中国科学院南京地质古生物研究所机构知识库

Although sphinctozoans, multi-chambered hypercalcified sponges, can be traced from the Cambrian, their reef-building capacity in the Early Paleozoic appears limited. The oldest sphinctozoan-coral-microbial reef is documented here, from the Upper Sanqushan Formation (Late Katian) of southeast China. This is also the first report of Ordovician sphinctozoans from South China. The sponges occur in a >120-m-thick reef that is mainly constructed by calcimicrobes (Kordephyton, Renalcis, and Epiphyton) with a low abundance of in situ metazoans, predominantly sphinctozoan sponges (Corymbospongia) and rugose corals (mostly Palaeophyllum and Streptelasma). Tetradium is the only tabulate coral preserved in growth position. Crinoids and brachiopods are common reef dwellers. Dasycladacean algae are rare and probably transported and stromatactis is abundant. Bio- and litho-facies in this area as well as the characteristics of the microbialite suggest that the reef developed in a deeper subtidal setting that was unfavorable for most metazoan reef builders. In contrast to the high-energy stromatolite-sphinctozoan reefs from the Late Silurian, this case represents a low-energy community, indicating that the first reef-building sphinctozoans might have originated in a relatively deep-water environment on seamounts of a back-arc basin during the Late Ordovician.