ÁREA FONTE, PALEOINTEMPERISMO E PROVENIÊNCIA DAS SEQUÊNCIAS DO CRETÁCEO SUPERIOR DA BACIA BAURU (SUDESTE DO BRASIL)

Abstract

Geochemical and mineralogical analyses of sandstones and mudstones from the Bauru Basin (SE Brazil) were undertaken to determine the provenance, tectonic setting and weathering during the Late Cretaceous. X-ray diffraction (XRD) analysis indicate that samples comprise of quartz, microcline and hematite. Illite, montmorillonite and palygorskite are the main clay minerals. X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) analyses determined the main chemical composition of the rocks from the Bauru Basin. Predominant major elements include SiO₂, Al₂O₃, Fe₂O₃, MgO, K₂O and TiO₂, and were used to determine the rock composition and classify them as Fe-sands, litharenites, sublitharenites, wackes and shales. Trace elements, including the rare earth elements and the ratios among them determined the source area and its tectonic setting. A correlation matrix including major and trace elements and plots of major and trace elements and values for the ratios such as La/Sc (1.47-4.86), (La/Yb)_c (3.86-20.44) and the Eu anomaly (Eu/Eu*= 0.62-0.92), compared to data from the literature indicate the source rock is associated with a continental passive margin tectonic setting. The sedimentary succession of the Bauru Basin derived from quartzitic to granitic-gneissic rocks of stable continental areas. Chemical Index of Alteration (CIA) and Chemical Index of Weathering (CIW) values range, respectively, from 64.83 to 92.3 and 84 to 98.2, indicating a moderate to intense weathering in the source area in a semiarid climate conditions.