东北大三江盆地群早白垩世存在统一湖盆的沉积学证据

大三江盆地群位于黑龙江省东部,中生代以来经历了多期构造运动,形成现今各自分割的10余个残余盆地。由于缺乏关键性证据,前人对大三江地区早白垩世是否存在统一湖盆存在争议。本次研究通过野外地质调查和钻井岩心观察,认为盆地总体缺乏边缘相沉积,并且主要以三角洲平原亚相和滨浅湖亚相为主。古水流恢复和重矿物特征显示,研究区主要存在西部和西北部、东部以及东南部三大物源体系,并且平面上具有由四周向中心汇聚的特征。地震资料反射特征显示下白垩统具有典型的断陷-坳陷复合结构,坳陷时期地层由各盆地中心至边部未出现明显的地层减薄现象,现今的盆地边界断裂多为后期对盆地进行改造、破坏的逆冲断裂。这些证据都是对大三江地区早白垩世存在统一湖盆的有力支撑。本研究不仅能为大三江盆地群原型盆地的恢复提供重要依据,也将为东北盆地群油气资源远景评价和进一步的勘探部署提供参考。

The sedimentary evidence for the existence of unified basin in Early Cretaceous in Dasanjiang basin group, Northeast China

Located in eastern Heilongjiang Province, the Dasanjiang basin group has experienced multiphase tectonic movement since Mesozoic, and formed a dozen of separated residual basins. Due to the lack of key evidence, there exists controversy concerning existence or nonexistence of a unified basin in Dasanjiang area during the early Cretaceous. The field geological survey and drilling core observation show that the basin lacks marginal facies, and is dominated by the delta plain subfacies and shore shallow lake subfacies. Paleocurrent recovery and heavy mineral characteristics show that the study area mainly has three major provenances existent respectively in the west and northwest, east and southeast, concentrated from the periphery to the center in space. The seismic reflection characteristics show that the lower Cretaceous strata have typical faulted-depression composite structure, and at the same time, the strata of the basin did not show obvious thinning from the center to the edge during the depression period. So the boundary faults of the basin mostly should be thrust faults which reformed the basin in later period. All the evidence strongly support the argument that the Dasanjiang area was a unified basin in the early Cretaceous. The results obtained by the authors provide an important basis for the restoration of prototype basin of Dasanjiang basin group and also offer a reference for the oil and gas resources substitution and exploration in Northeast China.