At Site 1167, because of a rapid downward increase in induration of the sediments, only one Adara temperature tool measurement from Core 188-1167A-5H (39.7 mbsf) was made. The seafloor temperature (TSF) and stabilized sediment temperature were determined using the TFIT software package (Table T11; Fig. F38). From these data, a geothermal gradient of 17.1°C/km was estimated.
The heat flow and downhole temperatures were estimated according to the methodology described in "In Situ Temperatures" in the "Site 1165" chapter. Using a measured thermal conductivity of 1.59 W/(m·°C) (see "Physical Properties"), the heat flow was determined to be 27.2 mW/m2. The estimated temperature at total depth (441.7 mbsf) was determined to be 7.1°C (Table T11; Fig. F39). The geothermal gradient and heat flow values (17.1°C/km and 27.2 mW/m2, respectively) (Table T11) are significantly less than those determined for Site 1165 (53.4°C/km and 51.4 mW/m2, respectively) (see "In Situ Temperatures" in the "Site 1165" chapter).
This difference in thermal conditions at Sites 1167 and 1165 may be due to differing thermal conductivities and sedimentation rates. At Site 1167, the thermal conductivity is 1.6 W/(m·°C) over the upper 100 mbsf (see "Physical Properties"); however, over a similar depth interval at Site 1165, the mean measured thermal conductivity was significantly lower, at 0.90 W/(m·°C) (see "Physical Properties" in the "Site 1165" chapter). In general, the thermal conductivities were higher throughout the sediment section at Site 1167. This higher thermal conductivity at Site 1167 allows for a greater rate of heat loss from the sediments. Also, sedimentation rates are higher at Site 1167 (up to ~400 m/m.y.) (see "Sedimentation Rates" in "Biostratigraphy and Sedimentation Rates") than at Site 1165 (15 m/m.y. in the uppermost Miocene to Pleistocene section) (see "Biostratigraphy and Sedimentation Rates" in the "Site 1165" chapter). The high sedimentation rate at Site 1167 may have significantly reduced the thermal profile of the sediments compared to that of Site 1165.
The depth to the base of the gas hydrate stability zone (GHSZ) was determined using the Ocean Drilling Program Pollution Prevention and Safety Panel hydrate stability equation, which was modified for seawater (Pollution Prevention and Safety Program, 1992). As only a small variation in the downhole thermal gradients was noted (Table T11), only the initial measured thermal gradient of 17.1°C was used to estimate the base of the GHSZ at 1190 mbsf.