At Site 1226, four different downhole tools were employed: the Adara temperature shoe, the DVTP, the PCS, and the DVTP-P. The results of these deployments are described in the three subsections below.
Fourteen reliable determinations of downhole temperature were made at depths between 0 and 400 mbsf at Site 1226 using the Adara APC temperature tool and the DVTP. Table T12 summarizes the deployments. As described in "Downhole Tools" in the "Explanatory Notes" chapter, in situ temperatures were estimated by extrapolation of the station data using thermal conductivities measured on adjacent cores to correct for the frictional heating on penetration. With the exception of the measurement from 310 mbsf, all of the temperature fits had 95% confidence intervals of <0.01°C.
The estimated in situ temperatures from both the Adara tool and the DVTP define a gradient of 0.0572°C/m in the upper 400 m of the sediment column (Fig. F28A). Extrapolating the temperatures using this temperature gradient yields a value of 25.9°C at the sediment/basement contact. Multiplying the gradient by an average thermal conductivity of 0.85 W/(m·K) (Fig. F26) yields a conductive heat flow estimate of 48.7 mW/m2 at Site 1226. This value lies near the center of global heat flow database values for this area (Pollock et al., 1993). The temperature data from Site 1226 define a profile that is much more linear than the curved profile measured at Site 1225. There is a very slight curvature that can be explained by the decrease in thermal conductivity with depth. Figure F28B shows a theoretical steady-state conductive temperature profile calculated using a constant heat flow of 48 mW/m2 and the measured thermal conductivities from the Hole 1226B cores. The consistency of the data with the calculated steady-state conductive profile indicates that basement temperatures are stable and advective heat transport by upward flow is negligible.
The DVTP-P was deployed twice at Site 1226. During the first run in Hole 1226B, at 241.9 mbsf there was an initial pressure increase of 0.2 MPa during penetration followed by a drop of 12 MPa. Within 2 min pressures abruptly rose again to roughly hydrostatic levels. An average pressure signal equivalent to in situ hydrostatic pressure with ~0.1-0.2 MPa of noise was recorded during the remainder of the 30-min deployment. The abrupt drop in pressure was attributed to a leak near the probe tip. The results of the second deployment in Hole 1226E at 326 mbsf show that the pressure leak was successfully repaired (Fig. F29). The pressure record rose as expected on penetration and then dropped to hydrostatic over the next minute. The pressure then remained constant at hydrostatic level with 0.1- to 0.2-MPa noise for the remainder of the 20-min deployment interval. These data indicate that the seal of the formation around the probe tip was probably not very good and that the tool should be pushed a greater distance into the formation in the future.
Two trial runs of the PCS were made at Site 1226 with extended cutting shoes under rotary drilling. The primary difference between these runs and those at Site 1225 was that targeted intervals were significantly deeper and harder. Core 201-1226B-42P, collected using a Christensen auger with carbide cutters, reached the rig floor at 6208 psi, although the edges of the bit were broken off. After placing this core in an ice bath, the pressure decreased logarithmically to 4907 psi over 150 min (Fig. F30). Approximately 60 mL of gas was released upon opening the tool to atmospheric pressure. Pressure-volume-time relationships during cooling and opening are entirely consistent with the collection of a core with little to no gas (Dickens et al., 2000). Using a Rock Bit International auger with PDC cutters, Core 201-1226E-21P recovered a 1.00-m core but at atmospheric pressure. Examination of the tool revealed that a chert layer was present at the level of the ball valve, which prevented the tool from sealing at depth. There was no damage to the cutting shoe or tool.
The APC-M tool was deployed in Hole 1226B continuously from Cores 201-1226B-5H through 20H and in Hole 1226E continuously from Cores 201-1226E-5H through 12H. The data recovered from the APC-M tool will be analyzed postcruise.