<p>To figure out the formation process of Lower Triassic polyhalite in the northeastern Sichuan Basin, detailed microfabric analyses were performed on three drill cores in the study area, culminating in the establishment of a geological model for the formation process of polyhalite. Five microfabric types, which can be subdivided into 10 specific subtypes, were identified in this model. Subgrained polyhalite, the principal constituent of polyhalite deposits, constitutes primary polyhalite that experienced dislocation creep during plastic deformation, occurring at least subsequent to the overall deposition of the Lower Triassic strata. Coarse-grained recrystallized polyhalite formed statically from subgrained polyhalite under the influence of diagenetic fluids. Microfolded polyhalite, along with pressure-solution and metasomatic polyhalite, reflects deformation and metasomatism under one or two episodes of tectonic stress. The formation timing of fibrous polyhalite remains ambiguous, but it is regarded as evidence of anhydrite replacement and is considered a relatively young type. These findings indicate that shape-deformed primary polyhalite comprises the main component of polyhalite deposits in the study area, with multiphase non-primary polyhalite formed via late-stage deformation and metasomatism. The results serve as a critical basis for analyzing the genetic mechanism of polyhalite and support further exploration and development in the region.</p>