Abstract
The Lower Cambrian black shale in the southwestern margin of the Yangtze Block not only records the early life explosion and paleoclimate fluctuation events, but also contains abundant shale gas resources. However, due to the influence of tectonic-sedimentary differentiation, the sedimentary paleoenvironment and organic matter enrichment mechanism in this area are not completely clear, which restricts the effective exploration and development of shale gas. Based on regional drilling data and analysis of major, trace, and rare earth elements from profile samples across different facies belts, this study determines variations in marine depositional conditions and organic matter (OM) enrichment mechanisms during the Early Cambrian. The results show that: (1) In the study area, the depositional setting changes from a continental margin in the west to a continental island arc toward the east. The detritus was derived mainly from the Kangdian Oldland. The paleoclimate shifted from dry and cold to warmer and more humid conditions, with moderate chemical weathering. During the deposition of the first Member of Qiongzhusi Formation(Q1), Hydrothermal activity was intense in the eastern area and decreased gradually to the west. (2) The depositional environment of the Q1 on the southwestern margin of the Yangtze Block evolved from restricted and anoxic in the west to weakly-restricted and anoxic in the east. During the subsequent deposition of the Second member of Qiongzhusi Formation (Q2), a marine regression transformed the basin. This shift resulted in predominantly oxic conditions, more open marine circulation, and a relative increase in terrigenous sediment supply. Dysoxic conditions persisted only locally within the trough valley. (3) Primary productivity was higher in Q1 than in Q2, with the deep-water trough and hydrothermal zones providing ample nutrients for OM enrichment. (4) In Q1, OM enrichment in the western provenance-influenced area was redox-controlled (preservation model), while in the eastern upwelling zone, increased nutrient input led to productivity-dominated control (productivity model). High-quality source rocks in the trough were co-controlled by high productivity and anoxic conditions: transgression brought nutrient input and formed anoxic bottom water, jointly promoting OM enrichment. In Q2, the preservation model dominated. These findings provide a scientific basis for selecting favorable targets for shale gas exploration.
Data availability
All the sampling sites are well away from protected areas like nature reserves, national parks, or any mining sites. The work was done entirely for academic research, and only small samples were taken without damaging the outcrops. The original contributions presented in this study are included in the article/supplementary material. Further inquiries can be directed to the corresponding author.
References
Wang, J. China Geological Publishing House,. Sedimentary evolution of the Neoproterozoic rift basin in South China: with a discussion on the relationship with Rodinia break-up. (ed. Wang, J.) 1-146 (2000).
Amthor, J. et al. Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian boundary in Oman. Geology 31, 431–434 (2003).
Och, L. M. et al. Redox changes in early cambrian black shales at Xiaotan section, Yunnan Province, South China. Precambrian Res. 225, 166–189 (2013).
Turner, E. C. & Bekker, A. Thick sulfate evaporite accumulations marking a mid-Neoproterozoic oxygenation event (Ten stone Formation, Northwest Territories, Canada). Geol. Soc. Am. Bull. 128, 203–222 (2016).
Wu, Y. et al. Paleo-environmental variation and its control on organic matter enrichment of black shales from shallow shelf to slope regions on the upper Yangtze platform during cambrian stage 3. Paleogeogr Paleoclimatol Paleoecol. 545, 109653 (2020).
Hammarlund, E. U. et al. Early cambrian oxygen minimum zone-like conditions at Chengjiang. Earth Planet. Sci. Lett. 475, 160–168 (2017).
Zhu, M. et al. The cambrian explosion: advances and perspectives from China. Sci. China Earth Sci. 49, 1455–1490 (2019).
Gao, P. et al. Silicification and Si cycling in a silica-rich ocean during the Ediacaran-Cambrian transition. Chem. Geol. 552, 119787 (2020).
Cai, C. et al. Interlinked marine cycles of methane, manganese, and sulfate in the Post-Marinoa Doushantuo cap dolostone. Geochim. Cosmochim. Acta. 346, 245–258 (2023).
Steiner, M. et al. Neoproterozoic to early cambrian small Shelly fossil assemblages and a revised biostratigraphic correlation of the Yangtze platform (China). Palaeogeogr Palaeoclimatol Palaeoecol. 254, 67–99 (2007).
Zoleikhaei, Y., Mulder, J. A. & Cawood, P. A. Integrated detrital rutile and Zircon provenance reveals multiple sources for cambrian sandstones in North Gondwana. Earth Sci. Rev. 213, 103462 (2021).
