Diagênese e proveniência dos arenitos da tectonossequência Rifte nas Bacias do Rio do Peixe Araripe, NE do Brasil

摘要

This thesis presents diagenetic and provenance studies of sandstones belonging to the RiftTectonosequence of the Rio do Peixe and Araripe basins. These basins are located in the interiorof Northeast Brazil aligned along the Trend-Cariri Potiguar. Their origin is related to the EarlyCretaceous rifting event. In terms of lithostratigraphy, the studied section corresponds to theAntenor Navarro, Sousa and Rio Piranhas formations of the Rio do Peixe Basin, and the MissãoVelha and Abaiara formations of the Araripe Basin, outcropping in the central-west CaririValley. A facies analysis was performed and identified nine distinct sedimentary facies for theRio de Peixe Basin and ten sedimentary facies for the Araripe Basin, individualized according tothe different rock types and their sedimentary structures. These facies associations to ledpaleoenvironments interpretations and their vertical succession allowed understanding theevolution of the depositional setting during the cronostratigraphic interval studied in thesebasins. Based on petrographic and diagenetic studies it was possible to characterize the textureand mineralogy of these sandstones, identifying their diagenetic stage and the grain frameworkprovenance. The petrographic study allowed to classify the lithotypes studied in both basins asquartzarenites. Such quartzarenites, in general, are rich in quartz, feldspar and lithic fragmentgrains, and at accessory levels tourmaline, sphene, zircon, epidote and other mineralogy. Thediagenetic history of the studied rocks proved to be very complex, being characterized by avariety mineral of phases that succeeded each other during the eo, meso and telodiageneticstages. According to the studied formation and the textural and compositional aspects of therocks, some processes were more or less active, while others were even absent. The eodiageneticstage is marked by mechanical infiltration of clays and early mechanical compactional processes.The mesodiagenetic phase is characterized by continuity of the mechanical compaction and thebeggining of chemical compaction, with quartz and feldspar overgrowths, precipitation ofkaolinite, alteration of framework grains to chlorite and illite, and finally, precipitation of opaqueminerals. The telodiagenetic stage is represented by the oxidation of some grains, matrix andcements. For the provenance analysis of the studied sandstones were used ternary diagramswhose vertices correspond to the percentage of quartz, feldspar and lithic fragments. This studyallowed identifies the source area of these rocks as continental blocks. It was also possible, basedon the chemical stability and mineralogical maturity of the rocks, recognize that the AntenorNavarro Formation of the Rio do Peixe Basin, and the upper section of the Missão VelhaFormation of Araripe Basin have less maturity and stability when compared with the otherstudied formations