歧口凹陷古近纪沉积体系特征

根据歧口凹陷地震剖面的不整合特征等,将古近纪划分为3个二级层序。沙三三段—沙三二段层序:歧口凹陷强烈断陷期,湖盆扩张,气候湿润,普遍发育半深湖深湖泥岩;沙三一段—沙一中段层序:沙三一段基底抬升,地层遭受剥蚀,沙二段时断陷活动减弱,湖水减退,沉积范围减少,沙一段中、下段沉积范围有进一步扩大,该期是重要沉积期;沙一上段—东营组层序:在继承了沙一中、下段的地层沉积之后,东营组早期沉积时期较为稳定,整体沉降较弱,晚期基底整体抬升,遭受剥蚀。

PALEOGENE DEPOSITIONAL SYSTEMS IN THE QIKOU SAG

The Paleogene in the Qikou Sag of Dagang oilfield was divided into three second-level sequences upon unconformities from seismic profiles. The sequence of Es33-Es32 was formed in the period of strong faulting and depression, while the basin of lake was expanding under humid climate. As the result, mudstone was widely developed in the semi-deep and deep lake. The sequence of Es31-Eslz was deposited in the uplifting period of Es31, when denudation prevailed. In the period of Es2, faulting became weak and the water level was dropping due to lake shrinkage. The lake was expanded again in Eslz and Eslx, and thus it was the major stage for deposition. The sequence of Esld and Ed inherited the depositional framework of Eslz, and the region was stable then in sedimentation. In the early stage of Ed, the basin was rather stable with weak subsidence, while in the later stage of Ed, denudation dominated due to uplifting of the basin.