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| Author(s): |
Milene Freitas Figueiredo
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Geociências (IG/BT) |
| Defense date: | 2006-02-24 |
| Examining board members: |
Marly Babinski;
Carlos José Souza de Alvarenga;
Paulo Cesar Boggiani
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| Advisor: | Marly Babinski |
| Abstract | |
This work presents a detailed isotopic (C, O, and Sr) chemostratigraphic study carried out on the Ediacaran carbonate succession from the northernmost part of the Paraguay Belt, in Mato Grosso, Brazil. The importance of this study is related to the Earth´s profound climate changes that took place during the Neoproterozoic, which have been recorded by enigmatic sequences composed of glacial deposits immediately overlain by carbonate rocks typical of warm climate. At least three glaciations are recognized: Sturtian (ca. 725 Ma), Marinoan (ca. 635 Ma), and Gaskiers (580 Ma). In order to correlate worldwide the successions deposited in this period and to understand the complex depositional environments, isotopic tools, especially chemostratigraphy, have been widely used. In the study area diamictites of the Puga Formation are overlain by carbonates of the Araras Group, and these, in turn, are covered by diamictites and carbonates of the Serra Azul Formation, which is defined here. The Araras Group carbonates exhibited d13C values between ? 1.7? at the base and + 4 ? at the top and 87Sr/86Sr ratios ranging from 0.7075 at the base to 0.7084 at the very top. These values are similar to those of post-glacial, non-cap Marinoan carbonate successions. The limestones of the Serra Azul Formation yielded d13C values between ? 7.5 and ? 3.2 ?, and 87Sr/86Sr ratios of ca. 0.7086, typical of post-Gaskiers cap carbonates. These isotopic results, together with sedimentological evidence, suggest that two important glaciations occurred during the depositional history of the northernmost Paraguay Belt. (AU) | |