IODP

doi:10.2204/iodp.pr.320T.2009

Physical properties

Physical properties were measured on core material recovered during Expedition 320T to test the new installation of the shipboard measurement systems and the users' ability to upload and retrieve data from the LIMS. Magnetic susceptibility, GRA bulk density, and compressional wave velocity were measured on the whole-core sections with the WRMSL. Magnetic susceptibility data collected on the WRMSL are discussed along with magnetic susceptibility data collected on the Special Task Multisensor Logger (STMSL) and the SHMSL in "Paleomagnetism." Natural gamma ray (NGR) activity was measured on a new separate track. Thermal conductivity was measured only on several sections of Core 320T-U1330B-10H because of problems with the new system (likely user error). Split-core measurements on the working half of the core included VP and MAD. A single test of the AVS sediment strength system was also performed, resulting in a satisfactory measurement.

Profiles of whole-core bulk density and VP as well as split-core VP are shown in Figure F13. Bulk density initially increases from a value near 1.40 g/cm3 at the seafloor to ~1.65 g/cm3 at 15 mbsf. Thereafter, bulk density is generally variable between 1.60 and 1.65 g/cm3 to the bottom of the cored interval at 92 mbsf. In the density data plotted in Figure F13 a tendency can be seen in each individual core to have low-to-high density gradient from top to bottom. This has been observed before in soft sediments and is probably an artifact produced by pullout of the piston core.

Compressional wave velocity measured with the WRMSL generally stays close to that of water at ~1440 m/s. There is a systematic difference of ~150 m/s (10%) between the measurements of VP made on the whole-round core and those made on the split core. The cause for this variation was not determined. In either case velocity does not vary appreciably with depth.

Bulk density, grain density, and porosity as determined from discrete samples using the MAD system are illustrated in Figure F14. Bulk density values generally agree with those measured by the WRMSL and are reasonably constant with depth. Of the eight determinations of grain density, three are anomalous, exhibiting values >3 g/cm3 rather than the expected range of 2.20 g/cm3 (biogenic silica) to 2.72 g/cm3 (calcium carbonate). The addition of ~15% pyrite (grain density = 5 g/cm3) could account for the high values, but there was no indication of that much pyrite in the samples. Sampling for MAD specifically avoided the pyrite-rich burrows observed locally throughout the cores. Unfortunately, the dried samples whose weights and volumes were used to calculate grain density were already destroyed in the chemistry laboratory during the carbonate analysis process by the time the anomalies were discovered. Future expeditions will have to monitor these measurements to assess whether there is a real problem. There was no MAD sampling of Core 320T-U1330B-10H because the whole-round sections were left intact for training purposes. Porosity is ~75% in the upper 20 m and decreases as the sediment compacts to <70% by 80 mbsf (Fig. F14).

NGR data were successfully measured from the core sections. Data from Hole U1330B are shown in Figure F15. All of the count levels are low, reflecting the mainly biogenic nature of the sediment. The relatively higher readings in the upper 5 m and the decline to near background levels below that depth may be the result of a postglacial increase in the dust component of the sediment and/or some function of biological and geochemical influences.

The thermal conductivity measurement system collects data (time-temperature curves during heating cycles) but routinely fails to derive a thermal conductivity value from those data. Postmeasurement processing of the data files offline resulted in reasonable thermal conductivity values of ~1.2 W/(m·K) in Core 320T-U1330B-10H.

Downhole measurements

The FlexIt and APCT-3 downhole tools were tested during coring operations in Hole U1330B. The FlexIt tool is used for core orientation and was run in all cores. The APCT-3 tool provides the temperature of the formation and was run on Cores 320T-U1330B-5H, 7H, and 9H. The Sediment Temperature Tool (SET) tool was not run because of time constraints.

During each run of the three APCT-3 tools, mudline temperatures were taken for 5 min both before and after shooting the APC core. Each tool was left in the sediment for 10 min to allow the temperature to equalize prior to pulling out the tool (Fig. F16).

The tools measured a mudline temperature of ~2°C and a sediment temperature ranging from 4.57°C at 45 mbsf to 6.25°C at ~83 mbsf (Fig. F17).

The FlexIt tool was purchased as an APC core orientation tool to replace the aging Tensor tools used during ODP and Phase 1 of IODP. The same type of tool has been run successfully on the D/V Chikyu during expeditions in 2008. The FlexIt tool is run in the sinker bar assembly of the APC tool. The FlexIt is lowered through the drill string until the APC lands in place. The string is then held steady for 5 min while the FlexIt orients prior to shooting the APC core. Data collected from the FlexIt tools are still being processed.