Enrichment of organic carbon in marine source rocks in China under the control of deglaciation climate

Key words: 
• deglaciation /
• organic carbon /
• source rock /
• paleoclimate /
• weathering /
• upwelling /
• volcanism

Abstract: Some studies suggest that there is a causal relationship between climate and organic carbon enrichment, but the relevant reports mainly focus on high temperature, high insolation, marine transgression, and cyclical patterns. A comprehensive model establishing the coupling relationship between different climate conditions and the abundance of organic matter in basins from the perspective of the Earth system has not yet been developed. The main source rocks corresponding to large oil and gas fields in China are distributed in various geological periods. Source rocks from the Mesozoic and Cenozoic are mainly developed during periods of high-latitude greenhouse climate, while source rocks from the Paleozoic and Precambrian are mainly developed during periods of deglaciation at mid to low latitudes. The distribution of source rocks during the deglaciation spans four periods: the Neoproterozoic, the Ediacaran-Cambrian transition, the Ordovician-Silurian transition, and the Permian. The unique climate conditions during the deglaciation play a crucial role in the enrichment of organic carbon. The warming and climate fluctuations during the deglaciation, along with changes in ocean currents and volcanic activity, collectively lead to increased productivity of water and oxygen depletion, thereby promoting the accumulation of organic matter and the formation of source rocks. This relationship model between deglaciation climate and source rock reflects the control of the Earth system of oceans, land, and atmosphere on organic carbon enrichment under the influence of climate cycles. It can be used to guide the discovery of major oil and gas fields. However, the contribution of each factor to organic matter enrichment still needs to be quantitatively analyzed through the establishment of ocean-climate models and productivity models.