H H H H H H H H H Supplementary Information Table 1 The calculated Average Chain Length (ACL) is based on the The calculated Average

73 74 Chapter 5

Astronomical constraints on the duration of the early Jurassic Hettangian stage and recovery rates following the end-Triassic mass extinction (St. Audrie’s Bay/East Quantoxhead, UK)

The end-Triassic environmental crisis with major extinctions in the marine realm is followed by successive recovery in the early Jurassic Hettangian stage. Accurate chronology of events is however still poorly constrained. In this study, combined field observations and physical and chemical proxy records, covering the uppermost Triassic and lower Jurassic marine successions of St. Audrie’s Bay and East Quantoxhead (UK), have been used to construct a floating astronomical time-scale of ~2.5 Myr. This time-scale is based on the recognition of meter-scale cycles in limestone and black shale predominance and similar-scale variability in physical and chemical proxy- records. Three to five individual black shale beds occuring within these meter-scale sedimentary bundles, are interpreted to reflect precession-controlled changes in monsoon intensity, while the bundles are are interpreted as forced by the ~100 kyr eccentricity cycle. On the basis of these findings, we propose an astronomically constrained duration of the Hettangian stage of 1.8 Myr and unequal duration of Hettangian ammonite zones (P. planorbis zone: ~250 kyr; A. liasicus zone: ~750 kyr; S. angulata zone: ~800 kyr). The end-Triassic recovery interval preceding the first Jurassic ammonite occurrence is constrained to 6 precession cycles (~120 kyr). The extinction interval and coinciding negative Carbon Isotope Excursion (CIE) represent 1 to 2 precession cycles (~20-40 kyr). Cyclostratigraphic correlation to the astronomically tuned Geomagnetic Polarity Time-Scale of the continental Newark Basin (USA), allows to locate the stratigraphic position of the Triassic-Jurassic and Hettangian-Sinemurian boundary in the continental realm. 13 Continuous low δ CTOC values throughout the Hettangian and early Sinemurian, succeeding volcanic activity in the Central Atlantic Magmatic Province (CAMP), may reflect a long-term change in Earth’s global biogeochemical cycles, which seem not to fully recover for several million years.

75 Astronomically forced early Jurassic climate change

76 Chapter 5

1. Introduction

The end-Triassic earth experienced a severe environmental crisis with major extinctions in the marine realm (Raup and Sepkoski, 1982), pronounced changes in terrestrial ecosystems (Olsen et al., 2002; McElwain et al., 2009), and large turnovers in global biogeochemical cycles (Hesselbo et al., 2002). Large parts of Jurassic chronostratigraphy, including the Triassic-Jurassic (T-J) boundary, are based on north- west European ammonite biochronology (Palfy, 2008). However, estimates on absolute ages for the base of the Jurassic period and the duration of lower Jurassic stages largely vary. An accurate geological time-scale is of crucial importance to effectively integrate temporal data from different geological disciplines (e.g. stratigraphy, paleontology, geochemistry, geophysics) and allow detailed correlations between different outcrops yielding crucial information of the T-J boundary interval. Independent time constraints allow to better constrain the pace of geological processes (e.g. sedimentation rate, plate velocity, subsidence/uplift rates) and is of particular importance for understanding recovery rates of ecosystems and biota after the end-Triassic mass extinction. We studied a ~120 m long, marine sedimentary sequence in St. Audrie’s Bay and East Quantoxhead (Figure 1), which includes the Global boundary Stratotype Section and Point (GSSP) for the base of the Sinemurian stage (Bloos and Page, 2002). The studied late Rhaetian (Triassic) to lower Sinemurian (early Jurassic) time interval covers the complete Hettangian stage and comprises the end-Triassic mass extinction and subsequent early Jurassic recovery interval (Warrington et al., 2008). The north Somerset coastal region was in the Jurassic located at the passive margin of the Tethys Ocean. The lack of nearby volcanic activity and deposition of ash layers made the use of radiometric dating techniques impossible. We propose to assign astronomical parameters to observed oscillations in lithology and physical and chemical proxy-records. This approach provides cyclostratigraphic constraints on (i) the pace of early Jurassic recovery rates, (ii) the duration of the Hettangian stage, and (iii) the duration of Hettangian ammonite zones. We tune the biostratigraphically well-constrained early Jurassic marine proxy records to the astronomically tuned Geomagnetic Polarity Time-Scale (GPTS) of the continental 13 Newark Basin and discuss the duration of perturbations in the δ CTOC signature in relation to volcanic emissions in the Central Atlantic Magmatic Province.

2. Geological background

2.1 Chronostratigraphy Absolute age estimates for the T-J boundary evolved from ~192 Ma (Van Hinte, 1976), to ~208 Ma (Kent and Gradstein, 1985), ~212.5 Ma (Bayer, 1987) and ~199.6 Ma (Palfy et al., 2000). Contradicting dating results in this time interval may be caused by the use of different isotopic chronometers. For example, the latest Rhaetian in the Argana Basin and the High Atlas (Morocco) is 40Ar/39Ar dated between ~200.3 and 198.0 Ma (Marzoli et al., 2004) and the earliest Hettangian in the Fundy Basin is U-Pb dated at ~201.27 Ma (Schoene et al., 2006). The duration of the Hettangian was previously estimated at ~4 Myr (Kent and Gradstein, 1985) and ~9 Myr (Haq et al., 1987; 1988). With increased availability of radiometric dating methods, its duration decreased to ~3.1 Myr in the GTS2004 (Gradstein et al., 2004). New constraints on latest Rhaetian (~201.58 +/- 0.28

77 Astronomically forced early Jurassic climate change

-6˚ -4˚ -2˚ 52˚ 52˚

Cardiff Bristol

Bristol Channel

East Quantoxhead 51˚ St. Audrie’s Bay 51˚

Plymouth

50˚ 0 50 100 50˚

-6˚ -4˚ -2˚

Figure 1 Location of the St. Audrie’s Bay (51°10’54.70’’N/3°17’09.79’’W) and East Quantoxhead (51°11’27.91’’N/ 3°14’12.25’’W) sections are located in south-west England along the Somerset shoreline, on the south coast of the Bristol Channel.

Ma) and uppermost Hettangian (~199.53 +/- 0.29 Ma) ages are based on zircon U-Pb dating (Schaltegger et al., 2008) of ash layers in the marine Pucara Basin (Utcubamba valley, northern Peru) and indicate a duration of the Hettangian between ~1.48 and ~2.62 Myr. Cyclostratigraphic estimates of ~2.4 Myr for the Hartford sequence (Hartford Basin, USA) (Kent and Olsen, 2008) and magnetostratigraphic correlation to the Paris Basin Montcornet core (Yang et al., 1996) support a duration of the Hettangian stage of only a few million years.

2.2 Palaeoenvironment and biostratigraphy The upper Triassic Blue Anchor, Westbury and Lilstock Formations (Fm) in the UK, are succeeded by the uppermost Rhaetian and lower Jurassic Blue Lias Fm, which covers the Hettangian stage and continues well into the Sinemurian. The Williton Mb (Blue Anchor Fm; Figure 2) was deposited in a shallow marine environment (Warrington et al., 2008) and is thought to represent the initial late Triassic marine transgression in SW Britain (Hesselbo et al., 2004). Fluctuations in relative sea level likely controlled the distribution of facies from the succeeding Westbury Fm (Hesselbo et al., 2004). The transition from the Westbury to Lilstock Fm (lower Cotham Mb) may reflect subsequent shallowing of the depositional environment from upper shelf to peritidal water depths (Wignall and Bond, 2008). The deformed limestone beds (0.5 m thick) in the middle of the Cotham Mb are followed by an erosional surface, which may indicate temporary emergence (Hallam and Wignall, 1999; Hesselbo et al., 2004; Warrington et al., 2008). The following upper

78 Chapter 5

Cotham Mb may represent a coastal environment (Mander et al., 2008) with a flooding surface at the Cotham to Langport Mb transition (Hesselbo et al., 2004). The Langport Mb (Lilstock Fm) was deposited either in a shallow lagoonal environment in a broad and shallow seaway (Warrington et al., 2008), or during sea level rise on a carbonate ramp (Hesselbo et al., 2004). Sea-level change at the Lilstock to Blue Lias Fm transition is disputed with either a sea-level fall (Wignall and Bond, 2008) or a sea-level rise and the final drowning of the carbonate platform (Hesselbo et al., 2004). The sedimentary basin was surrounded by partly emerged platforms (Radley, 2008). The early Jurassic Blue Lias Fm was deposited during a phase of rapid flooding allowing the development of laminated, organic-rich shales (Hallam, 1995, 1997; Warrington et al., 2008). The Blue Lias Fm has been subject to extensive bio-, chrono- and chemostratigraphic studies (Hallam, 1987; Smith, 1989; McRoberts and Newton, 1995; Weedon et al., 1999; Hesselbo et al., 2002; Deconinck et al., 2003; Hounslow et al., 2004; Mander and Twitchett, 2008; Warrington et al., 2008; Korte et al., 2009). The most important outcrops are located in the Lyme and Dorset regions (south-west coast, UK) and the northern Somerset coast (this study, Figure 1). The T-J boundary section at St. Audrie’s Bay (51°10’54.70’’N/3°17’09.79’’W) was previously proposed as GSSP for the base of the Jurassic (Warrington et al., 1994 and 2008) with the first occurrence (FO) of the ammonite Psiloceras planorbis in the basal part of the Blue Lias Fm as principal boundary marker (Warrington et al., 2008). The slightly lower FO of Cerebropollenites thiergartii pollen may represent a terrestrial marker for the base of the Jurassic in this section (Bonis et al., submitted). Recently however, the Kuhjoch section (Hillebrandt et al., 2007) was accepted as T-J boundary GSSP. The East Quantoxhead outcrop (51°11’27.91’’N/ 3°14’12.25’’W) is located 3 km east of St. Audrie’s Bay at Limekiln Steps. The Blue Lias Fm in this section contains the GSSP for the base of the Sinemurian (Bloos and Page, 2002).

2.3 Lithology The sedimentary sequence of the Blue Lias Fm in the St. Audrie’s Bay and East Quantoxhead sections is marked by distinct alternations of homogeneous and inhomogeneous limestone beds and marls to shales. Limestone beds are mostly impure micrite mud- to wackestones and are 10 to 20 cm thick with extremes up to 50 cm. The limestone facies consists of fine-grained, predominantly clay-grade sediments containing varying proportions of siliciclastic clay minerals and micrite (Paul et al., 2008). They are suggested to have settled primary from suspension without any subsequent disturbance (Weedon, 1985/86). Some of the limestone beds have been diagenetically altered by redistribution of calciumcarbonate cement (Campos and Hallam, 1979; Hallam, 1986; Paul et al., 2008) with prolonged sulphate reduction and pyrite formation (Bottrell and Raiswell, 1989). This process led pale marls to cement into hard limestone beds that show an irregular lateral distribution. Limestones are interspersed by siliciclastic marl and shale intervals, which are a few centimeters up to several meters in thickness. These beds mainly consist of pale- grey marls, dark-grey marls and organic-rich laminated black shales (Paul et al., 2008). Siliciclastic sediments consist of (land-derived) clay minerals and organic particles from increased productivity combined with terrigenous input (Weedon 1985/86).

79 Astronomically forced early Jurassic climate change

12000 Number of cycles based on 11800 proxy-filters (Figure 5) 11600 [24] 11400 B 21 11200 [23] 11000 10800 B 20 10600 [22] 10400 B 19 10200 [21] 10000 9800 B 18 L 18 [20] 9600 9400 B 17 Sinemurian Bucklandi L 17 [19] 9200 9000 L 16 [18] 8800 8600 L 15 [17] 8400 L 14b 8200 [16] L 14a 8000 B 13 7800 L 13b 7600 [15] L 13a 7400 B 12 [14] 7200 7000 B 11 [13] 6800 Schlotheimia angulata B 10 6600 [12] 6400 B 9 6200 L 9 [11] 6000 5800 B 8 b L 8 b [10] 5600 B 8 a 5400 L 8 a [9] 5200 B 7 5000 L 7 [8]

Stratigraphic position (in cm) 4800 B 6 4600 4400 L 6 [7] 4200 B 5 4000 L 5 [6] 3800 Alsatites liasicus 3600 B 4 3400 L 4 [5] 3200 B 3 b 3000 L 3 b [4] B 3 a 2800 L 3 a [3] 2600 Hettangian

Jurassic L 2 [2] 2400 2200 L 1 [1] 2000 planorbis P. 1800 L 0 [0]

1600 Blue Lias Fm 1400 Lilstock 1200 Fm Triassic 1000 Rhaetian 800 600 400 Westbury Fm Westbury 200 Blue 0 Anchor Fm

80 Chapter 5

Sedimentary rhythms in the Blue Lias Fm consequently consist of a laminated black shale that grades up to a dark-grey marl, and a pale-grey marl commonly with concretionary to tabular (cemented) micritic limestone, which than turns back into dark grey marls (Paul et al., 2008). These rhythms are not exclusively symmetrical as (organic rich) shales not always developed or sediments were diagenetically altered. The number of limestone beds is significantly different from the number of sedimentary rhythms, due to the differential secondary cementation (e.g. Paul et al., 2008). The origin of the rhythmic sedimentation has been matter of debate (Campos and Hallam, 1979; Weedon, 1985/86; Hallam, 1986; Bottrell and Raiswell, 1989; Smith, 1989; Paul et al., 2008), with few workers assigning orbital climate forcing as the dominant mechanisms. In this hypothesis, the rhythmic alternations of lithologies are assumed to represent ~20-kyr precession cycles while bundles of structurally different limestone beds resulted from harmonics between the ~20-kyr precession and 40-kyr obliquity (Weedon et al., 1999) or ~100-kyr eccentricity forcing (Paul et al., 2008). Distinct limestone-shale couplets in these sections are recognized over tens of kilometers at least suggesting chronostratigraphic significance and high-frequency climate control (Weedon, 1985/86; Smith, 1989).

