A deposição de tufas quaternárias no estado de Mato Grosso do Sul: proposta de definição da formação Serra da Bodoquena

Quaternary tufa deposits occur widely in the Serra da Bodoquena (state of Mato Grosso do Sul, Brazil), associated with the karst system that has developed on carbonate rocks of the Corumbá Group. The deposition of tufa is favored in the Serra da Bodoquena due to the predominance of autogenic waters, which allow for groundwater to be enriched in calcium carbonate. 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 activity and, as a result, the precipitation of carbonate. The lithological characteristics, the existence of clear and abrupt lines of contact and the easy mapping of the tufas make it possible to create a new unit, here named the Serra da Bodoquena Formation. Deposition in a distinct river basin and karst system justify separation from the Xaraiés Formation, even if their lithologies 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 the Xaraiés Formation in the Corumbá region. The new unit was divided into two members in order to represent catchment and waterfall deposits and micrite deposits named, respectively, Rio Formoso and Fazenda São Geraldo members. The older tufa deposits indicate greater deposition from 6530 cal years BP until 2700 cal years BP, when the decline began reaching the present fate. This more intensive deposition represents a period of more humid climate, which changed at around 2700 cal years BP when similar conditions to those found at present became established. The active deposition of tufas in the Rio Formoso Member is still significant, although limited to the courses of perennial or intermittent drainage channels.Depósitos quaternários de tufas ocorrem extensamente na Serra da Bodoquena (MS), associados ao sistema cárstico desenvolvido sobre rochas carbonáticas do Grupo Corumbá. A deposição de tufa é favorecida na Serra da Bodoquena pela predominância de águas autogênicas, que permite o enriquecimento da água subterrânea em carbonato de cálcio, que, através de inúmeras nascentes, alimenta os rios de superfície onde as tufas são depositadas. Estes rios possuem baixas quantidades de sedimentos siliciclásticos tornando suas águas muito límpidas, o que favorece a atividade biológica e, consequentemente, a precipitação de carbonato. As características litológicas, a existência de contatos claros e abruptos e a mapeabilidade das tufas possibilitaram a criação de uma nova unidade, denominada Formação Serra da Bodoquena. A deposição em bacia hidrográfica e sistema cárstico distintos justificam sua separação da Formação Xaraiés (Corumbá, MS), mesmo que parte das litologias seja semelhante. A Formação Serra da Bodoquena é descontínua, devido à própria natureza dos depósitos, formados em associação com a rede de drenagem, nunca ligados entre si ou com a Formação Xaraiés. A nova unidade foi dividida em dois membros para representar os depósitos de represas e cachoeiras e os de micritos, respectivamente: membros Rio Formoso e Fazenda São Geraldo. Os depósitos antigos de tufas indicam deposição mais expressiva do que atualmente, desde 6.530 anos cal A.P. até 2.700 anos cal A.P. onde inicia um decréscimo. Esta deposição mais intensa representa um período de clima mais úmido, que se alterou a partir de 2.700 anos cal A.P. quando se estabeleceram condições próximas à atual. A deposição atual de tufas no Membro Rio Formoso ainda é expressiva, porém restrita ao leito das drenagens perenes ou intermitentes

The Deposition of Quaternaty Tufas in Mato Grosso do Sul State: Proposal for the Definition of the Serra da Bodoquena Formation

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