Editorial: Fine-Grained Sedimentary Rocks: Sedimentary Processes, Diagenesis, Geochemistry and Their Relationship with Critical Geological Events

Yifan Li^1*Zhiyang Li²Jianguo Zhang¹Zhen Qiu³George Kontakiotis⁴Junwen Peng⁵Youwei Wang⁶

• ¹School of Energy Resources, China University of Geosciences, Beijing, China
• ²Texas A&M International University, Laredo, United States
• ³Research Institute of Petroleum Exploration and Development (RIPED), Beijing, China
• ⁴Department of Historical Geology and Paleontology, Faculty of Geology and Geoenvironment, School of Earth Sciences, National and Kapodistrian University of Athens, Athens, Greece
• ⁵University of Oklahoma, Norman, United States
• ⁶University of Virginia, Charlottesville, United States

Fine-grained sedimentary rocks are increasingly studied for their complex depositional processes, high organic content, reservoir potential, metal enrichment, and geochemical records of paleoenvironments (Ettensohn et al., 1987;Wignall, 1994;Stow et al., 2001;Aplin et al., 2011;Shahzad et al., 2024). Once seen as homogeneous suspension-settled deposits, flume experiments and sedimentological studies have revealed that they can form under high-energy conditions, influenced by floods, storms, and bottom currents (Schieber et al., 2007;Bohacs et al., 2014;Macquaker et al., 2014;Li et al., 2022;Mehmood et al., 2023). Additionally, finegrained sedimentary rocks may receive sediments of various origins and can be characterized by a complex composition comprising clay minerals, quartz, carbonates, feldspars, sulfides, biogenic debris, and organic matter (Taylor and Macquaker, 2000;Macquaker and Adams, 2003;Milliken, 2014;Camp et al., 2015). Diagenesis in these rocks is governed by mass-balance, fluid transport, and organic-inorganic interactions (Morad et al., 2000;Cobbold et al., 2013;Liang et al., 2018). Geochemical proxies link their formation to major tectonic and environmental events, including rifting, glaciation, volcanism, anoxia, mass extinctions, and hydrothermal activity (Algeo et al., 2012;Trabucho-Alexandre et al., 2012;Li et al., 2015;Qiu et al., 2022;Shen et al., 2025;Derkowski et al., 2013). These insights are vital to sedimentary and diagenetic theory-especially unconventional petroleum sedimentology (Qiu et al., 2020;Zou et al., 2022)-and to understanding Earth's sphere-system evolution. This research topic comprises ten papers presenting advances in the study of fine-grained sedimentary rocks from three perspectives: depositional processes, diagenetic mechanisms, and geochemical characteristics. Rocks focused in this volume encompass both marine and continental mudstones and shales, spanning strata from the Cambrian to the Eocene, and therefore are broadly representative. Through these case studies, we aim to further enrich the theoretical framework surrounding fine-grained sedimentary rocks.Wen et al. investigated the Beipiao Formation in western Liaoning and identified lithofacies formed under the influence of volcanic activities and sediment-gravity flows. Three depositional environments-shallow lake, semi-deep/deep lacustrine, and fan delta-were defined, with basin evolution transitioning from fan delta to deep lake and back, interbedded with volcanic deposits. Volcanism enhanced nutrient supply and organic matter preservation, while gravity flows transported plant fragments to deep lakes, leading to the enrichment of Type III kerogen.Feng and Zhang analyzed the ShangGanchaigou Formation in the western Qaidam Basin and identified seven architectural elements (distributary channels, bars, algal mounds, etc.) and three facies belts (proximal delta front, middle isolated lobes, distal algal-marl complexes).Short-term base-level cycles were documented as the dominant factor producing frequent facies variations. Reservoir connectivity was documented to decrease lakeward, revealing challenges in predicting heterogeneous reservoirs.Zhang et al. examined coevolution of minerals in lacustrine mudstones from Bohai Bay Basin.Fibrous calcite/ankerite precipitated in primary laminar fractures during peak organic-acid release, with elements supplied by early carbonate dissolution and smectite-illite transformation. Clay alteration led to the formation of microcrystalline quartz, feldspar dissolution, and the increase in pH allowed authigenic albite to form. Authigenic carbonates and colloidal pyrite regulated pore-fluid chemistry, while variations in organic matter governed pore pressure, acid levels, and diagenetic pathways. Basin by linking gamma/density logs to astronomical cycles and developed a high-resolution, isochronous framework. They showed that tectonics and orbital climate paced rhythmic sandmud progradation and proposed a 'synchronous heterotopy' lake-delta model with overfilling strata lagging eccentricity peaks, whereas balanced-filling strata coinciding with them.