Facies and paleo-environments in a stratigraphic succession of Paraíba do Sul River Deltaic Complex central portion (RJ, Brazil)

Abstract

The Paraíba do Sul River Deltaic Complex (PSRDC), located on the northern coast of Rio de Janeiro, is an important Quaternary coastal plain that encompasses part of the Campos Basin onshore portion. Although it has been the subject of sedimentological and stratigraphic studies since the 1940s, the works involving continuous, deep-range subsurface sampling is recent and few in number. Based on this, this paper seeks to contribute through lithological, faciological and paleoenvironmental information from the continuous core sampling of 2-TO-1-RJ (181 m) well and to support discussions about the evolution of PSRDC. Analysis of X-rays diffraction (XRD) in clay minerals, total organic carbon (TOC) and palynofacies were performed for the characterization of depositional paleo-environments. Radiocarbon dating was important for correlation with existing evolutionary models. With the support of petrographic descriptions, twelve sedimentary facies were identified, among them one conglomerate (Ccm), five sandstones (ACm, Am, Amf, Ae and ALm), one heterolithic (IF), two hybrids (Ab and Lh) and three mudstones (Lm, Ll and LAm), grouped in seven facies successions (SF-LA, SF-F1, SF-Dc, SF-M, SF‑F2, SF-Lg and SF‑F3), indicative of different stages of sedimentation. The results point to a basal sedimentation in a typical medium to distal portions of alluvial fans succeeded by deposition in the fluvial environment, both attributed to the São Tomé Member (Emborê Formation). These deposits were partially eroded by the excavation of an incised valley, filled by transgressive estuarine and marine deposits, of Pleistocene age (older than 40,000 years BP). The Holocene record is restricted to the first 13.40 m of the drillcore and suggests the installation of a paleolagoon, filled by a fluvial system.