川西坳陷中部上三叠统马鞍塘组沉积相特征

SEDIMENTARY-FACIES FEATURES OF UPPER TRIASSIC MAANTANG FORMATION,CENTRAL OF WEST SICHUAN DEPRESSION

上三叠统马鞍塘组是四川盆地西部地区最后一套海相碳酸盐岩地层,其中发育的礁滩等沉积微相是油气勘探的有利相带。为了探讨马鞍塘组滩、生物礁及礁滩组合的发育及分布情况,通过对比分析有关的钻井和野外资料,发现马鞍塘组厚度、岩性和沉积特征等在短距离内横向变化较大;新发现在孝泉—汉旺地区马鞍塘组底部发育有一北西向的砂屑滩;川西坳陷中部晚三叠世卡尼期的沉积相主要为同斜缓坡中的砂屑滩、鲕粒滩、生物碎屑滩和生物礁微相。除砂屑滩外,鲕粒滩、生屑滩和生物礁(点礁)微相都沿龙门山呈北东向发育,卡尼期末的沉积相为滨海潮汐相。

In west Sichuan Basin,the Upper Triassic Maantang Formation is the last one with marine carbonate rock;and the developed reef shoal is a favorable facies belt for exploration.In this study,some data from both drilling and outcrop on Maantang Formation are analyzed in order to explore the development and distribution of an association among shoal,bioreef and reef shoal.It is found that:(1) within a short distance,there is a great lateral variation of formation thickness,lithology and sedimentary feature;(2) there is a new discovery that in Xiaoquan-Hanwang area,a NW-trending fragmental shoal is developed at the formation bottom;(3) in the central of West Sichuan Depression,some sedimentary facies during the Carnian of later Triassic mainly include fragmental shoal,oolitic shoal,bioclastic shoal and bioreef developed in carbonate ramp;(4) besides fragmental shoal,the other ones with a NE-trending are developed along Longmenshan Mountain;and(5) a sedimentary facies developed during the end of Carnian is coastal tidal facies.