Die Klimaentwicklung Gondwanas zur Zeit des Jura
Zusammenfassung der Projektergebnisse
The aim of the project was to reconstruct the Jurassic temperature development of Gondwana based on stable isotope (δ18O, δ13C) , trace element (Mg/Ca, Sr/Ca) , and clumped isotope analyses of fossil shells. The temperature data produced for the different localities were used to reconstruct latitudinal temperature gradients. Finally, a comparison with literature data for Laurasia was carried out to show if European high-resolution temperature curves showing strongly fluctuating temperatures during the Jurassic are representative of global trends. The major results of the project were: Jurassic temperature data were reconstructed based on stable oxygen isotopes of belemnites, bivalves, and/or rhynchonellid brachiopods for Gondwanan study areas in Argentina, Chile, Madagascar, India (Kachchh, Jaisalmer, Indian Himalayas), Morocco, Algeria, Tunisia, Egypt, Israel, and Jordan. Eastern Gondwana (India, Madagascar) showed a steady, gradual temperature decrease from the Middle to Late Jurassic, which can be connected to the rifting of Gondwana. During this rift, the eastern part of the supercontinent drifted into higher palaeolatitudes leading to colder water temperatures. North-western Gondwana (Morocco, Algeria, Tunisia, Egypt, Israel, and Jordan) showed comparatively stable temperatures from the Middle to Late Jurassic. The absence of major temperature fluctuations is striking, but in contrast to Eastern Gondwana, palaeolatitudes (and palaeoenvironments) changed comparatively little through time. South-western Gondwana (Argentina, Chile) also showed comparatively stable temperature conditions over most of the Jurassic, but absolute temperature reconstructions are less reliable because of freshwater influence in some of the studied localities. In these areas, trace element analyses help to reconstruct water temperatures, because Mg/Ca-ratios in fossil oyster shells seem to be less influenced by salinity fluctuations. A comparison with data from Laurasia raises doubts whether temperature curves of Europe are representative of global conditions or instead were influenced by the regional complex palaeogeography of Europe with restricted basins and influx of water masses from the Boreal Sea in the north and the Tethys Ocean in the south changing the δ18O values of sea water. Reconstructed latitudinal temperature gradients in the Middle and Late Jurassic are mostly steeper than previously suggested and almost parallel to today. Only during the Kimmeridgian and Tithonian, warmer temperatures in Europe lead to the reconstruction of comparatively weak gradients. Considering a likely latitudinal gradient in the δ18O values of sea water for the Middle and Late Jurassic, reconstructed equatorial water temperatures were several degrees warmer than today (partly up to 34-35 °C). These warm temperatures might have constituted a stress environment for marine faunas and possibly explain the recorded low diversities of some equatorial ecosystems (e.g., coral reefs). In a methodological study, trace element analyses of modern bivalve shells from Panama showed that Li/Ca-ratios are strongly enhanced during phases of upwelling. In contrast, geochemical, sedimentological, and palaeoecological analyses in the Gondwanan study areas did not show evidence of upwelling during the Jurassic. High-resolution stable isotope (δ18O, δ13C) analyses of Jurassic oyster shells and belemnite rostra indicate seasonal temperature fluctuations at different palaeolatitudes comparable to today, for example: Egypt (palaeolatitude: ~ 3° N): seasonality of 2-3 °C, India (Kachchh; palaeolatitude: 30° S): seasonality of 4-5 °C, Madagascar (palaeolatitude: ~ 35° S): seasonality of 5-6 °C, and Argentina (palaeolatitude: ~ 40° S): seasonality of 11 °C. - In addition to the new temperature data, the field work conducted during the collection of samples led to improvements in our knowledge of the sedimentology, ammonite taxonomy, biostratigraphy, and palaeoecology for some of the study areas (e.g., Argentina, India).
Projektbezogene Publikationen (Auswahl)
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2017. Middle to Late Jurassic equatorial seawater temperatures and latitudinal temperature gradients based on stable isotopes of brachiopods and oysters from Gebel Maghara, Egypt. - Palaeogeography, Palaeoclimatology, Palaeoecology 468: 301-313.
Alberti, M., Fürsich, F.T., Abdelhady, A.A., Andersen, N.
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2019. First steps in reconstructing Early Jurassic sea water temperatures in the Andean Basin of northern Chile based on stable isotope analyses of oyster and brachiopod shells. - Journal of Palaeogeography 8: 33
Alberti, M., Fürsich, F.T., Andersen, N.
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2019. Paired Li/Ca and δ18O peaks in bivalve shells from the Gulf of Panama mark seasonal coastal upwelling. - Chemical Geology 529: 119295
Sadatzki, H., Alberti, M., Garbe-Schönberg, D., Andersen, N., Strey, P., Fortunato, H., Andersson, C., Schäfer, P.
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2019. Sedimentology of a prograding delta complex: The Jurassic succession of the Wagad Uplift in the Kachchh Basin, western India. - Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 292: 1-24
Alberti, M., Fürsich, F.T., Pandey, D.K.
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2019. The Middle to Upper Jurassic stable isotope record of Madagascar: Linking temperature changes with plate tectonics during the break-up of Gondwana. - Gondwana Research 73: 1-15
Alberti, M., Arabas, A., Fürsich, F.T., Andersen, N., Ziółkowski, P.
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2020. Isotopic evidence for partial geochemical decoupling between a Jurassic epicontinental sea and the open ocean. - Gondwana Research 82: 97-107
Danise, S., Price, G.D., Alberti, M., Holland, S.M.
