Inorganic geochemistry of Albian sediments from the Lower Saxony Basin NW Germany: palaeoenvironmental constraints and orbital cycles

Within the international ALBICORE project, Upper Albian sediments from a 245 m core (Kirchrode I) drilled in Hannover were studied by inorganic geochemical methods. More than 650 samples (minimum sample spacing 0.5 m) were analysed for major and minor element concentrations. This chemical database was used to reconstruct the depositional environment and to investigate the influence of high frequency Milankovitch cycles on the chemical composition of the sediments. emical composition of the sedimentary sequence is primarily controlled by variations in carbonate content, corresponding to Ca/Al ratios. Variations in both Ti/Al and Si/Al ratios are interpreted as fluctuations in detrital composition resulting from increases in smectite and quartz content in the upper section of the core. High amounts of reactive iron, but low pyrite concentrations, the lack of enrichment of redox-sensitive trace elements (V, Cr), and high Mn concentrations indicate oxic bottom water conditions and the absence of an oxygen minimum zone for the Upper Albian at the Kirchrode site. The nutrient-related trace elements (Ba, P, Zn) suggest a generally oligotrophic setting with slightly elevated productivity only in the uppermost Upper Albian. Only one layer was identified as containing volcanogenic material (at 87.20 m). This layer is characterised by elevated montmorillonite, Zr and Nb. Mass balance calculations for the entire core suggest that the high Mn values cannot be explained by riverine input alone. Therefore, a coastal oxygen minimum zone south of the Kirchrode site is postulated as an additional Mn source. variations in both carbonate content and Al-normalised concentrations of predominantly detrital elements, like Si and Ti, are seen in a 60 m interval (40–100 m), where sedimentological, palaeontological and geochemical data suggest stable depositional conditions. Although carbonate cyclicity, cyclicity in detrital input and nutrient-related element abundances do not correlate with each other, three strong peaks in the results of spectral analysis of these chemical data for this interval appear to correspond to Milankovitch frequencies in the eccentricity, obliquity and precession bands.