Daily Report for IODP Expedition 311, October 23, 2005
LOCATION: Sites U1325 (CAS-02C)/U1326 (CAS-03C)
SCIENCE UPDATE: After completing logging operations in Hole U1325C we collected a single mudline core from Hole U1325D, because doubts had risen about the depth of the sulfate/methane interface (SMI) as sampled in Hole U1325C. The new 4.7-m-long mudline core yielded measurable sulfate levels at the bottom of the core, indicating a SMI deeper than 4.5 mbsf, which is ~2.0 m deeper than the SMI in Hole U1325C. After completing Hole U1325D, we pulled the drill pipe back to ~1600 mbrf and transited in DP mode to Site U1326. We spudded Hole U1326B at 12:05 hr but the core contained only 1.55 m of sediment and we spudded a new hole. The first core at Hole U1326C recovered 3.93 m of sediment and we continued to advance the hole by APC coring. At an unexpected shallow depth of ~30 mbsf we hit APC refusal and switched to the XCB coring. Core U1326C-6X contained the first IR imaged cold spot at a depth of ~44 mbsf. One of the thermal anomalies from Core U1326C-6X was subsampled for interstitial water (IW) analysis. Closer inspection of the IW sample indicated that the IR imaged cold-spot was an 8-cm-thick sand unit apparently saturated with gas hydrate. The sample also contained several larger visible pieces of gas hydrate. It was also determined that the surrounding clay-rich sediments did not show any cold temperature or chlorinity anomalies. By midnight Hole U1326C had been advanced to 69.1 mbsf.