Major and minor element geochemistry of Lower Aptian sediments from the NW German Basin (core Hohenegglesen KB 40)

Abstract

Two hundred and thirty-three samples from the Hoheneggelsen KB 40 drill core, located 30 km SE of Hannover, Germany, were analysed for 12 major elements, 14 minor elements, degree of pyritization, and S-isotopic composition. This early Aptian sequence consists of three lithological units: an upper marly section (Hedbergellamarl) that was deposited under strictly oxic conditions, an underlying fish shale horizon (“Fischschiefer”) which represents an anoxic stagnant phase of sedimentation, and a lower clay-rich section (dark coloured claystones) including scattered thin paper shale horizons (“Blättertone”) reflecting a suboxic to anoxic water column. Major and minor element profiles mirror the changing sedimentology of the individual units which can be explained by different palaeoceanographic and climatic conditions. A major shift in major element ratios, which is probably a result of a different source of the terrigenous detrital material or of variations in weathering intensity, took place before the onset of fish shale sedimentation. The high-resolution sampling and analysis (sampling intervals 1 to 5 cm) allows the detection of small-scale variations in element contents in individual sedimentary units and in transitional stages of suboxic to anoxic (dark claystone to paper shale) or anoxic to oxic (fish shale toHedbergellamarl) palaeoenvironments.