The structure of acoustic basement and the seismic stratigraphy of the overlying sediments in the Yucatan basin were studied from approximately 4,700 km of UTMSI multichannel seismic reflection profiles (12 fold with air guns and explosive sources) and from available single-channel data. In the central part of the basin the basement lies beneath 1 ½ to 2 sec of sediments, at a total depth of 7 to 8 sec (2-way time). Several basement ridges, spaced 20 to 40 km apart with ½ of relief and trending east-west, were mapped. An east-west basement trend was also observed in the northeastern arm of the basin where the basement is at 6.5 to 7.0 sec with about 1 sec of sediments. Basement highs outcrop at two locations in the western part of the basin and are suitable for uture dredging. West of the basin along the continental slope, several linear elongated sediment-filled troughs with parallel northeast-southeast ridges to the east were observed. Since published refraction and gravity data indicate a typical oceanic crust beneath the Yucatan basin, we propose that the east-west basement features originated as closely spaced fracture zones during the opening of the basin by sea-floor spreading during Jurassic and Cretaceous.

The previously described "pelagic" sediments, which appear transparent on single-channel monitors, showed several unconformities and other sedimentary and deformational features in our data. The basin sediments were divided into several major depositional sequences based on unconformities and seismic character. The time-structure and isochronal maps indicate that although deposition was uniform over the basin in the earlier time, major deposition shifted from one area to the other in later periods.

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