High-precision sequence stratigraphic framework and sedimentary system evolution in the middle submember of the 3rd member of the Shahejie Formation in the Laizhouwan depression
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摘要: 莱州湾凹陷古近系沙河街组沙三中段发育典型的辫状河三角洲沉积体系。本文基于经典层序地层学理论,通过对莱州湾凹陷三维地震、主要钻井及取心、测井等资料综合分析,对莱州湾凹陷沙三中段层序地层特征及层序格架内沉积体系展布进行精细研究。将沙三中段整体划分为1个三级层序,并根据初次湖泛面、最大湖泛面及高水位体系域域内三角洲期次包络面的界定将沙三中段进一步划分为低水位体系域、湖侵体系域和高水位体系域3个体系域及6个四级层序。在层序格架内分析了研究区沙三中段沉积体系的展布特征及演化规律。沙三中段低水位体系域西部斜坡带发育扇三角洲沉积,北部陡坡带发育近岸水下扇沉积。湖侵体系域发育辫状河三角洲沉积,高水位体系域发育4期辫状河三角洲沉积、高水位体系域Ⅰ、Ⅱ期发育坡移浊积扇沉积。根据层序发育和油气成藏条件分析,认为沙三中段低水位体系域扇三角洲、湖侵体系域辫状河三角洲、高水位体系域坡I和II期的坡移扇沉积成藏条件最为有利,是下一步寻找岩性油气藏的优先目标。Abstract: The sequence stratigraphic framework and sedimentary system evolution are discussed on the basis of three-demensional seismic data,core examination and well logs for the middle submember of the 3rd member of the Shahejie Formation in the Laizhouwan depression. Collectively,the middle submember of the 3rd member of the Shahejie Formation may be involved in one third-order sequence,and subdivided into six 4th-order sequences. Three systems tracts including the lowstand,transgressive and highstand systems tracts are based on the first and maximum flooding surfaces and the bounding surface of the enveloping surface defined by the delta phases within the highstand systems tract. The fan delta and nearshore subaqueous fan deposits appear in the lowstand systems tract in the western and northern parts. The braided delta deposits and the slope turbidite fan deposits occur in the transgressive and highstand systems tracts,where the favourable lithologic traps may be recognized as preferred targets in the future exploration.
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