Initial Reports of the Deep Sea Drilling Project - Volume 77

This volume covers Leg 77 of the cruises of the Drilling Vessel Glomar Challenger. The drilling of Leg 77 in the southeastern Gulf of Mexico, western Straits of Florida is part of an overall program by the JOIDES Passive Margin Panel to study the evolution of the western North Atlantic passive margin. The nature and origin of the transitional crust and the overlying Mesozoic sedimentary sequences in the southeastern Gulf was the main objective of Leg 77. By drilling these rocks, it is possible to test, at least in part, the model for the early evolution of the Gulf basin. It also should provide information about the geologic history of adjoining provinces such as the Florida Bank, the Straits of Florida-Bahamas area, Cuba, the Yucatan Basin, and the Campeche Bank. More specifically, some of the general problems that these holes address include: 1) the tectonic evolution of the southeastern Gulf of Mexico and how it relates to the formation of the deep Gulf basin; 2) the nature, age, and origin of (a) the rifted basement (transitional crust) beneath the southeastern Gulf, (b) the synrift sediments associated with tilted basement blocks; and (c) the postrift pre-mid-Cretaceous sedimentary sequence of the southeastern Gulf; 3) a comparison between deep Gulf of Mexico sedimentation and deep North Atlantic Basin sedimentation, and the determination of the time at which the Straits of Florida opened up as a seaway between the Gulf and the Atlantic; 4) a key link for the Mesozoic paleogeography, paleoenvironments, and paleoceanography of the region; 5) the structural history of the southeastern Gulf and how it affected sedimentation; 6) the subsidence and thermal history of the southeastern Gulf; 7) the nature, age, and origin of the prominent mid-Cretaceous unconformity in the area; 8) The post-mid-Cretaceous sedimentary and paleoceanographic history of the western Straits of Florida. Taken a step further, the above objectives are part of the larger question of the early Mesozoic continent assembly and the low-latitude connection of Tethys and the Pacific. Leg 77 began in Ft. Lauderdale, Florida in December 1980 and ended in San Juan, Puerto Rico in February 1981.