This study seeks to reduce gaps in the sedimentological and stratigraphic understanding of the onshore portion of the Campos Basin (Brazil) through lithofacies analysis and paleoenvironmental interpretation of the Emborê and Barreiras formations based on the 2-JU-1-RJ drill core, the second stratigraphic well drilled in the Paraíba do Sul River Deltaic Complex (CDRPS). These units remain the focus of ongoing debate within the geoscientific community regarding their stratigraphic framework and associated depositional paleoenvironments. Eight lithofacies and three lithofacies successions (LS1–LS3) were identified and described, representing alluvial-fan and fluvial depositional systems. The Emborê Formation (São Tomé Member) comprises distal alluvial-fan deposits (LS1), overlain by sandy braided-river deposits with contributions from debris flows and mudflows (LS2). The Barreiras Formation is represented by sandy braided fluvial deposits characterized by episodic channel drowning and postdepositional sediment modification (LS3). From a sedimentological perspective, the Emborê Formation exhibits strong affinities with deposits of the Resende Formation (Resende and Volta Redonda basins) and the Rio Doce Formation (Espírito Santo Basin), both of which are attributed to the Eocene–Oligocene period. In contrast, the Barreiras Formation exhibits a sedimentary record comparable to that described in outcrops from the onshore sectors of the Campos and Espírito Santo basins.