EVOLUTIONARY PATTERN OF MISSISSIPPIAN REEFS AFTER THE LATE DEVONIAN MASS EXTINCTIONS: EVIDENCE FROM THE SHELVES AROUND SOUTH CHINA AND NORTH CHINA BLOCKS

Stromatoporoid-coral reef ecosystems, which flourished in the middle Palaeozoic, collapsed and disappeared during the late Devonian Frasnian-Famennian (F-F) and Hangenberg mass extinction events respectively. Microbial bioconstructions thrived after the F-F extinction, then gradually decreased and reached a minimum value at the end of Devonian. On the shelves around the South China and North China blocks (eastern Palaeotethys), the Mississippian reefs underwent the evolutionary episodes of recovery, proliferation and decrease. A recovery stage of microbial bioconstructions can be identified in the Tournaisian. Early Tournaisian stromatolites occurred in the eastern Gansu Province (near to North China Block), corresponding to the global microbial carbonate proliferation after the Hangenberg event. During the late Tournaisian, abundant carbonate mud mounds were exposed in the Guangxi Province (South China Block), which are similar in composition and sedimentary structure to the coeval Waulsortian carbonate mud mounds found on other palaeocontinents. Skeletal bioconstructions did not appear until the middle Visean, characterized by coral biostrome developed in the Guizhou Province, South China. Reef abundance and diversity obviously increased to a peak value during the late Visean, when coral reefs/biostromes, coral-microbial-bryozoan reefs, microbial-bryozoan-coral reefs and microbial reefs were present in the Guangxi and Guizhou provinces. Similar reefs were also recorded in Europe, North Africa, Australia, and Japan during this time. To date, no reefs have been documented in the Serpukhovian strata. The composition and evolutionary trend of the Mississippian reefs from the shelves around the South China and North China blocks resemble to other palaeocontinents. Relative sea-level changes accompanied with carbonate and non-carbonate facies variations triggered by the waxing and waning of Gondwana glaciation, played an important role on the Mississippian reef evolution.