Diamictites and sturtian Cap Dolomites Covering the jacobina group - Araras, North of Campo Formoso - Bahia

Abstract

Occurrences of diamictites with a probable glacial origin underlying limestones north of Campo Formoso - BA around Araras village, had already been described by some authors during the 60´s and 70´s. Some of these occurrences have been recorded in some geological maps of 1/100,000 scales and even in others of smaller scales. The importance of these occurrences which have been studied in greater detail is increased because of the now identified litho-structural similarities (and probable stratigraphic correlation) with those of Ituaçu, América Dourada, Morro do Chapéu (all of which overlie the Chapada Diamantina Group), as well as with those in the northern part of the São Francisco Craton (Patamuté, Bendegó etc. overlying TTG rock units of the basement). For all these cases there is evidence of foreland tectonics associated to the centripetal vergence of the Neoproterozoic fold belts, marginal to the craton. There are some additional observations of these rock units occurring in the level of the "Sul-americana Surface", thus demonstrating deep levels of erosion, which may be partially responsible for the present geographic separation of the whole original litho-stratigraphic context. Nevertheless it seems very clear that these records have somehow been sparsely distributed in the Cryogenian paleogeographic scenery, which may be an additional argument to contest the Snow Ball Earth theory. Some selected geological sections were undertaken in the surroundings of Araras which made it possible to discriminate 4 types of litho-structural relationships between the Jacobina Group (Orosirian) and the overlying diamictites of the São Francisco (Bebedouro Fm. Cryogenian).