Late Mesozic Tectonic Evolution And Prototype Of Suibin Depression In Shanjiang Basin

Mesozoic tectonic situation of Suibin area experienced the transformation from paleo-Tethys to Pacific tectonic domains, with mid to late Jurassic to early Cretaceous basin subsidence and filling controlled by paleo-Tethys domain, whereas late Jurassic to early Cretaceous basin reconstruction controlled by Pacific tectonic domain.From mid to late Jurassic to early Cretaceous, two depositional basins, with different original mechanisms, different extensions and different filling characteristics, developed successively in Suibin area. With the north-south extension, which was controlled by stress laxity after the close of paleo-Tethys and collision orogeny in mid Jurassic, local extensional fault depression developed along the pre-existing NEE striking weak structural belt and Sanjiang basin originated, with paralic facies Suibin Formation firstly, a sequent short interruption of sedimentation, and then an enhancement of subsidence with late Jurassic Shidongrong Formation exceeding original extensional depression. In late Cretaceous, regional stress transformed to N-S compression, sedimentary basin with roughly E-W striking develop, controlled by thrust from south to north in the margin of this basin, where Chengzihe, Muleng and Dongshan Formations deposited successively.Five stages of structure can be identified in Suibin area from late Mesozoic. The first one appeared to be extensional faulting in the later of the time when the Dongrong Formation deposited. The second one presented as adjustment to the subsidence situation from Dongrong to Chengzihe Formation by growth faulting when Didao to Chengzihe Formations deposited. The third one lasted from the end of Muleng Formation depositing to the end of the end of Dongshan Formation depositing and appeared to be thrusting and folding. The forth one appeared to be NW striking thrust and related folding in late Cretaceous. And the last one appeared as two strike-slip faults, which controlled the sedimentary circumstance of Baoquanling Formation, under the background of activity of Yilan-Yitong and Dunhua-Mishan strike-slip faults.Main structures formed after the Muleng Formation depositing in Suibin area appearing to be thrusting and folding, which were controlled by the compressional deformation of Pacific domain when Nadanhada Terrane collided to the continent. Typical structures were folds controlled by blind thrust faults. North to Songhuajiang River, thrust-fold systems thrusting from NWW to SEE formed between Jiangbin Fault-Junchuan Fault, Pudongnan Fault- Pudongbei Fault and Yongsheng Fault, which cotrolled strata fluctuation. South to Songhuajiang River, Majiatun-Donglintun fault and Sifanglinzi fault developed, which controlled the large roughly NS striking boxlike folds. In the crest of these boxlike folds, denudation controlled the relic of Muleng and Chengzihe Formations. Along Songhuajiang River, Song 1 and Song 2 faults activated not only in Cenozoic but also in the end of Muleng Formation, controlling regional structural circumstances. Thrusting directions were contrary between north and south of these two thrust faults.Regional structure line, striking roughly E-W, controlled the sedimentary basin of Suibin area in late Jurassic to early Cretaceous. Present characteristics of residual strata, as thicker in the west and thinner in the east, were related with the denudation after Muleng Formation, which was controlled by NNE striking thrust-fold system. The original model is contrary to predecessors, who proposed that present characteristics of residual strata were controlled by half-graben-basin with faulting in the western margin and overlapping in the eastern. Consequently, identification between salience and sag is a misunderstanding to folds controlled by blind thrusting.