Fault-related carbonates as evidence of continentalization during the Permian-Triassic of the Paraná Basin, Southern Brazil

Abstract

Carbonates in fault planes and fractures can serve as a geological record, accurately documenting an area's tectonic and paleoenvironmental evolution. Due to the precipitation as diferent events and under various conditions, these minerals enable the reconstruction of tectonic and hydrogeological conditions that shaped the local geological history. Additionally, compositional and isotopic analyses of these carbonates allow correlations with larger orogenic episodes, situating the local context within a broader regional or global tectonic framework. Therefore, multiple analyses were performed on five distinct carbonates precipitated in a thrust fault and fractures of the Rio do Rasto Formation's sandstones (southern Paraná Basin, Dom Pedrito, Brazil). Based on detailed fieldwork, petrography, X-ray diffraction, geochemical analyses (major, trace, and rare earth elements), and stable isotope, the carbonates were categorized into at least two main precipitation phases. The gouge carbonate, a described type indicates that crushing resulted from fault movement during tectonic reactivations subsequently its initial precipitation. The euhedral calcite crystals in the associated fractures indicate infilling under stable tectonic conditions, suggesting a late-stage cementation phase. These events developed at near-surface temperatures between 28 and 30 °C, influenced by brackish waters, likely from shallow marine environments preceding a continentalization event. The structural features of the outcrop, such as the reverse fault and "S"-shaped folds, suggest an association with compressive events linked to the San Rafael Orogeny, which affected parts of western Argentina and Chile during the Late Paleozoic.