3. Methods

Field expeditions to the St. Audrie’s Bay (SAB) and East Quantoxhead (EQH) outcrops were undertaken in 2007, 2008 and 2009. A ~10 m stratigraphic overlap between both localities is observed through distinct patterns of alternating limestone-shale sequences (Whittaker and Green, 1983). Over 700 samples were collected from a ~108 m interval (10-15 cm resolution) comprising the Rhaetian Lilstock Fm and the Rhaetian, Hettangian and lower Sinemurian part of the Blue Lias Fm. Only the marly to silty sediments and shales were studied for several chemical and physical proxy markers (CaCO3: 394 samples/ 109.5 m; Total Organic Carbon (TOC) content: 332 samples/ 94 m; magnetic 13 susceptibility (MS): 738 samples/ 109.5 m). The δ CTOC record of Hesselbo et al. (2002) was extended upwards with 317 samples (91.13 m) and a 2.4 m (14 samples) overlap. A high-resolution magnetic susceptibility record was measured (10-15 cm resolution within the shale intervals) on crushed and freeze-dried silty to marly sediments from the top of the Rhaetian Westbury and Lilstock Fm well into the Hettangian and Sinemurian Blue Lias Fm (Figure 5). Measurements were performed with a KLY-2 Susceptometer at the Paleomagnetic Laboratory ‘Fort Hoofddijk’, Utrecht University, the Netherlands. The presented values of each sample are weight-corrected averages of at least three measurements. The calcium carbonate content was measured on the same interval (20-30 cm resolution within the shale intervals, Figure 5). The weight-percentage of calcium

Figure 2 Lithological representation of the combined St. Audrie’s Bay and East Quantoxhead sections based on field observations (with stratigrapic position in cm). The studied stratigraphic sequence covers the upper Triassic (Rhaetian) to lower Jurassic (Hettangian and base Sinemurian). The assigned bundles on the right reflect changes in limestone predominance (L numbers). The assigned bundles on the left reflect changes in black-shale predominance (B numbers). The [numbers] on the far right reflect the stratigraphic position of maxima in the eccentricity-filters of proxy data (Figure 5).

81 Astronomically forced early Jurassic climate change

carbonate in a dry sample is represented by the weight loss of the sample after acid dissolution. About 0.9 g of powdered sediment was rinsed twice with 15 ml of 1 M HCl. To reach almost neutral pH values, the residue was additionally rinsed twice with 22.5 ml demi-water and subsequently freeze-dried. The total organic carbon (TOC) content (20-30 cm resolution) was measured on the Hettangian (starting in the upper Psiloceras planorbis zone) and Sinemurian marls and shales from the Blue Lias Fm (Figure 5). The carbon content of around 9 mg of homogenized de-carbonated sample residue was analyzed online on a CNS-analyzer (NA 1500) following standard procedures, at the Geochemistry group of the Department of Earth Sciences, Utrecht University. The TOC content of the sediment was calculated by multiplying the carbon content of the de-carbonated sample by the ratio between the weight of the de-carbonated sample and the original weight of the sample.

~ 1600 kyr ~ 1100~ kyr 1200 kyr~ 1300 kyr ~ 1400 kyr ~ 1500 kyr

~ 900 kyr ~ 1000 kyr ~ 700 kyr ~ 800 kyr ~ 300 kyr~ 400 kyr ~ 500 kyr ~ 600 kyr

Blue Lias Fm P. planorbis A. liasicus S. angulata Rhaetian Hettangian Triassic Jurassic

Figure 3 Cliff-face overview of the St. Audrie’s Bay section covering the T-J boundary and most of the Hettangian. Continuous black lines reflect ~100 kyr eccentricity cycles (based on field observations and filtered proxy-data).See Appendix 9

13 The δ CTOC values were measured on marls/shales from the same interval as the TOC record (~20-30 cm resolution), starting at 26.10 m from the base of the Hesselbo et al. (2002) C-isotope curve and covering most of the Hettangian and lower Sinemurian. Bulk organic C-isotope values were measured on homogenized de-carbonated sample residue, containing ~30 μg of carbon, by Elemental Analyzer Continuous Flow Isotope Ratio Mass Spectrometry using a Fisons 1500 NCS Elemental Analyzer coupled to a Finnigan Mat Delta Plus mass spectrometer at the Geochemistry group of the Department of Earth Sciences, Utrecht University. Isotope ratios are reported in standard delta notation relative to Vienna PDB. Analytical precision based on routine analysis of two internal laboratory standards for every ten samples indicated a standard deviation of < 0.06‰.

82 Chapter 5

Frequency analysis was performed on all proxy records with the AnalySeries program, edition 1.1.1 by Paillard et al. (1996). Data were linearly detrended before using the Blackman-Tuckey method (compromise predefined level, Barlett window). Power spectra (with a 90% confidence interval) of each proxy are reported in cycles/cm.

4. Results

4.1 Lithologic trends The upper Triassic and lower Jurassic sedimentary succession is marked by pronounced changes in lithology on a larger scale than the basic sedimentary rhythms discussed in section 2.3 (Figure 2 and Figure 3). The top of the Blue Anchor and the Westbury Fm are mainly represented by marly to silty shales (Figure 2). The succeeding Lilstock and lower part of the Blue Lias Fm (up to 26.5 m) and the upper Hettangian Schlotheimia angulata zone are marked by limestone predominance (Figure 2). Most of the Hettangian Alsatites liasicus and Sinemurian Bucklandi zones are again represented by marl/shale deposition.

4.1.1 Periodic oscillations in limestone predominance A detailed lithological representation of the St. Audrie’s Bay and East Quantoxhead outcrops (Figure 2) reveals periodic changes in limestone predominance and distinct bundles of limestone beds, at a similar scale to the bundles recognized by Smith (1989). These bundles are observed in most of the Hettangian and lower Sinemurian and arbitrarily numbered L0 to L18 (Figure 2). Cyclic variations in limestone bed predominance are best observed in the lower Hettangian (L0 to L9) and the Hettangian-Sinemurian transition (L15 to L18). Bundling of limestone beds is less clear in the limestone-dominated interval between 64.5–84 m (Figure 2). Field observations suggest that bundles L13-a/b and L14-a/b are potentially four separate bundles, similar to bundles L3-a,b and L8-a,b. The amount of individual limestone beds per bundle varies throughout the section. Most of the middle Hettangian A. liasicus zone (bundles L3 to L6) is marked by only one limestone bed per bundle, in contrast to the T-J transition and the upper Hettangian where one bundle consists of up to 8 to 10 limestone beds.

4.1.2 Periodic oscillations in black shale predominance The lithological representation of the Blue Lias succession also reveals pronounced changes in organic matter content, represented by distinct colour changes within the siliciclastic facies (Figure 2 and Figure 4). The pale-grey marls alternate with distinctly dark-grey to black, often laminated, organic-rich shales every ~60 to 100 cm. On a larger scale, two pronounced black shale beds (tens of centimeters thick) alternate with two to three less-developed black shales. Such bundles of 3 to 5 black shale horizons are observed throughout the Hettangian (Figure 4) and lower Sinemurian. In Figure 2, these bundles are tentatively numbered B3 to B21. The bundles are most pronounced in the A. liasicus zone (B3-B8) and lowermost Sinemurian, and less-pronounced in the uppermost Rhaetian and uppermost Hettangian (Figure 2). Black shales do occur in bundles B3, B10 and B11, but bundling of these beds is less straightforward.

83 Astronomically forced early Jurassic climate change

12000 St. Audrie’s Bay (UK) 11600

11200

10800

10400

10000

9600 Bucklandi 9200 Sinemurian

8800

8400

8000

7600

7200

6800 Schlotheimia angulata

6400

6000

5600 ~ 100 kyr

5200

4800

4400

4000

3600 Alsatites liasicus ~ 100 kyr

3200

2800 Hettangian

2400 Jurassic

~ 100 kyr 2000 planorbis P. Blue Lias Fm 1600 ~ 100 kyr Lilstock 1200 Fm Rhaetian Triassic 800

400 ~ 100 kyr Westbury Fm Westbury Blue ~100 kyr 0 Anchor Fm

Figure 4 Cliff-face overview of part of the Hettangian sedimentary sequence at St. Audrie’s Bay (with stratigrapic position in cm). Continuous black lines reflect ~100 kyr eccentricity cycles (based on field observations and filtered proxy-data). Black bars represent the stratigraphic position of black-shale horizons in the Hettangian A. liasicus and basal S. angulata ammonite zones in St. Audrie’s Bay. See Appendix 10

4.1.3 Periodic oscillations in limestone and black shale predominance

Comparison of the recognized bundles in limestone and black shale occurrence reveals that these co-occur but in opposite phase relationship (Figure 2). This is most clear for bundles B4 to B9 with bundles L4 to L9, in which B8 and L8 are less certain bundles. Altogether, bundles consist of a limestone-dominated and a shale-dominated interval. These bundles of limestone beds and black shales vary in thickness throughout the sedimentary sequence. On average both the limestone and the black shale bundles are around 4 m in thickness, with thicker (thinner) bundles occurring in shale (limestone) dominated intervals. The distance between the black shale horizons varies positively relative to the thickness of the assigned bundles. Based on lithological interpretation and field observations, we count 16 (possibly +4) bundles of limestone beds and black shales in the Hettangian, which reflect periodic changes in limestone and black shale predominance, and 59 individual black shales. Two bundles, L15 and L16, do not contain any black shales leaving 14 bundles with 4.2 (and possibly 3.2) individual black shales on average (Figure 2).

84 Chapter 5

4.2 Chemical and physical proxy records

13 Our δ CTOC record shows meter-scale fluctuations of ~2‰ around a -29‰ Hettangian and lower Sinemurian average (Figure 5). These values show, similar to lower Jurassic C-isotope data of Hesselbo et al. (2002), a ~2.5‰ negative offset relative to Rhaetian average values (Figure 5). Smaller amplitude oscillations at higher frequency (~0.5-1.5‰, ~80 cm), superimposed on the large-scale fluctuations, often coincide with individual black shale horizons (Figure 5). Not all black shale events may 13 however be recognized in the δ CTOC record due to too low resolution. The TOC, CaCO3 and magnetic-susceptibility records are all marked by similar small-scale (~80 cm) oscillations superimposed on larger meter-scale fluctuations (Figure 5). Fluctuations in TOC content, varying between almost 0 and 6% with peaks up to 10%, mainly occur in the shale dominated Hettangian A. liasicus zone and Sinemurian Bucklandi zone.

The CaCO3 content fluctuates with ~20% around a trend line that shifts from ~55% at the T-J transition to ~35% during the A. liasicus zone and gradually returns to ~50% in the upper Hettangian and lower Sinemurian (Figure 5). Note that the (potentially diagenetically-cemented) limestones are not included in the CaCO3 record. A similar but opposite trend line is observed for the magnetic susceptibility record. The large-scale 13 fluctuations in the δ CTOC and CaCO3 records are concurrent but opposite to the TOC and magnetic-susceptibility records.

4.3 Frequency analysis Spectral analysis was performed on the Hettangian and lower Sinemurian interval 13 of the δ CTOC record and the complete TOC and CaCO3 datasets. Power-spectra of the three proxy records show ~90% significant spectral power at ~3.5-4 m and at ~5.5-6 m (Figure 6). A band-pass filter that includes both peaks in the power-spectra indicates that these represent the larger meter-scale fluctuations observed in the proxy-records. The thickness of oscillations in the proxy-filters varies directly with the variation in thickness of the bundles of limestone and black-shale predominance that are observed in the field (Figure 5). Higher-frequency peaks in the power-spectra are likely related to the occurrence of individual black-shales. These are however not filtered due to too low resolution of the proxy records to resolve this cyclicity. The Hettangian stage is marked by 18 oscillations in the proxyfilters (Figure 5). The potentially four observed limestone bundles in the middle of the S. angulata zone (bundles L13-a/b and L14-a/b) are clearly recognized in the proxy-records as only two 100 kyr eccentricity cycles (Figure 5). Bundles L3-a/b and L8-a,b are marked 4 oscillations in the filters and likely represent four short eccentricity cycles.

5. Discussion

5.1 Palaeoenvironmental interpretation

13 Increased TOC values during black-shale intervals concur with depleted δ CTOC values, suggesting increased terrestrial organic matter influx as main driver of fluctuations in 13 the δ CTOC signature (Figure 5). Increased magnetic susceptibility values (with higher siliciclastic sediment input) also coincide with enriched TOC values and further suggest increased continental run-off. The formation of black shales in the western Tethys

85 Astronomically forced early Jurassic climate change 2200 kyr 2100 kyr 2000 kyr 1800 kyr 1700 kyr 1600 kyr 1500 kyr 1400 kyr 1300 kyr 1200 kyr kyr 1100 1000 kyr 900 kyr 800 kyr 700 kyr 600 kyr 300 kyr 200 kyr 100 kyr 2300 kyr 1900 kyr 500 kyr 400 kyr 0 kyr 2400 kyr 0 1 9 8 7 6 5 4 Magn. Susc. 3 2 1 0 7 [%] 0 3 5 CaCO 0 3 0 1 0 1 9 8 7 6 5 4 TOC [%] TOC 3 2 1 0 4 2 - 5 2 - 6 2 - 7 2 - [‰] org 8 C 2 - 13 δ 9 2 - 0 3 - 1 3 -

[9] [8] [7] [6] [5] [4] [3] [2] [1] [0] [24] [23] [22] [21] [20] [19] [18] [17] [16] [15] [14] [13] [12] [11] [10]

Blue Lias Fm Lias Blue Fm Westbury

Lilstock Fm

Blue Anchor Fm P. planorbis P. Bucklandi angulata Schlotheimia Alsatites liasicus Alsatites

Rhaetian Hettangian Sinemurian

Jurassic Triassic 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 2 4 6 8 0 2 4 6 8 0 0 9 9 9 9 9 8 8 8 8 8 7 7 7 7 7 6 6 6 6 6 5 5 5 5 5 4 4 4 4 4 3 3 3 3 3 2 2 2 2 2 1 1 1 1 1 0 0 0 0 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1

86 Chapter 5

realm was likely related to an enhanced hydrological cycle, leading to increased run-off, increased supply of terrestrial organic matter into the basin, a stratified water-column and anoxic bottom water conditions (Bonis et al., 2009). In this, we follow a similar interpretation for the Blue Lias succession as formulated by Weedon (1985/86). Changes in monsoonal activity have immediate consequences for the magnitude of precipitation rates, run-off and weathering patterns (Crowley et al., 1992; Vollmer et al., 2008). Modelling studies by Kutzbach (1994) suggest ~23 kyr precession cycle influence on rainfall and runoff over large parts of (sub-)tropical Pangaea. Black shale occurrence throughout the early Jurassic of England is suggested to be likely related to precession- scale variations in insolation and increased monsoonal activity in this low latitude region (at approximately 26°N, Kent and Tauxe, 2005). Global warming due to CAMP related

CO2 emissions (McElwain et al., 1999) and possible methane release from gas-hydrates (Beerling and Berner, 2002), may have further enhanced the already large heat gradient between the vast Pangaean landmass and its surrounding oceans. It may have caused the landward expansion of atmospheric circulation patterns (Bonis et al., 2009) and intensified monsoon activity (Crowley et al,. 1992).

