四川盆地西北部晚三叠世卡尼期的海绵斑块礁

四川盆地西北部晚三叠世卡尼期的海绵斑块礁是在1975年由张长俊、朱永铭及本文作者发现的。笔者对其进行了野外及室内研究。

LATE TRIASSIC(CARNIAN)SPONGE PATCHREEFS IN NORTHWESTERN SICHUAN BASIN

Since 1975,22 sponge patch-reefs have been found from the outcrops of the strata of Hanwang Formation(Carnic Stage,Upper Triassic)in northwestern Sichuan Basin.The patch-reefs,shaped like elliptical mounds are 40-60 meters high.The foundation for reef growth consists of an algal-oolitic bank at the bottom,overlain by a bioclastic bank.The core of each reef is composed of lime bafflestones,built by sponges with ramose and massive forms.The sponges constitute about 30-60% of the reef core rocks,in which we can still see the binding blue-algal traces.The tali around the core makes up the reef flanks.The inter-reef strata are made up of bioclastic limestones,interbedded with calcareous mudstones.The overlying sediments on the reefs are still those of mudstones,which progressively transformes into siltstones upwards,and represent a desalinated and reduced marine environment.The patch-reef group existed in a narrow Carnian gulf in northwestern Sichuan,and the seawater,passing through the ’Longmenshan’ Chain islets,came from its northwestern Songpan-Ganzi Tectogene.