Palaeoenvironmental changes and vegetation history during the Triassic-Jurassic transition Nina R. Bonis Palaeoecology Institute of Environmental Biology Department of Biology Faculty of Science Utrecht University Laboratory of Palaeobotany and Palynology Budapestlaan 4 3584 CD Utrecht The Netherlands [email protected] [email protected] ISBN 978-90-393-5269-4 NSG publication No. 20100129 LPP Contribution Series No. 29 Graphic design by Nick Liefhebber www.liefhebber.biz [email protected] Printed by GVO drukkers & vormgevers B.V. | Ponsen & Looijen, Ede Palaeoenvironmental changes and vegetation history during the Triassic-Jurassic transition Palaeomilieu veranderingen en vegetatiegeschiedenis 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 vrijdag 29 januari 2010 des ochtends te 10.30 uur door Nina Rosa Bonis geboren op 13 februari 1983 te Oosterhout Promotor: Prof. dr. A.F. Lotter Co-promotor: Dr. W.M. Kürschner The research reported in this thesis was funded by the ‘High Potential’ stimulation program of Utrecht University and financially supported by the LPP foundation. voor Joeri Contents General introduction and synopsis 10 Chapter 1 A detailed palynological study of the Triassic 16 - Jurassic transition in key sections of the Eiberg Basin (Northern Calcareous Alps, Austria) with W. M. Kürschner and L. Krystyn Published in Review of Palaeobotany and Palynology 156, 376-400 (2009) Chapter 2 Climate change driven black shale deposition 48 during the end-Triassic in the western Tethys with M. Ruhl and W. M. Kürschner Published in Palaeogeography, Palaeoclimatology, Palaeoecology. Special Issue: Triassic climate (in press) Chapter 3 Abrupt climate change during the 64 end-Triassic mass-extinction with W. M. Kürschner To be submitted Chapter 4 Atmospheric methane injection caused 78 end-Triassic mass extinction with M. Ruhl, G.J. Reichart, J.S. Sinninghe Damsté and W. M. Kürschner To be submitted Chapter 5 Milankovitch-scale palynological turnover 90 across the Triassic - Jurassic transition at St. Audrie’s Bay, SW UK with M. Ruhl and W. M. Kürschner Submitted to Journal of the Geological Society Chapter 6 Changing CO2 conditions during the end-Triassic 116 inferred from stomatal frequency analysis on Lepidopteris ottonis (Goeppert) Schimper and Ginkgoites taeniatus (Braun) Harris with W. M. Kürschner and J. H. A. Van Konijnenburg-Van Cittert Submitted to Palaeogeography, Palaeoclimatology, Palaeoecology Chapter 7 Vegetation history, diversity patterns, and climate 140 change across the Triassic-Jurassic boundary with W. M. Kürschner Submitted to Paleobiology References 166 Algemene inleiding en samenvatting 188 Dankwoord/Acknowledgements 194 Curriculum Vitae 196 Publications 197 Color Figures 199 SYNOPSIS General introduction and synopsis The Triassic-Jurassic (T-J) boundary, ~201.58 Ma (Schaltegger et al., 2008), is generally known as one of the ‘big five’ mass extinction events in Earth’s history (e.g., Newell, 1963; Raup and Sepkoski, 1982; Benton, 1995; Taylor, 2004). It is one of the least studied because complete and well-dated sections are scarce. To study this end-Triassic mass extinction event, a multidisciplinary project was initiated: ‘Earth’s and life’s history: from core to biosphere (CoBi)’. With a combined use of palaeomagnetism, cyclostratigraphy, geochemistry, and biogeology, questions about the timing, cause and patterns of the extinction were addressed. This thesis will focus on the biogeological aspect by using two techniques: palynology, and stomatal frequency analysis on fossil leaves. Explanations for the biotic turnover during the late Triassic have included both gradualistic and catastrophic mechanisms (e.g., Hallam and Wignall, 1997; Tanner et al., 2004; Hesselbo et al., 2007). Marine extinction could be related to shelf habitat loss during severe regression in the end Triassic (Hallam and Wignall, 1999), but this does not account for the extinctions in the terrestrial realm (e.g., tetrapods). A frequently proposed mechanism is massive volca- nism of the Central Atlantic Magmatic Province (CAMP), one of the largest known Phanero- zoic flood basalt provinces, related to the breakup of Pangaea (Wignall, 2001; Hesselbo et al., 2002; Knight et al., 2004; Marzoli et al., 1999, 2004; Schaltegger et al., 2008). This CAMP basalt volcanism can be associated with the following effects: rapid global warming, ocean anoxia or increased oceanic fertilization (or both), calcification crises, and a sharp decrease in carbon isotope values (Wignall, 2005). The T-J transition interval is characterized by two major perturbations in carbon isotope records described