Geologia USP. Série Científica (Oct 2009)
The Deposition of Quaternaty Tufas in Mato Grosso do Sul State: Proposal for the Definition of the Serra da Bodoquena Formation
Abstract
Quaternary tufa deposits occur widely in the Serra da Bodoquena (state of Mato Grosso do Sul, Brazil), associated withthe karst system that has developed on carbonate rocks of the Corumbá Group. The deposition of tufa is favored in theSerra da Bodoquena due to the predominance of autogenic waters, which allow for groundwater to be enriched in calciumcarbonate. By means of numerous springs, this groundwater supplies the rivers of the area where tufas are deposited.These rivers have small quantities of siliciclastic sediment, making the water very clear, which favors biological activityand, as a result, the precipitation of carbonate. The lithological characteristics, the existence of clear and abrupt linesof contact and the easy mapping of the tufas make it possible to create a new unit, here named the Serra da BodoquenaFormation. Deposition in a distinct river basin and karst system justify separation from the Xaraiés Formation, even if theirlithologies are partly similar. The Serra da Bodoquena Formation is discontinuous due to the nature of deposits, formed in association with the surface drainage network. The individual outcropping areas never interconnected with each other or with theXaraiés Formation in the Corumbá region. The new unit was divided into two members in order to represent catchment and waterfalldeposits and micrite deposits named, respectively, Rio Formoso and Fazenda São Geraldo members. The older tufa deposits indicategreater deposition from 6530 cal years BP until 2700 cal years BP, when the decline began reaching the present fate. This moreintensive deposition represents a period of more humid climate, which changed at around 2700 cal years BP when similar conditionsto those found at present became established. The active deposition of tufas in the Rio Formoso Member is still significant, althoughlimited to the courses of perennial or intermittent drainage channels.
