Understanding Hydrothermal Activity and Organic Matter Enrichment with the Geochemical Characteristics of Black Shales in Lower Cambrian, Northwestern Hunan, South China

Abstract

AbstractThere are many hydrothermal activities in the early Cambrian in northwestern Hunan, and Zhangjiajie and Xinhuang-Tianzhu are the concentration region which brings much influence during this time. Based on the total organic carbon, mineral composition, element analysis, and so on, the wells have no or little hydrothermal activity in HY1, XJD1, and XAD1 and may also have limited effects by the hydrothermal activity. However, the hydrothermal sediments can come to the wells during the sedimentary period of Niutitang formation. XJD1 has a clear diminishing trend on the intensity of hydrothermal activity. It also shows the high element enrichment by the hydrothermal activity. XAD1 show little influence in contrast, and HY1 is between them. The enrichment of the element is a result of the combination of effects of hydrothermal activity, anoxic/euxinic conditions, biological forces, etc. The hydrothermal activity can improve the paleoproductivity and especially enhance the reducibility in the sedimentary environment. Reducibility is one of the major factors affecting organic matter enrichment. Finally, the sedimentary model with hydrothermal activity can be established in the Ediacaran-Cambrian transition. That will help to understand the distribution laws of high-quality source rocks and provide evidences on shale gas exploration.