Late Tremadocian (Early Ordovician) reefs on the Yangtze Platform, South China, and their geobiological implications: a synthesis

Abstract This study provides an overview and discussion of controls on the distribution organic reefs during Early Ordovican Period, in Yangtze Platform, a region epicontinental sedimentary rocks South China. The Platform was located low latitudes Ordovician recorded rich diverse through that time. During late Tremadocian Epoch, dolomitic stratiform stromatolites were common supratidal to intertidal zones western while columnar formed deeper waters eastern Platform. Skeletal-dominated occurred upper subtidal settings central A transition from microbial-dominated metazoan-dominated with shallowing-upward cycles evident, indicating composition main reef-builders driven mainly by water depth. Increasing metazoan competition Great Biodiversification Event reduced abundance microbial reefs. Sufficient nutrient supply is interpreted have promoted development skeletal-dominated locally shallow especially represented expansion abundant solitary fossils lithistid sponges Calathium . High salinity environmental facilitated bloom near-shore locations. Low oxygen content deep may led absence skeletal these habitats, so mass occurrences shallower-water platform. No keratose sponge-bearing stromatolite can be confirmed across platform this interval.