MINERALOGY OF THE LOWER APTIAN SEDIMENTS FROM THE BOREHOLE HOHENEGGELSEN-KB-40, WITH SPECIAL EMPHASIS ON THE CLAY MINERALOGY

Lower Aptian sediments from the borehole Hoheneggelsen KB 40 in the so utheastern pare of the Lower Saxony Basin have been studied. The succe ssion consists of dark claystones with intercalated black, finely lami nated paper shales with the fish shale as the final black shale event followed by the Hedbergella marl. The mineralogy of the sediments is c haracterized by biogenic components, mainly calcite and variable amoun ts of organic carbon, by siliciclastic detritus, and diagenetically fo rmed minerals such as pyrite. The calcite content fluctuates considera bly throughout the profile because of changes in the marine palaeoenvi ronment. The terrigenous detritus (quartz and clay minerals) was obvio usly;supplied to the shallow marine epicontinental basin by the contin ent to the south. Reworked Upper Carboniferous mud- and siltstones may have delivered parr of the illite, kaolinite, chlorite and quartz. Te rrigenous detritus including the randomly interstratified vermiculite/ illites may have been derived from reworked pre-Aptian sediments or pa laeosols of the hinterland. The change in the mineralogical compositio n of the terrigenous detritus observed in the highest dark claystone h orizon directly below the fish shale is most probably the result of ch anges in the source areas and of the depositional regime. (C) 1998 Aca demic Press.