5.2 Astronomical forcing of Jurassic climate The continuous presence of meter-scale sedimentary cycles, both in limestone and in black-shale predominance, and their co-occurrence with cyclical patterns in the proxy-records argues for a stable allogenic forcing mechanism, likely to be astronomical forcing of Jurassic climate. Here, we argue that the occurrence of meter-scale black shale bundles, that include an average of 3.7 individual black shale beds, are controlled by the ~100 kyr eccentricity cycle, with individual black shales being driven by precession. The ratio of precession to short eccentricity is about 1 to 5 (~18-21.5 kyr to ~100 kyr) in early Jurassic times (Berger et al., 1992). In such an orbitally-controlled system, not all individual precession cycles within an eccentricity cycle are expected to develop as black shales. During eccentricity minima the amplitude of precession may be too low in order to cross the threshold for black shale deposition. Neogene sapropel patterns deposited in the Mediterranean Sea for example, exhibit 2 to 5 sapropels for every ~100 yr eccentricity cycle. At times of prolonged eccentricity minima related to the 405 kyr cycle, sapropels lack or occur at 41 kyr obliquity frequency, reducing the amount of sapropels considerably (Hilgen et al., 2000; Hüsing et al., 2007). The individual black shale to black shale bundle patterns found in the Blue Lias Formation are thus in line with expected precession to short eccentricity forcing. Eccentricity-controlled late Triassic climate oscillations have also been recorded in St. Audrie’s Bay, the mid-Germanic Basin and in the Newark Basin (Olsen and Kent,

13 Figure 5 The δ CTOC [‰], TOC [%], CaCO3 [%] and Magnetic-Susceptibility proxy-records, covering the upper Rhaetian to lower Sinemurian time-interval (with stratigrapic position in cm). Red band-pass filters reflect ~100 kyr eccentricity oscillations in the proxy-records. The filters are 13 based on two distinct peaks in the power-spectra with a bandwidth of 263-727 cm for the δ CTOC

record, 306-788 cm for the TOC record and 286-669 cm for the CaCO3 record. Grey shading represent tentatively assigned ~400 kyr eccentricity cycles. Data from the first ~28.5 m of the 13 δ CTOC record is from Hesselbo et al. (2002). Numbers on the right of the lithological column represent the number of 100-kyr eccentricity cycles from the base of the Hettangian stage. See Appendix 11

87 Astronomically forced early Jurassic climate change

1996; Kemp and Coe, 2007; Vollmer et al., 13 140 Power spectrum: δ Corg [‰] 2008). Terrestrial climate response on 100 100 kyr Eccentricity peak, with 3.86 m periodicity on high band pass filter (50-784 cm) kyr eccentricity modulation of insolation can 120 90% confidence interval 5.97 m 3.64 m (A) occur in low-latitude land areas affected 100 by fluctuations in monsoon intensity 80 (Crowley et al., 1992). Orbital-controlled eccentricity cycles in palynofacies and 60 organic and inorganic proxy records in the Relative power 40 Jurassic of England typically cover four to five precession cycles (Van Buchem et al., 20

1994; Waterhouse, 1999‑a,b). Eccentricity- 0 0.00 0.004 0.008 0.012 0.016 0.020 scale increases in marine and terrestrial Cycles/ cm palynomorph concentrations in the upper 1400 Power spectrum: TOC [%] Triassic and lower Jurassic St. Audrie’s Bay Eccentricity peak, with 4.41 m periodicity on high band pass filter (50-861 cm) sequence (this study) coincide with low 1200 90% confidence interval 6.08 m 4.03 m (B) relative spore abundances and low magnetic 1000 susceptibility values (Figure 7), further 800 suggesting orbitally-controlled fluctuations in the strength of the hydrological cycle. 600

Eccentricity strongly modulates the Relative power 400 intensity of precession-scale climate forcing, especially also visible in the organic proxy- 200 records (Figure 5). A strongly enhanced 0 0.000 0.004 0.008 0.012 0.016 0.020 hydrological cycle in concurrence with the Cycles/ cm negative CIE at the mass extinction interval 20000 Power spectrum: CaCO3 [%] Eccentricity peak, with 4.01 m periodicity is suggested by highly increased relative 18000 on high band pass filter (50-713 cm) 90% confidence interval spore abundances with precession-scale 5.72 m 3.62 m 16000 (C) fluctuations (Figure 7). Wet phases in the 14000 lower Jurassic of St. Audrie’s Bay are likely 12000 enhanced during eccentricity maxima when 10000 the northern hemisphere summer resides in 8000 perihelion. Relative power 6000

4000 5.3 Cyclostratigraphic constraints on the 2000 duration of the Hettangian stage 0 0.000 0.004 0.008 0.012 0.016 0.020 Based on cyclostratigraphic inter- Cycles/ cm pretation of lithology, the Hettangian is Figure 6 Power spectra of time- marked by 16 (but up to 20) bundles in 13 series analysis of (A) the δ CTOC, (B) limestone and black shale predominance. the Total Organic Carbon and (C) the

CaCO3 proxy-records. All three power This time interval is however marked by 18 spectra show main frequency peaks filtered oscillations in the proxy-records. with a ~3.8 and ~5.8 m periodicity. The 400 kyr orbitally forced eccentricity cycle is regarded as the most persistent eccentricity cycle over the past 200 Ma and it is clearly recognized in the Newark Basin (Olsen and Kent, 1996). It is, similar to most of the Triassic in the Germanic Basin (Bachmann and Kozur, 2004), not well recognized

88 Chapter 5

in the north Somerset coastal sections of St. Audrie’s Bay and East Quantoxhead. Tentatively assigned 400 kyr cycles, based on tens of meters-scale oscillations in the 13 chemical proxy-records (and especially the δ CTOC and TOC records (Figure 5)), suggest that the two intervals with shorter cycles (bundles L3-a,b and L8-a,b) should, rather than enhanced obliquity forcing during a long-term eccentricity minimum, also be considered as 100 kyr eccentricity cycles. The potentially four observed limestone bundles in the middle of the S. angulata zone (bundles L13a/b and L14a/b) are clearly recognized in the proxy-records as only two 100 kyr eccentricity cycles (Figure 5). We therefore consider a 1.8 Myr duration of the Hettangian stage as most feasible. A previous cyclostratigraphic study on magnetic-susceptibility records of the Blue Lias Fm in Lyme Regis, south-west England (Weedon et al., 1999), showed periodic fluctuations that are also regarded as an orbitally-controlled climate signal. They suggest an approximately equal duration of Hettangian ammonite zones and a minimum duration of 1.29 Myr for the Hettangian stage. The Lyme Regis outcrop however, is marked by a significant hiatus in the top of the S. angulata zone (of about 50%) relative to the sedimentary sequences of St. Audrie’s Bay/East Quantoxhead and the Burton Row borehole (Smith, 1989). Previous estimates on the duration of the Hettangian stage, based on absolute radiometric dating techniques, varied significantly (Kent and Gradstein (1985): ~4 Myr; Haq et al. (1987; 1988): ~9 Myr; Gradstein et al. (2004): ~3.1 Myr). Our interpretation of the duration of the Hettangian stage is however well within the error-margin of the most recent radiometric estimated duration of ~2.05 +/- 0.57 Myr (Schaltegger et al., 2008).

5.4 Cyclostratigraphic constraints on recovery rates and Hettangian ammonite zones Biological and biogeochemical changes at the T-J transition have been extensively studied at St. Audrie’s Bay (Warrington et al., 2008 and references therein). The timing of recovery patterns is however poorly understood as no accurate chronostratigraphic framework is yet available. The first Jurassic Psiloceras planorbis ammonites in St. Audrie’s Bay occur ~6 m stratigraphically above the end of the extinction event (Figure 7) and mark the onset of post-extinction ecological recovery after the end-Triassic mass extinction. Precession-induced climate forcing in the late Triassic Lilstock Fm may be reflected by periodic variations in relative spore abundance (Figure 7) (Bonis et al., submitted), suggesting a ~20-40 kyr duration of the extinction interval and concurrent negative CIE. The Jurassic P. planorbis is suggested to have its FO 6 precession cycles above the extinction event, suggesting a ~120 kyr duration of the end-Triassic recovery interval (~140-160 kyr including the extinction interval) (Figure 7). A similar ~100 kyr duration for the end-Triassic ammonite gap is also estimated by Hillebrandt and Krystyn (2009). They suggest that the first Jurassic ammonite P. planorbis in the north-west European sections may be ~250 kyr younger than P. spelae. Their correlation of the earliest Jurassic bio-events in the western Tethys realm (Eiberg Basin) and those in north-west Europe (Great Britain and Ireland), however, is based on estimated sedimentation rates rather than a concise and independent stratigraphic age model. Moreover, considering a sedimentation rate of 3 cm/kyr for this time interval in St. Audrie’s Bay, a hiatus of ~200 kyr would imply that about 6 m of the sedimentary record is lacking, which may

89 Astronomically forced early Jurassic climate change

interval

Recovery (~120 kyr)

Bivalve extinction Bivalve

LO Conodonts LO

Palynological assemblage changes assemblage Palynological Jurassic pollen Jurassic

Foraminiferal assemblage changes assemblage Foraminiferal

Dinoflagellate assemblage changes assemblage Dinoflagellate

- zone - liasicus Alsatites Jurassic ammonites Jurassic planorbis P. zone 0 0 1 0 8 0 6 0 4 0 2 abundance [%] Relative spores 0 5 5 *10 *10 4 2 5 5 0 *10 *10 1 2 1 conc. [ppg] 9 8 Terr. palynomorph Terr. 0 0 conc. [ppg] Marine palynomorph 7 6 5 4 2 4 - TOC [%] TOC 3 5 2 - 2 6 1 2 - 0 7 [‰] 2 - org 8 C 2 - 13 δ 9 2 - 0 3 - 1 3 -

[7] [6] [5] [4] [3] [2] [1] [0]

Anchor Fm Anchor Blue Lias Fm Lias Blue Fm Westbury

Blue

Fm P. planorbis P. Alsatites liasicus Alsatites

Lilstock Rhaetian Hettangian

Jurassic Triassic 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 8 6 4 2 0 5 4 4 4 4 4 3 3 3 3 3 2 2 2 2 2 1 1 1 1 1

90 Chapter 5

be rather unlikely. By contrast, our data show a very similar C-isotope pattern in both regions, with the FO of Cerebropollenites thiergartii pollen in concurrence with a ~3.5‰ negative shift (Ruhl et al., 2009). The FO of C. thiergartii is closely succeeded (by only few meters) by the FO of P. planorbis and P. spelae in St. Audrie’s Bay and the Eiberg Basin, respectively. Consequently, our data suggests only a slightly younger age (~40- 60 kyr) for the first Jurassic ammonites in the north-west European sections compared to those in the western Tethys Ocean. This would imply a short duration for the Tilmanni Standard ammonite Zone after Hillebrandt and Krystyn (2009). Alternatively, previous palynological and C-isotope stratigraphy correlations (Ruhl et al., 2009; Kürschner et al., 2007) could be incorrect and a sedimentary hiatus or condensed interval marks the basal Blue Lias Fm. Yet, a sedimentary break is not observed in the field nor in any of the proxy records. The P. planorbis ammonite zone is succeeded by the A. liasicus zone (at ~28 m), the Schlotheimia angulata zone (at ~58 m) and the Bucklandi zone (at ~91 m). Based on the assumption of equal duration of ammonite zones, it was suggested that variations in thickness of ammonite zones in the Hettangian are largely related to changes in sedimentation rate (Weedon, 1985/86). Orbitally induced cycles in limestone and shale predominance and the periodic occurrence of black-shales throughout the Hettangian and lower Sinemurian strongly suggest relatively continuous sedimentation rates and different ammonite zone durations. Unequal duration of ammonite zones in the Blue Lias Fm of south-west England was already suggested by Smith (1989). We show that the first Jurassic ammonite zone in St. Audrie’s Bay covers about 2.5 eccentricity cycles (~250 kyr) and is significantly shorter than the subsequent two Hettangian ammonite zones (A. liasicus zone: ~750 kyr and S. angulata zone: ~800 kyr). The duration of the P. planorbis zone may be critically influenced by increased origination/mutation rates of earliest Jurassic ammonites caused by environmental stress during enhanced, CAMP related, volcanic activity.

13 5.5 The early Jurassic δ CTOC record The T-J transition interval is marked by two pronounced negative excursions in 13 δ CTOC records at several locations around the world (Palfy et al., 2001; Guex et al., 2004; Galli et al., 2007; Ward et al., 2007; Ruhl et al., 2009). The St. Audrie’s Bay outcrop along the Somerset coast is marked by the short initial negative CIE of 5‰ that is separated from the succeeding and longer main negative CIE by a 3.5‰ positive excursion (Hesselbo et al., 2002). The main negative CIE in bulk organic matter coincides 13 with a similarly shaped but smaller (~2‰) negative CIE in the δ CCARB-Oyster record of the same section (Korte et al., 2009). Negative CIEs at the T-J boundary may therefore be regarded as actual recorders of carbon cycle perturbation that are likely (in-)directly related to massive CO2 release during CAMP volcanism (Hesselbo et al., 2002). The CAMP related basalt deposition in the Newark Basin however, is astronomically constrained

13 Figure 7 The δ CTOC [‰] and TOC [%] proxy-records of St. Audrie’s Bay (with stratigrapic position in cm), relative to terrestrial (green curve) and marine (blue curve) palynomorph concentrations and relative spore abundance (red curve). First and last occurrences and marine and terrestrial assemblage changes are based on Warrington et al. (2008). See Appendix 12

91 Astronomically forced early Jurassic climate change H26r H25r H24r E23r 4 4 3 2 1 3 2 1 5 4 4 4 3 2 1 3 2 1 3 2 1 4 4 3 2 1 3 2 1 [C] [B] [D] Hartford Basin (Eastern US) [0 kyr] [900 kyr] [800 kyr] [700 kyr] [600 kyr] [500 kyr] [400 kyr] [300 kyr] [200 kyr] [100 kyr] [-140 kyr] [2300 kyr] [2200 kyr] [2100 kyr] [2000 kyr] [1900 kyr] [1800 kyr] [1700 kyr] [1600 kyr] [1500 kyr] [1400 kyr] [1300 kyr] [1200 kyr] kyr] [1100 [1000 kyr] [2400 kyr] 0 1 9 8 7 6 5 4 TOC [%] TOC 3 2 4 1 2 - 0 5 2 - 6 2 - 7 2 - [‰] org 8 2 C - 13 δ 9 2 - 0 3 - 1 3 -

[9] [8] [7] [6] [5] [4] [3] [2] [1] [0] [23] [22] [21] [20] [19] [18] [17] [16] [15] [14] [13] [12] [11] [10] [24]

Blue Lias Fm Lias Blue Anchor Fm Anchor Westbury Fm Westbury

Blue

Lilstock Fm Schlotheimia angulata Schlotheimia Alsatites liasicus Alsatites bucklandi P. planorbis P.

