内蒙古二连盆地阿北凹陷下白垩统近岸水下扇沉积特征*

阿北凹陷位于内蒙古二连盆地东北部，面积约600 km²，是二连盆地勘探潜力最大的凹陷之一。针对阿北凹陷复杂的地质构造，充分利用岩心、录井、测井以及地震等资料，详细分析了阿北凹陷北部陡坡带下白垩统近岸水下扇沉积特征和分布规律。研究表明，近岸水下扇和扇三角洲在岩相组合、沉积构造、粒度特征、电性特征和地震反射特征方面均有较大区别，综合反映以重力流为主的沉积环境。阿尔善期北部陡坡带发育大规模水下扇，扇体规模自下而上逐渐向北部物源方向减小，到腾格尔期沉积了一大套深湖—半深湖暗色泥岩，近岸水下扇砂砾岩体下切到深湖—半深湖暗色泥岩中，决定了研究区近岸水下扇砂体具有优越的成藏条件。

Sedimentary characteristics of nearshore subaqueous fans of the Lower Cretaceous in Abei sag of Erlian Basin,Inner Mongolia

Abei sag， with 600 km² of area，is one of the most promising exploration area in northeastern Erlian Basin, Inner Mongolia. Considering the complicated geological structure of Abei sag，based on core，logging，well logging and seismic data，this paper analyzed the depositional characteristics and distribution laws of nearshore subaqueous fans in the Lower Cretaceous in northern steep slope zone of the Abei sag in Erlian Basin.The results show that the subaqueous fan and the fan-delta facies were different in lithologic series，sedimentary structure，grain size characteristics，well logging curve and seismic reflection structure，which indicated the gravity flow depositional environment.The deposition of northern steep slope zone developed large-scale nearshore subaqueous fans，and the distribution scale of the fan bodies reduced to northern provenance step by step in ascending order during the Aershan Age.The dark colored mudstones of deep lacustrine and half-deep lacustrine was formed，which the sand bodies of the near-shore subaqueous fans cut down during Tenggeer Age.It makes the study area of the nearshore subaqueous fans have superior oil and gas accumulation conditions.