Carbonate ramp deposition: Middle to upper carboniferous microfacies of Eastern Anhui and Southern Jiangsu, China

Abstract

The Huanglong limestone and the Chuanshan limestone (Middle to Upper Carboniferous) from three sections in Eastern Anhui, China, is described with regard to the microfacies types and the biota (especially the calcereous algae). 21 microfacies types have been distinguished (including 2 of the overlying Qixia limestone). The algal flora is characterized by beresellid and donezellid algae, common red algae and rare phylloid algae; the algal flora indicates the Huanglong limestone is Middle Carboniferous when compared with the Eurasian stratigraphy. Microfacies types as well as diagenetic features (vadose crystal silt, meniscus cement) point to a morphological differentiation of the depositional area into shallow marine environments bathymetrically slightly different and which in parts were affected to some extent by minor sea level fluctuations. The sedimentation pattern of the Huanglong Formation and the Chuanshan Formation can be described with the “carbonate ramp model”, i.e., sedimentation on a sloping topographic surface which is subject to open-marine and open-lagoonal conditions. A “homoclinal ramp” position can be assumed for the transgressive Huanglong carbonates as well as for the regressive Chuanshan carbonates.