Holocene barrier overstepping, estuarine rollover and drainage merging in a sub-tropical bay

A combination of abundant accommodation and high rates of sediment delivery can allow estuarine incised valleys to archive post-glacial coastal evolutionary processes, including the effects of geological controls on valley positioning and stratigraphic evolution. Seismic-stratigraphic and vibracoring investigations in Babitonga Bay, Santa Catarina, Brazil revealed four main stratigraphic units related to the Upper Pleistocene and Holocene Transgressive System Tract (TST) and Highstand System Tract (HST). The interior of Babitonga Bay was subaerially exposed during lower sea levels, forming two distinct incised valleys. The first was established over the Palmital Shear Zone, while the second was formed beneath the modern Main Channel. During the period of Holocene sea-level rise, a coastal lagoon-barrier system was formed and overstepped, leaving remnants on the shallow shelf. Estuarine facies migrated landward until the drainage systems of the adjacent valleys were unified into the single estuarine basin of Babitonga Bay. During late Holocene sea-level fall, the back-barrier lagoon was infilled and prograding barriers and sandy spits developed in estuarine mouths. This study captures the unique geological framework and post-glacial evolutionary history of Babitonga Bay, illustrating the evolution of a stable tectonic valley in response to rising sea level and changing coastal morphodynamics during the subsequent phase of sea-level fall. It broadens our understanding of the response of similar coupled estuary / coastal sedimentary systems environments in response to sea-level change. •Holocene evolution in a tectonic valley.•Rising sea-level overstepped a barrier system, while estuaries rollover landward.•Bay system formed due two tectonic estuarine valleys amalgamation.•Findings in estuarine tectonic valleys unification may give clues about tectonic valleys drown.