Rhaetian Sinemurian Hettangian

Jurassic Triassic St Audries Bay & East Quantoxhead (UK) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 8 2 6 0 6 2 8 4 0 6 2 8 4 0 6 2 8 4 0 6 2 8 4 0 6 2 8 4 0 0 0 1 1 2 9 9 8 8 8 7 7 6 6 6 5 5 4 4 4 3 3 2 2 2 1 1 1 1 1 1 1 1

Figure 8 Correlation of the ~100 kyr eccentricity filters of chemical proxy-records in St. Audrie’s Bay/East Quantoxhead to the tuned lithology and eccentricity forced precession envelope of the Hartford Basin (Kent and Olsen, 2008) (with stratigrapic position in cm). Orange lines represent the stratigraphic position of [B] the Talcott/Orange Mt Basalt, [C] the Holyoke/ Preakness Basalt and [D] the Hampden/Hook Mt Basalt in the Hartford Basin and possible time- equivalent intervals in St. Audrie’s bay. See Appendix 13

92 Chapter 5

to a duration of ~600 kyr (Olsen et al., 2003; Whiteside et al., 2007). Volcanic activity and CAMP related CO2 emissions may therefore be restricted to the early Hettangian. 13 Our extended δ CTOC curve exhibits continuously low values throughout the Hettangian and early Sinemurian and prolongs the duration of the main CIE to over 2.3 Myr (Figure 5). These data imply that either CAMP related volcanic activity lasted much longer than 13 recorded in the continental basins of the eastern US, or that the δ CTOC signature is not directly related to volcanic emissions. The main negative CIE may rather reflect a long- term ecosystem change with a shift to new steady state values following uppermost Triassic and basal Jurassic CAMP volcanism. Although new species began to evolve already in the lower Hettangian, biogeochemical cycles likely not fully recovered for several million years similar to delayed biogeochemical recovery following the Permian- Triassic (Payne and Kump, 2004; Galfetti et al., 2007) and Cretaceous-Paleogene mass extinctions (D’Hondt et al., 1998). 13 The ~2‰ fluctuations (with a ~3.8-5.8 m thickness) in theδ CTOC record of St. Audrie’s Bay coincide with observed bundles in black shale and limestone domination and are interpreted as 100 kyr eccentricity controlled climate cycles. This interpretation 13 may further improve the correlation potential of δ CTOC signatures in the Triassic-Jurassic transition interval. It may suggest that the C-isotope curves in the Eiberg Basin (Ruhl et al., 2009) including the base of the Jurassic GSSP at Kuhjoch, represent a duration of ~200-300 kyr following the initial CIE. Previous studies spanning the Hettangian and early Sinemurian, show a distinct 13 13 positive excursion in the δ CTOC (Williford et al., 2007) and bulk δ CCARB (Van de Schootbrugge et al., 2008) signature in the Kennecott Point (Queen Charlotte Islands, British Columbia, Canada) and Val Adrara (Italy) sections, respectively. The positive excursion in the latter section may be directly related to distinct changes in facies. An early Jurassic positive excursion in the Kennecott Point section may, similar to the early Triassic positive CIEs following the Permian-Triassic mass extinction, be related to local ecological conditions and explained by increased marine primary productivity under high atmospheric CO2 values (Payne and Kump, 2007).

5.6 Cyclostratigraphic constraints for correlation of the marine and continental realms Late Triassic to early Jurassic cyclostratigraphic time control is also well established in the continental sequences of the Newark Supergroup (Olsen and Kent, 1999; Kent and Olsen, 2008). Orbitally controlled sedimentary cycles in these sections, mainly with precession and eccentricity wavelengths, mark one of the longest continuous sedimentary records available. Additional palaeomagnetic studies resulted in a high resolution astronomically calibrated geomagnetic polarity timescale of over 30 Myr. This high resolution time frame constrained the duration of CAMP deposition in the eastern United States to ~580-610 (+/- 100) kyr (Olsen et al., 1996; Whiteside et al., 2007). Biostratigraphic time control in the Newark sequences is unfortunately hampered by the lack of age diagnostic fossils and provinciality of fossils. Several palaeomagnetic correlations between the Newark and St Audrie’s Bay sequences have been proposed (Hounslow et al., 2004; Knight et al., 2004; Whiteside et al., 2007; Marzoli et al., 2008), but our study shows that some of these correlations are rather unlikely. Correlation of the extinction interval and negative CIE in St. Audrie’s Bay and the suggested extinction

93 Astronomically forced early Jurassic climate change

interval marked by terrestrial ecosystem changes in the Newark Basin (Olsen et al., 2002), is independently supported by our data. Both records are marked by a long- term eccentricity minimum, ~1.3 Ma after the extinction interval (Figure 8), reflected by poorly developed lake deposits in the continental sedimentary record and poorly developed black shale events in the marine realm. Our correlation implies however that reversed polarity chron SA5n.1r in the UK, is not recorded or absent in the Newark sequence. It may represent an extremely short excursion of the normal palaeomagnetic field, which is not demonstrated in the Newark Basin. Alternatively, this chron, which is only based on one single sample of admitted poor palaeomagnetic quality (Hounslow et al., 2004) may be an artifact. Additionally, chron SA5r, although demonstrated for the Moroccan lava sequences (Knight et al., 2004), has yet not been recorded in the Newark sequence. Our suggested cyclostratigraphic correlation of the marine St. Audrie’s Bay succession to the astronomically tuned GPTS of the Newark Basin, shows (i) the position of the marine defined Rhaetian-Hettangian and Hettangian-Sinemurian boundaries in the continental record, (ii) time-equivalent intervals of CAMP deposition in the marine realm and (iii) the position in the marine record of three reversed polarity chrons at the Hettangian-Sinemurian transition. Our correlation suggests that (i) the Triassic-Jurassic boundary is positioned between the Orange Mt/Talcott and Preakness/Holyoke basalts in the continental Newark and Hartford Basins, respectively (Figure 8). This position is supported by a recent palynological study in the Fundy Basin (Cirilli et al., 2009). We suggest the position of the base of the Sinemurian in the middle of the Mittinegue Mb of the Hartford Basin (eastern USA). Deposition of (ii) the Orange Mt and time-equivalent basalts of the eastern US coincide with negative values following the initial CIE by ~20 kyr (Figure 8). Deposition of the subsequent Preakness and Hook Mt time-equivalent basalts coincide with already 13 low δ CTOC values during the main CIE and diminished carbonate deposition in the marine record. The onset of volcanic activity and the possible release of methane from clathrates (Beerling and Berner, 2002) at the extinction interval possibly initiated long-term changes in global biogeochemical cycles. Subsequent volcanic phases may therefore have been of less influence. Our proposed correlation also suggests (iii) the position of a short (~50 kyr) reversed polarity chron (Kent and Olsen, 2008) in the middle of the S. angulata zone and two reversed chrons in the lower Bucklandi zone of south-west England.

6. Conclusions

Combined field observations and proxy studies from the marine sedimentary sequence of St. Audrie’s Bay and East Quantoxhead demonstrate simultaneous fluctuations in black-shale and limestone predominance and chemical proxy-records. Time-series analysis of the proxy-records shows a main periodicity between ~3.8-5.8m for these oscillations. Each oscillation is marked by ~3-5 black-shale horizons that are likely controlled by changes in monsoon intensity with a precession-wavelength. The meter-scale oscillations are therefore regarded as orbitally forced ~100 kyr eccentricity

94 Chapter 5

cycles. Our data constrains the duration of the Hettangian to 1.8 Myr. Lower Jurassic ammonite zones are suggested to be unequal in duration, with the P. planorbis zone: ~250 kyr, the A. liasicus zone: ~750 kyr and the S. angulata zone: ~800 kyr. The recovery interval between the end-Triassic mass extinction and the first Jurassic ammonite occurrence is defined by 6 precession cycles (~120 kyr). The extinction interval and coinciding negative CIE may be represented by 1-2 precession cycles (~20- 40 kyr). Our cyclostratigraphic correlation of the St. Audrie’s Bay/East Quantoxhead succession to the astronomically tuned GPTS of the Newark Basin for the first time suggests the stratigraphic position of the continental equivalent of the marine defined T-J and Hettangian-Sinemurian boundary. The first would be positioned above the Orange Mt and time-equivalent basalts and the latter would be located in the Mittinegue Mb of the Hartford Basin (eastern USA). This correlation suggests no apparent influence of the 13 CAMP related final volcanic phases on the δ CTOC signature. The longer lasting negative carbon isotope excursion at the base of the Hettangian continues throughout the lower Jurassic and may reflect a shift to new long-term steady state values following CAMP volcanic activity in the early Hettangian. Although new species began to evolve already in the lower Hettangian, Earth’s biogeochemical cycles may have not fully recovered for several million years.

Acknowledgements

MR, MD and NB thank M. Hounslow for extensive field assistance during the 2007 field expedition. A. van Dijk is acknowledged for laboratory assistance during C-isotope measurements. This study is funded by the High Potential program of Utrecht University, the Netherlands.

95 96 Chapter 6

Multiple late Triassic carbon cycle perturbations observed in continental and marine C-isotope records from the western Tethys (Austria) and NW European sections (UK and Germany)

The end-Triassic carbon cycle perturbation, coincident with major marine extinctions and continental ecosystem changes, is marked by a ~5-6‰ negative carbon isotope excursion (CIE). We show that these events are preceded by two successive 2-3‰ Rhaetian negative excursions in marine and continental 13 δ CTOC records from the western Tethys (Eiberg Basin, Austria) and north-west European sections. A coinciding, albeit slightly 13 smaller, negative excursion in our δ CLepidopteris ottonis leaf-record, suggests successive 13C depletion of the late Triassic global atmosphere and oceans. Oxidation of organic carbon by subsurface thermal metamorphism of organic rich strata may be one potential mechanism to transfer isotopically light carbon to the exogenic carbon pool.

97 Multiple late Triassic C-cycle perturbations

98 Chapter 6

1. Introducition

The late Triassic (~201.6 Ma; Schaltegger et al., 2008) is a period of repeated biotic turnover in the marine and terrestrial realm (Raup and Sepkoski, 1982; Benton, 1993; Benton, 1995; Olsen et al., 2002; Tanner et al., 2004; Kiessling et al., 2007; Lucas and Tanner, 2008; Kürschner and Herngreen, in press) that culminate at the Triassic- Jurassic (T-J) transition. It is often referred to as one of five major mass extinctions in the Phanerozoic. The end-Triassic mass extinction closely coincides with the onset of extensive flood basalt volcanism in the Central Atlantic Magmatic Province (CAMP) (Deenen et al., submitted; Marzoli et al., 2004; Marzoli et al., 1999) and the release of 13C depleted methane from gas-hydrates (Beerling and Berner, 2002; Chapter 4). It is directly related to disruption of the global C-cycle, with a 5-6‰ negative perturbation in terrestrial and marine C-isotope records (Hesselbo et al., 2002; Korte et al., 2009; Ruhl et al., 2009; Chapter 4). This suggests a causal relationship between the transfer of carbon to the atmosphere and oceans (with atmospheric CO2 concentrations rising up to 2400 ppmv (McElwain et al., 1999)), climate change and marine and terrestrial extinctions (Huynh et al., 2005; Chapter 4). Enhanced late Triassic (Norian and Rhaetian) extinction levels are potentially also related to multiple CO2 driven climate fluctuations (Prochnow et al., 2006; Cleveland et al., 2008). Yet, late Triassic C-isotope excursions have not been recorded. We performed a δ13C study on two Rhaetian (late Triassic) sedimentary sequences from the marine and continental realm in the western Tethys Ocean (Austria) and Germanic Basin (Germany) (Figure 1). A C-isotope study on Lepidopteris ottonis leaves from the same section in the Germanic Basin directly reflects atmospheric-13C changes during the studied time interval.

2. Palaeogeography and lithology

The Rhaetian Eiberg Member (Mb) (Kössen Formation (Fm)) formed as part of an extensive carbonate platform at the western Tethys passive margin (Kürschner et al., 2007). The Eiberg section (47°32’59.98’’N/12°10’07.32’’E) was located in the central and deepest part of the Eiberg Basin, which itself formed between the newly growing carbonate reefs of the Oberrhaet Limestone (Golebiowski, 1990). The Eiberg section is, in contrast to several shallower sections in the Eiberg Basin (Ruhl et al., 2009), marked by deposition of a ~6 m marly interval in the upper Kössen Fm, preceding the end- Triassic negative CIE at the extinction interval (Figure 2-B). The ~10 m Rhaetian Haupt-Ton sedimentary sequence in the Wüstenwelsberg section (50°08’38.61’’N/10°48’14.15’’E) (south-western end of the Germanic Basin), is the continental equivalent of the marine Contorta-beds in the more central part of this basin (Bloos, 1990). The grey organic rich clays directly succeed fluviatile to coastal Haupt Sandstein deposits (Figure 2-D) (Bloos, 1990). The Haupt-Ton in this section contains several leaf-bearing horizons (Bonis et al., submitted) and is marked by organic rich shales and coal deposits in the middle of the succession (Figure 2-D). This lithostratigraphic unit is succeeded by the Oberer Sandstein and time equivalent organic rich Triletes-beds (Figure 2-D and Supplementary Information Figure 1).

