Paleoenvironment and Organic Characterization of the Lower Cretaceous Lacustrine Source Rocks in the Erlian Basin: The Influence of Hydrothermal and Volcanic Activity on the Source Rock Quality

Piao Wu; Hou Dujie; Lanzhu Cao; Ronghua Zheng; Xiuli Wei; Xiaoxiao Ma; Zhe Zhao; Jianwen Chen

doi:10.1021/acsomega.2c03487

Paleoenvironment and Organic Characterization of the Lower Cretaceous Lacustrine Source Rocks in the Erlian Basin: The Influence of Hydrothermal and Volcanic Activity on the Source Rock Quality

ACS Omega. 2023 Jan 3;8(2):1885-1911. doi: 10.1021/acsomega.2c03487. eCollection 2023 Jan 17.

Authors

Piao Wu^{1

2}, Hou Dujie³, Lanzhu Cao⁴, Ronghua Zheng⁴, Xiuli Wei⁴, Xiaoxiao Ma³, Zhe Zhao³, Jianwen Chen^{1

2}

Affiliations

¹ Qingdao Institute of Marine Geology, Qingdao 266237, China.
² Laboratory for Marine Mineral Resources, Laoshan Laboratory, Qingdao 266237, China.
³ School of Energy Resources, China University of Geosciences, Beijing 100083, China.
⁴ Research Institute of Petroleum Exploration and Development, PetroChina Huabei Oilfield Company, Renqiu 062550, China.

Abstract

Lower Cretaceous lacustrine source rocks in the Erlian Basin are highly heterogeneous. It is important to assess and explain these heterogeneities for the reconstruction of paleoenvironments and the prediction of high-quality source rock distributions. In this study, well-logging, organic, and elemental geochemical data were comprehensively analyzed for the source rocks of Member 4 of the Aershan Formation (Fm) and Member 1 of the Tengger Fm in the southern Bayindulan (BNAN), southern Wulanhua (WLHs), Anan, Aer, and southern Wuliyasitai sags of the Erlian Basin. The variability in sedimentary environments, sources of organic matter of the source rocks in different sags, and the influence of hydrothermal and volcanic activity on the source rock quality in the Erlian Basin were assessed. The results reveal that the source rocks can be divided into four types of organic facies (A, B, BC, and C). Organic facies A-B present hydrogen indices (HIs) higher than 400 mg/g and are mainly composed of mudstone and thick (average thickness >50 m) dolomitic mudstone, with biomarkers characterized by a Pr/Ph ratio lower than 1.0, a gammacerane/C₃₀ hopane (Gam/C₃₀H) ratio higher than 0.2, and a C₁₉ tricyclic terpane/C₂₃ tricyclic terpane (C₁₉/C₂₃TT) ratio lower than 0.6. Organic facies BC-C are composed of mudstone with an HI < 400 mg/g, with biomarkers characterized by a Pr/Ph ratio higher than 0.8, a Gam/C₃₀H ratio lower than 0.2, a C₁₉/C₂₃TT ratio higher than 0.6, and a sterane/hopane ratio lower than 0.4. Dolomitic mudstone belonging to organic facies A-B is mainly developed in the BNAN, WLHs, and Anan sag and is characterized by a fault-controlled distribution in the sag, a right-declined rare earth element pattern, and an enrichment in the elements of Ba, Cu, Zn, Fe, and Ni. The genesis of high HI dolomitic mudstone is associated with hydrothermal and volcanic activity because the hydrothermal fluid or hydrolysis of volcanic ash result in increasing input of reducing gas and soluble nutrient ions, thus promoting the formation of anoxic and saline Cretaceous lakes with high primary productivity.