Middle Visean (Mississippian) coral biostrome in central Guizhou, southwestern China and its palaeoclimatological implications

Abstract

A middle Viséan (Mississippian) coral biostrome is reported for the first time from the Shangsi Formation in Yashui area, central Guizhou Province, southwestern China (palaeogeographically located in eastern Palaeotethys). The biostrome, which is about 500 m across and 2.5–3.9 m thick, is laterally variable and composed of rugose and tabulate corals with low taxonomic diversity comprising 4 rugose and 1 tabulate coral species belonging to 5 genera. Three growth stages of the biostrome are distinguished, based on different compositions of coral taxa. Average coral contents of the biostrome increase from 38.7% to 72.0% upward and themain builders are Siphonodendron pentalaxoidea, Syringopora sp. and Kueichouphyllumsinense. Associated fossils include abundant brachiopods, crinoids and common foraminifers togetherwith rare calcareous algae, bryozoans, gastropods and ostracods. Relative sea-level changes are interpreted to have controlled growth and demise of the biostrome, which grew continuously during sea-level rise and decreasing water energy, as evident from the gradually increasing of micrite content and in situ coral colonies. However, the biostrome declined and died as the sea level fell and hydrodynamic energy strengthened, indicated by an increase of bioclasts and sparry calcite cement (indicating lack of micritic matrix due to higher energy) overlying the biostrome. This coral biostrome has similar biotic composition to middle to late Viséan coral biostromes in Europe and North Africa (western Palaeotethys). The approximately coeval occurrence of coral biostromes in both eastern and western Palaeotethys suggests that a relatively global warm episode existed during the Viséan Stage.