99 Multiple late Triassic C-cycle perturbations

Figure 1 Palaeogeographic location of end-Triassic and early Jurassic strata of (A) St. Audrie’s Bay (UK), (B) Wüstenwelsberg (Germany) and (C) Eiberg and Tiefengraben sections (Austria). Early Mesozoic continent configuration and basalt, dike and sill outcrops in the Central Atlantic Magmatic Province (Modified after Quan et al. (2008) and van de Schootbrugge 30°N B et al. (2009)). See Appendix 14 A C

0°

Cratonic landmasses Marginal marine Marginal marine Deep ocean Extend of CAMP flood basalts 1000 km Basalt outcrops, sills and dikes

3. METHODS

13 Sample preparation and δ CTOC measurements on marine and continental sediments from the Eiberg and Wüstenwelsberg section respectively, was performed according to Ruhl et al. (2009). Measurements were performed by Elemental Analyzer Continuous Flow Isotope Ratio Mass Spectrometry using a Fisons 1500 NCS Elemental Analyzer coupled to a Finnigan Mat Delta Plus Mass Spectrometer at the Geochemistry group of the Department of Earth Sciences, Utrecht University. Values are given in Figure 2-B and 2-E and reported relative to Vienna PDB. The variability in the C-isotope composition of two internal laboratory standards for every ten samples, demonstrate a standard deviation (StD) of < 0.071‰. Dupli- and triplicate C-isotope measurements on bulk leaf material of single Lepidopteris ottonis leaf-pinnules (Supplementary Information Figure 2) from the 13 Wüstenwelsberg section were similar as δ CTOC measurements. L. ottonis leaves were extracted from the clayey sediments of the Haupt-Ton and subsequently rinsed with demi-water. Remaining sedimentary particles still attached to the leaves, were removed by ultrasone (<30s). Dupli- and triplicate δ13C measurements on several L. ottonis leaves from one stratigraphic horizon, had a StD between 0.07-0.50‰. Simple mass balance calculation were computed, using end-Triassic boundary conditions of Beerling and Berner (2002) and:

13 13 13 13 δ Ctot * MTot = (δ Coc * Moc) + (δ Catm * Matm) + (δ Cadd * Madd)

100 Chapter 6

4. RESULTS

13 The Rhaetian marine Eiberg Mb is marked by two distinct δ CTOC negative excursions of up to 3‰ from Rhaetian averages of ~-26.5‰ (Figure 2-B), and succeeded by the ~6‰ negative CIE at the end-Triassic mass extinction interval. The observed C-isotope signature in the Eiberg Basin closely resembles the T-J boundary C-isotope record of St. Audrie’s Bay (Figure 2-C), with two up to 3‰ negative CIEs preceding the end-Triassic C-cycle perturbation and extinction interval, by ~5.5 m. The continental Haupt-Ton sedimentary sequence in the Germanic Basin is marked by negative C-isotope excursions of up to 3‰ from average Rhaetian values of ~-24‰ (Figure 2-D). The T-J transition at Wüstenwelsberg is marked by the lack of organic remains. The 13 top of the section is however marked by ~4‰ depleted δ CTOC values and a typical Jurassic pollen assemblage (Bonis et al., submitted), similar to the longer-lasting basal Jurassic negative CIE in St. Audrie’s Bay and the Eiberg Basin (Figure 2-D). C-isotope values of several Lepidopteris ottonis leaves per leaf-bearing horizon in the Wüstenwelsberg section (Figure 2) show background values of ~-27‰, which are typical for C3 plants and inline with previous L. ottonis C-isotope measurements (Bocherens et al., 1993). A ~1‰ negative CIE in this record closely coincides with the 13 13 first observed negative CIE in the Rhaetian δ CTOC record. The variance in δ CL. ottonis values per leaf-bearing horizon is however relatively large. No leaves were preserved in 13 concurrence with the most negative δ CTOC values (Figure 2-E). Changes in atmospheric- 13 13 δ C values were therefore possibly up to ~2-3‰ larger than observed in the δ CL. ottonis record (Figure 2-E).

5. DISCUSSION

The end-Triassic is punctuated by a major perturbation in the global carbon cycle, with a ~5-6‰ negative CIE in organic C-isotope records (Hesselbo et al., 2002; Ruhl et al., 2009). This event closely coincides with increased end-Triassic marine extinction levels (Raup and Sepkoski, 1982; Benton, 1995) and pronounced changes in terrestrial ecosystems (Benton, 1993; Olsen et al., 2002; McElwain et al., 2008). The major end- Triassic C-cycle perturbation and extinction event likely originates from the massive and abrupt release of methane from hydrates (Beerling and Berner, 2002; Chapter 4).

This may be triggered by enhanced CO2 emissions in the Central Atlantic Magmatic Province (CAMP) (Hesselbo et al., 2002; Marzoli et al., 2004; Deenen et al., submitted) and caused enhanced greenhouse warming and hydrological cycling (Chapter 4). Increased late Triassic (Norian/Rhaetian) extinction levels (Benton, 1993; Lucas and Tanner, 2008; Kürschner and Herngreen, in press) may also be related to (global) climate perturbations, with elevated CO2 concentrations in the atmosphere and oceans (Prochnow et al., 2006; Cleveland et al., 2008). However, no C-isotope perturbations have yet been shown to mark the late Triassic. We show for the first time two successive up to 3‰ negative excursions inthe 13 continental δ CTOC record from the Rhaetian Haupt-Ton of the Wüstenwelsberg section (Germanic Basin) (Figure 2-D). These excursions are likely directly related to similar negative CIEs in the Rhaetian marine Westbury Fm (UK) (Figure 2-C) (Hesselbo et al., 2002). Both records also closely resemble the marine C-isotope signature of the upper

101 Multiple late Triassic C-cycle perturbations

Tethys realm NW European basins (Eiberg basin, Austria) UK Germany 15 14

Limestone Organic rich sand 13 A C D 127 Grey shale Sandstone 22 11 Dark grey shale 10 21 Sand Psiloceras planorbis

9 Hettangian-Jurassic Hettangian-Jurassic 20 8

7 19 21 6 18

Hettangian -Jurassic 20 5 17 4 19

3 16

Blue Lias Fm 18 No ammonites CAMP volcanism CAMP volcanism CAMP

2 Rhaetian-Triassic 15 17 1 no fossils transition zone

Kendlbach Fm-Tiefengraben Mb Kendlbach Fm-Tiefengraben 14 16 0 15 6 End-Triassic mass extinction & C-cycle perturbation 14 12 B Lilstock Fm 5 13 11 12 10 4 11 Rhaetian-Triassic 9 10 3 Kössen Fm-Eiberg Mb 8 9

7 2 * * 8 6 7 * Fm Westbury * 1 5 6

Rhaetian-Triassic 5 0 4 Haupt-ton/ Contorta-beds 4 3 -1 3 2 2 -2 1 1 0 -3 E 0

Blue Anchor Fm 2 ?

-4 1 ~3‰ ~2‰? Postera-beds? 0

-27 -26 -25 -24 -29 -28 -27 -26 -25 Haupt Sandstein/

-33 -31 -29 -27 -25 -31 -29 -27 -25 -29 -27 -25 -23 -29 -27 -25 13 13 13 13 δ Corg [‰] δ Corg [‰] δ Corg [‰] δ Cleaves [‰]

13 Figure 2 The end-Triassic/early Jurassic δ CTOC records of (A) Tiefengraben (Austria; Kürschner et al., 2007), (B) Eiberg (Austria; this study) and (C) St. Audrie’s Bay (UK; Hesselbo et al., 2002). 13 13 Figure D and E show the end-Triassic δ CTOC and δ CLepidopteris ottonis records of Wüstenwelsberg (Germany; this study). Stratigrahic horizons marked by (*) possibly reflect late Triassic C-cycle perturbations, which are due to the release of 13C depleted carbon to the exogenic carbon pool, by subsurface thermal metamorphism of organic rich strata. See Appendix 15

Choristoceras marshii zone in the Eiberg Basin (Tethys Ocean) (Figure 2-B). The new negative C-isotope excursions in several Rhaetian marine and continental basins, preceding the end-Triassic C-cycle perturbation by few (~4.5-8) meters, suggests multiple and global late Triassic carbon cycle perturbations. Atmospheric-13C depletion 13 is directly indicated by the ~1‰ negative excursion in the δ CL. ottonis record (Figure 2‑E). 13C depletion of the Rhaetian exogenic carbon pool may even be ~1-2‰ larger, 13 13 assuming linear development of the δ CTOC and δ CL. ottonis records. More negative δ13C values of L. ottonis and other Mesozoic leaves (Bocherens et al., 1993; Sun et al., 2003), might reflect increased carbon fractionation due to reduced

102 Chapter 6

water‑stress in a swamp-like environment. Relatively wet palaeo-environmental conditions throughout the upper Rhaetian Haupt-Ton in the Germanic Basin are however suggested by the high relative abundance of spore producing plants (Bonis et al., submitted). Minor changes in water-stress and stomatal conductance likely only caused a slight increase in carbon fractionation of L. ottonis plants.

The early Mesozoic is already marked by elevated CO2 concentrations (Royer et al., 2001; Fletcher et al., 2007), which dramatically increase at the T-J boundary interval (McElwain et al., 1999). Our data shows that the late Triassic, possibly similar to the Paleocene and Eocene greenhouse world (Zachos et al., 2001; Cramer et al., 2003; Zachos et al., 2008), may be marked by multiple climate and C-cycle perturbations. Negative excursions in Rhaetian δ13C records suggest a repeated transfer of 13C depleted carbon to the late Triassic exogenic carbon pool. The release of isotopically light carbon to the Mesozoic and late Paleozoic atmosphere and oceans is often linked to magma- intrusion in organic-rich sediments (Svensen et al., 2004; McElwain et al., 2005; Svensen et al., 2009). The high-volume fissure lavas from CAMP extrusives, with a surface area potentially in excess of 107 km2, originated from a vast intrusion complex of tholeiitic dikes and sills that are distributed over the north and south-American and African continents (Olsen, 1997; Marzoli et al., 1999; McHone, 2000 and references therein; McHone, 2000; Olsen et al., 2003; Marzoli et al., 2004). The intrusion complex partially pre-dates the first CAMP extrusives in the northeastern US and Moroccan continental basins by only few 100’s of kyrs (Marzoli et al., 1999; McHone, 2006; Nomade et al., 2007). Intrusion of dikes and sills into late Triassic (continental) basin deposits potentially thermally altered and oxidized organic rich strata in the subsurface. Using a simple mass balance calculation with end-Triassic boundary conditions (Beerling and Berner, 2002), we compute that a 2-3‰ depletion of the exogenic carbon pool requires the release of ~7400-11000 Gt of carbon from a subsurface terrestrial organic carbon reservoir (of ~-25.3‰). Alternatively, Rhaetian carbon cycle perturbations may be, similar to events at the end-Triassic mass extinction interval, related to the release of ~2900-4300 Gt of isotopically light carbon from methane hydrates (~-60‰).

6. CONCLUSIONS

We show that the end-Triassic global carbon cycle perturbation, coincident with the end-Triassic mass extinction, is preceded by two successive 2-3‰ negative excursions 13 in marine and continental δ CTOC records from the western Tethys and NW European sections. Rhaetian atmospheric-13C depletion is further suggested by a similar negative 13 13 excursion in the δ CL. ottonis leaf-record. This suggests the transfer of C depleted carbon to the Rhaetian exogenic carbon reservoirs. Our data shows multiple late-Triassic C-cycle perturbations that potentially contributed to prolonged and increased late Triassic extinction levels. We suggest that subsurface thermal alteration and oxidation of organic rich strata is one potential mechanism to release isotopically light carbon as CO2 to the atmosphere and oceans. This could be related to the intrusion of a vast amount of end- Triassic dike and sill complexes into early Mesozoic continental strata surrounding the Central Atlantic rift basins. At present it is not possible to directly link the new CIE with one of the Rhaetian extinction levels. However, the existence of pre-end Triassic CIEs fits

103 Multiple late Triassic C-cycle perturbations

better with the idea of a prolonged period of environmental changes and biotic turnovers, as known from the fossil record (Lucas and Tanner, 2008), than with one catastrophic extinction at the T-J boundary. More detailed Rhaetian C-isotope records going back into the early Late Triassic have to be established in order to complete the complex history of Late Triassic extinctions.

Chapter 6

Supplementary Information

Stratigraphic background

The duration of the Rhaetian stage and stratigraphic position of the Norian-Rhaetian and Rhaetian-Hettangian boundaries, were often adjusted with changing preference of biostratigraphic boundary markers (Supplementary Information Figure 1). The proposed Global boundary Stratotype Section and Point (GSSP) for the base of the Rhaetian stage at Steinbergkogel (western Tethys realm, Austria) (Krystyn et al., 2007), is marked by three potential boundary markers. Two proposed boundary markers, the first occurrence (FO) of the Misikella hernsteini and M. posthernsteini conodont species, assign most of the Sevatian 2 to the Rhaetian. The third potential boundary marker, the FO of the ammonite Vandaites stuerzenbaumi, strongly reduces the duration of the Rhaetian. The studied interval in the western Tethys Eiberg Basin comprises the upper part of the Rhaetian Choristoceras marshii zone in the Kössen Fm and is succeeded by the Schattwald beds (which are time-equivalent to the pre-planorbis beds) (Hillebrandt et al., 2007). The uppermost Rhaetian pre-planorbis beds directly succeed the base of the Jurassic, which is defined by the FO of Psiloceras spelae tirolicum ammonites in the Kuhjoch section (Hillebrandt et al., 2007). The Rhaetian stage in the Germanic Basin originally represented the upper Keuper. The lower, middle and upper Rhaetian division in the Germanic Basin heavily relies on lithostratigraphic units with particular guide fossils. The Rhaetian stage was later confined to the uppermost Arnstadt Fm/ lower- middle Postera-beds and the subsequent Exter Fm (Bachmann and Kozur, 2004). The middle to upper Rhaetian Exter Fm consists of the (Postera) Haupt-Sandstein and the Contorta (Haupt-Ton) and Triletes beds. However, correlation of the Rhaetian substages in the Tethys realm and Germanic Basin is biostratigraphically not well-established. The Contorta-beds may be related to the upper C. marshii ammonite zone in the Tethys Ocean (Lund, 2003) and the Westbury Formation (Fm) in the boreal realm (Bachman and Kozur, 2004).

104 Chapter 6

Ammonite Germanic Tethys Germanic Basin Tethys realm NW Europe (sub-) zone std Basin realm Eiberg Basin

Nitsch, Lund, Bachmann Epi- Kozur, 2003 Krystyn et al., Lund, von Warrington This study 2005 2003 & Kozur, continental & 2007 2003 Hillebrandt et al., 2008 2004 Triassic Chanell et al., Base Rhaetian et al., 2007 International 2003 GSSP Symposium proposal Guide 1998 Psiloceras Jurassic P. spelae P. spelae planorbis zone palynolo- tirolicum zone gical flora zone Hettangian (Lias) Hettangian (Lias) Hettangian (Lias)

pre- pre- pre- planorbis planorbis/ planorbis Schattwald beds Schattwald beds beds beds transition zone Uppermost Rhaetian Uppermost Rhaetian Hettangian (Lias) Uppermost Rhaetian

Triletes- Triletes- Triletes Triletes-beds/ Lilstock Triletes- beds beds beds Oberer Sandst. Fm beds Contorta- Contorta- Contorta- ultima

beds Contorta- beds/ Misikella Westbury beds/

Postera- beds beds Haupt- Fm Haupt-

beds Contorta - ton ton C. marshii zone C. marshii zone Unter Postera- Exter Fm Haupt Mb

Rhaet beds Haupt Choristoceras zone Sandstein/ Williton Postera Schieffer Postera- Choristoceras marshii Sandstein/ Sandstone beds Postera-

Upper Rhaetian beds Rhaetian Rhaetian

Middle & Rhaetian Rhaetian

lower Blue Anchor Fm Eiberg Member (Kössen Formation) (option 1) (option 2) Postera- (option 3) beds/ Rydon Mb Arnstadt

Fm Ch. haueri Misikella posthernsteini suessi Lower Rhaetian Sevatian 2 R. suessi zone Sevatian 2 Cochloceras M. posthernsteini Misikella hernsteini Vandaites stuerzenbaumi Vandaites Sevatian 2 Norian Norian Norian Norian Sevatian 1 Sev 1 Sevatian 2 Twyning Mudstone Twyning Sevatian 1

Supplementary Information Figure 1 Overview of Rhaetian subdivision in the Tethys realm, Germanic Basin and NW Europe (Epicontinental Triassic International Symposium Guide, 1998; Channell et al., 2003; Kozur, 2003; Lund, 2003; Bachmann and Kozur, 2004; Nitsch, 2005; Hillebrandt et al., 2007; Krystyn et al., 2007; Warrington et al., 2008). Grey band shows suggested correlation of the Rheatian (sub-)stage based on carbon isotope stratigraphy.