Jin, C. et al. Controls on organic matter accumulation on the early-Cambrian Western Yangtze Platform, South China. Mar. Pet. Geol. 111, 75–87 (2020).
Liu, W. et al. Variable depositional environments and organic matter enrichment of early cambrian shales in the middle Yangtze region, South China. J. Asian Earth Sci. 259, 105874 (2024).
Zhang, T. et al. Sedimentary geochemical characteristics and organic matter enrichment of the lower cambrian Qiongzhusi formation in the Sichuan basin. Nat. Gas Geoscience. 35, 688–703 (2024).
Zhou, Y. et al. Cyclostratigraphy research on Well-logging of the lower cambrian Qiongzhusi formation in Southwestern Sichuan basin. Acta Sedimentol. Sin. 42, 142–157 (2024).
Kimura, H. & Watanabe, Y. Oceanic anoxia at the Precambrian-Cambrian boundary. Geology 29, 995–998 (2001).
Gao, P. et al. Volcanic and hydrothermal activities recorded in phosphate nodules from the lower cambrian Niutitang formation black shales in South China. Palaeogeogr Palaeoclimatol Palaeoecol. 505, 381–397 (2018).
Liu, W., Gao P., Lash, G.G. & Xiao, X. Co-evolution of life and environment during the early cambrian of South china: implications for organic matter enrichment. Earth-Sci. Rev. 271, 105294 (2025).
Xu, H. et al. Provenance, sedimentary paleoenvironment and organic matter accumulation mechanisms in shales from the lower cambrian Qiongzhusi Formation, SW Yangtze Block, China. Mar. Pet. Geol. 181, 107520 (2025).
Xie, X., Zhu, G. & Wang, Y. The influence of syngenetic hydrothermal silica fluid on organic matter preservation in lower cambrian Niutitang Formation, South China. Mar. Pet. Geol. 129, 105098 (2021).
Dong, L. et al. Understanding hydrothermal activity and organic matter enrichment with the geochemical characteristics of black shales in lower Cambrian, Northwestern Hunan, South China. Lithosphere 2241381 (2022).
Lu, C. et al. Geochemical constraints and astronomical forcing on organic matter accumulation of Marine–Continental transitional shale deposits in the Qinshui basin during the Carboniferous–Permian transition. ACS Earth Space Chem. 8, 616–629 (2024).
Ning, S. et al. Lithofacies types and distribution of High-Quality shale driven by sedimentary environments: A case study of the Qiongzhusi formation shale. Earth Sci. 50, 3631–3650 (2025).
Wang, J. et al. Paleoenvironmental reconstruction and organic matter accumulation mechanisms in the cambrian Qiongzhusi shale: A high-resolution case study of the Chengjiaba section, Northern margin of Sichuan basin. Acta Sedimentol. Sin. https://doi.org/10.14027/j.issn.1000-0550.2025.004 (2025).
Xiong, L. et al. Sedimentary paleoenvironment and organic matter enrichment mechanism of the Qiongzhusi formation in Jingyan-Jianwei area, Southwest Sichuan. Nat. Gas Geoscience. 35, 2091–2105 (2024).
Wang, S. et al. Multiple controls on the paleoenvironment of the early cambrian marine black shales in the Sichuan Basi, SW china: geochemical and organic carbon isotopic evidence. Mar. Pet. Geol. 66, 660–672 (2015).
Chen, W. et al. Geochemical characteristics and paleoenvironmental significance of lower cambrian Maidiping and Qiongzhusi formations in Southwestern Sichuan basin: A case study of well JS1. Acta Sedimentol. Sin. 42, 1784–1798 (2024).
Xu, H. et al. Quartz types, silica sources and their implications for porosity evolution and rock mechanics in the paleozoic longmaxi formation shale, Sichuan basin. Mar. Pet. Geol. 128, 105036 (2021).
Li, C. et al. Coupled oceanic oxygenation and metazoan diversification during the early-middle cambrian? Geol. (Boulder). 45, 743–746 (2017).
Tan, J. et al. Depositional environment and hydrothermal controls on organic matter enrichment in the lower cambrian Niutitang shale, Southern China. AAPG Bull. 105, 1329–1356 (2021).
Liu, K. et al. Increased productivity as a primary driver of marine anoxia in the lower cambrian. Palaeogeogr Palaeoclimatol Palaeoecol. 491, 1–9 (2018).
