Organic matter enrichment in the first member of the Xiagou formation of the lower Cretaceous in the Jiuquan Basin, China

The sources and enrichment of organic matter in a sediment core in the first member of the Xiagou Formation(K_1g^1) from the Chang 2-2 borehole of the Jiuquan Basin,NW China,have been examined using Rock-Eval,maceral,carbon isotopes and biomarker data.This data indicates that highly variable organic matter sources and preservation conditions in response to climate change.TOC content,HI,and δ^(13)C value were strongly correlated with the abundance of gammacerane,woody organic matter content,steranes/hopanes ratio,and C_(29) sterane content.This correlation demonstrates the importance that the control of the salinity of the depositional environment and organic matter sources can have upon the enrichment,type,and carbon isotopic composition of organic matter.In the Jiuquan Basin's relatively high temperature and arid climate,high salinity lakes with high primary productivity of algae,planktons,and bacteria,and good organic matter preservation conditions(anoxic bottom water) resulted in the enrichment of isotopically-light algae-bacterial organic matter.In the Jiuquan Basin's regions with a relatively low temperature and wet climate,fresh lakes with low primary productivity of algae,planktons,and bacteria received significant terrigenous high plants input,resulting in the deposition of a low abundance of isotopically heavier terrestrial organic matter.