Environmental Information in Reddish-Grey Lacustrine Rhythmic Deposits of the Core Niu-38 in the Upper and Middle Members of Shahejie Formation,in Dongying Depression,Shengli Oilfield

Key words: 
• rhythmic deposit /
• climatic cycles /
• flocculation /
• bioturbation /
• spectral Analysis /
• response to climate

Abstract: Based on multidisciplinary analyses of sedimentology,environmental magnetism,ichnology, mineralogy and geochemistry, it is found that,in the reddish- grey lamination in rhythmic deposits,there are various features about flocculent deposits with high susceptibility , high contents of total Fe and free Fe, and higher grades of bioturbation,showing that changes with chemical sedimentation caused by climatic cycles are the main controlling factor on the rhythmic beddings, and bioturbation could accelerate changes in micro-chemical environment on surface between water and sediments.Results from spectral analysis on time sequences show that the reddish-grey rhythmic deposits were controlled by decade-or century-level climatic periods which might be related to several astronomic cycles,such as sunspot or solar magnetic field. The influence of these astronomic factors on climatic changes is not likely very strong, but this kind of rhythmic bedding could be visible,probably resulting from the sensitive response of chemical sedimentation to climatic cycles ,and or the lacustrine chemical environment was nearby the sedimentary threshold for flocculation during the period in the upper and middle member of Shahejie Formation.