Paper No. 140-26
Presentation Time: 3:15 PM
FLUVIAL BARS AND FLOODPLAIN DEPOSITS NEAR A HIGH ACCOMMODATION ZONE (NEOCOMIAN TO BARREMIAN SãO SEBASTIãO FORMATION, TUCANO BASIN, NORTHEASTERN BRAZIL)
Rift basins are characterized by great structural complexity, with the interaction among transfer zones, master faults and minor faults controlling the structural highs and depocenters. The distribution of these features results in differential rates of subsidence and accommodation, implying in variations in the form of preservation and in the architecture of fluvial systems. Areas with higher rates of accommodation can be responsible for greater preservation of architectural elements related to floodplains. Scenarios of this type are found in the eastern part of the Central Tucano Sub-Basin, which witnessed the highest rates of accommodation in the whole Recôncavo-Tucano-Jatobá rift system (Early Cretaceous, Northeastern Brazil), related to the movement of a basin-border fault near the Cícero Dantas low and the Vaza Barris Transfer Zone. In this area, fluvial deposits of the São Sebastião Formation crop out (Neocomian to Barremian), showing the intercalation between the deposits of sandy fluvial bars and fine-grained floodplains. The interaction between these elements is interpreted as the consequence of frequent channel avulsion, induced by local tectonic movements capable of shifting the channels laterally and thus promoting abandonment and the installation of environments dominated by the settling of fine particles. The comparison of these deposits with the successions dominated by sandy bars of the central areas of the same basin suggest that local tectonic controls, variations in the tilt of the basin floor and higher subsidence rates were responsible for the preservation of the floodplain deposits.