渤海湾盆地新生代各坳陷沉降的时空差异性

渤海湾盆地的成因机制主要与坳陷的构造位置、边界条件及深部因素有关。各坳陷沉降的时空差异性是这种复杂性的一种表现形式。本文通过渤海湾盆地主要坳陷的沉降史和各坳陷沉降差异对比,发现时空差异具体表现在下列3方面。1)在几个主要的裂陷幕构造沉降(或总沉降)均具有越往东部沉降量越大的趋势,如孔店组和沙河街组四段裂陷主要分布在济阳坳陷、昌潍坳陷和大型断裂部位,这与新生代盆地演化的开始阶段有关,并叠加有大型断裂(如郯庐断裂)的左行走滑作用。2)构造沉降量分析表明在经历沙河街组三段沉积期的主裂陷幕后,除了沙河街组一段沉积期沉积中心往西(黄骅坳陷)迁移外,沙河街组一段至东营组沉积期总体表现为随时间向东北部递进渐变式迁移,新近纪又回迁至渤中地区。3)与该区沉降规律相异的是冀中坳陷和临清坳陷(昌潍坳陷因特殊的构造位置除外),表现为在整体沉降过程中局部挤压或抬升反转的沙河街组二段沉积期,这两者的沉降量及沉降速率反而变大,不但比同时期其它坳陷大,亦比坳陷本身的其它裂陷期大。控制各坳陷发育差异间的主要原因,一是有北东东向的新生构造发育,二是有北西西向的变换断层影响。

Space-time discrepancy of depressional evolution in the Bohai Bay Basin during Cenozoic

There are the Changwei,Jiyang,Huanghua,Jizhong(Central Hebei),Bozhong(Central Bohai),Linqing and Liaodong Bay Depressions in the Bohia Bay Basin.Based on typical curves of buried history,correlation of subsidence rate and sedimentary rate of each depressions in the Bohai Bay Basin during Cenozoic,it could be found that the subsidence and basin evolution of the Bohai Bay area had an obviously space-time discrepancy among the Cenozoic depressions.1)In each main rifting stage,the subsidence scale seemed stronger in the east than that in the west,such as in the first rifting(the sedimentary period of the Kongdian Fornation and the 4th Member of Shahejie Formation)because this period was a beginning of Cenozoic rifting period in Bohai Bay area,superimposed with pull-apart action by sinistral strike-slipping of the Tan-Lu fault.2)After the main rifting episode(sedimentary period of the 3rd Member,Shahejie Formation),the subsidence center migrated generally westwards to the Huanghua Depression during sedimentary period of the 1st member,Shahejie Formation.Furthermore,the subsidence center migrated northeastwards(the Bozhong,Liaodong Bay and northern Jiyang Depressions)during sedimentary period of the 1st Member,Shahejie Formation and Dongying Formation.In Neogene,the subsidence center changed bach to central Bohai area.3)The Linqing and Jizhong Depressions seemed to be an exception in the space-time evolutional tendancy mentioned-above.Regionally,the sedimentary period of the 2nd Member,Shahejie Formation was a compressional or partly reversed period,when the depressional rate of the both was bigger not only than that of the other synchronous depressions,but also than that in the orther structural stages of themselves.The exception of the Linqing and Jizhong Depressions might be resulted from neogenic NEE-striking Cenozoic structure and the NWW-striking transfer fault zones.