川西前陆盆地晚三叠世构造层序岩相古地理特征

晚三叠世是川西前陆盆地形成、演化的重要时期。根据野外剖面、钻井岩心和物探资料,参考前人研究成果,将川西前陆盆地上三叠统划分为3个构造层序。以构造层序体系域为编图单元,系统编制了川西前陆盆地晚三叠世的岩相古地理图,揭示了该期岩相古地理演化规律。构造层序TS1始于印支运动第Ⅰ幕,川西地区处于浅海及海陆过渡环境,对应的地层是马鞍堂组和小塘子组。构造层序TS2包含须家河组二段—三段,此期龙门山地区开始形成以逆冲推覆作用为主的造山带雏形,为川西前陆盆地形成期,沉积环境为海陆过渡相。构造层序TS3为川西前陆盆地发展期,发育的地层为须家河组四段—五段,受安县运动的影响,龙门山逆冲褶皱成山,研究区为陆相沉积环境。构造运动是控制晚三叠世川西前陆盆地形成、演化的主要因素。

Tectonic and sequence based lithofacies paleogeographic features of Late Triassic in western Sichuan Foreland Basin

The Late Triassic in the Western Sichuan Foreland Basin is a key to understand the evolutionary history of this basin.Using bore hole,outcrop,and seismostratigraphic data,the authors studied the tectonic sequence of the Upper Triassic in the Western Sichuan Foreland Basin.The Upper Triassic was divided into three tectonic sequences.Taking the tectono-sequence system tract as the mapping unit,it also systematically maped the lithofacies paleogeographic chart and discussed the evolutionary features.The results indicated that Tectonic Sequence 1(TS1) includes Ma'antang Formation and Xiaotangzi Formation,and it evolve from episode Ⅰ of Indo-Sinian Movement.There were developed neritic and marine-continental transition environment in the Western Sichuan Foreland Basin.TS2 includes the Second and Third members of the Xujiahe Formation.The Western Sichuan Foreland Basin started forming and developed marine-continental transition environment in TS2.TS3 includes the Fourth and Fifth members of the Xujiahe Formation.Because of influence by the Anxian Movement,the Longmenshan Thrust Belt was uplifted and formed mountains,which changed the Western Sichuan Foreland Basin into a terrestrial sedimentary environment.The most important factor controlling the basin formation and evolution of the Late Triassic in the Western Sichuan Foreland Basin is tectonic activity.