Análise de fácies, proveniência e diagênese da formação botucatu entre Araguari e Uberlândia, Minas Gerais (NE da Bacia do Paraná).

Abstract

The Botucatu Formation (Upper Jurassic/Lower Cretaceous) of the Paraná Basin consists mainly of eolian quartz sandstones with medium to large through cross stratification. In the Triangulo Mineiro region of southeast Brazil, between the cities of Uberlândia and Araguari, the Botucatu Formation consists of facies diametrically different from those traditionally described and attributed to this unit. Litothypes of the Botucatu Formation in this region include sandy conglomerate, conglomerate, and sandstone in discordant erosional contact over neoproterozoic augen gneisses of the Brasília Fold Belt. Overlying the sandstone and conglomerate is a thick sequence of volcanic rocks from the Serra Geral Formation. In this way, methods involving analysis of lithofacies, paleocurrents, modal count of detrital composition, lithoclast count and determination of the ZTR index were applied. Analysis of the lithofacies in the study area indicates deposition in a distral braided fluvial system for the Botucatu Formation in northeastern areas of the Paraná Basin during the Lower Cretaceous. The distinct occurrence of rudaceous facies indicates relatively proximal source areas. Rounded to well-rounded quartz grains with high sphericity indicate that the fluvial system received contributions from eolian sources. Paleocurrent data based on imbricated clasts suggest sediment dispersal from NW source areas. Analysis of sedimentary provenance based on detrital composition, composition of lithoclasts and heavy minerals advocate recycled orogen as source areas. The paleocurrent and provenance data are convergent and strongly suggest that the main lithotypes that provided sediments for the fluvial system of the Botucatu Formation in the northeasternmost part of the Paraná Basin were muscovite schists and quartzites of the Araxá B Group of the Brasilia Fold Belt. The presence of mechanically infiltrated clays, oxidation of ferromagnesian minerals, and authigenic quartz and feldspar confirm the deposition of the Botucatu Formation in a continental environment with an arid to desert climate. The multi-proxy approach used in the present work proved effective for the detailed study of the active depositional processes on the northeastern margin of the Botucatu paleodesert.