Jia, Z. et al. Characteristics and geological implications of rare Earth elements in black shale in hydrothermal sedimentation areas: A case study from the lower cambrian Niutitang Fm shale in central and Eastern Guizhou. Nat. Gas Ind. B. 38, 44–51 (2018).
Yeasmin, R. et al. Climatic-oceanic forcing on the organic accumulation across the shelf during the early cambrian (age 2 through 3) in the mid-upper Yangtze block, NE Guizhou, South China. J. Asian Earth Sci. 134, 365–386 (2017).
Li, D. et al. Carbon and strontium isotope evolution of seawater across the Ediacaran–Cambrian transition: evidence from the Xiaotan section, NE Yunnan, South China. Precambrian Res. 225, 128–147 (2013).
Gao, P. et al. Stratigraphic framework, redox history, and organic matter accumulation of an early cambrian intraplatfrom basin on the Yangtze Platform, South China. Mar. Pet. Geol. 130, 105095 (2021).
Zhu, M. et al. Lithostratigraphic subdivision and correlation of the cambrian in China. J. Stratigr. 45, 222–249 (2021).
Fu, X. et al. Evaluation of source rocks and petroleum system of the lower cambrian Maidiping formation-Qiongzhusi formation in the Middle-Upper Yangtze region. China Pet. Explor. 27, 103–120 (2022).
Wang, P. et al. Geochemical characteristics of element Qiongzhusi group in Dianqianbei area and paleoenvironmental significance. J. China Univ. Pet. (Natural Sci. Ed). 45, 51–62 (2021).
Min, H. Characteristics and Formation Mechanism of Highly over-mature Shale Gas Reservoirs in Lower Cambrian Qiongzhusi Formation in the Southwestern Yangtze Plate (Chengdu University of Technology, 2020).
Luo, J. et al. Lithofacies paleogeography and distribution of High-quality shale of the cambrian Qiongzhusi formation in the Dianqianbei depression. Acta Sedimentol. Sin. 41, 1257–1270 (2023).
Zou, C. et al. Unveiling the oldest industrial shale gas reservoir: insights for the enrichment pattern and exploration direction of lower cambrian shale gas in the Sichuan basin. Engineering 42, 278–294 (2024).
Chen, Q. et al. Provenance study for the paleozoic sedimentary rocks from the West Yangtze block: constraint on possible link of South China to the Gondwana supercontinent reconstruction. Precambr Res. 309, 271–289 (2018).
Fang, X., Wu, L., Geng, A. & Deng, Q. Formation and evolution of the Ediacaran to lower cambrian black shales in the Yangtze Platform, South China. Palaeogeogr Palaeoclimatol Palaeoecol. 527, 87–102 (2019).
Zi, J. et al. LA-ICP-MS U-Pb Zircon ages of volcaniclastic beds of the third member of the Sinian (Ediacaran) Dengying formation in Leshan, Sichuan, and a discussion on the rift evolution in the basin. Geol. Rev. 63, 1040–1049 (2017).
Zhong, Y. et al. Features of extensional structures in pre-Sinian to cambrian strata, Sichuan Basin, China. J. Chengdu Univ. Technol. (Natural Sci. Ed). 40, 498–510 (2013).
Zhao, W. et al. Discovery of Wanyuan-Dazhou intracratonic rift and its exploration significance in the Sichuan Basin, SW China. Pet. Explor. Dev. 44, 659–669 (2017).
Liu, S. et al. Control of intracratonic Sags on the hydrocarbon accumulations in the marine strata across the Sichuan Basin, China. J. Chengdu Univ. Technol. (Natural Sci. Ed). 43, 1–23 (2016).
Wang, Z. et al. Tectonic paleogeography of late Sinian and its significances for petroleum exploration in the Middle-Upper Yangtze region, South China. Pet. Explor. Dev. 47, 884–897 (2020).
Van der Weijden, C. H. Pitfalls of normalization of marine geochemical data using a common divisor. Mar. Geol. 184, 167–187 (2002).
Tribovillard, N., Riboulleau, A., Lyons, T. & Baudin, F. Enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in mesozoic limestones and shales. Chem. Geol. 213, 385–401 (2004).
Taylor, S. R. & McLennan, S. M. The Continental Crust: Its Composition and Evolution. (Ed. Hallam, A.) 1-312Blackwell Scientific Publications, (1985).
Nesbitt, H. W. & Young, G. M. Early proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature 299, 715–717 (1982).
