Stratigraphic framework and depositional ciclicity of middle pleistocene-holocene sedimentary systems of the southern shelf of Campos Basin, Brazil
Résumé
Seismic analysis of about 3,000 km of sparker seismic lines allowed us to address a first order stratigraphic and stratal architecture scenario encompassing the shallow sedimentary record (~ 300 milliseconds) of the southern continental shelf of Campos Basin, Brazil. Five major seismic sequences were identified (sequences Sq1 to Sq5), bounded by large margin-scale unconformities (horizons S1-S5). These seismic sequences were interpreted as a succession of depositional sequences induced by repeated glacio eustatic cycles limited by seismic horizons interpreted as master sequence boundaries, representing diachronous periods of erosion originated at times of deepest sea-level lowstands, related to periods of most extensive subaerial exposure of the shelf. These surfaces were reworked during subsequent times of sea level rise. Sequences Sq1-Sq4 are essentially composed of seaward-thickening stacks of forced-regression wedges, implying periods of declining accommodation space for sediments; whereas sequence Sq5 exhibit architectural elements of mostly transgressive units. Comparison between seismic lines and available chronostratigraphic data from the oil industry's exploratory wells made it possible to place the stratigraphic sequences Sq1-Sq5 within the Middle Pleistocene-Holocene interval (last ~ 500 kyr). Correlation of chronostratigraphic data and ?18O-derived information on glaciation-related global sea level variations (Marine Isotope Stages, MIS), also supports the hypothesis that sequences Sq1-Sq4 are fourth-order forced-regression sequences that record 100-120 kyr glacioeustatic cycles and high amplitude sea-level variations (± 100-145 m) for the last ~ 500 kyr, while deposits labeled as Sq5 are mostly represented by Latest Pleistocene-Holocene transgressive and highstand units