162 Preliminary Report

Site 907

Site 907 was cored initially on Leg 151. The first Hole 907A was contacted and penetrated into a basalt sill at approximately 220 mbsf, and ADARA temperature measurements were taken during the piston coring operation. The Leg 162 drilling plan was to core two additional APC holes in order to construct a complete sediment section and provide additional sampling material. Because there was no interest in recovering the igneous contact, it was planned that both holes would be terminated slightly above the total depth of Hole 907A.

At 0304 hr on 1 August 1995 the positioning beacon was deployed, initiating Hole 907B. A site location error of 3 min (1.5 nmi) to the east was discovered in the Leg 162 prospectus when the PDR showed nearly 100 m more water depth than at Hole 907A. The beacon was released and subsequently recovered, and the vessel was offset in dynamic positioning (DP) mode to the correct site coordinates while the pipe was being tripped.

A standard APC/XCB BHA was used for all holes at Site 907, including a nonmagnetic drill collar. Hole 907B was offset 15 m to the north of Hole 907A, and Hole 907C was offset the same distance north of Hole 907B. The mudline was established for each hole. The APC firing depth was offset by a few meters for subsequent holes to establish continuous sediment sections.

Routine piston coring proceeded without incident at Holes 907B and 907C until the scientific target depths were reached. All cores, beginning with Cores 907B-3H and 907C-3H, were oriented using the Tensor tool. The positioning beacon was released and subsequently recovered at 1138 hr on 2 August, and the vessel was secured for transit and started underway for Site 985.

To Operations Site 985

162 Table of Contents

Publications Home

(ODP Home)