Rare earth elements of carbonate rocks from the Bambui Group, southern Sao Francisco Basin, Brazil, and their significance as paleoenvironmental proxies

Autor(es)

de Paula-Santos, Gustavo Macedo ^{[1, 2]} ; Caetano-Filho, Sergio ^[1] ; Babinski, Many ^[1] ; Enzweiler, Jacinta ^[2]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Geociencias, Rua Logo 562, Cidade Univ, BR-05508080 Sao Paulo - Brazil

^[2] Univ Estadual Campinas, Inst Geociencias, Rua Carlos Gomes 250, BR-13083855 Campinas, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Precambrian Research; v. 305, p. 327-340, FEB 2018.
• Citações Web of Science: 13

Resumo

Rare Earth Elements plus Y (REY) data obtained for carbonate rocks of the Bambui Group in the southern portion of the Sao Francisco basin match the C and Sr isotope variations that subdivide the unit in three Chemostratigraphic Intervals (CI-1 to CI-3). The lower CI-1 samples exhibit flat REY shale normalised distributions that record a high freshwater input in the basin after a glacial period. The subsequent marine transgression diminished the continental influence and initiated the development of La, Gd, and Y positive anomalies in the CI-2 samples. Interestingly, a ``seawater{''} like REY pattern is present in the CI-3 samples, which correspond to the closure of the Sao Francisco Basin. Rather than open marine conditions, the CI-3 records a decrease in the silicate chemical weathering of sources located on the marginal belts of the Sao Francisco craton due to higher denudation rates and a change in the dissolved influx towards carbonate rocks. The resultant high concentration of carbonate ions in the restricted sea induced a REY fractionation process similarly to that of the modern ocean. Constant positive Ce/Ce{*} values throughout the shallow and deep sections suggest anoxic early diagenetic conditions, inefficient circulation and stratified water column, which could have worked as a barrier for life diversification in the basin at the Ediacaran-Cambrian limit. Finally, our data show that the REY concentrations of ancient biochemical environments are not an unequivocal tool either to track open and restricted marine settings or to distinguish proximal and distal environments. (AU)

• Processo FAPESP: 17/00399-1 - Intemperismo químico e fluxo de nutrientes para o oceano no Ediacarano superior e suas relações com a diversificação da vida
• Beneficiário: Gustavo Macedo de Paula Santos
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 16/06114-6 - O Sistema Terra e a evolução da vida durante o Neoproterozoico
• Beneficiário: Ricardo Ivan Ferreira da Trindade
• Modalidade de apoio: Auxílio à Pesquisa - Temático