Ph. D. student WEI Hengye and his teacher CHEN Daizhao provide sedimentological, mineralogical and geochemical data to constrain the processes of accumulation of organic matter in the lower Chihsia Formation in western Hubei Province, South China.

The lower part of the Chihsia Formation, reported here, was deposited in an intrashelf basin and is characterised by black laminated marlstones/shales intercalated with dark-grey limestones/dolomites in which metre-scale shallowing (or cleaning)-upward cycles are ubiquitous. Each cycle is composed of basal marlstone/shale and upper limestone. The organic matter is concentrated exclusively in the shaley bases of these cycles, and shows systematic, cyclic variations in abundance up through the succession. An integrated approach of pyrite morphology and multiple geochemical proxies was used to determine the mechanism of organic accumulation.

Fig.1. Box-and-whisker plots showing framboid-size variations in sediments at the studied section. (Image by WEI)

Fig.2. Vertical variations of TOC contents, cabonate contents, total Fe contents (FeT), FeT/Al ratios, pyrite Fe (FeP), high reactive iron (FeHR), unreactive iron contents (FeU), FeHR/FeT ratios, DOP values, pyrite sulphur contents (Sp), δ34Spy values, and ratios of pyrite framboids in sediments from the Enshi section. (Image by WEI)

Wei et al. Organic accumulation in the lower Chihsia Formation (Middle Permian) of South China: Constraints from pyrite morphology and multiple geochemical proxies. Palaeogeography, Palaeoclimatology, Palaeoecology. 2012, 353–355: 73–86 （Download Here）