PRE-SILURIAN BASINS AT THE MID-WESTERN PORTION OF PARNAÍBA PROVINCE
Parnaíba Basin, Pre-Silurian, Tectonic Framework, Foreland Systems
This research presents the results of the interpretation of a 2-D seismic grid in the mid-western portion of the Parnaíba Basin, focusing on the pre-Silurian interval and the crystalline basement. Pre-Silurian grabens have been interpreted in the substrate of the basin, with implications to the subsidence controls and development of the syneclisis during the Paleozoic. The pre-silurian basin in the region of Balsas (MA) is compartmentalized by a structural high in two main depocenters. In the eastern sector of the study area, the pre-Silurian strata have an external wedge shape geometry which thickens towards an important N-S trending normal fault, about 100 km long, which bounds this depocenter to the east. In turn, the depocenter to the west of the structural high exhibits contractional structures. It was possible to individualize two seismic sequences in the pre-Silurian section. SEQ 1 is characterized by a package of high-amplitude parallel reflectors with regular thickness, which form a smooth arc over the structural high. SEQ 2 is characterized by low-frequency and low-amplitude reflectors, presenting as east-dipping parallel seismic facies. Both seismic sequences are deformed by folds and thrusts in the western sector of the study area, opposed to the extensional style observed to the east. It is proposed that the pre-Silurian interval corresponds to wedge-top deposits of a foreland system associated with the collision between the Parnaíba Block and the Amazon Craton along the Araguaia Belt, during the amalgamation of Western Gondwana in the Neoproterozoic.