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doi:10.2204/iodp.proc.308.203.2008

Introduction

The objective of this report is to present in situ pressure and temperature data measured using downhole pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 (see the "Expedition 308 summary" chapter). These data have also been presented and interpreted in Long et al. (2007a) (see the “DOWNHOLE” folder in “Supplementary material”). Pressure and temperature data are critical for constraining fluid flow, heat flow, and hydraulic and thermal diffusivity. In addition, temperature affects sediment diagenesis and microbial activity. Expedition 308 is dedicated to the study of overpressure and fluid flow on the Gulf of Mexico continental slope. Knowledge of the pore pressure, and stress regime in general, is critical for evaluating submarine slope stability. It has been hypothesized that overpressure, pore pressures in excess of hydrostatic pressure, can weaken the strength of sediments and thus cause slope instability near the seafloor (Davis et al., 1983; Dugan and Flemings, 2002). Overpressure and the shallow-water flow frequently cause operational problems during drilling (Ostermeier et al., 2001).

Three sites were drilled in Brazos-Trinity Basin IV and three sites were drilled in Ursa Basin during Expedition 308 (Figs. F1, F2, F3). To document the in situ pore pressure and temperature, we deployed two types of pressure penetrometers: the temperature/​dual pressure probe (T2P) and the Davis-Villinger Temperature-Pressure Probe (DVTPP) (Fig. F4). The DVTPP was deployed previously during Ocean Drilling Program Legs 190, 201, and 204 (D’Hondt, Jørgensen, Miller, et al., 2003; Long et al., 2007a; Moore, Taira, Klaus, et al., 2001; Tréhu, Bohrmann, Rack, Torres, et al., 2003). The T2P is a new tool under development as a cooperative effort between Pennsylvania State University, Massachusetts Institute of Technology (MIT), and IODP-Texas A&M University (TAMU) (Expedition 308 Scientists, 2005; Flemings et al., 2006; see also the “PHYSPROP” folder in “Supplementary material”).

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