Inorganic Geochemistry of Albian Sediments from NW-Germany: Paleoenvironment
Alfred Wegener Institute for Polar and Marine Research,
Research Department Potsdam, Telegrafenberg A 43, 14473 Potsdam, FRG
Institute for Chemistry and Biology of the Sea
University of Oldenburg, P.O. Box 2503, 26111 Oldenburg, FRG
Within the scope of the Boreal Cretaceous Cycles Project (BCCP) upper Albian sediments from the 250 m long core Kirchrode 1/91 drilled near Hannover were analysed by geochemical methods. The chemical data are applied for paleoenvironmental reconstructions, additional high resolution studies were carried out to identify orbital induced cyclicity (for the latter see Rachold & Brumsack 1994, this volume).
The chemical composition of the Kirchrode 1/91 sediments is primarily controlled by - in distinct sections - cyclic variations in carbonate content. Additional fluctuations in detrital material composition can be related to a climatically induced increase in smectite and quartz content in the upper section of the core.
Volcanogenic layers are characterised by an enrichment of a different type of smectite in combination with high Zr- and Nb-concentrations especially in the finest grain size fraction. The geochemical signals can be paralleled with anomalies in the logging data sets.
Low degrees of pyritization and the missing enrichment of redox sensitive trace metals indicate oxic bottom water conditions, the occurrence of an oxygen minimum zone at the place of sedimentation can be excluded. However, a slight increase of Ba/Al- and P/Al-ratios in the uppermost section of the core is explained by an elevated productivity due to "coastal upwelling". Furthermore stronger wind intensities manifest in higher Zr/Al- and Ti/Al-ratios in this interval.
Strong variations in Sr-concentrations of the pure carbonates are not related to diagenetic mobilisation of Sr only, but also to fluctuations in the Sr-content of the primary carbonate material.
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