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doi:10.2204/iodp.proc.327.106.2011

Downhole measurements

Determining heat flow through the sediment column and estimating uppermost basement temperatures were important operational goals at Site U1363. Sediment temperature measurements were attempted at numerous depths during sediment coring at Site U1363 using the APCT-3 and SET tools. The records will require careful processing to estimate in situ temperatures by fitting the data to decay curves for the frictional heating pulse on penetration, based on the thermal properties of the sediments, and to assess data quality and reliability. However, time did not allow for that processing to be completed during Expedition 327. Here we present only the original records of temperature versus time, with a qualitative indication of the quality of the data based on visual inspection and brief shipboard attempts to fit the data to reasonable decay curves.

It is not possible to determine if the data are of high enough quality for reliable interpretation based on a simple presentation of the temperature versus time record (as shown with figures in this chapter). Instead, the data must be processed using a range of possible sediment properties (constrained by physical property measurements, lithostratigraphic information, and core information from other sites) and different parts of the record from each deployment to assess the reliability of the results. The consistency between successive deployments in the same hole will also be assessed as part of postexpedition research.

In Hole U1363B, four deployments were made with the APCT-3 for Cores 327-U1363B-3H through 6H, but it appears that acceptable data were collected only during the deployments for Cores 3H and 5H at 21.5 and 40.5 mbsf, respectively (Fig. F11). The deployments during Cores 4H and 6H appeared to be affected by probe motion during measurement and associated movement of cool bottom water around the coring shoe (Fig. F12). Cores 4H through 6H were partial strokes because of difficulty in penetrating sandy turbidites. APC coring was suspended after Core 6H. A single deployment of the SET tool was attempted in Hole U1363B after Core 8X, but this deployment also showed evidence of probe motion when in the sediment, and measured temperatures were close to bottom water values (Fig. F13).

APC coring was not attempted in Hole U1363C, but the SET tool was deployed three times deep in the section. The first deployment before Core 327-U1363C-2X showed evidence of probe motion (Fig. F13), but the two deployments before Cores 3X and 5X appear to have provided reliable data at ~184 and 203 mbsf, respectively (Fig. F14). These measurements suggest that temperatures in uppermost basement in Hole U1363C are close to 30°C, as estimated from surface heat flow data (Hutnak et al., 2006).

During the final day of operations, three deployments were made with the APCT-3 in Holes U1363F and U1363G, both located very close to Grizzly Bare outcrop, where the sediment cover was <40 m. Two deployments were made on Cores 327-U1363F-3H and 4H at 28.5 and 35.0 mbsf; both returned reasonable data, but the second was of better quality and indicated a basement temperature of ~7°C (Fig. F15). In Hole U1363G, the single deployment on Core 327-U1363G-2H at 16.0 mbsf yielded good data, also suggesting a basement temperature close to 7°C.

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