Structure and development of the continental margin of British Honduras

The continental margin of British Honduras is characterized by elongate ridges that are sub-parallel with the coast and that diverge slightly northward. Each ridge apparently is formed by aligned fault blocks composed of continental basement rock that rotated and subsided during rifting of the margin. The western part of the Cayman Ridge may be underlain by similar rock that extends southwestward into the margin.

Little sediment has been trapped in the basins between the ridges, presumably as a result of long-term, low rates of sedimentation. A canyon system that is controlled by both fault-block ridges and cross faults transects the margin and opens into the Yucatan Basin. Deep-sea sediments are characterized by a succession of pelagic deposits above acoustic basement rocks; these deposits are covered by turbidites that have formed deep-sea fan deposits in some places. The change from pelagic to turbidite deposition may have occurred at the end of Cretaceous time when regional uplift provided a source for clastic materials. The principal channel for transport of sediment to the deep sea is believed to be a graben that extends northeastward from the southwest corner of the Gulf of Honduras.

Development of the margin may have begun in Late Jurassic time when sphenochasmic rifting created the ancestral Gulf of Honduras. Near the end of Cretaceous time, a new set of motions began, with the Caribbean plate moving relatively eastward and slightly away from the North American plate. This new motion resulted in continued movement of basement blocks through Tertiary and Quaternary time. Although this margin is not young, it has a geomorphically youthful aspect in that the sedimentary sequences do not obscure the rift structures.