塔西南坳陷古新统蒸发岩沉积条件及成因模式初探

Sedimentary Condition and Genetic Mode of Paleocene Evaporites in the Southwestern Depression of the Tarim Basin

基于近期野外地质调查及钻井资料整理,对塔西南地区古新统蒸发岩沉积特征、展布规律及成因模式进行了初步探讨。研究表明,塔西南古新统吐依洛克组蒸发岩以石盐岩为主,为海退过程中的产物;阿尔塔什组蒸发岩以石膏岩或者硬石膏岩为主,为缓慢海侵的产物。吐依洛克组石盐岩沉积是海退背景下、多级盆地卤水回流的结果,其受控于同时期区域性构造运动和海平面变化等多种因素。古新世早期,从卡拉库姆盆地向东至费尔干纳-阿富汗-塔吉克盆地再到塔西南地区,在空间上表现为一个自西向东水体盐度逐渐升高的湖链系统。在塔西南与最西部特提斯海之间,以石膏相为主的预备盆地的出现,是导致塔西南地区吐依洛克组蒸发岩以石盐岩为主而显著缺乏石膏岩的主要原因。这种多级次级盆地中卤水的回流作用对盐类物质向后期分异具有积极意义,指示了塔西南古新统具有较好的成钾远景。

Based on recent field investigation and compilation of well data,in this paper we conducted a tentative discussion on the sedimentary characteristics,distribution and genetic mode of the Paleocene evaporites in the southwestern Tarim basin.Results show that,the Tuyiluoke Formation typified by halite resulted from regression process but the Aertashi Formation marked by gypsum or anhydrites was a product of a slow transgression.The halite deposit of Tuyiluoke Formation,as a result of brine reflux within multi-subbasin system under a regression background,was controlled by multiple factors including regional tectonic activities and sea level changes.The sedimentary configuration during the early Paleogene from the Kalakumu Basin westward to the Fergana-Afghan-Tajik Basin to the southwestern Tarim Basin in the east displays a lake chain system with salinity increasing from west to east.Therefore,we conclude that the occurrence of preparation basin characterized by gypsum deposits between the southwestern Tarim Basin and the Tethys to the west resulted in the dominate halite deposits and the absence of gypsum deposits in the southwestern Tarim Basin during the Tuyilluoke Formation formed.The proposed genetic mode of brine reflux within a lake chain system is positive to a higher differentiation of salt materials,indicating a better prospect of potash formation in the southwestern Tarim Basin during the early Paleocene.