Sedimentological characterization of the quaternary deposits in the region between Marilia and Presidente Prudente, Sao Paulo State, Brazil

Sedimentologic characterization and provenance studies of quaternary colluvial deposits (9 +/- 1 to 980 +/- 100 ky B.P. - dated by luminescence) were based on textural and mineralogical analyses. These deposits occur extensively between Marilia and Presidente Prudente (Sao Paulo State, Brazil), superimposed on the Bauru Group sedimentary rocks or the Serra Geral Formation basaltic rocks, both of Cretaceous age. They are distributed irregularly throughout the study area and are studied by sedimentologic and morphologic methods. These deposits are composed of very fine to coarse-grained unconsolidated sands, mostly constituted by quartzose monocrystalline grains reddened by iron oxide and hydroxide impregnation. Analyses of grain sizes indicated that total granulometric distributions are richer in the clay fraction than in the sedimentary rocks located. Non-micaceous transparent heavy minerals studied microscopically in fine-grained as well as in very fine-grained sands showed that zircon, tourmaline, staurolite and rutile are present in all the samples. Differences in grain sizes among the colluvial deposits and the Bauru Group sedimentary rocks are attributable to pedogenetic processes.