Daily Report for IODP Expedition 311, October 13, 2005
LOCATION: Site U1328 (CAS-06A)
SCIENCE UPDATE: We started APC coring operations in Hole U1328C after drilling to 56 mbsf, where operations were halted because of weather in Hole U1328B. We successfully recovered a pressurized PCS core at a depth of 92 mbsf. At a depth of 103.5 mbsf we switched to XCB coring due to APC refusal. DVTPP temperature measurements were carried out at ~150 and ~197 mbsf, but the data from both runs were degraded by an apparent electronic problem in the tool. By midnight, Hole U1328C had been advanced to 235 mbsf. Core recovery is relatively good, varying between 70 and 75% with the XCB core system. Unlike the upper 35 mbsf cored in Hole U1328B, most of the section within the predicted depth interval for the methane hydrate stability zone in Hole U1328C, is characterized by only subtle IR anomalies, suggesting low gas hydrate concentrations. However, special high resolution pore-water analyses of some low-magnitude IR anomalies showed that gas hydrate was preferentially occupying sand layers possibly at higher concentrations. A core recovered from just above the depth of the seismically inferred BSR depth showed significant low temperature IR anomalies that were subsampled for interstitial water and microbiological analyses. PCS Core U1328B-4P, recovered from 14.5 mbsf in the Hole 1328B, was extruded after degassing (22 L of gas) and X-ray imaging. Comparing the X-ray images from before and after the degassing experiment showed major disruption of the sediment, especially around X-ray inferred massive gas hydrate lenses. Almost the entire core was subsampled for interstitial and headspace gas analyses.