Origin and deposition of organic matter in continental chert of the Middle Permian Gufeng Formation in the northeastern Yangtze platform

摘要

The Middle Permian Gufeng Formation in the northeastern Yangtze platform, China, contains radiolarian chert that is characterized by black color, high content of Fe, Mo, Ni, Cu, and Zn. Based on the inorganic geochemical features, previous work concluded that the cherts were deposited under sulfate-reducing conditions. In this study, organic carbon (C_(org)), N and S contents of the cherts and H/C and O/C ratios of kerogen were examined to explore the origin of the organic matter. The concentration of C_(org) in the black chert is extremely high relative to other cherts in accretionary complexes and continental platforms. The average C/N ratio of organic matter is 35, indicating that the organic matter originates from land plants. The kerogen from the chert is classed as type Ⅳ based on the H/C and O/C ratios, suggesting that oxidized or reworked organic matter was supplied to the Gufeng basin. Therefore, the organic matter is considered to originate from terrestrial plants or reworked material from land. Due to the depositional setting on a continental platform, nutrient supplied with organic matter from land probably played an important role in abundant biogenic productivity and sedimentation of the radiolarian chert on the continental platform.