FORAMINIFERAL ZONES AND TRANSGRESSIVE-REGRESSIVE CYCLES OF THE LATE MISSISSIPPIAN (SERPUKHOVIAN) HEZHOU FORMATION AT FENGHUANGSHAN, SOUTH CHINA

The Hezhou Formation [=Hochow Limestone], deposited between the Gaolishan Formation and Huanglong Formation, is located on the Lower Yangtze Platform of South China and is composed of shallow subtidal to intertidal carbonates with frequently and cyclically intervening subaerial exposure surfaces of siliciclastic/clay rocks. There are different opinions about its age. As the parastratotype of the Hezhou Formation, the Fenghuangshan section has more complete exposure than the stratotype, making it an ideal locality to study the foraminiferal succession and transgressive-regressive depositional cycles.

In the Chinese Carboniferous foraminiferal scheme, the Eostaffella hohsienica foraminiferal zone, which was first identified within the Hezhou Formation, has unclear chronostratigraphic limits. Based on specimens from the Fenghuangshan section, this long-ranging zone can be replaced by three zones of cosmopolitan species. In ascending order, they are the Asteroarchaediscus Zone (latest Visean?–early Serpukhovian), Eostaffellina paraprotvae Zone (late Serpukhovian), and Monotaxinoides transitorius Zone (latest Serpukhovian).

From detailed field measurements and thin section studies, twelve major microfacies and five transgressive-regressive cycles are recognized in the Hezhou Formation. According to the Pennsylvanian foraminifers found in sediments infilling the karsted limestone that forms the uppermost part of the Hezhou Formation, the debate on the cause of this karst surface can be resolved. It was a result of long-term karstification from the early Bashkirian to early Moscovian.