Discussion on classification and naming scheme of fine-grained sedimentary rocks

Lacustrine sedimentary formations potentially contain hydrocarbons. The lacustrine sedimentary rocks of the Ziliujung and Xintiangou Formations have been investigated for their hydrocarbon potential using low-pressure nitrogen adsorption (LP-N2A), low-field nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), total organic carbon (TOC), rock-eval pyrolysis (Rock-Eval), gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), X-ray fluorescence spectrometry (XRF), and inductively coupled plasma mass spectrometry (ICP-MS). The results show that the normalized difference of the pore parameters between the two formations is less than 10%, and the pores are mainly slit-like mesopores with high porosity. Macropores and micropores are often developed in the quartz skeleton, while mesopores often occur among organic matter, clay minerals, carbonate minerals, and pyrite particles. The organic matter abundance of the Ziliujing Formation is relatively high. Additionally, the organic matter types of the two formations are mainly type II and type III, and the sources of the organic matter are plankton and bacteria which have reached the mature gas production stage. The palaeoenvironmental differences between the depositional periods of the two formations lie within 10% of each other. The warm and humid climate promotes the development of quartz minerals to further enhance the proportion of both micropores and macropores, and the clay minerals, carbonate minerals, and pyrite carried in the terrigenous detritus are closely associated with the total organic carbon (TOC), which promotes the development of mesopores to enhance the porosity. The reservoir, organic matter, and palaeoenvironmental characteristics of fine-grained sedimentary rocks in the two formations are similar, and both of them have good potential for development. The above results provide a basic geological theoretical basis for unconventional oil and gas exploration in the northeastern margin of the Sichuan Basin.

Section: Comparison Of Organic Matter Characteristics Between the Zil...mentioning

confidence: 99%

“…Fine-grained sedimentary rock is composed of silt-grade and clay-grade clastic particles with sizes less than 62.5 µm and a proportion of more than 50% [1,2]. These rocks are rich in oil and gas resources and are regarded as important hydrocarbon source rocks with wide exploration perspectives [3,4].…”

Section: Introductionmentioning

confidence: 99%

Comprehensive Comparison of Lacustrine Fine-Grained Sedimentary Rock Reservoirs, Organic Matter, and Palaeoenvironment: A Case Study of the Jurassic Ziliujing Formation and Xintiangou Formation in the Sichuan Basin

Li,

Wu,

et al. 2024

“…Based on previous research results and petrological observations, the lithologies of the study interval include siltstone, mudstone, and carbonate rocks, representing fine-grained sedimentation [48]. Considering the background of the study area and the results of XRD, this study proposes a ternary lithology classification system and divides the rocks into three categories: carbonate minerals, felsic minerals, and clay minerals.…”

Section: Rock Type Classificationmentioning

confidence: 99%

Lithofacies Characteristics of Continental Lacustrine Fine-Grained Sedimentary Rocks and Their Coupling Relationship with Sedimentary Environments: Insights from the Shahejie Formation, Dongying Sag

Guo,

Shi,

et al. 2024

Lacustrine fine-grained sedimentary rocks in the Dongying Sag of the Bohai Bay Basin in China exhibit significant potential for hydrocarbon exploration. This study investigates the lithofacies types and sedimentary evolution of the Paleogene Shahejie Formation’s lower third member (Es3l) and upper fourth member (Es4u), integrating petrological and geochemical analyses to explore the relationship between lithofacies characteristics and sedimentary environments. The results show that the fine-grained sedimentary rocks in the study area can be classified into 18 lithofacies, with seven principal ones, including organic-rich laminated carbonate fine-grained mixed sedimentary rock lithofacies and organic-rich laminated limestone lithofacies. In conjunction with analyses of vertical changes in geochemical proxies such as paleoclimate (e.g., CIA, Na/Al), paleoproductivity (e.g., Ba), paleosalinity (e.g., Sr/Ba), paleo-redox conditions (e.g., V/Sc, V/V + Ni), and terrigenous detrital influx (e.g., Al, Ti), five stages are delineated from bottom to top. These stages demonstrate a general transition from an arid to humid paleoclimate, a steady increase in paleoproductivity, a gradual decrease in paleosalinity, an overall reducing water body environment, and an increasing trend of terrestrial detrital input. This study demonstrates that the abundance of organic matter is primarily influenced by paleoproductivity and paleo-redox conditions. The variations in rock components are predominantly influenced by paleoclimate, and sedimentary structures are affected by the depth of the lake basin. Special depositional events, such as storm events in Stage II, have significantly impacted the abundance of organic matter, rock components, and sedimentary structures by disturbing the water column and disrupting the reducing conditions at the lake bottom. The present study offers crucial insights into the genesis mechanisms of continental lacustrine fine-grained sedimentary rocks, facilitates the prediction of lithofacies distribution, and advances the exploration of China’s shale oil resources in lacustrine environments.

“…Controlled by the Cenozoic Himalayan movement, the basin began to undergo rifting in the early Eocene and entered the post-rifting stage in the late Oligocene. The tectonics gradually stabilized, forming the present-day Bohai Bay Basin [12,13]. The Zhanhua Sag is located in the northeastern part of the Jiyang Depression in the Bohai Bay Basin.…”

Section: Geological Settingmentioning

confidence: 99%

“…Classification schemes for fine-grained sedimentary rocks often use clay, felsic, and carbonate minerals as the three end members. These schemes divide fine-grained sedimentary rocks into four categories, namely claystone, siltstone, carbonate rock, and mixed fine-grained sedimentary rock, with the boundary set at a content of 50% for each end member [2,12,22,23]. However, the above scheme makes it difficult to accurately reflect the rocks' sources.…”

Section: Sediment Compositionsmentioning

confidence: 99%

Study on the Differential Distribution Patterns of Fine-Grained Sedimentary Rocks in the Lower Third Member of the Shahejie Formation in Zhanhua Sag, Bohai Bay Basin

Xia,

Zhang,

Zhong

2024

Due to the diverse types of sedimentary source supply systems, the research on the distribution patterns of fine-grained sedimentary rocks in rifted lake basins is relatively underdeveloped. The authors of this article selected the lower third member of the Shahejie Formation (Es3L) in Zhanhua Sag as a research object. Using rock core, thin section, and other data, we analyzed rock types and genesis mechanisms, identified the spatiotemporal distribution patterns of facies within the sag, and established a fine-grained depositional model for the rifted lake basin. Five lithofacies were identified, revealing the differential distribution patterns of fine-grained sedimentary rocks in the region. The northern steep slope zone and the deep depression zone are characterized by the deposition of gravity flow-formed terrestrial layered-pebbly mudstone and gravity flow-formed mixed-source pebbly mudstone, respectively. In the central lake basin zone, mixed-source laminated mudstone with vertical rhythmic interlayers has developed. In the southern gentle slope zone, biologically cemented endogenic irregularly bedded algal limestone and chemically precipitated endogenic laminated limestone have developed. The characteristics of strong northern and weak southern terrestrial inputs in the study area control the differential distribution of lithofacies, and based on this, a fine-grained rock depositional model for the rifted lake basin was established.