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

Abstract

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.

Aeolian construction and alluvial dismantling of a fault‐bounded intracontinental aeolian dune field (Teruel Basin, Spain); a continental perspective on Late Pliocene climate change and variability

“…, 2006). In the Cambrian Guaritas Group (Brazil), alluvial fans occur in a narrow belt along the border fault and aeolian dune fields developed in the extensional basin (Marconato et al. , 2009).…”

“…The Palaeoproterozoic Baker Lake half-graben (Canada) also displays marginal alluvial fans associated with border faults and the development of lake systems and aeolian dunes (Rainbird et al, 2003;Hadlari et al, 2006). In the Cambrian Guaritas Group (Brazil), alluvial fans occur in a narrow belt along the border fault and aeolian dune fields developed in the extensional basin (Marconato et al, 2009). The Caherbla Group (Devonian, Ireland; Horne, 1975) displays a coexisting faultsourced alluvial fan, fluvial and aeolian dune deposits, the latter encroaching onto the outer slopes of the fan.…”

Fácies sedimentares e elementos arquitetônicos das Formações Serra do Apertado e Pedra Pintada na Região das Minas do Camaquã - RS

“…Trabalhos sobre a arquitetura deposicional das sucessões de dunas eólicas da Pedra Pintada seguiram-se à tese inédita de Paim (1994), destacando-se as interações eólico-fluviais (Paim, Chemale Jr., Lopes, 2002;Paim e Scherer, 2003, 2007Scherer, Paim, Melo, 2003;Teixeira et al 2004;Almeida, 2005;Marconato et al, 2009). …”

Análise de proveniência dos arenitos conglomeráticos do Grupo Guaritas (RS): implicações para o paleoclima e a paleogeografia da sub-bacia Camaquã Central no Eocambriano

“…Posteriormente, Marconato et al (2009) apresentam estudos de proveniência em depósitos de leques aluviais, referentes à Formação Pedra das Torrinhas, e fluviais entrelaçados, pertencentes à Formação Serra do Apertado, próximos da borda leste do Grupo Guaritas. Identificam que, apesar das paleocorrentes similares em ambos os ambientes de sedimentação, com sentido do vetor resultante para NW, na Formação Pedra das Torrinhas predominam seixos compostos por quartzo milonito e granito miloníti-co, com menor contribuição de clorita xistos, enquanto na Formação Serra do Apertado, a proveniência é mais diversificada, com seixos e calhaus de granitos, granitos miloníticos, riolitos e quartzo milonitos.…”