【摘要】 沾化凹陷新近系馆陶组(Ng)广泛发育了一陆相螺化石层。来自螺化石层上下沉积层位的馆陶组和明化镇组(Nm)泥灰岩的C、O、Sr、Nd同位素的分析结果显示,螺化石层所在Ng4段泥灰岩具有比其上下部泥灰岩较低的δ13C值和较高的δ18O值,而螺化石埋藏层位的泥灰岩具有相对较低的δ13C和87Sr/86Sr值以及相对较高的δ18O值。143Nd/144Nd比值在剖面上的变化不明显,反映Ng、Nm沉积时期凹陷具有稳定的物源区;而C、O、Sr同位素组成的系统变化则指示了古沉积环境的变化。其中Ng4段沉积时期气候相对干热,Ng3、Nm1+2段沉积时期气候相对湿热;螺化石层泥灰岩所表现出的低87Sr/86Sr值和螺化石壳体相对高的δ13C和δ18O值可能代表了区域上一次重要的气候干热化事件,该时期大气降水明显减少,湖泊蒸发量较大,使得盆地的水体盐度增加,水体中87Sr/86Sr降低和δ18O值增加,同时水体营养生物和河流输入的营养物质减少,致使田螺最终死亡。随后环境气候相对湿热,生物生产力提高和碎屑物质供应的增加使得87Sr/86Sr值和δ13C值增加,大气降水补给导致沉积介质的δ18O值降低。更多还原

【Abstract】 The occurrence of nonmarine snail fossils in Neogene sediments from the Zhanhua Sag in Shengli Oilfield,eastern China suggests the environmental change during the deposition of the terrestrial sediments.Major-,trace-elements and C,O,Sr and Nd isotopic compositions of the deposits in the successive profiles of Neogene Guantao and Minghuazhen Formations(Fms.) were analyzed for delineating the possible causes for such a sedimentary variation.The results show relatively higher δ 13C and δ 18O values in snail fossils,while relatively lower δ 13C and 87Sr/86Sr values in the associated sediments.The sediments from Ng4 member have relatively higher δ 18O values and relatively lower δ 13C values,and then shifted to higher δ 13C values and lower δ 18O values in Ng3,Nm1+ 2.The isotopic signatures indicate a much drier and hotter climate during the stage of Ng4.The change in climate and sedimentary environment might be important causes for the death of nonmarine snails in the Zhanhua Sag.In the stage of Ng3+ Nm1+ 2,the climate was becoming warm and wet,so the sediments deposited contemporarily were recorded with higher 87Sr/86Sr,δ 13C values,and lower δ 18O values.更多还原