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doi:10.2204/iodp.proc.317.105.2011

Heat flow

Geothermal gradient

Only one temperature measurement was made using the APCT-3 in Core 317-U1353A-5H, and its result was poor because the cooling curve was irregular (Fig. F45; Table T20). Accordingly, it was not possible to determine the geothermal gradient and heat flow.

Thermal conductivity

Thermal conductivity was measured in whole-round core sections from Holes U1353A and U1353B using the full-space needle probe method. Measurement frequency was usually more than once per core with five measuring cycles at each point. This included 21 points in Hole U1353A (0.4–53.2 m CSF-A; unless otherwise noted, all depths in this section are reported in m CSF-A) and 75 points in Hole U1353B (0.7–585.5 m) (Table T21). The middle of each section was chosen as the measurement point unless a void or crack was observed (see "Heat flow" in the "Methods" chapter). Few lithologic variations occur in each section at Site U1353, so this sampling procedure was appropriate. Probe V10701 was used, and heating power was kept to ~3 W for the full-space method.

Thermal conductivity data were discarded when (1) contact between the probe and sediment was poor, (2) thermal conductivity was close to that of water (0.6 W/[m·K]) because of sediment dilution during coring, or (3) measurements were taken in caved layers such as shell hash. In most cases, the first two criteria were controlling parameters for monitoring measurement quality. Good results were obtained from 7 points in Hole U1353A and 39 points in Hole U1353B, covering depth intervals of 7.7–31.1 and 5.2–413.5 m, respectively (Table T21). Although the number of measuring cycles was increased to five based on experience gained from Site U1352, many measurements were still discarded because of poor contact caused by loose sediments.

Thermal conductivity measurements at Site U1353 range from 1.122 to 1.840 W/(m·K) (average = 1.546 W/[m·K]) (Table T21). These results are slightly higher than those from Sites U1351 and U1352 for the equivalent depth interval (above ~414 m), probably resulting from the lower porosity at Site U1353 compared to Sites U1351 and U1352. For the uppermost 130 m, thermal conductivity values are also higher at Site U1353 than in the same interval at nearby ODP Site 1119 (Shipboard Scientific Party, 1999). High conductivities at Site U1353 may be due to high concentrations of quartz (6.5–12.5 W/[m·K]) in fine-grained sediment, including the clay-sized fraction (see "Lithostratigraphy"), and/or carbonate cementation (0.5–4.4 W/[m·K]).

Thermal conductivity versus depth data from Holes U1353A and U1353B are consistent (Fig. F46A). Two downhole increasing trends can be recognized: an increasing trend from 0 to 32 m, reaching a peak at ~30 m, and a subsequent drop followed by another increasing trend from 32 to 414 m. The origin of the peak at ~30 m is unclear because bulk density and porosity are fairly constant from 20 to 80 m (see "Physical properties"). However, a similar feature was observed at shelf Site U1351, although the peak at Site U1353 is more pronounced. The following linear trends can be fitted to the thermal conductivity data:

and

where z is depth (m CSF-A).

Thermal conductivity, in general, correlates negatively with porosity and positively with bulk density (Fig. F46B–F46C). For sand, these correlations are weaker than for lithologies such as mud.

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