Facies and isotopic signature (Sm-Nd) of Barra de Tabatinga Formation: new insights on the registration of a pleistocenic marine paleolevel in northeastern Brazil

This paper represents the integration and interpretation of past data, field geology, with subsequent laboratory analysis, carried out in the coastal region, eastern coast of Rio Grande do Norte, between Baía Formosa and Natal, regarding the stratigraphic record of a marine level pleistocene. The relative variation of the shoreline and its morphological features are directly associated to tectonic and paleoclimatic interferences. These variations model the locally acting depositional systems, stacking lithostratigraphic units with single signatures, with respect to lithotype, sedimentary structures, diagenesis, depositional age and crystallization age of the source rock. Sedimentological and granulometric evaluations indicate low energy environments of deposition, correlated to intermarine systems. For this purpose outcrops were described, slides were prepared, and a granulometry analysis was carried out. Sm-Nd isotopic analyses, including sediments adjacent to the shoreline, were performed with the aim of characterizing isotopic signatures and identifying their probable source areas. After information processing, it was possible to characterize and insert in the regional stratigraphy, Barra de Tabatinga Formation, deposited possibly during a transgressive pleistocene pulse, with medium to coarse sand granulometry, and isotopic signature concentrated in the lower Paleoproterozoic (Siderian), different from the units under and superimposed, respectively, Barreiras Group (very heterogeneous granulometry and isotopic signature distributed throughout the entire Paleoproterozoic) and Coastal Eolic Deposits (fine to medium sand granulometry). (author)