Moradi, A. V. et al. Geochemistry of the miocene oil shale (Hançili Formation) in the Çankırı-Çorum Basin, central turkey: implications for paleoclimate conditions, source-area weathering, provenance and tectonic setting. Sediment. Geol. 341, 289–303 (2016).
Fedo, C. M., Young, G. M., Nesbitt, H. W. & Hanchar, J. M. Potassic and sodic metasomatism in the Southern Province of the Canadian shield: evidence from the paleoproterozoic Serpent Formation, Huronian Supergroup, Canada. Precambrian Res. 84, 17–36 (1997).
Cullers, R. & Podkovyrov, V. Geochemistry of the mesopro-terozoic Lakhanda shales in southeastern Yakutia, russia: implications for mineralogical and provenance control, and recycling. Precambrian Res. 104, 77–93 (2000).
Wei, H. Productivity and redox proxies of palaeo-oceans: an overview of elementary geochemistry. Sediment. Geol. Teheyan Geol. 32, 76–88 (2012).
Tribovillard, N. et al. Trace metals as paleoredox and paleoproductivity proxies: an update. Chem. Geol. 232 (1–2), 12–32 (2006).
Grevenitz, P., Carr, P. & Hutton, A. Origin, alteration and geochemical correlation of late permian airfall tuffs in coal measures, Sydney basin, Australia. Int. J. Coal Geol. 55, 27–46 (2003).
Floyd, P. A. & Leveridge, B. E. Tectonic environment of the devonian Gramscatho Basin, South cornwall: framework mode and geochemical evidence from turbiditic sandstones. J. Geol. Soc. Lond. 144, 531–542 (1987).
Liu, H. et al. Geochemistry of the black rock series of lower cambrian Qiongzhusi Formation, SW Yangtze Block, china: reconstruction of sedimentary and tectonic environments. Open. Geoscience. 13, 166–187 (2021).
Wu, D. et al. Sequence filling and evolutionary model of the lower cambrian Maidiping Qiongzhusi formations in Sichuan basin and on its periphery. Oil Gas Geol. 44, 764–777 (2023).
Wei, H. Characteristics and Hydrothermal Biota of the Early Cambrian Black Rock Series in Guizhou Province (Implications for Hydrothermal Sedimentation (Guizhou University, 2008).
Wei, H., Yang, R., Gao, J. & Wang, W. Primary study on the sediment structures in Black-shale-series deposits of the basal Cambrian, Guizhou Province. Geoscience 26, 673–681 (2012).
Chu, C. et al. Influence on formation of yuertusi source rock by hydrothermal activities at dongergou Section, Tarim basin. Acta Sedimentol. Sin. 34, 803–810 (2016).
Bau, M. Rare-earth element mobility during hydrothermal and metamorphic fluid-rock interaction and the significance of the oxidation state of europium. Chem. Geol. 93 (3–4), 219–230 (1991).
Zheng, F. & Song, G. Application of Eu anomaly in geology. Acta Petrol. Sin. 39 (9), 2832–2856 (2023).
German, C. R. et al. Hydrothermal scavenging of rare-earth elements in the ocean. Nature 345, 516–518 (1990).
Michard, A. Rare Earth element systematics in hydrothermal fluids. Geochim. Cosmochim. Acta. 53 (3), 745–750 (1989).
Ghosal, S. et al. Geochemistry of the heavy mineral sands from the Garampeta to the markandi beach, Southern Coast of Odisha, india: implications of high contents of REE and radioelements attributed to placer monazite. J. Earth Syst. Sci. 129 (1), 152 (2020).
Fedo, C. et al. Unravelling the effects of potassium metasomatism in sedimentary rocks and paleosols, with implications for paleoweathering conditions and provenance. Geology 23, 921–924 (1995).
Li, X. et al. Overview of the application and prospect of common chemical weathering indices. Geol. J. China Univ. 28, 51–63 (2002). (in Chinese with English abstract).
Chen, J. et al. Zr/Rb ratio in the Chinese loess sequences and its implication for changes in the East Asian winter monsoon strength. Geochim. Cosmochim. Acta. 70, 1471–1482 (2006).
Yu, L. et al. Analysis of organic matter enrichment and influences in fine-grained sedimentary strata in saline lacustrine basins of continental fault depressions: case study of the upper sub-section of the upper 4th member of the Shahejie formation in the Dongying Sag. Acta Sedimentol. Sin. 42, 701–722 (2024).