from many sections within and outside the Tethys realm. An end-Triassic relatively short lived ‘initial’ negative carbon isotope excursion (CIE) precedes a more gradual excursion (‘main’ CIE) at the base of the Jurassic (e.g., Pálfy et al., 2001; Hesselbo et al., 2002; Guex et al., 2004; Kürschner et al., 2007; Ward et al., 2007; Ruhl et al., 2009). The release of large amounts of carbon dioxide (CO2) in the atmosphere by CAMP volcanism induced climate change and could have caused biotic disturbance (McElwain et al., 1999; Hesselbo et al., 2002; Tanner et al., 2004). Methane release from gas hydrates represents another important event that has been suggested to be associated with the end-Triassic volcanism (e.g., Pálfy et al., 2001; Beerling and Berner, 2002; Wignall, 2005). An alternative catastrophic mechanism causing the extinction is an extra- terrestrial impact (Olsen et al., 2002a, b) but to date, no convincing evidence has been found for an impact-caused mass extinction. Examples of end-Triassic biotic disturbances are: an extinction among tetrapods (e.g., Olsen et al., 2002b; Lucas and Tanner, 2007a), abrupt and substantial changes in the composition of brachiopod and bivalve communities (Hallam, 1981; Kiessling et al., 2007; Tomašových and 10 SYNOPSIS Siblík, 2007; Mander et al., 2008), the final extinction of conodonts with sporadic survivors persisting into the Hettangian (Pálfy et al., 2007), a global radiolarian faunal change (Long- ridge et al., 2007; Pálfy et al., 2007), the final disappearance of the already low-diversity ammonite assemblages (Simms and Ruffell, 1990; Hallam, 2002) and a collapse of reef ecosystems (e.g., Kiessling et al., 2007). However, the severity and patterns (i.e., abrupt, stepwise or gradual) of the end-Triassic extinctions are disputed (e.g., Hallam, 2002; Bambach et al., 2004; Tanner et al., 2004; Lucas and Tanner, 2008). Although the T-J transition is characterized by extinctions in the marine realm, evidence for a floral turnover is ambiguous. A recent study from the Germanic Basin showed a severe vegetation shift across the T-J boundary, linked to CAMP volcanism (Van de Schootbrugge et al., 2009). A major extinction of 60% of sporomorph taxa followed by a sharp spore spike at the T-J boundary is claimed in the Newark Basin, USA (Fowell and Olsen, 1993; Fowell et al., 1994; Olsen et al., 2002a, b). This spore spike is followed by a conifer (Cheirolepidiaceae) pollen dominated palynoflora which is used by Cornet (1977) and Fowell et al. (1994) to mark the base of the Jurassic in the Newark Basin. By contrast, most palynological studies from Europe show gradual changes in assemblages at the T-J transition (e.g., Warrington, 1974; Morbey, 1975; Lund, 1977; Schuurman, 1979; Achilles, 1981; Kürschner et al., 2007). Also the T-J plant macrofossil record is equivocal. Quantitative macrobotanical data from East Greenland showed that Triassic forests with high-diversity communities were replaced by lower diversity forests and that there was a gradual extinction prior to the T-J boundary (McElwain and Punyasena, 2007; McElwain et al., 2007). On the contrary, the palynological record from Greenland shows no major diversity or assemblage changes, or conclusive evidence for an extinction event (Raunsgaard Pedersen and Lund, 1980; Koppelhus, 1997). Palynological records across the T-J boundary are controversially discussed because of the paucity of sections with a sufficient time resolution and/or well established stratigraphic framework. Furthermore, many records are qualitative (i.e. absence/presence data). There- fore, it is important to carry out detailed quantitative studies. The presence of both well- preserved ammonites and palynomorphs in key T-J boundary sections from the Northern Calcareous Alps (Austria) and southern UK allow for an integration of terrestrial microfloral events in a marine biostratigraphic framework. The palynological records presented in this thesis are used to 1) obtain a firm palynostratigraphic framework for the T-J boundary interval, 2) make a reconstruction of past changes in vegetation and climate, and 3) understand the magnitude and nature of the floral turnover as evidenced by palynology. The Kuhjoch section in the Karwendel syncline (Northern Calcareous Alps, Austria) has recently been approved as the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic period. The first occurrence (FO) ofPsiloceras spelae tirolicum has been chosen as the primary boundary marker (Von Hillebrandt et al., 2007; Von Hillebrandt and 11 SYNOPSIS Krystyn, 2009). Chapter 1 presents a detailed quantitative palynological and carbon isotope