Rochas carbonáticas da Faixa Paraguai Sul e bacia de Corumbá: origem, litoestratigrafia e implicações evolutivas para o Neoproterozoico

Abstract

Ediacaran carbonate deposits and tectono-metamorphic processes associated with the Brasiliano–Pan-African Orogeny are recorded in the Southern Paraguay Belt. This interaction results in the juxtaposition of carbonate units with distinct evolutionary histories within Neoproterozoic terrains. The accurate identification of carbonate lithofacies is of fundamental importance for defining depositional systems and lithostratigraphic units in a sedimentary basin, being essential for reconstructing the various events of its evolutionary history. In this context, this study aims to distinguish carbonate lithotypes of sedimentary origin from those modified by hydrothermal and/or metamorphic processes. Carbonate rock samples were analyzed using petrography, cathodoluminescence, and X-ray diffraction (XRD), integrated with field data and a re-evaluation of available geological maps, to redefine the lithostratigraphy of the carbonate units. Two groups of carbonate rocks were identified in the Corumbá and Bodoquena range regions. Group 1 is characterized by intense recrystallization, development of foliation, and association with siliciclastic and metamorphic minerals, reflecting low-grade metamorphic conditions and fluid–rock interaction. This group predominantly exhibits typical textures such as granoblastic and porphyroblastic. Group 2 preserves primary sedimentary structures, such as laminations and stromatolites, in addition to a predominantly carbonate composition (calcite or dolomite), typical of platform deposits. Furthermore, this group comprises two facies associations: (i) tidal flat and platform margin, belonging to the Bocaina Formation, subdivided into seven microfacies; and (ii) a carbonate ramp corresponding to the Tamengo Formation, subdivided into four microfacies. The distinction between these groups allows the crystalline carbonate rocks to be associated with the Cuiabá Group, deposited in a mixed platform environment and later subjected to burial, low-grade metamorphism, and hydrothermal influence; whereas the well-preserved carbonate rocks are attributed to the Corumbá Group (Bocaina and Tamengo formations), with less post-depositional modification. These results allowed the proposal of an evolutionary model for the region, involving sedimentary deposition, tectonic deformation, and fluid circulation, contributing to the understanding of tectono-sedimentary events that occurred during the Neoproterozoic in the southern Tocantins Province.