Mechanism of Organic Matter Enrichment of Lower Cretaceous Yixian Formation in the Xiushui Basin,Northern Liaoning Province:A case study of well LFD1
[Objective]The Xiushui Basin,located in northern Liaoning,is a small faulted basin formed in the Me-sozoic,and developed the Lower Cretaceous Yixian Formation with large sedimentary thickness.It is of great impor-tance to understand the mechanism of organic matter enrichment.[Methods]In this study,sediment samples were collected from well LFD1.Total organic carbon(TOC)content,stable carbon isotopic composition(δ13Corg)and the distribution of molecular markers(aliphatic hydrocarbons,steranes and hopanes)from members 2 and 3 of the Yixi-an Formation were analyzed.[Results and Discussions]The results show that the TOC ranged from 0.01%to 4.78%,and the organic matter was mature.The vertical variations of the bulk organic parameters(TOC and δ13Corg)and biomarker indices indicated that the profile could be divided into four stages.Stage I:The initial content was en-hanced by volcanic activity that enabled the depostions of great amount of organic matter and low δ13Corg values.Stage II1:High δ13Corg values suggest increased input from land plants.The biomarker indices show a relatively anoxic envi-ronment at this stage.Stage II2:The sedimentary environment is anoxic-weakly oxic.Algae and aquatic plants flour-ished in the lake,and the abundant organic matter facilitated the deposition of organic-rich source sediments.Stage III:A more rapid sedimentation rate diluted the abundance of organic matter.However,water column was stratified and lake evolved into anoxic environment at the beginning and end of this stage,which favored high organic matter content deposition.
Yixian Formationbiomarkerssedimentary environmentsource of organic matter
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