Alluvial-eolian interaction in a Cambrian rift margin: the Pedra das Torrinhas and Pedra Pintada formations (Guaritas Group, RS)

Anais da Academia Brasileira de Ciências

André Marconato²  Renato P. Almeida¹  Maurício G. M. Santos²  Jorge E.s. Nóbrega²  Rogério B. Souza¹ 

[1] ,Universidade de São Paulo Instituto de Geociências Programa de Pós-Graduação em Geoquímica e GeotectônicaSão Paulo SP ,Brasil

关键词: alluvial-eolian interaction;    Pedra das Torrinhas Formation;    Cambrian;    reservoir analogue models;    marginal rift facies;    interação aluvial-eólica;    Formação Pedra das Torrinhas;    Cambriano;    modelos análogos de reservatório;    fácies de margem de rift;   

DOI  :  10.1590/S0001-37652009000400018

来源: SciELO

【 摘 要 】

This work presents a study of selected outcrops from the Pedra das Torrinhas Formation of the Guaritas Group (Cambrian, Camaquã Basin), near the basin bordering Encantadas Fault Zone. The studied succession includes alluvial fan deposits that pass laterally into eolian deposits. Sedimentary facies and architectural element analysis were performed, followed by sedimentary petrography and microscopic porosity analysis, aiming to characterize the porosity of the deposits and its spatial distribution. The main objective was to contribute to a better understanding of the porosity spatial distribution in depositional systems characterized by the interaction between alluvial and eolian processes, with special reference to deposits formed prior to the development of terrestrial plants. Porosity values are related to depositional processes, with higher porosities associated to eolian dune deposits (mean of 8.4%), and lower porosity related to interdunes (mean of 3.4%) and alluvial fans (mean of 4.3%). Architectural elements analysis revealed the spatial relationships of these deposits, a response to the interplay of the eolian and alluvial processes. The integration of porosity data reveals that the interaction of alluvial and eolian processes results in heterogeneous distribution of porosity at the facies association scale. Eolian reworking of alluvial facies increases porosity whereas sheet-flood and other alluvial processes in the interdune areas reduce porosity.

【 授权许可】

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