Input, Preservation and Dilution of Organic Matter: Influence on The Organic Matter Enrichment of The Lacustrine Mudstones in The Deep Formations of Songliao Basin, Ne China
The deep formations (including the Jurassic Huoshiling (J3h), Cretaceous Shahezi (K1sh), and Yingcheng (K1yc) formations) in the Songliao Basin of China possess numerous natural gas. Moreover, as the transition and beginning of the Cretaceous lacustrine sedimentation, the mudstones deposited in the deep formations recorded sufficient information on the tectonic activities, paleoclimate, paleoenvironment, and paleontology. During the deposition, the paleoclimate was cold and semi-humid to arid, and the paleosalinity was moderate to high salinity. The redox conditions were mainly reducing to sub-reducing, sub-reducing to oxidizing, and sub-reducing to sub-oxidizing conditions for the J3h, K1sh, and K1yc, respectively. The K1sh mudstone is evaluated as the best source rock, followed by the J3h and K1yc. The organic matter (OM) sources are mainly a mixed-source of aquatic microorganisms and terrestrial higher plants, and from the J3h to the K1yc, the contents of aquatic microorganisms decrease and those of terrestrial higher plants increase. The bioprodutivities during the J3h, K1sh, and K1yc were estimated as moderate, high, and low, respectively, and the dilution degree was evaluated as low, moderate, and high, respectively. For the OM enrichment in the J3h mudstone, the predominant controlling factor was moderate biopreoductivity and favorable reducing preservation condition, called bioproductivity and preservation model. For the OM enrichment in the K1sh mudstone, the main controlling factors were high bioproductivity, moderate terrestrial input, and favorable sub-reducing preservation condition, called bioproductivity, terrestrial input, and preservation model. For the OM enrichment in the K1yc mudstone, the main controlling factor was high OM dilution, named dilution model.
Keywords - Lacustrine Mudstone, Biomarker, Trace Element, Organic Matter Enrichment, Deep Formation, Songliao Basin.