Initial Pressure Data from the IODP Expedition 336 CORKs at North Pond
Abstract
In fall of 2011, IODP Expedition 336 cored and instrumented two new CORK observatories in Holes U1382A and U1383C in the "North Pond" sedimented basin in 7 Ma crust west of the mid-Atlantic Ridge. We report the first 6-7 months of pressure data recovered from the two new CORKs during operations with the ROV Jason from R/V Maria S. Merian in April of 2012. North Pond is also the setting of DSDP Hole 395A, which had been cored in 1975-1976 and instrumented in 1997 with an original CORK that was recovered during Expedition 336. Its pressure and downhole temperature data had last been downloaded in 2001, and we also report the subsequent ~6 years of data that were recorded before logger memory filled and logging stopped in 2007. Of the new installations, Hole U1382A was a relatively shallow new hole near Hole 395A, and was instrumented with a single seafloor reference pressure gauge and single formation gauge. Hole U1383C was a deeper hole, with downhole packers intended to isolate three different formation zones with independent formation pressure gauges in addition to the reference seafloor gauge. In both holes, the initial data suggest a slight formation overpressure relative to hydrostatic, which is somewhat surprising given that Hole 395A had a long history of downhole flow of cold ocean bottom water into the formation. Initial analysis of tidal loading as registered in the formation zones in both new holes shows an attenuation and phase lag relative to the seafloor signal that is consistent with that registered in the original Hole 395A CORK (Davis et al., 2001). However, there is essentially no difference in attenuation and phase among the three formation zones in Hole 1383C. This suggests that, while the uppermost CORK seals worked, the downhole packers may not have completely sealed and/or that the entire drilled section is naturally so well connected hydrologically that the same response to tidal loading is seen at all levels.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMOS24B..02B
- Keywords:
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- 0450 BIOGEOSCIENCES / Hydrothermal systems;
- 3021 MARINE GEOLOGY AND GEOPHYSICS / Marine hydrogeology;
- 3036 MARINE GEOLOGY AND GEOPHYSICS / Ocean drilling;
- 3050 MARINE GEOLOGY AND GEOPHYSICS / Ocean observatories and experiments