Xiao, B. et al. Identification of organic matter enrichment factors in marine sedimentary rocks based on elements Mn, Co, cd and mo: application in the Northern margin of Sichuan Basin, South China. Geol. Rev. 65, 1317–1330 (2019).
Tribovillard, N., Algeo, T. J., Baudin, F. & Riboulleau, A. Analysis of marine environmental conditions based on molybdenumuranium covariation-Applications to mesozoic paleoceanography. Chem. Geol. 324–325, 46–58 (2012).
Algeo, T. J., Ingall, E. & Sedimentary Corg P ratios, paleocean ventilation, and phanerozoic atmospheric PO2. Palaeogeogr Palaeoclimatol Palaeoecol. 256, 130–155 (2007).
Algeo, T. J. & Tribovillardb, N. Environmental analysis of paleoceanographic systems based on molybdenum-uranium covariation. Chem. Geol. 268, 211–225 (2009).
Algeo, T. J. & Lyons, T. W. Mo-total organic carbon covariation in modern anoxic marine environments: implications for analysis of paleoredox and paleohydrographic conditions. Paleoceanography 21, PA1016 (2006).
Tang, D. et al. Mo-U covariation as an important proxy for sedimentary environment redox Conditions-Progress, problems and prospects. Geoscience 29, 1–13 (2015).
Algeo, T. J. & Tribovillard, N. Environmental analysis of paleoceanographic systems based on Molybdenum-Uranium covariation. Chem. Geol. 268, 211–225 (2009).
Wignall, P. B. & Twitchett, R. J. Oceanic anoxia and the end permian mass extinction. Science 272, 1155–1158 (1996).
Jones, B. & Manning, D. A. C. Comparison of geochemical indices used for the interpretation of Palaeoredox conditions in ancient mudstones. Chem. Geol. 111, 111–129 (1994).
Algeo, T. J. & Liu, J. A re-assessment of elemental proxies for paleoredox analysis. Chem. Geol. 540, 119549 (2020).
Fan, Q., Xia, G., Li, G. & Yi, H. Analytical methods and research progress of redox conditions in the Paleo-Ocean. Acta Sedimentol. Sin. 40, 1151–1171 (2022).
Eagle, M. et al. A comparison between excess barium and barite as indicators of carbon export. Paleoceanography 18, 1021 (2003).
Algeo, T. J. et al. Spatial variation in sediment fluxes, redox conditions, and productivity in the Permian–Triassic panthalassic ocean. Palaeoecology 308, 65–83 (2011).
Xiong, Z. et al. Paleoproductivity and paleoredox conditions during late pleistocene accumulation of laminated diatom Mats in the tropical West Pacific. Chem. Geol. 334, 77–91 (2012).
Schoepfer, S. D. et al. Total organic carbon, organic phosphorus, and biogenic barium fluxes as proxies for paleomarine productivity. Earth-Sci. Rev. 149, 23–52 (2015).
Acknowledgements
The authors thank Jianli Zeng for his invaluable suggestions during the writing of this article.We would also like to extend our sincere gratitude to the two anonymous reviewers for their valuable and constructive comments, as well as to the Editor for overseeing the handling of the manuscript.
Funding
National Natural Science Foundation of China (No.: 41772150); National Science and Technology Major Project, (No.:2017ZX05063002009).
Author information
Authors and Affiliations
Contributions
Conceptualization, T.Z. and H.M.; Methodology, J.L.; Validation, H.S. and Z.Z.; Formal analysis, J.L. and H.M; Investigation, J.L.; Resources, H.S. and H.M.; Data curation, H.M., Z.Z. and J.L.; Writing—original draft preparation, J.L; Writing—review and editing, T.Z., X.Z and J.L.; Visualization, J.L.; Supervision, T.Z., X.Z. and H.S.; Project administration, T.Z.; Funding acquisition, T.Z. All authors have read and agreed to the published version of the manuscript.
Corresponding authors
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Information
Below is the link to the electronic supplementary material.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
About this article
Cite this article
Luo, J., Zhang, T., Min, H. et al. Sedimentary environment evolution and organic matter enrichment mechanisms of the cambrian Qiongzhusi Formation in the southwestern Yangtze Block. Sci Rep (2026). https://doi.org/10.1038/s41598-026-39633-x
Received:
Accepted:
Published:
DOI: https://doi.org/10.1038/s41598-026-39633-x
