Factors controlling organic matter enrichment in the Lower Cambrian Niutitang Formation Shale on the eastern shelf margin of the Yangtze Block, China

Abstract

The degree of organic matter (OM) enrichment in shale determines its oil and gas potential. To understand the factors controlling this OM enrichment, we have used petrological and geochemical analyses to study the Lower Cambrian Niutitang Formation Shale in the eastern shelf margin of the Yangtze Block. Our results reveal that the total organic carbon (TOC) content of the Niutitang Formation Shale varies significantly throughout the vertical section. The lower part of the Niutitang Formation has a high TOC content, likely due to its formation in a dysoxic/anoxic environment with intense upwelling that favored OM enrichment. The middle part of the Niutitang Formation has the highest TOC content, which can be attributed to its formation in an environment with more hydrothermal activity, moderately upwelling, high paleosalinity, dysoxic/anoxic conditions, and moderately restricted water contents. Finally, the upper part of the Niutitang Formation records the lowest TOC contents because it likely formed in an oxic to dysoxic environment with weakly restricted hydrographic conditions that did not favor the preservation of OM. Therefore, these data demonstrate that the factors controlling OM enrichment in the Niutitang Formation Shale on the shelf margin include intense upwelling, greater amounts of hydrothermal activity, high paleosalinity, dysoxic/anoxic conditions, and moderately restricted water contents.