Depositional systems constraining the distribution of hydrothermal dolostone geobodies: A case study of Permian Guadalupian dolostone in the eastern Sichuan Basin

Abstract

Lithological heterogeneity can be an important factor in regulating the spatial distribution of hydrothermal dolostone (HTD) geobodies. Understanding HTD genesis is crucial for improving our ability to predict subsurface HTD occurrence within sedimentary frameworks. This study investigates HTD development within the Permian Guadalupian carbonate successions of the eastern Sichuan Basin, China, providing significant insights into HTD formation processes. Through systematic sedimentological analysis of four outcrop sections (Fangniuba, Shangping, Tuotuoba, and Wuyangba), we identified eight distinct lithofacies and five lithofacies associations (LA1–LA5). Integrating field observations with data from adjacent sites, we performed a comprehensive evaluation of the depositional sequences, sedimentary environments, and petrophysical properties of the Guadalupian carbonate strata. These carbonates display a distinctive shallowing-upward sequence overlain by a deepening-upward succession. Notably, Guadalupian dolostones are consistently hosted within the middle portions of the shallowing-upward sequences across all studied sections. Petrological and mineralogical analyses further reveal preferential dolomitization in thin- to medium-bedded wackestone containing nodular cherts (LA2), which served as lateral conduits for hydrothermal fluid migration. Enhanced fracturing is observed within these lithologies, particularly along bedding planes and around nodular chert margins, reflecting their greater susceptibility to petrophysical modification. This preferential dolomitization reflects the interplay of carbonate texture, rock permeability, and fracture susceptibility, which collectively establish optimal diagenetic conditions for fluid-rock interaction. Our findings demonstrate that depositional lithological heterogeneity constrains HTD distribution through two key pathways: (1) primary lithological controls (including permeability variations and mud content), and (2) mechanically influenced properties (particularly bed thickness and nodular cherts). This heterogeneity, established during initial deposition to shallow-burial phases, fundamentally preconditioned subsequent HTD formation and distribution during later hydrothermal fluid emplacement.