Sedimentary structures and bedding features observed in the shales, siltstones, and fine-grained sandstones of the Sao Sebastiao and Ilhas formations resemble those of turbidite sequences in many respects, but graded bedding, considered to be the only reliable index of turbidity-current action, is essentially lacking. Current bedding predominates, and evidence provided by ripple marks, flute and groove casts, and other criteria indicates that current directions were mainly southerly, along rather than down the west-dipping depositional slope. Analogies with structures, textures, and bedding of the Pleistocene and Recent sediments of the Mississippi delta (where present-day longshore current movement is also predominantly along the slope and perpendicular to channel axes) suggest that the Reconcavo basin deposits were deltaic in origin.

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