Paleomorphology of the northwestern of the Quadrilátero Ferrífero (central Brazil) : stratigraphic and geochronological evidence of a pleistocene alluvial fan system.

Abstract

This paper presents data on the fragments of ancient sedimentary deposits placed around the Piedade and Casa Branca streams, important right bank tributaries of the Paraopeba River. From these data, it was possible to establish a picture regarding the paleomorphology and paleodrainage of the area. The methodological steps adopted consisted of the definition of sedimentary facies, as well as the establishment of their sedimentary provenance (U/Pb method in detrital zircons) and deposition age (OSL in quartz). Through the facies analyses, it was possible to show channel facies (Gt) associated with debris flows (Gmm) and sieve deposits (Gh). In the sedimentary provenance stage, spectra of ages congruent with those found in literature for the Moeda and Cauê Formations were identified, suggesting that the Moeda mountain range is a source area. We also analyzed data on the sediments of the current bed, which indicate the same provenance, showing that the current courses constitute an embedded analog of the paleochannels. The data herein obtained corroborate the hypothesis that the eastern periphery of the Bonfim Complex was dominated by a system of alluvial fans between 9.5 ± 1 and 15.5 ± 1.6 ka before present, whose remnants are preserved on the current hilltops and mid slopes of the basement landscape.