LEG 100

Shakedown - Northeastern Gulf of Mexico

The Ocean Drilling Program, successor to the Deep Sea Drilling Project, commenced its field operations on 11 January 1985 with an 18-day shakedown cruise. The cruise came after an extensive conversion and overhaul of the newly chartered drilling vessel, JOIDES Resolution. This drillship is 470 ft long and 70 ft wide with a displacement of 16,596 tons, a derrick towering 217 ft above the waterline, and the ability to employ a drillstring of 30,000 ft (9,146 m) in water depths up to 27,000 ft (8,632 m). The drill ship offers dedicated facilities for studies in sedimentology, paleontology, petrology, geochemistry, geophysics, paleomagnetics, and physical properties accommodated within its twelve on-board laboratories spanning seven decks of the ship in addition to facilities for photography, electronics, and refrigerated core storage.

During the inaugural cruise, three holes were drilled at Site 625 on the west Florida Shelf to document the sedimentological, paleontological, geochemical, geotechnical, and geomagnetic characteristics of the sedimentary sequences, to correlate alternating sedimentary and erosive sequences to world-wide changes in sea level over the past several million years, and to test the advanced piston coring (APC) and extended core barrel (XCB) drilling and coring systems. Hole 625B was the deepest of the three holes drilled and penetrated to 235.2 m subbottom. This hole was continuously cored with the APC system through 197.1 m of Plio-Pleistocene section. The XCB system continued to termination depth in the Lower Pliocene. At the third hole (Hole 625C), an attempt was made to obtain a complete section of the uppermost Quaternary by overlapping the APC cores taken in the previous hole between 5 and 44.5 m subbottom. A visual comparison between the overlapping piston cores indicates that the sequences in each are closely matched. On the basis of physical properties and magnetic susceptibility data, we believe that no more than about 10 cm of material remained unsampled after the double APC coring.

During Leg 100, the on-board scientific, drilling, and operational equipment was tested under varying sea conditions and generally performed to, or even exceeded, expectations. Following Leg 100, the ship was able to depart Miami on 31 January, after only two days in port, for Leg 101, the first fully operational, internationally staffed cruise of the Ocean Drilling Program.