ELEMENT GEOCHEMISTRY OF THE CARBONATE SOURCE ROCK OF THE LOWER PERMIAN CHIHSIA FORMATION IN CHAOHU REGION, ANHUI AND THEIR IMPLICATIONS

The Lower Permian carbonate deposits of the Chihsia Formation located in Chaohu, Lower Yangtze are studied in this paper, with emphasis on the relationship between paleoproductivity, redox conditions and the formation of source rock, upon the basis of element geochemistry. The results demonstrate that Ba and TN have evident relations with biological deposition and can be used as a geochemical proxy for paleoproductivity. V/(V+Ni)ratio, as a geochemical proxy to reconstruct the paleoredox, indicates that the Chihsia Formation was formed in an oxygen-deficient environment. The above mentioned proxies suggest that paleoproductivity and paleoredox have close relation with sea level fluctuation. The effective matching of algae productivity and preservation condition made the region favorable for source rock formation while the Chihsia Formation was deposited. High quality source rocks mainly occur in the lower part of the Middle Limestone Member of the Formation.