Deposicional Sequences of the Central Portion of Paraíba do Sul Deltaic Complex (RJ, Brazil)

The Paraíba do Sul Deltaic Complex (PSDC), located in the north of Rio de Janeiro State, comprises the Quaternary deposits of Campos basin onshore portion. The region is characterized by Pleistocene and Holocene beach ridges plains in its south and north portions, respectively, and fluvio-lagoonal deposits in its central portion, stands out for acting as an important storage and by-pass area of sediments to deep waters. The main studies developed in PSDC were based, mainly, in surface data and a few shallow subsurface data. The paucity of deep subsurface data, leading to questionable interpretations and generate a lack of studies that allow the characterization of the sedimentary succession and its distribution. The present study aims the high-resolution stratigraphic analysis and characterization of three deep drillcores (2-TO-1-RJ, 2-MU-1-RJ and 2-BG-1-RJ), in order to provide a better understanding of the evolution of the PSDC central portion. This study allowed the characterization of Emborê Formation (São Tomé Member), a noun outcropping unit, and PSDC deposits, which is represented by four depositional sequences (Q100, Q200, Q300 and Q400) bounded by discordant erosive surfaces. Q100 and Q200 were developed as from forced regressive events, responsible for incised valleys formation in the study area. In the subsequent transgressive phases, the incised valleys were drowned giving origin to an estuarine system in Q100 and an estuarine to open marine system in Q200, which is attributed to the maximum transgressive occurred around 123,000 years BP. Q300 is characterized by a new relative sea level fall phase that promotes localized erosion landward and a lagoon development seaward, as may be observed at 2-TO-1-RJ and 2-MU-1-RJ drillcores, respectively. A following transgressive-regressive (normal regressive) phase allowed the development of extensive beach-ridges plain in the study area. The drillcores correlation suggest a neotectonic activity between Q200 and Q300 depositional sequences, which was responsible for NW-SE structures movement and uplift of the area covered by 2-BG-1-RJ drillcore. The Q400 represent the development of a Holocene lagoon (associated to the maximum transgressive occurred around 5,100 years BP) and its infill by fluvial systems. The presented data and interpretations reveal that genesis and the distribuition of PSDC deposits were controlled by relative sea level changes and, also, by neotectonic movement. The depositional evolution was much more complex than the previous models suggest.