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
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摘要: 通过环境磁学、沉积学、遗迹化石学与地球化学对牛３８井厘米级红灰韵律层的综合研究发现红层中具明显的胶体凝聚现象，其磁化率值、总铁与游离铁含量较高，层内生物扰动作用相对较强，表明气候变化引起的化学沉积是控制韵律旋回的主因，底栖生物的潜穴活动促进了沉积界面处微化学环境的变化。经频谱分析等时序分析法的估算可知该红灰韵律层是受十年级与百年级主周期的控制，可能与太阳黑子或太阳磁场活动等天文周期有关。虽然此类天文周期对地球气候变化的影响能力也许不强，但由于化学沉积对气候变化反应灵敏，而且可能当时湖水化学环境正处于胶体沉积的临界值附近，因而水体化学性质稍有偏离即可导致韵律层的形成。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.
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Key words:
- rhythmic deposit /
- climatic cycles /
- flocculation /
- bioturbation /
- spectral Analysis /
- response to climate
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