Supplementary Informa-tion Figure 2 Three Lepi-dopteris ottonis leaves from the Wüstenwelsberg section (Germany). Scale-bar is in mm. The two smaller leaf-parts on the right likely represent the tip of L. ottonis branches. See Appendix 16

105 106 References

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119 120 Algemene introductie

Het totaal antropogene vrijkomen van 5000 Gigaton (5000 miljard ton) koolstof in de atmosfeer en oceanen in de komende eeuwen, heeft waarschijnlijk een grote invloed op het aardse klimaat en de biosfeer (Caldeira en Wickett, 2003; Allen et al., 2009). De mate van verwachte toekomstige klimaatveranderingen zijn afhankelijk van vaak niet goed begrepen terugkoppelingsmechanismen tussen het vrijkomen van koolstof en het klimaat. Begrip van grenscondities voor antropogene broeikasgas-emissies in relatie tot klimaatverandering, is nodig om een relatief stabiele staat van het systeem aarde te verzekeren (Rockström et al., 2009). De aardse geologische geschiedenis wordt gekenmerkt door perioden van (grote) veranderingen in de koolstofkringloop, die vaak samenvallen met verandering in het klimaat en verlies aan biodiversiteit. In de laatste duizenden jaren heeft de mensheid enkel relatief kleine klimaat- en milieuveranderingen ervaren. Grote veranderingen in het klimaat voltrokken zich wel gedurende de evolutie van de mens in het Pleistoceen (Hays et al., 1976). Tijdsintervallen waarin gelijke hoeveelheden koolstof vrijkwamen als tegenwoordig, kwamen enkel tientallen tot honderden miljoenen jaren geleden voor. Het begrijpen van potentiële causale verbanden tussen het massaal vrijkomen van koolstof en klimaatveranderingen in deze tijdsintervallen, maakt betere voorspelling voor toekomstige milieu- en klimaatveranderingen mogelijk. Het bestuderen van deze tijdsintervallen vergroot ook het begrip van causale verbanden tussen koolstofkringloop en klimaatveranderingen en veranderingen in de ontwikkeling van ecosystemen, soorten samenstelling en de snelheid van evolutie. De oorzaak van deze wereldwijde extincties in deze tijdsintervallen varieerde waarschijnlijk, maar begrip van onderliggende mechanismen zal bijdragen aan essentiële inzichten in oorzaken en gevolgen van huidige (door de mens geïnitieerde) veranderingen in klimaat, milieu, ecosystemen en verlies aan biodiversiteit (Sala et al., 2000).

Het onderzoek dat in dit proefschrift wordt gepresenteerd is onderdeel van een multi-disciplinair onderzoeksproject “Earth’s and Life’s History: From Core to Biosphere (CoBi)”, gericht op het beter begrijpen van oorzaak, gevolg en timing van veranderingen in terrestrische en mariene ecosystemen en de wereldwijde koolstofkringloop, gedurende de Trias-Jura overgang en vooral gedurende de massa extinctie in het eind-Trias (~201.5 miljoen jaar geleden; Schaltegger et al., 2008).

Het eind-Trias wordt vaak beschouwd als een van de vijf grote massa-extincties van het Phanerozoic (de laatste ~542 miljoen jaar van de aardse geschiedenis) (Raup en Sepkoski, 1982; Benton, 1995). In tegenstelling tot de plotselinge en catastrofale massa-extinctie op de Krijt-Paleogeen grens die wordt toegeschreven aan de inslag van een meteoriet (Smit en Hertogen, 1980; Smit en ten Kate, 1982), is de eind-Trias massa- extinctie uitgestrekt over meerdere miljoenen jaren (Tanner et al., 2004; Kiessling et al., 2007; Kürschner en Herngreen, in press). Het verlies aan wereldwijde biodiversiteit

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culmineerden aan het einde van het Trias, met extincties in de oceanen en op de continenten (bijvoorbeeld: ammonieten (Geux et al., 2004), bivalven (McRoberts and Newton, 1995), radiolarian (Ward et al., 2001) en Theropoden (Olsen et al., 2002) en sterk veranderende assemblages van marine micro-organismen (bijvoorbeeld: dinoflagellaten en foriminiferen (Hesselbo et al., 2002)) en veranderende samenstelling van vegetatie op het land (Kürschner et al., 2007; Bonis et al., 2009; McElwain et al., 2009). Het massa-extinctie interval in het eind-Trias geeft een duidelijk voorbeeld van wereldwijde veranderingen in de biosfeer, maar mogelijke oorzaken van deze gebeurtenissen worden hevig bediscussieerd en varieren in concept van buitenaardse tot interne oorzaken. De ontdekking van een iridium anomalie samen met het massaal voorkomen van sporen (een sporen-piek), suggereerde de inslag van een metoriet (Olsen et al., 2002). Ondersteunend bewijs zoals gebroken kwarts kristallen en een inslagkrater ontbreken echter (Tanner et al., 2004). Massa-extinctie intervallen worden ook vaak gerelateerd aan grootschalige vulkanische activiteit en massale verspreiding van uitvloeiingsgesteenten (Wignall, 2001; Courtillot en Renne, 2003). Het ontstaan van grootschalige vulkanische afzettingen (Large Igneous Provinces: LIPs) in de Centraal Atlantische Magmatische Provincie (CAMP) in het eind-Trias en begin Jura, wordt toegeschreven aan het opbreken van het supercontinent Pangea. Het resulteerde mogelijk in het massaal vrijkomen van

CO2 en SO2 (Beerling en Berner, 2002; Wignall et al., 2007; van de Schootbrugge et al., 2009), met broeikas-opwarming, het aantasten van ecosystemen en anoxische omstandigheden in de oceanen tot gevolg. Aannames over het begin en de duur van CAMP-gerelateerde vulkanische activiteit zijn nog steeds controversieel (Marzoli et al., 2004; Whiteside et al., 2007; Marzoli et al., 2008; Whiteside et al., 2008). Fundamentele vragen over de oorzaaken en causale verbanden tussen wereldwijde veranderingen in biogeochemische cycli, klimaatveranderingen en grootschalige veranderingen in de biosfeer worden nog steeds hevig bediscussieerd.

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GSSP voor de basis van het Jura

De aandacht voor de massa-extinctie aan het einde van het Trias nam, in tegenstelling tot eerdere en latere massa-extincties, pas vrij recentelijk toe, toen meer en meer Trias-Jura grenssecties ontdekt werden en bestudeerd konden worden. De Trias-Jura grens is daarom pas een van de laatste die door de Internationale Commissie voor Stratigrafie aan een bepaalde sectie en punt (Global boundary Stratotype Section and Point: GSSP) voor de basis van het Jura wordt toegekend. In de afgelopen jaren en gedurende het verloop van dit onderzoek is er voortdurend gediscussieerd over welk kenmerk het begin van het Jura het best typeert. Een duidelijk herkenbare negatieve koolstofisotopen-excursie (Carbon Isotope Excursion: CIE) is nu duidelijk gedocumenteerd, in en buiten het eind-Trias Eiberg bekken (Hoofdstuk 1) en deze kan nu beschouwd worden als een wereldwijd fenomeen (Hoofdstuk 4). Het valt samen met het massa-extinctie interval en het was een van de voorgestelde kenmerken voor de basis van het Jura. Het eerste voorkomen van Psiloceras spelae ammonieten werd ook voorgesteld en uiteindelijk gekozen als kenmerk voor de basis van het Jura (Hillebrandt et al., 2007). Twee ondersoorten van deze ammonieten soort, Psiloceras spelae spelae en Psiloceras spelae tirolicum (Hillebrandt en Krystyn, 2009), komen ongeveer tegelijkertijd voor het eerst voor in de New York Canyon (Panthalassa oceaan) en Eiberg secties (westelijk Tethys oceaan). De Kuhjoch sectie in het Eiberg bekken werd voorgesteld (Hillebrandt et al., 2007) en uiteindelijk gekozen als GSSP voor de basis van het Jura. De sedimentaire opeenvolging in deze sectie is uitgebreid bestudeerd tijdens dit onderzoeksproject (Bonis et al., 2009; Ruhl et al., 2009) en een deel van de data wordt weergegeven en besproken in de hoofdstukken 1, 2, 3 en 4 van dit proefschrift.

Synopsis

Het massa-extinctie interval aan het einde van het Trias geeft een goede mogelijkheid voor het bestuderen en analyseren van mogelijke causale verbanden tussen het vrijkomen van koolstof, klimaatverandering en het dalen van wereldwijde biodiversiteit en veranderen van ecosystemen. De studie die in dit proefschrift gepresenteerd wordt, richt zich voornamelijk op mogelijke veranderingen in de wereldwijde koolstofkringloop in het eind-Trias. Het onderzoekt veranderingen in de grote van stromen tussen de exogene uitwisselende koolstofreservoirs (bijvoorbeeld de atmosfeer, oceanen en vegetatie op het land). Het exogene koolstofreservoir is, onder onveranderde omstandigheden, gekenmerkt door constante stromen en constante reservoir groottes en een constante verblijfsduur van koolstof in elk reservoir. Veranderingen in deze factoren kunnen het relatieve voorkomen van 13C en 12C isotopen in deze reservoirs beïnvloeden. Dit kan worden weergegeven door veranderingen in de δ13C waarden van deze reservoirs.

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Koolstof kan ook aan de exogene koolstofreservoirs worden toegevoegd vanuit externe bronnen met een afwijkende koolstofisotopen signatuur (bijvoorbeeld de aardkorst of -mantel). Beide processen kunnen gedurende de Trias-Jura overgang mogelijk wereldwijde veranderingen in de koolstofkringloop tot gevolg hebben gehad. De studie, gepresenteerd in dit proefschrift, heeft onder andere tot doel het karakter, de grootte, oorzaken en gevolgen van mogelijke wereldwijde veranderingen in de koolstofkringloop gedurende de Trias-Jura overgang te reconstrueren. Het combineert chemo- en biostratigrafisch onderzoek om het potentieel van hoge resolutie koolstofisotopen datasets voor stratigrafische correlatie in het eind-Trias te onderzoeken. Ook worden causale verbanden tussen koolstofkringloop veranderingen en veranderingen in het klimaat, onderzocht.

Hoofdstuk 1 van dit proefschrift, “Triassic-Jurassic organic carbon isotope stratigraphy of key sections in the western Tethys realm (Austria)”, onderzoekt het gebruik van hoge resolutie koolstofisotopen datasets als stratigrafisch hulpmiddel voor het correleren van verschillende Trias-Jura grens secties. Sedimentaire opeenvolgingen van het Trias-Jura grensinterval zijn in verschillende mariene bekkens in de wereld gekenmerkt door een duidelijk negatieve koolstofisotopen-excursie ten tijde van de massa-extinctie in het eind-Trias (Palfy et al., 2001; Hesselbo et al., 2002; Guex et al., 2004; Ward et al., 2004; Galli et al., 2005; Galli et al., 2007; Ward et al., 2007; Wignall et al., 2007; Williford et al., 2009). De grootte van de gemeten excursies en hun positie ten opzichte van biostratigrafische voorkomens van (fossiele) overblijfselen van (micro-)organismen, varieert. In dit hoofdstuk presenteren we hoge resolutie koolstofisotopen-data van acht secties in het Eiberg bekken (Noordelijke Kalk Alpen, Oostenrijk), waaronder ook de GSSP voor de basis van het Jura. We tonen aan dat deze secties worden gekenmerkt door een eerste negatieve koolstofisotopen-excursie, tegelijkertijd met het extinctie-interval in het eind-Trias en een tweede verschuiving naar negatievere δ13C waarden aan de basis van het Jura. De data die in dit hoofdstuk wordt gepresenteerd, suggereert dat hoge resolutie koolstofisotopen-data een goede stratigrafische correlatie mogelijk maakt van verschillende secties in het Eiberg bekken, in het eind-Trias.

In hoofdstuk 2 van dit proefschrift, “Climate change driven black shale deposition during the end-Triassic in the western Tethys”, worden hoge resolutie geochemische en biologische datasets van verschillende secties in het Eiberg bekken, waaronder de GSSP voor de basis van het Jura, geïntegreerd. Het onderzoek is voornamelijk gericht op het massa-extinctie interval in het eind-Trias dat gekenmerkt wordt door de negatieve koolstofisotopen-excursie. We presenteren een model waarin een verhoogde toevoer van organisch materiaal van het land naar de zee is gerelateerd aan een versterkte hydrologische kringloop en toegenomen erosie van het achterland. Een verlaagd zoutgehalte van het oppervlaktewater van de oceaan is mogelijk mede oorzaak van het massaal voorkomen van groen-algen. Stratificatie van de waterkolom in het Eiberg bekken leidde mogelijk tot zuurstofloze condities op de zeebodem en het afzetten van organisch rijke sedimentaire lagen ten tijde van de negatieve koolstofisotopen- excursie en de massa-extinctie in het eind-Trias.

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Hoofdstuk 3 van dit proefschrift, “Sedimentary organic matter characterization of the Triassic-Jurassic boundary GSSP at Kuhjoch (Austria)”, onderzoekt de mechanismen achter organisch rijke afzetting in het eind-Trias Eiberg bekken. In dit hoofdstuk presenteren we geïntegreerde geochemische, palynologische en koolstofisotopen-data. We laten zien dat het sedimentaire interval, gekenmerkt door de negatieve koolstofisotopen-excursie in het eind-Trias, ook wordt gekenmerkt door enkel kleine veranderingen in het type kerogeen in het sediment. Deze is voornamelijk afkomstig van het land en dit suggereert dat veranderingen in δ13C waarden door de tijd echt zijn en dat deze ware veranderingen in de wereldwijde koolstofkringloop weergeven. In dit hoofdstuk bespreken we ook de milieuveranderingen die leiden tot het afzetten van deze organisch rijke lagen in het Eiberg bekken in het eind-Trias.

De oorzaak van de wereldwijde massa-extinctie in het eind-Trias, is een van de belangrijkste openstaande vragen. In hoofdstuk 4 van dit proefschrift, “Atmospheric methane injection caused end-Triassic mass extinction”, bespreken we de mogelijke oorzaak van een wereldwijde verandering in de koolstofkringloop en de gevolgen daarvan voor massa-extinctie en veranderingen in klimaat en ecosystemen. De grootte van de koolstofkringloop verandering is gebaseerd op koolstofisotopen-metingen van specifieke molecuul fragmenten (lange koolstof ketens: n-alkanen) die afkomstig zijn van de bladwassen van landplanten. De verkregen data suggereert dat eerdere theorieën die wijzen op het toenemend vulkanisme als belangrijkste oorzaak van de wereldwijde koolstofkringloop verandering, onrealistisch zijn. De grootte en snelheid van verandering in δ13C waarden, suggereert dat voornamelijk lichte koolstofisotopen vanuit een methaan reservoir zijn vrijgekomen in de atmosfeer en oceanen. We laten verder zien dat het vrijkomen van koolstof en het veranderen van de wereldwijde koolstofkringloop samenvalt met een sterke opwarming en toegenomen hydrologische kringloop. De data die in dit hoofdstuk gepresenteerd worden suggereren causale verbanden tussen het massaal vrijkomen van koolstof in de atmosfeer, klimaatverandering en de wereldwijde uitstervingen in het eind-Trias.

