Aspectos da evolução termomecânica da Plataforma de Florianópolis e da Bacia de Pelotas

Abstract

Passive continental margin sedimentary basins are typically characterized by two subsidence stages. In the first stage, during the rift phase, a period in which subsidence is caused by crustal stretching processes (mechanical subsidence). After this stage, the subsidence rate decreases substantially due to the densification of the crust due to the gradual decrease in temperature (thermal subsidence). The analysis of the history of subsidence of sedimentary basins consists in reconstructing the rates of variation of the sedimentary accumulation and of the substrate of the basin as a function of time, by punctual form (1D), linear (2D), or in a volume (3D) From the curves, profiles and accumulation volumes of compacted and decompressed sediments.. The backstripping, the objective of this work, is a geophysical analysis technique that consists of the application of an approximate isostatic balance that allows isolates the sedimentary load component from the total subsidence component and obtaining the subsidence caused by tectonics. The latter is influenced by three dynamic variables, namely - i- deposited sediments ( ( )), ii- Water depth depth ( ( )) and iii- Global variation of the sea level ( ). For this we use a MatLab language-based program, BasinVis 1.0, which allows the analysis and visualization of the subsidence of a sedimentary basin in a knowable workflow. The analysis of information from three wells on the Florianópolis platform and a fourth in the Pelotas Basin provided the basis for the determination of porosity, depth of basement and sedimentary load, used in the backstripping modeling. This allowed the calculation of tectonic subsidence, lithospheric stretching accompanying the sedimentary and tectonic histories of such areas. The particular conditions of diastrophism to which these regions have been subject since the installation of the rifte revealed that there are in fact interesting specificities in the subsidence curves in these processes already recommended in other occasions and that were also observed in the context of evolution of other basins of the Brazilian southeast margin.