Sedimentary cycles in a Mesoproterozoic aeolian erg-margin succession: Mangabeira Formation, Espinhaço Supergroup, Brazil

Aeolian systems were abundant and widespread in the early Proterozoic, post-2.2 Ga. However, the majority of aeolian successions of such great age are intensely deformed and are preserved only in a fragmentary state meaning that, hitherto, few attempts have been made to apply a sequence stratigraphic approach to determine mechanisms of aeolian construction, accumulation and preservation in such systems. The Mangabeira Formation is a well preserved Mesoproterozoic erg successions covering part of the São Francisco Craton, northeastern Brazil. The lower unit of the Mangabeira Formation (~ 500 m thick) comprises aeolian deposits of dune, interdune, and sand-sheet origin, as well as some of waterlain origin. These deposits are organized into vertically stacked depositional cycles, each 6 to 20 m thick, and characterized by aeolian sandsheet and waterlain deposits succeeded by aeolian dune and interdune deposits indicative of a drying-upward trend. Aeolian cross-strata exhibit a mean dip direction to the north. Each of these cycles likely arose in response to climatic oscillation from relatively humid to arid conditions, possibly related to orbital forcing. The lower unit of the Mangabeira Formation comprises up to 14 erg sequences. The accumulation and preservation of each was determined by the relative rate of water-table rise and the availability of sand for aeolian transport, both of which changed through time, resulting in the preservation of a succession of repeated drying-upward cycles

Granitóides Brasilianos Precoces do Cinturão Dom Feliciano: Caracterização Geoquímica e Discussão Estratigráfica

Neste trabalho é apresentada uma revisão geral das principais características geoquímicas dos granitoides cálcio-alcalinos precoces do Escudo Sul-rio-grandense e suas implicações na restrição de modelos de evolução geotectônica propostos para o Cinturão Dom Feliciano durante o Ciclo Brasiliano. Discussões acerca dos aspectos estratigráficos, estruturais e metamórficos dessas rochas são igualmente apresentadas, com o objetivo de estabelecer uma cronologia para o magmatismo granítico em relação aos principais eventos tectono-termais responsáveis pela estruturação deste cinturão durante o Proterozóico Superior