Een goede controle op het relatieve voorkomen en de duur van gebeurtenissen tijdens de transitie van het Trias naar het Jura is essentieel om de mechanismen, die de massa extincties in het het eind-Trias en het ontstaan van nieuwe soorten in het vroeg- Jura tot gevolg hebben, te kunnen bestuderen. In hoofdstuk 5 van dit proefschrift, “Astronomical constraints on the duration of the early Jurassic Hettangian stage and recovery rates following the end-Triassic mass extinction (St. Audrie’s Bay / East Quantoxhead, UK)”, presenteren we hoge resolutie fysische en geochemische data en veldobservaties, die het tijdsinterval van het eind-Trias en het vroege Jura beslaan. Cyclische veranderingen in de hoeveelheid energie die de aarde ontvangt van de zon, bepaald door de afstand van de aarde tot de zon, worden via cyclische veranderingen in het klimaat in het sediment vastgelegd. We kennen de duur van deze cycli en we kunnen het voorkomen van deze cycli in het geologisch archief “aflezen”. Dit maakt het mogelijk om snelheden van processen in het geologisch verleden te achterhalen. We construeren een zwevende astronomische tijdschaal van ongeveer 2,5 miljoen jaar die gebaseerd is op het herkennen van ~100.000 jaar excentriciteit cycli in het voorkomen van kalkrijke

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versus organisch rijke afzettingen, als ook in chemische datasets. Individuele organisch rijke lagen geven mogelijk precessie-gestuurde veranderingen in moesson-intensiteit weer. Op basis van deze bevindingen kunnen we de duur van het Hettangian (de eerste stage van het Jura), de duur van ammonietenzones in het Hettangian, de duur van het extinctie-interval en de daaropvolgende snelheid van herstel bepalen. Cyclostratigrafische correlatie naar de astronomisch bepaalde “Geomagnetic Polarity Time-Scale” van het continentale Newark bekken (in het oosten van de VS), maakt het vaststellen van de Trias-Jura en Hettangian-Sinemurian grenzen in het continentale bereik mogelijk. Verder 13 wordt de betekenis van de continue lage δ CTOC waarden gedurende het Hettangian en de onderste helft van het Sinemurian en volgend op het CAMP vulkanisme bediscussieerd. Deze geven mogelijk lange termijn veranderingen in wereldwijde biogeochemische cycli weer.

Het niveau van uitstervingen was niet alleen hoger in het boven-Rhaetian (eind-Trias). De laatste stages van het Trias (het Carn, Noor en Rhaet) worden ook al gekenmerkt door een sterkere afname van wereldwijde biodiversiteit op het land en in zee. Om mogelijk causale verbanden tussen koolstofkringloop veranderingen en extincties te onderzoeken, hebben we een deel van het boven-Rhaet in verschillende secties in noordwest Europa en de Tethys oceaan onderzocht. In hoofdstuk 6 van dit proefschrift, “Multiple late Triassic carbon cycle perturbations observed in continental and marine C-isotope records from the western Tethys (Austria) and NW European sections (UK and Germany)”, laten we zien dat negatieve koolstofisotopen- excursie in het de eind-Trias voorafgegaan wordt door twee opeenvolgende negatieve 13 koolstofisotopen-excursies in mariene en terrestrische δ CTOC datasets van het boven- Rhaet in Duitsland en Oostenrijk. Een gelijktijdige negatieve excursie in δ13C waarden van bladeren suggereert het vrijkomen van lichte koolstofisotopen in de atmosfeer. Oxidatie van organisch koolstof door het ondergronds verbranden van organisch rijke afzettingen is een van de mogelijke mechanismen om lichte koolstofisotopen aan het exogene koolstofreservoir toe te voegen.

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127 128 Acknowledgements

It’s the end of the world as we know it… It’s the end of the world as we know it… It’s the end of the world as we know it… ...and I feel fine - REM -

For some reason this tune keeps going through my head as I start writing these final pages of my thesis. Coincidentally these lines refer both to the subject of my thesis: a rapidly changing world, as to the end of the world as I know it: me being a PhD student… and I feel fine. The start of my research four years ago felt like the beginning of an adventure (and it truly often was). However, it is also great to complete this booklet and to defend my thesis. The past four years wouldn’t have been this great without the help of many people within and outside academia. Although this is one of the very last pages of my thesis, it probably is one of the very first (and for some of you the only ;-)) pages that you are going to read, so I will try to make sure not to forget any one of you… here we go…

The research that I carried out in the past four years was part of a multi-disciplinary project: Earth’s and life’s history: from core to biosphere (CoBi), initiated by Wolfram Kürschner and Wout Krijgsman. This project enabled three PhD students (Nina, Martijn and myself) to work on one of the most interesting time intervals in earth history, a mass extinction event! Not to much was known about the end-Triassic event and this allowed us to address exciting questions regarding its origin, nature, timing etc. The project allowed us to travel to several warm, cold, windy and wet places for field work and to meet many nice and interesting people at conferences. I would like to thank Wolfram (my co-promotor) for all the opportunities, the nice field trips, the advice, the help and discussions in the past four years. It has been great! I would also like to thank Wout for the pleasant fieldworks and discussions. I want to thank my promotor, Andy Lotter, for welcoming me in his group, the Laboratory of Palaeobotany and Palynology, first as a MSc. student and later as a PhD student. Thanks for all the interest and help! The past four years would not have been the same without my fellow CoBi-team- members Nina Bonis and Martijn Deenen. I am glad that we got along really well, both during our long field days and during our long pub-nights and also during the many hours of travelling together (over 60.000 km together in a car, jeep, plane and train!). We had many (mostly nice) discussions both in the field and in Utrecht and I truly believe that our individual researches and the advancement we made in understanding events at the TJB, greatly benefited from our combined efforts. Thank you for the good scientific cooperation and the great memories and also thank you for your friendship!

129 Acknowledgements

Thanks to all the people at the LPP and the Geoscience department, for their help, interest, discussion and for giving me many good memories of life during and after working-hours. Many of you became good friends during the past four years, thanks: Nina, Judith, Katya (my three room-mates), Adriana, Emmy, Maarten, Frederike, Peter S., Emi, Leonard, Sander, Wade, Diederik, Peter B., Jeroen, Gianluca, Luke, Qing, Rike, Henk B., Oliver, Appy, Francesca, Timme, Marjolein, Boris, Walter, Henk V., Han, Johan, Roel, Zwier en Hans. Jan, Natasja and Arnold, also thanks for all the help in the lab! Tammo, Martin, Maurits and Mischa, it was nice working with you on your BSc. / MSc. theses. Many people greatly contributed to the research presented in this thesis: Gert- Jan Reichart and the whole Utrecht Biogeochemistry-team (including Gijs, Cornelia, Elisabeth, Els and Julia): thank you for allowing me in your labs and assisting me where- ever possible. Hemmo Abels, thanks for training my cyclostrat-eyes and the good times in the field. Leopold Krystyn, Axel von Hillebrandt, Mark Hounslow, Michael Szurlies and Harry Veld, thank you for your guidance in the field and our discussions! Thanks to all the people at the Paleomagnetic Laboratory Fort Hoofddijk for the interest and the nice chats, and especially to Cor Langereis and Silja Hüsing for working together in the field.

A special word of thanks to my two paranymphs, Quintijn and Emi, thank you guys!

Many people made life pleasant by both being interested in my work, but more importantly also by not talking about mass extinctions: …well, many of those are already mentioned above, maar natuurlijk ook Guus, Saskia, Joeri, Steven, Steffi, Ingrid, Sjoerd, Michiel, Marlies, Wilburt, Korien, Peter, Melanie, Osvald, Sacha, Guillaume (merci), Nelly, Hanna, Heidi, Sander, Liesbeth, Wim, Susan, Tjeerd, Rianne, Tjeerd.

Natuurlijk wil ik ook alle familie graag bedanken, de families Ruhl, Lamers, Kwakkel en Knotter, voor de interesse in de afgelopen jaren, en natuurlijk vooral Antal, Sanne en mijn ouders José en Wim, bedankt!

De persoon die misschien wel het meeste heeft bijgedragen aan mijn leven in de afgelopen jaren, is mijn liefje, Limke, dankjewel.

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131 132 Curriculum Vitae

Micha Ruhl werd geboren in Horn, op 16 april 1980. Hij behaalde zijn HAVO diploma in 1997 en vervolgens zijn VWO diploma in 1999, aan de Scholengemeenschap St. Ursula in Horn. Alvorens te beginnen met zijn universitaire studie, werkte en reisde hij een jaar in Australië en Thailand. In 2000 begon hij met de studie Aardwetenschappen aan de Universiteit Utrecht (UU) en in 2001 vervolgde hij zijn studie in de specialisatie richting Biogeologie. Een deel van zijn doctoraal opleiding genoot hij, binnen het kader van het Europees uitwisseling programma ‘Erasmus’, aan de Georg-August-Universität Göttingen in Duitsland. In de laatste twee jaar van zijn opleiding verrichtte hij twee afstudeer onderzoeken. Het eerste onderzoek, onder begeleiding van Dr. Tanja Kouwenhoven (Stratigrafie en Paleontologie, UU) en Dr. Henko de Stigter (Departement voor Mariene Geologie, Nederlands Instituut voor Onderzoek der Zee (Royal NIOZ)), werd zowel aan de UU als aan het Royal NIOZ uitgevoerd en richtte zich op de respons van benthische foraminiferen assemblages op een veranderende aanvoer van terrigeen sediment door een diepzee canyon van het Portugees continentaal plat naar de diepzee. Hij nam vervolgens deel aan een onderzoekscruise onderleiding van Dr. Henk de Haas (Royal NIOZ), naar diepzee koraal afzettingen en methaan vrijkomen voor de kust van Marokko, Portugal en Schotland. Het tweede afstudeer onderzoek vond plaats bij Palaeoecologie (Laboratorium voor Palaeobotanie en Palynologie), onder begeleiding van Dr. Wolfram M. Kürschner. Deze studie richtte zich op het reconstrueren van palynologische, palynofacies en geochemische veranderingen op de Noor-Rhaet grens (laat Trias), in twee gesteente formaties van het ondiepe en diepere deel van het continentaal plat van de noordwestelijke Tethys oceaan. In 2006 behaalde hij het MSc. diploma. In dat jaar trad hij ook in dienst als promovendus bij de leerstoelgroep Palaeoecologie in een multidisciplinair project gericht op de Trias-Jura overgang. Het promotieonderzoek werd begeleid door Prof. Dr. André F. Lotter als promotor en Dr. Wolfram M. Kürschner als co-promotor. Het project werd geïnitieerd door Dr. Wolfram M. Kürschner en Dr. Wout Krijgsman en het werd gefinancierd binnen het High Potential programma van Universiteit Utrecht.

Micha Ruhl was born on the 16th of April 1980 in Horn. He obtained his HAVO diploma in 1997 and his VWO diploma in 1999 from the secondary school St. Ursula. Before starting his university education, he spent one year working and travelling in Australia and Thailand. He started his education in Earth Sciences at Utrecht University (UU) in 2000 and continued within the Biogeology curriculum in 2001. During his studies, he participated in the European exchange program ‘Erasmus’ and visited the Georg-August- Universität Göttingen in Germany. In the last two years of his university education he worked on two MSc.-research theses. The research of the first thesis, supervised by Dr. Tanja Kouwenhoven (Stratigraphy and Paleontology, UU) and Dr. Henko de Stigter (Department of Marine Geology, Royal Netherlands Institute for Sea Research (Royal

133 Curriculum Vitae

NIOZ)), was performed at both Utrecht University and Royal NIOZ. It aimed to reconstruct the response of benthic foraminiferal communities in the lower Nazaré Canyon on a changing supply of terrigenous matter through this canyon in the Portuguese continental margin. Subsequently, he participated in a scientific-cruise supervised by Dr. Henk de Haas (Royal NIOZ), to study deep sea coral communities and methane-seeps of the coast of Morocco, Portugal and Scotland. The second MSc.-research was performed at the Laboratory of Palaeobotany and Palynology (Palaeoecology) and supervised by Dr. Wolfram M. Kürschner. This research aimed to reconstruct palynological, palynofacies and geochemical changes across the Norian-Rhaetian (late Triassic) boundary, in shallow and deeper marginal marine sedimentary formations in the northwestern Tethys Ocean. He obtained his MSc.-degree in 2006. He started his PhD-study at the Laboratory of Palaeobotany and Palynology (Palaeoecology), in the same year. His research was supervised by Prof. Dr. André F. Lotter and Dr. Wolfram M. Kürschner and it was part of a multi-disciplinary project on the Triassic-Jurassic boundary, initiated by Dr. Wolfram M. Kürschner and Dr. Wout Krijgsman. This project was financed within the High Potential program of Utrecht University.

134 Curriculum Vitae

135 136 Publications

Ruhl, M., Kürschner, W.M. and Krystyn, L., 2009. Triassic-Jurassic organic carbon isotope stratigraphy of key sections in the western Tethys realm (Austria). Earth and Planetary Science Letters, 281(3-4): 169-187.

Bonis, N.R., Ruhl, M. and Kürschner, W.M., 2009. Climate change driven black shale deposition during the end-Triassic in the western Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, in press.

Ruhl, M., Veld, H. and Kürschner, W.M., accepted pending revision. Late Triassic back shale formation in the western Tethys Ocean: Sedimentary organic matter characterization of the Triassic-Jurassic boundary GSSP at Kuhjoch (Austria). Earth and Planetary Science Letters.

Bonis, N.R., Ruhl, M. and Kürschner, W.M., accepted pending revision. Milankovitch- scale palynological turnover acroos the Triassic-Jurassic transtion at St. Audrie’s Bay, SW UK. Journal of the Geological Society.

Deenen, M.H.L., Ruhl, M. Bonis, N.R., Krijgsman, W., Kürschner, W.M., Reitsma, M., Van Bergen, M. J., accepted pending revision. A new chronology for the end-Triassic mass extinction. Earth and Planetary Science Letters.

