Mesozoic Fault Activity And Its Oil And Gas Senses In Jiyang Sag

Fault activity of Mesozoic in Jiyang depression should be a significant content for prototyping basin and tectonic evolution studying of Mesozoic basin. In this dissertation, sedimentology, historical geology, structural geology, geophysics, structural dynamics/geometric, plate structure etc were combined properly. Taking Jiyang depression as studying object, fault distribution of different periods was analyzed, and thus discussing their structural dynamics. Using tectonic subsidence history modeling and denudating relationship between hanging wall and foot wall in Mesozoic faults, fault activity characteristics were discussed. The main innovative achievements had achieved were as bellow:1. Since Mesozoic, Jiyang depression had undergone multiple phases of tectonic evolution, and the developing characteristics of faults in each structural stage controlled not only the prototype basin pattern, but also the denudation and alteration of the previous basin. Since indo-china movement, although was reconstructed complicatedly, the Mesozoic basin faults were easily differentiated. At the basis of several main Mesozoic faults had been affirmed, coordinated with residual sedimentary pattern of Mesozoic and Paleozoic, and partial movement properties of faults, a model for north-western fault movement in Jiyang depression was formed. A point of view was supported that during Indo-China movement, the Jiyang depression was controlled by NW stress, at the same time of produced large thrust faults, thrust blocks on hanging wall strike-slipped between each other, and thus formed nowadays northwestern and northeastem">" structure of low-lying controlling faults. During late Mesozoic and Cenozoic periods, fault linkage and fault propagation and fault rotation enlarged the former fault scale, which displayed not only curving pattern of basin controlling fault, but also anomalistic distribution of residual Mesozoic strata. Under this condition, it was well understood by the response between tectonic background and regional time and space transformation.2. Integrated using datum such as survey well, drilling, and earthquake profile and so on to model subsidence history in Jiyang depression. The results demonstrated each subsidence condition in different stages and different area of basin evolution. In this region,the basin had two dominant subsidence period, each was later Eocene, that is the fist formation of Kongdian in 54—51Ma; the next was the third formation of Shahejie in 40—33Ma. Further more, the second important subsidence time was considered since 40Ma more truly.3. Taking good use of reverse order idea of denudation and sediment in faults, an applicable calculating method of thrust fault throw for residual basin in Mesozoic Jiyang depression was formed besides its forming theory, applicable condition. The result pointed out the veracity and application of thrust fault throw, by precondition mentioned above, according to regional structural subsidence and denudation thickness of different fault and fold tip, thrust fault throw of Mesozoic main basin control fault in Jiyang depression were calculated. The thrust fault throws are not approximate, which have a 1000m-2000m differences such as Zizhen and Yangxin faults. The two conceivable explain to this is that fault thrust has waving property but not like it completely, it has a character of alternation of large and small, that is fluctuation. Another explain to this is that due to asymmetric extrusion between two block, the developed series of faults are too easily collapse to maintain their initial state.