Abstract of the interior of the Caribbean Plate as well as that of the Yucatán Basin. Proceeding from northwest to southeast, the basins and ridges of the Caribbean, exclusive of active plate margins, are the Yucatán Basin and the Cayman Ridge, part of the North American Plate; and the Nicaraguan Rise, Colombian Basin, Beata Ridge, Venezuelan Basin, Aves Ridge, and Grenada Basin, which make up part of the Caribbean Plate. Geologic history of the subject areas is limited to Mesozoic and Cenozoic time, with the possible exception of the Upper Nicaraguan Rise, which may be partly underlain by a core of pre-Mesozoic rocks. History of crustal formation, probably occurring in the Cretaceous or the Jurassic for most of the Caribbean sea floor, has not been well established because drillholes encountered a basaltic sill/flow sequence, which may postdate initial crustal formation, and because the Caribbean interior is isolated structurally by plate boundaries, relict and active. Identification of magnetic anomaly sequences has been speculative. Time of formation and structural development of the Yucatán and Grenada Basins are as yet also speculative; the basins possibly formed in early Cenozoic time. Evolution of the Caribbean interior is largely that of accumulation of sediments through the Late Cretaceous and Cenozoic, and structural response to stresses applied to existing crust and lithosphere. Some lithosphere was probably consumed along relict subduction zones (upper Nicaraguan Rise, Cayman Ridge, Beata Ridge?, and Aves Ridge) during Late Cretaceous and early Cenozoic time. Apparently, no major plate boundary has extended through the

Abstract The margins of the Caribbean plate are characterized by varying amounts of strike-slip faulting and compressional folding, thrusting, warping, and extensional faulting. The Cayman Trough is a predominantly strike-slip transform boundary except for a short segment of a spreading ridge (Macdonald and Holcombe, 1978; Holcombe and Sharman, 1983). The Barbados Ridge- Lesser Antilles Arc system and the Middle America Trench-Central America Arc system are predominantly compressional, convergent boundaries. The other boundaries have experienced Neogene strike-slip faulting, compression, and extension across a broad plate boundary zone. Because we are dealing with several rigid plates in relative motion with respect to each other, we believe that the Neogene pattern has undergone slow secondorder changes with time (Dewey, 1975). The Neogene and Quaternary pattern has been quite different from Paleogene and Cretaceous patterns of plate boundary organization and deformation (Ladd, 1976; Pindell and Dewey, 1982; Pindell and Barrett, this volume). In this chapter we will review the northern, southern, and eastern boundaries of the Caribbean; the western boundary with the Cocos plate is reviewed only briefly here and more fully in the eastern Pacific volume (von Huene, 1989). Place names referred to in this chapter can be found in Plate 1.

Abstract West of St. Croix, U.S. Virgin Islands, a small plateau (Fredericksted Plateau) sits atop the St Croix Ridge at a depth of 800–1200 m. It is separated from St. Croix by an island slope which is probably a fault scarp, and is bounded on the north by a steep escarpment which leads down to the floor of the Virgin Islands Trough. Numerous small submarine channels indent the island slope and coalesce downslope into three canyons (Shepard Canyon, Sprat Hall Canyon, and Fredericksted Canyon) which interrupt the otherwise gently sloping surface of the Plateau. Fredericksted Canyon is flanked by natural levees and a submarine "floodplain," suggesting that it is associated with an aggrading sedimentation regime. Shepard and Sprat Hall Canyons, on the other hand, are erosional features cut through hard limestone strata of varying resistance to erosion. Fredericksted Plateau is underlain by an unknown thickness of sedimentary strata; a northeast-southwest-trending syncline underlies Fredericksted Canyon. Whereas the older strata were folded with or blanketed on the synclinal structure, the youngest strata include horizontally bedded or gently inclined strata, filling the synclinal valley. The north escarpment coincides with the northwest limb of the syncline. The aggradation associated with Fredericksted Canyon probably proceeded until the level of the valley floor reached the elevation of the rim of the north escarpment in the vicinity of Shepard and Sprat Hall Canyons. Then, with sediments available as cutting tools for erosion, Shepard and Sprat Hall Canyons eroded headward across the Fredericksted Canyon depositional plain, capturing part of the island slope drainage.