Cup-shaped depressions (buracas) are common in northeastern Abrolhos Shelf (Brazil).

Two sedimentary units separated by an erosion surface comprise the depression walls.

The Pleistocene marine lower unit was subaerially exposed during the last glacial.

The Holocene top unit mainly consists of boundstone of encrusting organisms.

The buracas are last-glacial karst sinkholes deepened by Holocene carbonate accretion.