LOWER CARBONIFEROUS STRATIGRAPHY OF SOUTHEASTERN CHINA; SEQUENCES AS PROXIES FOR GONDWANA GLACIATIONS

Lower Carboniferous carbonate strata are well-developed and exposed in Guangxi Province, with various sedimentary types and abundant fossils. Depositional facies include platform, platform margin, intraplatform basin, and slope. This research is focused on Tournaisian successions in the Guilin area, especially at the Devonian/Carboniferous boundary. The goal is to determine timings for the Gondwana glaciations based on sea level changes, lithologic changes, and unconformities.

Upper Famennian to Lower Visean units are exposed at Huilong. This section mainly consists of shallow-water limestones with foraminifers, corals, and brachiopods, which developed on the shelf break. The Huilong Section includes the Etoucun Formation (Upper Famennian) and Yaoyunling Formation (Lower Tournaisian). Forams and corals make particularly good index fossils, and zonations have been applied here for correlations. The Etoucun Formation comprises thick-bedded to massive shallow-water limestones. It is very rich in rugose corals, and contains sparse Cystophrentis, indicating the Cystophrentis Zone (Upper Strunian). These beds correspond to the transgressive system tract (TST) of a third-order sequence, similar to those found in Western Europe.

The base of the Yaoyunling Formation is marked by the 2.5 m thick Shangyueshan Member, which contains thin-bedded limestones overlying a 20 cm thick bed of shale. This shale corresponds to the Hangenberg event, a time of major extinctions at the end of the Devonian. Above the Hangenberg event is a highstand (HST), of latest Famennian or earliest Tournaisian age. The entire formation is composed of about 80 m of shallow-water limestones, dolomitized in the upper part. A distinctive hematitic crust marks the top of the formation. These units, together with the dominant karst topography of the area, provide an ideal location for studying episodes of subaerial exposure. The effects of eustatic sea-level change and its marine offlap are very apparent here.