Chemical weathering rates of clastic sedimentary rocks from the Parana Basin in the Paulista Peripheral Depression, Brazil

Autor(es)

Spatti Junior, Eder Paulo ^[1] ; da Conceicao, Fabiano Tomazini ^[1] ; Fernandes, Alexandre Martins ^[1] ; Sardinha, Diego de Souza ^[2] ; Menegario, Amauri Antonio ^[3] ; Moruzzi, Rodrigo Braga ^[1]

Afiliação do(s) autor(es)

^[1] UNESP Univ Estadual Paulista, Inst Geociencias & Ciencias Exatas, Rio Claro, SP - Brazil

^[2] UNIFAL Univ Fed Alfenas, Inst Ciencia & Tecnol, Pocos De Caldas, MG - Brazil

^[3] UNESP Univ Estadual Paulista, Ctr Estudos Ambientais, Sao Paulo, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Journal of South American Earth Sciences; v. 96, DEC 2019.
• Citações Web of Science: 0

Resumo

The chemical weathering plays an important role in the processes of surface geochemistry, which is fundamental to understand the landscape evolution. The Parana Basin is an intracratonic sedimentary basin developed on the South American platform from Paleozoic to Cenozoic, with area of 1.5 x 10(6) km(2) and 5000 km(3) of clastic sediments and igneous rocks. The main clastic sedimentary rocks in the Parana Basin are sandstones and mudstones. Surprisingly, there are no studies assessing the chemical weathering rates of elastic sedimentary rocks from the Parana Basin under tropical climate conditions in Brazil or in South America. Thus, two small watersheds were chosen to assess the chemical weathering rates of clastic sedimentary rocks from the Parana Basin in the Paulista Peripheral Depression (Sao Paulo State, Brazil), i.e. the Monjolo Grande and Jacutinga stream basins. The chemical composition of rain and surface waters, as well as the chemical and mineralogical composition of the fresh rocks (sandstones and mudstones) and soil (horizon C) were characterized. The instantaneous daily flux indicates that ca. 60% of the dissolved solids loads are carried from October to March in both watersheds. The natural fluxes due to chemical weathering (F-w) were ca. 4.5 t km(-2) yr(-1), with a mixed of local rainwater and chemical weathering of sandstones and mudstones controlling the surface waters composition. The possible chemical weathering processes of sandstones and mudstones occur by quartz dissolution and partial hydrolysis (monossialitization) of albite, microcline and illite, respectively. The chemical weathering rates were of 0.3 and 0.8 m Myr(-1) for the Monjolo Grande and Jacutinga Streams basin, respectively, confirming the lower chemical weathering rates for clastic sedimentary rocks in relation to basalts (Parana CFB) of the Parana Basin and for the igneous and metamorphic rocks of the Ribeira Belt, other important geological units in the Sao Paulo State. In addition, these chemical weathering rates are also lower than the suggested for other rock types elsewhere, i.e., carbonates, basalts, granites, schist, gneisses or alkaline rocks. Finally, the effect of climate on {[}SiO2] was demonstrated, also described in basaltic and granitic watersheds, suggesting that the chemical weathering of sandstones and mudstones are more effective in the wet season. (AU)

• Processo FAPESP: 10/01540-0 - Avaliação da erosão hídrica, transporte de sedimentos e qualidade de água na bacia hidrográfica do Córrego Monjolo Grande (SP)
• Beneficiário: Sergio dos Anjos Ferreira Pinto
• Modalidade de apoio: Auxílio à Pesquisa - Regular