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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

Author:
Zuo, Fanfan, Heimhofer, Ulrich, Huck, Stefan, Adatte, Thierry, Erbacher, Jochen, Bodin, Stéphane
Source:
Palaeogeography, palaeoclimatology, palaeoecology 2019 v.517 pp. 1-15
ISSN:
0031-0182
Subject:
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
Abstract:
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.
Agid:
6281377