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Stratigraphy and ages of four Early Silurian through Late Devonian, Early and Middle Mississippian glaciation events in the Parnaíba Basin and adjacent areas, NE Brazil
Turbidity currents, tectonism, debris flows, glaciation, and other geologic processes are considered to be responsible for the generation of Silurian–Mississippian diamictites in northern Brazil. Processes that best account for the features observed in these strata are glaciation, deglaciation and sedimentary deformation. Four main glacial ages are identified to have occurred in the Parnaíba Basin during the Paleozoic. Glacially influenced deposits are found in the Lower Silurian, Upper Devonian, Lower Mississippian, and Middle Mississippian strata. The Parnaíba Basin is characterized by outcrops providing robust lithological evidence for three glacial ages, identified by lithological features and dated by palynological studies. A fourth glaciation, as old as Tournaisian, was recently recognized only in the subsurface of the basin. The glacial features were illustrated and the rocks accurately dated with palynomorphs based on very accurate palynological studies. Additional, palynological information, derives from outcrops and shallow boreholes drilled by a private company (Themag) and the National State Mineral Production Department (Departamento Nacional de Produção Mineral -DNPM), and the Brazilian Geological Survey Company (Companhia de Pesquisa de Recursos Minerais-CPRM). The purpose of this reexamination, including many new illustrations, interpretations and conclusions, is to evaluate primary sedimentological and paleontological data related to the above mentioned glaciations. Some authors remain skeptical about the record of Early to early Late Paleozoic glaciations in western Gondwana, especially in Brazil, mainly because evidence provided in the literature is relatively scanty. The Parnaíba Basin provides special conditions for the study of these glaciations, although evidence for each of them varies considerably as discussed in the text.