Characteristics and Sedimentary‐Diagenetic Model of Carbonate Rocks From Member 1 of the Cambrian Canglangpu Formation in the Sichuan Basin, SW China

Abstract

The Canglangpu Formation is a key stratigraphic interval for Cambrian oil and natural gas exploration and production within the Sichuan Basin, so integrated sedimentological and reservoir characterization of this unit is essential. Core‐based petrographic analysis shows that Member 1 (∼100 m thick) is made up mainly of carbonate lithologies—including grain‐supported dolomite, relict grain dolomite, crystalline dolomite, and grainstone—interbedded with clastic intervals sourced from the Hannan–Micangshan Massif. In contrast, Member 2 (∼160 m thick) comprises fine‐grained sandstones and siltstones, marking a clear shift to clastic‐dominated facies. Member 1 dolomites include two petrographically distinct fabrics: micritic–fine‐crystalline dolomite (D1) and medium‐ to fine‐crystalline dolomite (D2). In particular, D2 has lower δ 18 O (VPDB) signatures relative to D1, consistent with two end‐member dolomitization pathways—rapid precipitation from ambient‐temperature seawater and evaporative seawater seepage‐reflux, respectively. Together, early fibrous calcite cements occluding ooid intergranular porosity and trace‐element and rare earth element (REE) signatures of ooids preserved in dolomites of varying crystal sizes indicate dolomitization by marine‐derived brines during syngenetic to early penecontemporaneous stages. Moreover, the vertical stacking of distinct oolitic facies (Types I and II) is linked to sea‐level oscillations within high‐energy ooid shoal settings, which strongly controlled reservoir quality through subsequent meteoric and burial dissolution.