四川盆地下寒武统膏盐岩“多潟湖”沉积模式

早寒武世晚期四川盆地构造背景为"两隆夹一凹"的格局,气候干旱炎热,为膏盐岩的发育创造了有利条件。通过野外剖面、钻井剖面、岩石薄片及区域地质调查等资料,总结了下寒武统膏盐岩发育特征。基于岩性特征、岩性组合方式及分区的不同,对水动力特征、沉积构造、膏盐岩单层厚度、发育规模及位置等方面的差异进行对比,结合岩相古地理研究,建立了四川盆地下寒武统膏盐岩沉积模式。研究结果表明:1）膏盐岩主要以含膏白云岩类和石膏岩类为主,膏盐岩厚度介于0.74~419.9 m,具有分布广、变化大等特点,沉积中心分别位于重庆-合江一带、利川-彭水一线,整体上呈现"山字型"展布特征;2）膏盐岩岩性组合类型可分为:白云岩或泥（砂）岩夹膏盐岩组合、膏盐岩与白云岩呈韵律性互层组合、膏盐岩夹白云岩或页岩组合,分别发育于潮上带、潮上带相对低洼处及潮上带-潮间带上部水体较深且循环受限的凹陷处;3）膏盐岩主要形成于川东南静水潟湖、其次为川东及川西南扰动潟湖与混积潮洼,即"一主两副"的多潟湖环境。

“Multiple-lagoon” Sedimentary Model of the Lower Cambrian Gypsum-salt Rocks in the Sichuan Basin

The structural setting of the Sichuan Basin in the latter part of the Early Cambrian epoch appears as a sin-gle depression between two uplifts. The climate was hot and dry,favoring the development of gypsum-salt rocks, which characteristics were analyzed in a combination of field profile,drilling section,thin section and regional geo-logical survey. The present study of lithofacies paleogeography of gypsum-salt rocks compares the diverse hydrody-namic characteristics,sedimentary structure,single-layer thickness,development of areal scale and location,and fi-nally establishes a sedimentary model of Early Cambrian gypsum-salt rocks in the Sichuan Basin,with the following results. (1) The gypsum-salt rocks mainly comprise gypsum-bearing dolomite and gypsum rocks from 0.74 m to 419.9 m thick. The sedimentary centers are located in the Chongqing-Hejiang and Lichuan-Pengshui areas. The overall dis-tribution characteristics are "mountain type". (2) The lithological association of gypsum-salt rocks falls into three cat-egories:association of dolomite or mudstone (sand) rocks with gypsum-salt rocks,developed in the upper tidal zone;rhythmically interbedded associations of gypsum-salt rocks and dolomite in relatively shallow,low-lying areas in the upper tidal zone;and the association of gypsum-salt rocks with dolomite or shale in deeper depressions with re-stricted circulation in the upper-to inter-tidal zone. (3) In multiple-lagoons (one main lagoon and two subsidiary la-goons),the gypsum-salt rocks were formed mainly in static lagoons in southeastern Sichuan,with two subsidiary la-goons in disturbed lagoons in eastern Sichuan and in mixed tidal depressions in southwestern Sichuan.