四川盆地元坝地区上三叠统须家河组的潮控河口湾与潮控三角洲沉积

Tide-Dominated Estuarine and Deltaic Deposition of the Upper-Triassic Xujiahe Formation in the Yuanba Area,Sichuan Basin

通过盆地边缘地表剖面,以及元坝区岩芯的研究,发现须家河组并非长期以来人们普遍认定的陆相沉积,而是海岸系统产物。须二段属潮控河口湾环境,包括冲积河道、潮汐-河流水道、UFR沙坪、潮汐沙坝、泥坪和盐沼等相。须四段属潮控三角洲环境,包括三角洲平原河道、分流河口潮汐沙坝、三角洲前缘与前三角洲、泥坪与盐沼等相。这两种环境(沉积),都是海侵的产物,都是地史上的暂时现象。当其被充满时(海退),就变为潮坪-海岸平原环境,分别对应于须三段、须五段的细粒含煤序列。基于储层质量与原始沉积环境密切相关,划分了5类储层相。根据我们研究安岳地区须家河组的成功经验,提出了勘探建议。

Through outcropped profiles at the margin of Sichuan basin and study of core-sections in the Yuanba area,it has been revealed that the Xujiahe Formation is not the continental depositions as commonly inferred to since 1950s,but the product of coast system products.The 2nd Member of Xujiahe Formation belongs to tide-dominated estuarine in origin,including the facies of alluvial Channel,tidal-fluvial channel,UFR sand flat,tidal bar,mud flat and salt swamps.The 4th Member of the Formation is regarded as the product of tide-dominated delta,including the facies of delta-plain channel,distributary-mouth tidal bar,delta front,prodelta,mud flat and salt swamps.Both environments of tide-dominated estuary and delta are temporary phenomenon in geological history.When sediment supply is sufficient,this area becomes tidal flat-strand plain environment （deposition）,which corresponds to the coal-bearing fine-grained successions of the 3rd and 5th Member of Xujiahe Formation.Five types of reservoir facies are divided based on the close relationship between reservoir quality and sedimentary facies.Exploration suggestion is provided in this study based on experiences in the Xujiahe Formation in Anyue Area.