Paleoenvironment and organic matter enrichment of the Carboniferous volcanic-related source rocks in the Malang Sag, Santanghu Basin, NW China

Tian-Jun Li,Xin-Ning Li,Jun-Tian Liu,Xuan Chen,Zhi-Long Huang

doi:10.1007/s12182-020-00514-1

Abstract

Volcanic activity was quite frequent during the deposition of the Late Carboniferous Ha’erjiawu Formation in the Santanghu Basin. The petrology and organic and inorganic geochemical indicators were used to investigate hydrocarbon potential, paleoenvironmental conditions and organic matter enrichment of the mudstones. The results show that the oil generation capacity of the Ha’erjiawu Formation mudstones, which has abundant oil-prone organic matter (Type II kerogen with hydrogen index values mainly ranging from 250 to 550 mg HC/g TOC) in mature stage (Tmax values mainly ranging from 435 to 450 °C), is considerable. The Ha’erjiawu Formation was deposited in a dysoxic, freshwater-mildly brackish, and warm-humid environment. During its deposition, the Ha’erjiawu Formation received hydrothermal inputs. The volcanic hydrothermal activities played an important role in the organic matter enrichment. In addition, the total organic carbon (TOC) is significantly positively correlated with the felsic mineral content, but it is negatively correlated with the carbonate mineral content and C27/C29 ratios, indicating that terrigenous organic matter input also contributed to the primary productivity in the surface water. Therefore, the formation of the high-quality source rocks in the Ha’erjiawu Formation was jointly affected by the hydrothermal activity and the terrigenous organic matter input.

Highlights

IntroductionThe preservation conditions that favor the formation of high-quality source rocks mainly include an anoxic water column caused by geographical isolation, variations in the paleowater depth, or biological activity (Demaison and Moore 1980; Katz 1990)
High-quality source rocks are generally characterized by high organic matter abundance and stable distribution, and they are the material basis for the formation of largeand medium-sized oilfields (Magoon and Dow 1991; Qin 2015; Xiao et al 2015; Li et al 2017; Ghassal et al 2018; Edited by Jie HaoState Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijng 102249, ChinaCollege of Geosciences, China University of Petroleum (Beijing), Beijing 102249, ChinaResearch Institute of Exploration and Development, PetroChina Tuha Oilfield Company, Hami, Xinjiang 839009, ChinaZhang et al 2018)
The formation of organic-rich rocks associated with hydrothermal activity has been reported in non-marine basins in China, especially the Lucaogou Formation in Santanghu Basin

Summary

Introduction

The preservation conditions that favor the formation of high-quality source rocks mainly include an anoxic water column caused by geographical isolation, variations in the paleowater depth, or biological activity (Demaison and Moore 1980; Katz 1990). The paleoproductivity model mainly includes that the enrichment of organic matter due to high primary productivity in the surface water. As long as the paleoproductivity is high, even if the sedimentary water column is oxic, high-quality source rocks will develop under these conditions (Meyers and Arnaboldi 2005). The formation of organic-rich rocks associated with hydrothermal activity has been reported in non-marine basins in China, especially the Lucaogou Formation in Santanghu Basin

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Conclusion