塔里木盆地寒武纪层序岩相古地理

Lithofacies paleogeography of Cambrian sequences in the Tarim Basin

通过钻井取心及露头沉积相观察、地震层序解释及地震相分析,结合蛇绿混杂岩带分布及板块构造演化等区域地质资料,对三级层序地层格架下的塔里木盆地寒武纪岩相古地理特征进行了研究。结果表明,塔里木板块内部存在3个孤立碳酸盐台地(塔西台地、罗西台地及库鲁克塔格台地)及其间深水沉积区的古地理格局,塔西南地区存在寒武系深水盆地相沉积分布区,并且该深水盆地相沉积分布区可能是以和田河气田为代表的塔西南地区海相油气藏的主力烃源区。发生于早震旦世和早寒武世的塔里木板块北缘大陆裂谷运动,以及震旦纪—寒武纪的张裂构造环境控制了塔里木板块内部多个孤立碳酸盐台地及其间深水沉积区的形成。从早寒武世到晚寒武世,虽然塔里木板块内的古地理格局总体没有发生大的变化,但以塔西台地为主的孤立碳酸盐台地均发生了进积—加积作用而变得更大,并且不同时空台地边缘类型及其叠置型式也发生了变化,主要表现为早寒武世以发育缓坡—(斜坡坡度较小的)弱镶边台地边缘为主,中—晚寒武世以发育弱镶边—(斜坡坡度较大的)镶边台地边缘为主。

Through sedimentary facies observations on coring and outcrop samples,seismic sequence interpretations and seismic facies analyses,the present paper,integrated regional geological data of ophiolite-melange belts with those of plate tectonic evolution,firstly compiled 4 lithofacies paleogeography maps of Cambrian sequences in the Tarim Basin under the third sequences stratigraphic framework.We discovered 3 Cambrian isolated carbonate platforms（the western Tarim platform,western Lop Nor platform and Kuruktag platform） and some inter-platform deepwater depositional regions within the Tarim plate and suggested that Cambrian deepwater basinal-facies depositional regions distributed in southwestern Tarim might be chief source rocks of marine oil-gas reservoirs represented by the Hetianhe gas field,this point of view is very important to marine oil gas exploration in the Tarim Basin,especially in the SW Tarim area.The continental riftogenesis of the northern margin of the Tarim plate occurred initially in Early Sinian and Early Cambrian,and the Sinian-Cambrian pull-apart structural condition controlled the formation of several isolated carbonate platforms and inter-platform deepwater depositional areas within the Tarim plate.From Early Cambrian to Late Cambrian,these isolated carbonate platforms represented by the western Tarim platform expanded universally due to progradation and aggradation though the paleogeographic framework as a whole did not change much within the Tarim plate,meanwhile,changes occurred in types and superimposition patterns of platform margins in different time-space domains,namely ramp to feebly rimmed platform margins were dominant in Early Cambrian,while feebly rimmed to rimmed platform margins became dominant in Middle-Late Cambrian.