柴达木盆地西部新生界陆相湖盆碳酸盐岩沉积环境与沉积模式

Sedimentary environments and sedimentary model of carbonate rocks in the Cenozoic lacustrine basin,western Qaidam Basin

利用野外露头、岩心、测井录井和分析化验资料,对柴达木盆地西部(简称"柴西地区")新生界干柴沟组湖相碳酸盐岩进行了研究,划分了其沉积微相类型,研究了其分布规律,分析其形成环境和控制因素,并建立了相应沉积模式。该区湖相碳酸盐岩在垂向上与碎屑岩频繁互层,湖相碳酸盐岩包括颗粒灰岩、藻灰岩、泥晶灰岩和混积岩4大类11种,划分出了灰泥坪、颗粒滩、藻丘(礁)、浅湖湾以及(半)深湖泥灰岩相等5种沉积微相。通过分析不同碳酸盐岩及其微相时空展布特征,认为其发育主要受控于湖盆构造运动、湖平面变化、陆源碎屑注入、古气候与古水介质条件、古地貌与古水深环境,并在此基础上建立了柴西湖相碳酸盐岩的沉积模式。研究认为柴达木盆地西部干柴沟组沉积时期,湖盆为典型咸化湖盆,构造活动相对稳定,湖平面上升达到峰值。碳酸盐岩主要发育在湖侵期,高频湖平面变化形成了碳酸盐岩与碎屑岩频繁互层。在枯水期,盆地坡折处发育碎屑岩滩坝或三角洲前缘沉积;在湖侵期,盆地坡折处发育了鲕粒滩及藻灰岩,盆地洼陷区发育泥灰岩或灰质泥岩。

This paper focuses on the lacustrine carbonate strata of the Ganchaigou Formation of Cenozoic in western Qaidam Basin. Based on field outcrop survey,core sample identification,analysis data,andwell logging data,the types distribution and sedimentary facies of carbonate deposits in the study area were studied. By analyzing the forming control factors,corresponding depositional model is established to guide the exploration. Research shows that the western Qaidam Basin is a typical saline lacustrine basin. There are four types and 11 kinds of lacustrine carbonates including grain limestone,algal limestone,crystal limestone and peperite carbonate developed in western Qaidam Basin which were mainly deposited in five microfacies of lime-mud flats,grain bank,algal reef,lake-bay and semi-deep lake facies. By analyzing the spatial and temporal distribution characteristics of different carbonates and microfacies,the conclusion is made that the development of lacustrine carbonates in western Qaidam Basin is mainly controlled by the basin tectonic movements,injection of terrigenous clastics,water palaeosalinity under the ancient climate and palaeotopography with different palaeo-water-depth. On this basis,a comprehensive vertical depositional model of lacustrine carbonate with associated gypsum-salt rock in western Qaidam Basin is established. The research indicated that,during the sedimentary period of the Ganchaigou Formation in western Qaidam Basin,the lacustrine basin was typical saline lacustrine basin with stable tectonic activities; whereas the lake level reached the peak. Carbonate rocks,which were developed in the transgression stage,were frequently interbedded with clastic rocks due to the high-frequency lake level changes. In the low-water season,clastic beach bars or delta front deposits were developed at basin slope; while at lake transgression stage,oolitic banks and algal limestones were developed at the basin break in slope,and marlite and lime mudstones were developed in the depression area of the basin.