Marine geophysical investigations off the northern tip of the Antarctic Peninsula by the Brazilian Antarctic Program in 1987 and 1988 have revealed the complex geologic evolution and structure of the Bransfield Basin, and the Bellingshausen continental margin. The Bransfield Basin, within the Bransfield Strait, has an asymmetrical profile with a steeper slope along its northern margin and a conspicuous spreading center closer to the South Shetland Islands. A sedimentary wedge deposited along the southern margin of the basin forms the northern continental margin of the Antarctic Peninsula. Structural features and sedimentary sequences in this wedge show an Atlantic-type margin setting with an older rift sequence and a younger drift sequence.

The Bellingshausen continental margin shows a well-developed continental rise, including a deep-sea fan to the north of Adelaide Island, a steep continental slope and a broad continental shelf. At the outer shelf, clinoforms indicate a prograding shelf to slope environment similar to that of the continental shelf of an Atlantic-type margin. These sediments have prograded above an erosional unconformity, below which tilted and faulted layers are observed and appear to represent an earlier "active" margin setting. A basement high occurs at the eastern limit of the younger passive margin sedimentary wedge, and a closed and buried basin has been discovered to the east of the basement high. The basement high and the closed basin could represent an eroded island arc and a fossil backarc bas n, respectively.

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