四川盆地及邻区上二叠统一下三叠统海槽的深水沉积特征

四川盆地及邻区广元-旺苍、城口-鄂西、开江-梁平海槽是上二叠统一下三叠统飞仙关组（P3-T1f）的深水碳酸盐沉积区。该区上二叠统上部大隆组是硅质岩、硅质泥岩、硅质灰岩组合，含放射虫、有孔虫等化石，厚125—29．0m，为海槽裂陷期凝缩沉积。三叠系飞仙关组下部为远洋沉积的暗色泥岩、微晶碎屑灰岩和重力流沉积的浊积岩、角砾灰岩组成的深水碳酸盐沉积，厚50．0～300．0m，是裂陷期后的海槽充填沉积。海槽相区沉积在晚二叠统世末达到最大海泛面沉积了大隆组。海平面缓慢下降期沉积了补偿充填性质的飞仙关组深水碳酸盐岩。海槽相区上二叠统一下三叠统飞仙关组构成了一个完整的三级层序。深水沉积物的有机碳平均值高达6．21％，是良好的烃源岩。但在海槽相区上二叠统不发育生物礁，飞仙关组缺乏鲕粒岩。

Petroleum geological characteristics of deep water deposits in Upper Permian-Lower Triassic trough in Sichuan basin and adjacent areas

Three troughs, namely Guangyuan-Wangcang, Chengkou-Exi, and Kaijiang-Liangping, in Sichuan basin and its adjacent areas, is filled with deep water carbonates of the Upper Permian-Lower Triassic of Feixianguan Formation. The Dalong Formation in the upper part of the Upper Permian in the area is a condensed succession of 12.5-29m in thickness deposited in the troughs in the chasmic stage. It is composed of silicalite, siliceous mudstone, and siliceous limestone, with fossils such as radiolarans and foram. While the lower part of the Triassic Feixianguan Formation is a filled succession of 50-300m in thickness deposited in the troughs in post-chasmic stage. It is deep water carbonates consisting of a pelagic melanic mudstone and microcrystalline calclithite, as well as turbidites and breccia limestone from gravity flow. The Dalong Formation was deposited at the end of the late Permian when the maximum flooding surface occurred in the trough area. And the deep water carbonates of Feixianguang Formation were deposited during slow regression. The Upper Permian-Lower Triassic Feixianguan Formation constitutes a complete third-order sequence. The deep water carbonates are source rocks of excellent quality with TOC up to 6.21%. But no organic reefs were developed in the Upper Permian and the Feixianguan Formation is lack of oolite.