The Characteristics Of Tectonics And Hydrocarbon Accumulation Of Jizhong Depression In Late Cenozoic Era

Jizhong depression, as one of subordinate tectonic unit of Bohaiwan basin, has the same evolution as the basin , which rifted in early Cenozoic and depressed in late Cenozoic. Late Cenozoic characteristics of tectonics and hydrocarbon accumulation of the depression are focused on in this paper. Guantao and Minghuazhen formation were developed in Neogene, Gu'an, Yangliuqing, Ouzhuang formation in Quarternary. They are featured by fluvial facies in the depression except lacustrine-bog facies in wuqing sag. Hebei Plain including the depression received six times sea transgressions in Quarternary. Tectonic movements in the depression and its neighborhoods, esp. in Bo-zhang zone, acted strongly in late Cenozoic. Faults trending NNE-NE dextrally sheared violently associated with kinds of fault assemble styles, for instance , en echelon-like, feather-like, broom-like in plane and positive-flower-like, comb-like, superimposed "Y" like etc. in profile. Bo-zhang zone striking NW, suffered strongly sinistral tensional shear movement. In late Cenozoic, violent thickness variance of Neogene sediment in the northern area, active seisms in Tangshan-Hejian-Cixian zone and Bo-zhang zone, six times invasions in Quarternary and migrantion of river channels, fault movements, etc., as the geological phenomena, all indicate active tectonic natures, which were dominated by dextral shear stress trending NNE. Tectonics in late Cenozoic Jizhong Depression was responded to by united efforts of contraction in deep Earth, and plate movements controlled by paleo-Pacific plate downgoing to Eurasion plate with direction changing and speed increasing ,and influenced by striking-line effect from strong collision between Indian Plate and Eurasian Plate in late Cenozoic. Tectonic movements in late Cenozoic had either positive or negative effect on hydrocarbon accumulation before Neogene. Deposit and fault structures controlled oil and gas accumulation in late Cenozoic, whose main source beds are Es1 and Es3 (Es1 was the most favorable ), container rock was sand of paleo-river channels and key passage was faults. Southern middle area of the depression as main Neogene hydrocarbon accumulative area, also is the most favourable prospect target. The wings of anticlines in Chaheji-Maxi-Hejian faulted zone and Wuqing sag possessed hydrocarbon accumulation conditions. In late Cenozoic, high speed and large thickness sediment, lacustrine bog facies, fairly weak fault movements in central Wuqing sag, resulted in biogenic and biogenic-thermo-catalytic gas pool with large possibility.