Shaoyun Chen , Yongqiang Yang , Zaixing Jiang , Xiaojuan Wang , Longwei Qiu , Yerejiepu Habulashenmu
{"title":"Clay mineral of different lithofacies in a continental shallow water delta: Insights from paleoclimate and diagenesis","authors":"Shaoyun Chen , Yongqiang Yang , Zaixing Jiang , Xiaojuan Wang , Longwei Qiu , Yerejiepu Habulashenmu","doi":"10.1016/j.sedgeo.2025.106869","DOIUrl":null,"url":null,"abstract":"<div><div>Clay minerals in clastic sediments carry important geological information, with their composition and variations reflecting key geological processes. This study investigates the differential clay mineral assemblages among lithofacies within the Middle Jurassic continental shallow-water delta system of the Sichuan Basin, China. Integrated geochemical and XRD analyses demonstrate the significant influence of paleoclimate-driven weathering and diagenetic alteration on clay mineral assemblages. The invariant geochemical characteristics (such as Ti/Al) across different mudstone confirm a uniform provenance, establishing paleoclimate-controlled weathering processes as the principal determinant of clay mineral composition, with negligible provenance influence. Chemical weathering intensity, controlled by the depositional paleoclimate, is a primary factor influencing clay mineral composition in mudstones. In warm, humid climates, abundant rainfall and strong chemical weathering lead to kaolinite enrichment and smectite depletion in black shale facies. Conversely, in cooler, drier climates, physical weathering dominates, resulting in significant illite formation in red mudstone and paleosol facies. In sandstone facies, clay minerals are controlled by diagenetic fluid composition and flux. Chlorite content is related to the primary permeability of the sandstone, while illite content is influenced by K<sup>+</sup> concentration in diagenetic fluids, with stronger illite enrichment in areas of intense feldspar dissolution. The smectite-to-illite transformation is common in both sandstone and mudstone facies, with its extent influenced by the openness of the diagenetic system and K<sup>+</sup> availability. In humid conditions, feldspar dissolution in an open system leads to K<sup>+</sup> advection into sandstone, reducing smectite-to-illite transformation in mudstones. In semi-arid conditions, feldspar dissolution occurs in closed systems during burial, with K<sup>+</sup> diffusing into mudstones, promoting greater illitization in mudstones than in sandstones. This study provides insights into how paleoclimate and diagenesis control clay mineral transformations in sedimentary rocks.</div></div>","PeriodicalId":21575,"journal":{"name":"Sedimentary Geology","volume":"481 ","pages":"Article 106869"},"PeriodicalIF":2.7000,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Sedimentary Geology","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0037073825000648","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
Clay minerals in clastic sediments carry important geological information, with their composition and variations reflecting key geological processes. This study investigates the differential clay mineral assemblages among lithofacies within the Middle Jurassic continental shallow-water delta system of the Sichuan Basin, China. Integrated geochemical and XRD analyses demonstrate the significant influence of paleoclimate-driven weathering and diagenetic alteration on clay mineral assemblages. The invariant geochemical characteristics (such as Ti/Al) across different mudstone confirm a uniform provenance, establishing paleoclimate-controlled weathering processes as the principal determinant of clay mineral composition, with negligible provenance influence. Chemical weathering intensity, controlled by the depositional paleoclimate, is a primary factor influencing clay mineral composition in mudstones. In warm, humid climates, abundant rainfall and strong chemical weathering lead to kaolinite enrichment and smectite depletion in black shale facies. Conversely, in cooler, drier climates, physical weathering dominates, resulting in significant illite formation in red mudstone and paleosol facies. In sandstone facies, clay minerals are controlled by diagenetic fluid composition and flux. Chlorite content is related to the primary permeability of the sandstone, while illite content is influenced by K+ concentration in diagenetic fluids, with stronger illite enrichment in areas of intense feldspar dissolution. The smectite-to-illite transformation is common in both sandstone and mudstone facies, with its extent influenced by the openness of the diagenetic system and K+ availability. In humid conditions, feldspar dissolution in an open system leads to K+ advection into sandstone, reducing smectite-to-illite transformation in mudstones. In semi-arid conditions, feldspar dissolution occurs in closed systems during burial, with K+ diffusing into mudstones, promoting greater illitization in mudstones than in sandstones. This study provides insights into how paleoclimate and diagenesis control clay mineral transformations in sedimentary rocks.
期刊介绍:
Sedimentary Geology is a journal that rapidly publishes high quality, original research and review papers that cover all aspects of sediments and sedimentary rocks at all spatial and temporal scales. Submitted papers must make a significant contribution to the field of study and must place the research in a broad context, so that it is of interest to the diverse, international readership of the journal. Papers that are largely descriptive in nature, of limited scope or local geographical significance, or based on limited data will not be considered for publication.