Paper No. 140-28
Presentation Time: 3:45 PM
FACIES AND ARCHITECTURAL ELEMENTS OF THE MARIZAL FORMATION: POST RIFT DEPOSITS FROM A RIFT BASIN IN THE CRETACEOUS
The Recôncavo Tucano Jatobá basin (Northeastern Brazil) is part of an aborted rift basin in the southern portion of the Gondwana during its Early Cretaceous breakup. The onset of the basin formation is recorded as lacustrine environments, which gave place to fluvial environments along the Neocomian and prevailed in the Aptian, with the deposition of the Marizal Formation. Previous works on this unit interpreted a fluvial system with evidences of transverse and axial rivers in the Central and northern Tucano segments of the basin, fed from the rift shoulders, suggesting short transport distances. In the present work the architectural elements analysis carried out in the central segment of the basin suggests a predominance of conglomerates and pebbly sandstones associated with scour fill elements with bar migration averaging towards the southwest, associated with aeolian dunes formed by northeastward palaeowinds. The southern segment, on its turn, record the superimposition of few 0.1-1.0 m thick dune sets of cross stratified and well sorted sandstones, organized in up to 4.5 m of aeolian dunes and fluvial deposits, both migrating to southwest. Dune heights and laterally persistent architecture resembles fluvial deposits, although textural and local pin stripe features show evidence of an aeolian origin. These results suggest an increase in the maturity of sediments southwards and the persistence of a fluvial system, with a lower contribution from proximal sources when compared to northernmost segments of the basin. The increased maturity can either be the result of reworked sedimentary sources adjacent to the site of deposition or alternatively indicate the distal part of the upstream larger river system. Paleocurrent data from fluvial and aeolian deposits reveal the continuity of flows towards southwest, which could be indicative of local reworking of aeolian dune fields by fluvial flows of the same trunk river interpreted for the northernmost portion.