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Climatic fluctuations and seasonality during the Kimmeridgian (Late Jurassic): Stable isotope and clay mineralogical data from the Lower Saxony Basin, Northern Germany

Zuo, Fanfan, Heimhofer, Ulrich, Huck, Stefan, Adatte, Thierry, Erbacher, Jochen, Bodin, Stéphane
Palaeogeography, palaeoclimatology, palaeoecology 2019 v.517 pp. 1-15
Bivalvia, Kimmeridgian age, basins, calcite, clay, climatic factors, dry environmental conditions, evaporation, hinterland, humid zones, humidity, illite, models, oxygen, oysters, sea level, stable isotopes, surface water temperature, Germany
In previous palaeoclimatic models, the Kimmeridgian stage has been defined as a typical greenhouse-time interval with weak latitudinal gradients. However, palaeoclimatic information based on biogenic low-Mg calcite δ18O for the Kimmeridgian is still limited. Here, shell materials (n = 81) precipitated by brachiopods, oysters and Trichites bivalves from the Lower Saxony Basin, Northern Germany are evaluated for their potential to act as archive for marine sea-surface temperatures. Furthermore, the associated clay mineral assemblages based on bulk materials are used to infer hinterland weathering patterns and overall climatic conditions simultaneously. The established sea-surface temperature curve reveals an overall slightly warming trend through the Kimmeridgian. Weak seasonality (~4 °C) in sea-surface temperatures is documented by oxygen isotope variations measured along the growth lines of a large Trichites shell. Distinctly higher δ18O values observed in the Lower Kimmeridgian (late Baylei Chron) are interpreted to be related to the short-term influx of cooler boreal water masses. Judging from the corresponding smectite-dominated interval, however, the positive oxygen isotope anomaly may also be partly explained by a relatively drier climate causing enhanced δ18Oseawater values due to intensified evaporation. The kaolinite/(illite + chlorite) ratio points to a slightly long-term decrease in humidity through the Kimmeridgian on the landmasses surrounding the LSB. The short-term fluctuations in humid/arid conditions correlate significantly with sea-level changes, with humid climates accompanying high sea-levels and arid climates accompanying low sea-levels. Results from this study provide new insights into Late Jurassic climatic dynamics and help to establish a reliable Subboreal Late Jurassic sea-surface temperature curve.