Located in Santa Cruz Cabrália (BA), the Yaya River crosses deposits of the Barreiras Formation and a paleo-estuary within the Quaternary barrier-island system. In April 2023, following heavy rainfall, the sand barrier that channels its flow towards the mouth was breached, forming a 50-meter-wide channel, exposing a trench 34 meters long and 6 meters high. In the context of addressing the climate crisis, understanding geological records and paleoenvironmental evolution aids in comprehending natural processes to better cope with extreme events. The trench was observed in the field, photographed, and sampled. Granulometric (sieving) and chronostratigraphic analyses (LOE) were conducted on the sediments. From field mapping and stratigraphic interpretation, two depositional units and their surfaces were identified. The first unit, U1, extends from the base of the trench to approximately ~2.5 meters in height and spans laterally up to 11 meters. It consists of poorly sorted, bimodal, slightly gravelly white sands with a symmetrical distribution, similar to the sands of the current channel. It features downlap layers and parallel undulating channel structures. Covering U1, U2 reaches 5 meters in height and 34 meters in length, with well-sorted, unimodal medium to coarse sands interspersed with heavy mineral (HM) rich strata, showing a negative asymmetry, similar to beachface sediment. U2 exhibits oblique downlap strata bounded by HM-rich erosive surfaces. Strata truncated by a 1.5-meter deep and 3-meter-wide channel, filled with parallel and wavy onlap stratification with smaller channels, are present. In the upper portion of U2, slightly gravelly sands with nearly flat parallel stratifications predominate; at its top, fine sands represent the active surface of the backshore. The facies succession indicated an upward-fining sequence, marking an environmental transition from a fluvial setting to a coastal environment with beach channeling, characterized by a significant erosive period between 3,360±350 and 2,550±245 years.
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