莱南斜坡带沙四段—沙三下亚段原型盆地恢复及其对沉积的控制

摘要

莱州湾凹陷南部斜坡带后期经历多次大规模构造运动改造,导致原始盆地面貌不清,沉积体系分布不明确.以构造演化分析为主线,通过地震解释、声波时差法和趋势厚度法相结合,对沙河街组早期沙四段—沙三下亚段沉积时期的原型盆地面貌及其配置关系进行了恢复,并明确了不同沉积体系的平面分布及控制因素.研究表明: (1)沙四沉积时期,莱南斜坡带整体受断裂伸展活动引起的块体差异升降,西部受两组东西向断层分割形成3个东西向展布的断槽,东部及南部为潍北凸起的隆起区,早期断层分割东西古地貌变化; (2)沙三下沉积时期,整体快速沉降,西部受东西向断裂差异抬升,形成局部高地,潍北凸起东部一部分后期逐渐淹没于水下,形成宽缓台地背景; (3)不同物源体系供给控制了沙四段扇三角洲与辫状河三角洲差异分布,古地貌与物源差异供给共同控制了沙三下亚段湖相碳酸盐岩与风化残积相的发育与垂向分布.沉积体系的发育和分布对于盆地原型面貌具有重要的响应关系.%The south slope zone of the Laizhouwan Sag in the late stage has been reformed in many large-scale tectonic movements, resulting in the unclear appearance of the original basin and the unclear distribution of the sedimentary system.Based on the tectonic evolution analysis as the main line, through seismic interpretation, sound wave time difference method and trend thickness method, prototype basin at the sedimentary period and its configuration relationship have been recovered in the lower third sub-member and the fourth member of the Shahejie Formation at the early paleogene, and the planar distribution and controlling factors of different sedimentary system have been cleared.Study showed that: ( 1) At the sedimentary period of the fourth member of the Shahejie Formation, the whole south slope zone of the Laizhouwan Sag were lifted and dropped due to block differences caused by fault extension, in the west three east-west spreading fault trough were formed by two groups of east-west trending faults and the east and south areas were the uplift areas of the Weibei salient.The early faults resulted in the palaeogeomorphology differences in the east and west.(2) At the sedimentary period of the lower third sub-member of the Shahejie Formation, the whole south slope zone went through rapid settlement and the west part was uplifted by the differences between the east and west faults, forming a local highland.Part of the eastern Weibei salient submerged in water later, forming broad platform.(3) Different provenance supply systemcontrolledthe differential distributionin Fan delta and braided river delta of the fourth member of the Shahejie Formation.Geomorphology together with the provenance supply differentiation controlled the development of lacustrine carbonate rocks and weathered eluvial facies and their vertical distribution in the lower third sub-member of the Shahejie Formation.The development and distribution of sedimentary systems have an important response relation to basin prototype.