Control of climate events caused by the volcano on organic matter enrichment in the lacustrine source rocks of the Ordos Basin, central China

Abstract

We systematically analyze the geochemical characteristics of source rocks of the Yan Chang Formation in the Ordos Basin to reveal the influence mechanisms of the volcano on lacustrine organic matter enrichment. Organic matter enrichment is not synchronous with the volcanic eruption in time, but it has a “hysteresis” effect. The evidence of volcanic activity mainly includes two aspects: one is a large amount of volcanic ash in black shale, and the other is a negative shift of organic carbon isotopes of source rocks and finding that black shale was affected by climate events caused by the volcano. The climate event caused by the volcano has three effects on organic matter enrichment in black shale: (1) it brought nutrients for the growth of organisms and released a large amount of greenhouse gases, such as CO2, to accelerate photosynthesis and promote the growth of organisms; (2) a large amount of toxic gases, such as SO2 and H2S, were released and O2 was consumed and diluted in the air, forming a severe anoxic environment and accelerating the preservation of organic matter; and (3) it caused extremely hot weather, resulting in long-time surface runoff and other climate events, increasing input of terrestrial organic matter, and forming light components of hydrocarbons.