Most extreme greenhouse climate conditions in the last 200 million years occurred during the Cretaceous time, between 120-80 Million years ago. Greenhouse climate pulses lasting thousands of years left their signature in sedimentary archives of the Cretaceous time. This study investigates impact of rapid climate change on oceanography and marine biota.

Lay summary
Mid-Cretaceous (120-90 million years) marine sediments from the former Tethys Ocean contain some of the best records of major climate perturbations and of response mechanisms of the biosphere to these perturbations. Greenhouse climate pulses, triggered by extreme volcanic activity, resulted in episodic black shale deposits on global scale, known as Oceanic Anoxic Events (OAE's). Several OAE's (OAE1a-1d) are recorded in sedimentary archives of Aptian-Albian age (120-100mio years), indicating that ocean conditions and climate were "unstable" during this time. A shift to more stable oceanic conditions occurred in the Latest Albian. The change in paleoceanography was accompanied by a progressive warming of low latitude climate. This shift from an "unstable ocean mode" to a more "stable ocean mode" seems related to changes in plate tectonics and opening or closing of seaways and it may have been related to a long-term rise in atmospheric carbon dioxide levels. Until today it remains debated why greenhouse pulses in the Aptian-Albian resulted in Oceanic Anoxia and unstable oceanography, while the long-term warming shifted oceanography into a stable mode. The study will improve our understanding of the complex interactions between climate change and perturbations of the global carbon cycle and their link to tectonically induced reorganization of oceanography.In part I of this study, the transition into Cenomanian greenhouse climate and into Cenomanian "chalk Seas" is traced in marine sediments of the alpine Tethys Seaway and the hypothesis that the opening of the equatorial Atlantic Gateway (EAG) triggered these changes is tested. Our new chemostratigraphic data along an East-West and North-South transect through the Alpine Tethys offer detailed information on timing of change to Cenomanian Oceans, while sedimentological investigations tell about changes in oceanography in pelagic and shelf settings.In part two of this study the hypothesis that climate and oceanography triggered a global change in Aptian-Cenomanian oceanography is tested. This project will focus on the eastern equatorial Arabian carbonate platform in Oman. The impact of climate, oceanography and sea level during time of major change will be traced in the Nahr Ur and Natih Formations. The Arabian carbonate system will be calibrated with Tethyan pelagic and neritic records and special focus will be given to black shale episodes.