四川木里海相侏罗纪地层的发现及地质意义

Discovery of marine Jurassic strata at Muli,Sichuan,and its geological implications

在川滇金沙江-哀牢山结合带以东,从未发现过海相侏罗纪地层。笔者最近在其以东数百公里的四川省木里县瓦厂地区的甘孜-理塘结合带以东发现广泛分布的含层孔虫Claodocoropsismirabilis,珊瑚Thecosmiliacf.WeberiRegny,Pratethmoscf.discus,水螅Spongiomorphacf.robusta等生物群的海相侏罗纪地层。此套地层下部为陆源碎屑岩,上部为富产层孔虫、珊瑚、水螅的正常广海台地相碳酸盐岩,底部以底砾岩与下伏晚三叠世曲嘎寺组平行不整合接触。其岩性、生物组合均可与西藏昌都地块侏罗纪地层对比。本区侏罗纪沉积盆地是在晚三叠世古特提斯洋闭合的基础上,随新特提斯洋开合而发展演化的,消亡于古近纪初期。

Until recently marine Jurassic strata have never been discovered to the east of the Jinsha River-Ailao Mountain junction belt in the Sichuan-Yunnan border region.Recently the au thors have found widespread marine Jurassic strata to the east of the Garzê-Litang junction belt at Wachang,Muli,Sichuan,which contain such biological groups as the stromatoporoid Claodocoropsis mirabilis,the corals Thecosmilia cf.Weberi Regny and Prate-thmos cf.discus,and the hydrazoan Spongiomorpha cf.robusta.This sequence of strata consists of terrestrial clastic rocks in the lower part and normal abyssal platform car-bonate rocks yielding abundant stromatoporoids,corals,and hydrazoans in the upper part.At the base the basal conglomerate of the sequence disconformably overlies the Late Triassic Qugasi Formation.The litholo-gy and biological assemblage of this area can be correlated with those of the Jurassic strata of the Qamdo massif,Tibet.The Jurassic sedimentary basin in the area developed and evolved on the basis of the closing of the Late Triassic Paleo-Tethys Ocean and with the opening and closing of the Neo-Tethys Ocean.