Previous   |   Next

doi:10.2204/iodp.proc.323.104.2011

Downhole measurements

Because of uncertain hole conditions in Hole U1340A and the potentially higher yield of logs for cruise objectives at Site U1341, the logging program was deferred until Site U1341 was drilled. The only downhole measurements made at Site U1340 were APCT-3 in situ temperature measurements.

Temperature measurements

The downhole temperature measurements at Site U1340 included four APCT-3 deployments in Hole U1340A (Table T18). During its deployment in Core 323-U1340A-3H, the APCT-3 failed to couple properly with the formation and the recorded data could not be used. The measured temperatures range from 5.67°C at 70.4 m DSF to 9.79°C at 165.4 m DSF and closely fit a linear geothermal gradient of 43.4°C/km (Fig. F42). The temperature at the seafloor was 2.8°C based on the average of the measurements at the mudline during all APCT-3 deployments. A simple estimate of the heat flow can be obtained from the product of the geothermal gradient by the average thermal conductivity (0.851 W/[m·K]; see "Physical properties"), which gives a value of 36.9 mW/m², within the range of previous measurement in the area (the global heat flow database of the International Heat Flow Commission can be found at www.heatflow.und.edu/index.html).

Considering the variations in thermal conductivity with depth, a more accurate measure of the heat flow in a conductive regime can be given by a "Bullard plot." The thermal resistance of an interval is calculated by integrating the inverse of thermal conductivity over depth. If the thermal regime is purely conductive, the heat flow will be the slope of the temperature versus thermal resistance profiles (Bullard, 1939). Thermal resistance calculated over the intervals overlying the APCT-3 measurements is shown in Table T18, and the resulting linear fit of the temperature gives a slightly higher heat flow value of 37.8 mW/m².

Top of page   |   Previous   |   Next