Zachos, J.C., Kroon, D., Blum, P., et al., 2004 Proceedings of the Ocean Drilling Program, Initial Reports Volume 208

2. EXPLANATORY NOTES1

Shipboard Scientific Party2

INTRODUCTION

The “Explanatory Notes” chapter presents information that will help the reader understand our shipboard observations and measurements, which are the basis for the preliminary conclusions found throughout this volume, and also help the interested investigator select samples for further analysis. This information concerns only shipboard operations and analyses reported in the Leg 208 Initial Reports volume of the Pro- ceedings of the Ocean Drilling Program (ODP). Methods used by various investigators for shore-based analyses of Leg 208 samples will be de- scribed in the individual scientific contributions published in the Scien- tific Results volume and in publications in various professional journals. A significant part of this chapter is material that has been presented in previous ODP Proceedings volumes, as ODP strives to keep well-estab- lished and accepted standard procedures consistent from leg to leg. Other issues more specific to Leg 208, such as instruments, methods, and procedures that were relatively new in the framework of the evolv- ing ODP shipboard environment or that were used specifically to ad- dress Leg 208 objectives, are presented here in greater detail.

OPERATIONS

Site Locations

At all Leg 208 sites, Global Positioning System (GPS) coordinates from precruise site surveys were used to position the vessel on site. 1 Once the vessel was positioned on a site, the thrusters were lowered and Examples of how to reference the whole or part of this volume. a reference beacon was deployed. Although the automated stationkeep- 2 Shipboard Scientific Party ing system of the vessel usually uses GPS data, the beacon provides a addresses. backup reference in case of problems with the transmission of satellite Ms 208IR-102 SHIPBOARD SCIENTIFIC PARTY CHAPTER 2, EXPLANATORY NOTES 2 data. The final site position was the mean position calculated from the GPS data collected over a significant portion of the time the site was oc- cupied. At the end of operations at a site, the beacon was retrieved and the thrusters were retracted before the vessel proceeded to the next site.

Drilling Operations

Two coring systems were used during Leg 208: the advanced hydrau- lic piston corer (APC) and the extended core barrel (XCB). The APC is a “cookie cutter”–type system that cuts cores with minimal coring distur- bance. The drill pipe is pressured up until one or two shear pins that hold the inner barrel to the outer barrel fail. The inner barrel strikes out and cuts the core. The driller can detect a successful cut or “full stroke” by the pressure gauge on the rig floor. Whenever possible, the APC was used during Leg 208 because it yields the least disturbed cores. When “APC refusal” occurs in a hole before the target depth is reached, the XCB is used to advance the hole. The XCB is a rotary sys- tem with a small cutting shoe extending below the large rotary bit. The smaller bit can cut a semi-indurated core with less torque and fluid cir- culation than the main bit and thus optimizes recovery. If the forma- tion becomes even more indurated, the rotary core barrel (RCB) is used. The RCB system is the most conventional drilling system, but it was not needed during Leg 208. Both the APC and XCB systems use the same bottom-hole assembly (BHA), and switching from one to the other does not require a pipe trip. 7 The standard BHA used at all Leg 208 sites comprised a 9 /8-in APC/XCB polycrystalline diamond bit, a bit sub, a seal bore drill collar, a landing saver sub, a modified top sub, a modified head sub, a nonmagnetic drill collar, five 8¼-in drill collars, a tapered drill collar, six joints of 5½-in drill pipe, and one crossover sub. The BHA length was 136 m with a to- tal weight of 35,000 lb. When it became necessary to drill over stuck core barrels, the standard steel barrel assem