龙门山地区中泥盆统观雾山组沉积相及其演化分析

Sedimentary facies and evolution analysis of the Middle Devonian Guanwushan Formation in the Longmenshan area

以龙门山地区北川甘溪凉水洞剖面实测资料为基础,对中泥盆统观雾山组沉积相及其演化进行了分析,认为观雾山组底部以碎屑岩沉积为主,主要发育河流相和无障壁滨岸相;碎屑岩之上发育碳酸盐岩台地相和碳酸盐缓坡相。其中碳酸盐台地可划分为台地边缘生物礁、台地边缘浅滩和台地前缘斜坡等3种亚相,碳酸盐缓坡可划分为浅水缓坡、深水缓坡等2种亚相;碳酸盐台地和碳酸盐缓坡可以在特定的环境下发生相互转化,其识别标志主要有角砾礁灰岩和滑动变形构造。龙门山地区观雾山组经历了早期和晚期2个沉积演化阶段,早期旋回底部为碎屑岩沉积、中上部以碳酸盐台地为主,晚期以碳酸盐缓坡为主。本研究为龙门山地区观雾山组岩相古地理恢复提供了基础。

Based on the measured data of the Beichuan-Ganxi-Liangshuidong section in the Longmenshan area,the sedimentary facies and evolution of the Middle Devonian Guanwushan Formation are analyzed.It is considered that the bottom of the Guanwushan Formation is dominated by clastic rocks,and mainly the fluvial and and barrier-free shore facies are developed;carbonate platform facies and carbonate gentle slope facies are developed above clastic rocks.Among them,the carbonate platforms can be divided into three sub-facies of platform margin reef,platform margin shoal and platform foreslope;the carbonate gentle slopes can be divided into shallow water gentle slope and the deep water one.The carbonate platform and carbonate gentle slope can be transformed into each other in a particular sedimentary environment,and the main identification marks are the breccia reef limestone and sliding deformation structure.The Guanwushan Formation in the Longmenshan area has experienced two phases of sedimentary evolution in the early and late stages.The bottom of early cycle is composed of clastic sediments,the middle and upper parts are dominated by carbonate platform,and the carbonate slope is dominated in the late stage.This study provides the basis for the lithofacies paleogeographic recovery of the Guanwushan Formation in the Longmenshan area.