福山凹陷古近系沉降特征时空差异性及其形成机制

Research on temporal diversity of settlement characteristics of Paleogene,Fushan Sag

福山凹陷区域构造复杂,研究程度较低,而针对构造沉降史的研究几乎为空白。应用EBM盆地模拟系统对福山凹陷沉降史进行回剥分析的结果表明,福山凹陷先后经历裂陷期、断拗转换期和裂后期,且沉降速率的变化呈现幕式特点。裂陷早期自裂陷Ⅰ幕开始西部次凹沉降速率大于东部次凹,但到裂陷Ⅲ幕东部次凹沉降作用加强,沉降速率反而大于西部次凹;从沉降中心发育的位置看,裂陷初期沉降中心位于凹陷西部的皇桐地区,到裂陷晚期(裂陷Ⅲ幕)沉降中心已经逐步迁移到了东部的白莲地区,而拗陷期区域沉降中心继续向北东方向迁移;这种东、西次凹沉降速率的垂向差异性以及整个凹陷古近系沉降中心自西向东迁移的规律,反映出福山凹陷东、西次凹沉降特征的时空差异性特点。研究结果表明,东、西次凹控凹断层活动差异性以及福山凹陷受区域非对称性拉伸作用是造成这种沉降时空差异性的内在机制。

Tectonic is very active in Cenozoic of Beibuwan Basin,Fushan Sag located in margin of Beibuwan Basin,whose regional tectonic of Paleogene is very complicated and research level is low, without study of tectonic subsidence history. Application of EBM basin modeling system for subsidence history in Fushan Sag, the back stripping analysis shows that; Fushan Sag has successively suffered rift period, transformational period and depression period, the changing of subsidence rate emerges 'episode' characteristic ; west secondary depression sedimentation rate is higher than which in east secondary depression since chasmic Ⅰ episodic period, but from the chasmic Ⅲ episodic, the east secondary depression sedimentation increased, so, the sedimentation rate is higher than which in west secondary depression. From the location of the center of subsidence, at the early period of chasmic, the subsidence center is located in the Huang Tong region of western depression, but at the advanced of chasmic( chasmic Ⅲ episodic),the center of subsidence gradually migrates to the Bailian region of eastern depression, then, the regional center of subsidence continues migration to the northeast. Vertical sedimentation rates of the east and west secondary depression are different, besides, regional subsidence center migrates from west to east of Paleogene in Fushan Sag, reflecting the east and west secondary depression in Fushan Sag having space-time diversity in the characteristics of subsidence; Research finds that the tectonic activity diversity of secondary depression and Fushan Sag suffered by regional asymmetric extension effect is inner mechanism which has caused this space-time diversity of east-west settlement.