The discontinuous coastal exposures of the Bragantina Platform preserve sedimentological information on Cenozoic siliciclastic deposits but do not, by themselves, reveal the geometry of buried channelized bodies along adjacent shallow-subsurface transects. This study asks whether two short Ground-Penetrating Radar (GPR) profiles at Brasília Beach, Outeiro Island, northern Brazil, resolve distinct channel-fill architectures and bounding surfaces that cannot be traced in the nearby cliff exposure. Two profiles (160 and 190 m long) acquired with a 200 MHz shielded monostatic antenna image approximately the uppermost 3 m beneath their acquisition surfaces. Independently, the coastal cliff exposes at least two fining-upward sedimentary cycles with conglomeratic bases, clayey-sandy deposits, planar-parallel mud-rich intervals, a mottled horizon, and local inclined heterolithic stratification (IHS). Profile 1 contains an asymmetric channel-shaped reflection package extending to approximately 3 m apparent depth, with divergent and undulating reflections and a locally chaotic interval. Profile 2 images a shallower channel-shaped package, approximately 1.5 m deep on the interpreted depth scale, dominated by planar/subparallel and gently undulating reflections, with an interpreted basal erosional truncation. These contrasting configurations document differences in shallow channel-fill geometry along the surveyed transects; they do not establish that both profiles image the same channel or stratigraphic horizon. IHS in the coastal exposure supports tidal influence in the local depositional succession but does not independently prove tidal influence in each radar-imaged body. Because a direct stratigraphic tie between the cliff succession and GPR intervals has not been demonstrated, outcrop observations are used as sedimentological context rather than bed-by-bed calibration. The radargrams neither identify the Barreiras–Post-Barreiras contact nor provide a sufficient test of regional neotectonic hypotheses. The value of the dataset lies in its local-scale comparison of two shallow channelized reflection architectures and in an explicit assessment of the interpretive limits of their comparison with nearby coastal outcrops.