Hillebrandt, A. v., Krystyn, L., Kürschner, W. M., Bonis, N. R., Ruhl, M. & Urlichs, M., with contributions by Bown, P., Kment, K., McRoberts, Ch., Simms, M. & Tomasovych, A., 2009. A candidate GSSP for the base of the Jurassic in the Northern Calcareous Alps (Kuhjoch section; Karwendel Mountains, Tyrol, Austria). International Subcommission on Jurassic Stratigraphy, Triassic/Jurassic Boundary Working Group Ballot 2008, 44 pp.

137 Appendices

Appendix 1 Chapter 1, Figure 3, page 22 of this thesis 6 2 - CIE [‰]

8 2 - org C initial 0 Eiberg 3 13 - δ 2 3 0 - 0 0 5 - 5 8 2 -

[‰] 0 3 - org C 2 13 3 - δ 4 3 0 - 0 0 6 1 Kammerköhralm - 4 5 2 -

7 2 - [‰] 9 org 2 - C 1 13 3 - δ 3 3 - Scheibelberg 0 0 0 0 5 1 5 2 - [‰] 7

2 - org 9 C 2 - 13 1 δ 3 -

0 0 0

0 0 0 0 CIE main 3 3 2 1 Schlossgraben - 2 5 - 2

[‰] 7 - 2 org 9 C - 2 13 1 δ - 3 3 - 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 1 2 3 4 5 6 7 8 9 0 1

9 8 7 6 5 4 3 2 1 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9

1 1 1 1 1 1 1 1 1 1 2 2 - 1

depth in cm in depth

Eiberg Mb Eiberg Schattwald beds Schattwald grey Tiefengraben Mb Tiefengraben grey

gr Tg Mb

Rhaetian Restentalgraben Hettangian

CIE main 5 - 2 7 [‰]

- 2 9 org - 2 C 1 13 - 3 δ CIE 3 - 3 initial 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

8 7 6 5 4 3 2 1 depth in cm in depth - 1 - 2 - 3

Eiberg Mb Eiberg Tiefengraben Mb Tiefengraben

Hettangian Rhaetian

Kendlbachgraben CIE main 4 - 2

6 [‰] - 2 8 org - 2 C 0 13 - 3 δ 2 - 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 5 6 7 8 9 0 1

1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 depth in cm in depth

Eiberg Mb Eiberg Schattwald beds Schattwald grey Tiefengraben Mb Tiefengraben grey

gr Tg Mb Hettangian Hochalplgraben Rhaetian

CIE main 3 - 2 5

- 2 [‰] 7 - 2 org 9 C - 2 13 Small shear zone Grey marly to silty sediments Red marly to silty sediments from the Schatwald beds Limestones 1 δ - 3 3 - 3 0 0

0 0

0 0 0 0 0 0 0 0 0 0 0 0 0

0 0

0 0 0 0 0 0 0 0 0 0 0

1 0

7 8 9 8 7 6 5 4 3 2 1 - 1 - 2 depth in cm in depth 1 1

Schattwald beds Schattwald grey Tiefengraben Mb Tiefengraben grey

Tiefengraben Mb Tiefengraben Mb Eiberg

grey Tg Mb

Kendlbach Fm Kendlbach Fm Kössen

Hettangian Rhaetian

Triassic Kuhjoch/ Ochsentaljoch Jurassic

138 Appendices

Appendix 2 Chapter 2, Figure 3, page 38 of this thesis drier s e 0 0 0 wetter 0 3 grey ) 0 0 Foraminiferal test linings Acritarchs Botryococcus sp. Prasinophyt Dinoflagellate cysts 0 0

. 0 s

p 0 g

s errestrial (

n 0

s T

& aquatic ( black )

l 1 c

t palynomorphs conc. [ppg]

o l

r 0

t 0 0

f 0

B 1 n 1

e m

y 0

0 0

h 8 o 8

p F

i s

t 0 0 0

a 6 6

6 s y r

h c

a 0 0

i l

l 4 4 r 4 Aquatic

e c

g A

f 0 0 0

o 2 2 2

7 g

2 r - 8

9 o 2 2 - - 9 2 0 1 - 3 3 - - δ 13C 2 3 1 3 3 3 - - - iefengraben T Kuhjoch Hochalplgraben 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 0 4 0 6 2 8 4 0 6 0 9 8 7 6 5 4 3 7 6 5 4 3 2 1 - - 7 7 6 6 5 5 5 4 3 2 2 2 2 2 2 2

(cm)

(cm) 1 1 1 1 1 1 1 1 Depth

(cm)

Depth Depth b M . E b M . E b M n e b a r g n e f e i T b M n e b a r g n e f e i T b M n e b a r g n e f e i T b M g r e b i E

m F h c a b l d n e K m F . K m F h c a b l d n e K m F n e s s ö K m F h c a b l d n e K m F . K

139 Appendices

25 μm a 25 μm b

14mm

25 μm c

Appendix 3 Chapter 2, Figure 4, page 41 of this thesis

Appendix 4 Chapter 2, Figure 5, page 43 of this thesis

140 Appendices

Appendix 5 Chapter 3, Figure 2, page 52 of this thesis 9 0 . 0 0 2 1

[h] 6 tot 0 . 0 N 0 [%] 8

g r

8 o 2 C - 13

0 3 δ [a] - 2

Figure 2 beds Schattwald

Tiefengraben Mb Tiefengraben Eiberg Mb Eiberg

Kössen Fm Kössen Kendlbach Fm Kendlbach

Rhaetian uppermost 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 8 6 4 2 0 2 4 6 8 2 4 6 8

- - - -

1 1 1 1 1 1 tratigraphic position (cm) position tratigraphic s - - - - -

141 Appendices

Appendix 6 Chapter 4, Figure 1, page 64 of this thesis

Kuhjoch, Austria

1200 Organic rich shales Organic poor shales 1100 Limestones LO Triassic organisms FO Jurassic organisms 1000 Assemblage changes

900 UK Bay, St. Audrie’s

800 Newark supergroup basins, USA Queen Charlotte Islands, Canada

700 Ammonites Jurassic Hettangian

600

500 Triassic Rhaetian

400 Pollen/ spores Molluscs Echinoidea Foraminifera Ostracodes

Stratigraphic position (cm) 300

200 CAMP volcanism CAMP 100 Kendlbach Fm Tiefengraben Mb Tiefengraben 0 Methane event Triassic pollen/ spores Triassic -100 Eiberg Mb Kössen Fm Palynology

-200 Foraminifera Dinoflagellates Ammonites -32 -31 -30 -29 -28 -27 -26 -25 -24 Ostracodes LO Conodonts

13 Radiolarian turnover bulk δ CTOC Bivalve extinction Theropod dinosaur turnover

142 Appendices

Appendix 7 Chapter 4, Figure 2, page 66 of this thesis

δ13C n-alkanes -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 40

-10 Extinction interval Stratigraphic position (cm)

-20 Onset of biocalcification crisis Kuhjoch ~ 5‰ -30 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 - Temperature + - Humidity + 13 δ CTOC

δ13C n-alkanes -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 280 ~ 6‰ ~ 5‰ 270

260

250 Onset of biocalcification crisis

240 Extinction interval

230 Stratigraphic position (cm)

220 Hochalplgraben ~ 5‰ 210 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 - Temperature + - Humidity + 13 δ CTOC 13 δ CTOC 13 δ C-[C25-C27-C29-C31-C33-C35] 13 δ C-[C17-C18-C19-C20-C21-C22-C23]

143 Appendices

Appendix 8 Chapter 4, Supplementary Information Figure 2, page 70 of this thesis

240 0

230 -10 Stratigraphic position (cm)

240 0

270 30

260 20

250 10

240 0

230 -10 Stratigraphic position (cm) 220 -20 E F 210 -30 26 27 28 29 30 26 27 28 29

ACLC25-C33 ACLC25-C33

-25 -26 -27 -28 -29 -30 -31 -32

-33 -34

C n -alkanes per sample -36 -35 13 δ -38 -37 G H -40 -39 17 19 21 23 25 27 29 31 33 35 17 19 21 23 25 27 29 31 33 35 n-alkane c-chainlength n-alkane c-chainlength

Supplementary Information Figure 2 144 Appendices

Appendix 9 Chapter 5, Figure 3, page 82 of this thesis S. angulata

~ 1000 kyr

~ 900 kyr

~ 1600 kyr

~ 800 kyr

~ 1500 kyr A. liasicus

~ 700 kyr

~ 1400 kyr ~ 600 kyr

~ 1300 kyr

~ 500 kyr

~ 1200 kyr

~ 400 kyr ~ 1100 kyr

~ 300 kyr P. planorbis P. Hettangian Jurassic Blue Lias Fm Rhaetian Triassic

145 Appendices

Appendix 10

Chapter 5, Figure 4, page 84 of this thesis

~ 100 kyr 100 ~

~ 100 kyr 100 ~ ~100 kyr ~100

St. Audrie’s Bay (UK) St. Audrie’s

Blue Lias Fm Lias Blue Westbury Fm Westbury

Lilstock Fm Blue Anchor Fm Bucklandi angulata Schlotheimia liasicus Alsatites P. planorbis P.

Rhaetian Sinemurian Hettangian

Jurassic Triassic 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 8 2 6 0 6 2 8 4 0 6 2 8 4 0 6 2 8 4 0 6 2 8 4 0 6 2 8 4 0 0 0 1 1 2 9 9 8 8 8 7 7 6 6 6 5 5 4 4 4 3 3 2 2 2 1 1 1 1 1 1 1 1

146 Appendices

Appendix 11 Chapter 5, Figure 5, page 86 of this thesis 2200 kyr 2100 kyr 2000 kyr 1800 kyr 1700 kyr 1600 kyr 1500 kyr 1400 kyr 1300 kyr 1200 kyr kyr 1100 1000 kyr 900 kyr 800 kyr 700 kyr 600 kyr 300 kyr 200 kyr 100 kyr 2300 kyr 1900 kyr 500 kyr 400 kyr 0 kyr 2400 kyr 0 1 9 8 7 6 5 4 Magn. Susc. 3 2 1 0 7 [%] 0 3 5 CaCO 0 3 0 1 0 1 9 8 7 6 5 4 TOC [%] TOC 3 2 1 0 4 2 - 5 2 - 6 2 - 7 2 - [‰] org 8 C 2 - 13 δ 9 2 - 0 3 - 1 3 -

[9] [8] [7] [6] [5] [4] [3] [2] [1] [0] [24] [23] [22] [21] [20] [19] [18] [17] [16] [15] [14] [13] [12] [11] [10]

Blue Lias Fm Lias Blue Fm Westbury

Lilstock Fm

Blue Anchor Fm P. planorbis P. Bucklandi angulata Schlotheimia Alsatites liasicus Alsatites

Rhaetian Hettangian Sinemurian

147 Appendices

Appendix 12 Chapter 5, Figure 7, page 90 of this thesis

interval

Recovery (~120 kyr)

Bivalve extinction Bivalve

LO Conodonts LO

Palynological assemblage changes assemblage Palynological Jurassic pollen Jurassic

Foraminiferal assemblage changes assemblage Foraminiferal

Dinoflagellate assemblage changes assemblage Dinoflagellate

[7] [6] [5] [4] [3] [2] [1] [0]

Anchor Fm Anchor Blue Lias Fm Lias Blue Fm Westbury

Blue

Fm P. planorbis P. Alsatites liasicus Alsatites

Lilstock Rhaetian Hettangian

Jurassic Triassic 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5

148 Appendices

Appendix 13 Chapter 5, Figure 8, page 92 of this thesis H26r H25r H24r E23r 4 4 3 2 1 3 2 1 4 4 5 4 3 2 1 3 2 1 3 2 1 4 4 3 2 1 3 2 1 [C] [B] [D] Hartford Basin (Eastern US) [0 kyr] [900 kyr] [800 kyr] [700 kyr] [600 kyr] [500 kyr] [400 kyr] [300 kyr] [200 kyr] [100 kyr] [-140 kyr] [2300 kyr] [2200 kyr] [2100 kyr] [2000 kyr] [1900 kyr] [1800 kyr] [1700 kyr] [1600 kyr] [1500 kyr] [1400 kyr] [1300 kyr] [1200 kyr] kyr] [1100 [1000 kyr] [2400 kyr] 0 1 9 8 7 6 5 4 TOC [%] TOC 3 2 4 1 2 - 0 5 2 - 6 2 - 7 2 - [‰] org 8 2 C - 13 δ 9 2 - 0 3 - 1 3 -

[9] [8] [7] [6] [5] [4] [3] [2] [1] [0] [23] [22] [21] [20] [19] [18] [17] [16] [15] [14] [13] [12] [11] [10] [24]

Blue Lias Fm Lias Blue Anchor Fm Anchor Westbury Fm Westbury

Blue

Lilstock Fm Schlotheimia angulata Schlotheimia Alsatites liasicus Alsatites bucklandi P. planorbis P.

Rhaetian Sinemurian Hettangian

Jurassic Triassic St Audries Bay & East Quantoxhead (UK) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 8 2 6 0 2 6 0 4 8 2 6 0 4 8 2 6 0 4 8 2 6 0 4 8 2 6 4 8 0 0 0 1 1 2 1 1 2 2 2 3 3 4 4 4 5 5 6 6 6 7 7 8 8 8 9 9 1 1 1 1 1 1

149 Appendices

Appendix 14 Chapter 6, Figure 1, page 100 of this thesis

30°N B A C

0°

Cratonic landmasses Marginal marine Marginal marine Deep ocean Extend of CAMP flood basalts 1000 km Basalt outcrops, sills and dikes

Appendix 16 Chapter 6, Supplementary Information Figure 2, page 105 of this thesis

150 Appendices

Appendix 15 Chapter 6, Figure 2, page 102 of this thesis

Tethys realm NW European basins (Eiberg basin, Austria) UK Germany 15 14

Limestone Organic rich sand 13 A C D 127 Grey shale Sandstone 22 11 Dark grey shale 10 21 Sand Psiloceras planorbis

9 Hettangian-Jurassic Hettangian-Jurassic 20 8

7 19 21 6 18 Hettangian -Jurassic 20 5 17 4 19

3 16

Blue Lias Fm 18 No ammonites CAMP volcanism CAMP volcanism CAMP

2 Rhaetian-Triassic 15 17 1 no fossils transition zone

7 2 * * 8 6 7 * Fm Westbury * 1 5 6

Rhaetian-Triassic 5 0 4 Haupt-ton/ Contorta-beds 4 3 -1 3 2 2 -2 1 1 0 -3 E 0

Blue Anchor Fm 2 ?

-4 1 ~3‰ ~2‰? Postera-beds? 0

-27 -26 -25 -24 -29 -28 -27 -26 -25 Haupt Sandstein/

-33 -31 -29 -27 -25 -31 -29 -27 -25 -29 -27 -25 -23 -29 -27 -25 13 13 13 13 δ Corg [‰] δ Corg [‰] δ Corg [‰] δ Cleaves [‰]

151