Daily Science Report 17 -- Tuesday, 28 December 2010
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Location
After getting used to generally good to exceptional recovery in the upper 100 m of the igneous basement at this site, today’s Cores U1372A-26R (170.6-175.4 mbsf), -27R (175.4-180.2 mbsf), -28R (180.2-185.0 mbsf), -29R (185.0-189.8 mbsf), -30R (189.8-194.6 mbsf), -31R (194.6-204.2 mbsf), -32R (204.2-209.0 mbsf), -33R (209.0-213.8 mbsf), -34R (213.8-218.6 mbsf), and -35R (218.6-223.4 mbsf) were retrieved with fluctuating recovery between 19% and 115%. This is caused by the predominance of hyaloclastics in this interval resulting in frequent jamming of the core catcher and also in breakouts in the formation that get stuck between the drill collars and the borehole wall. The recovered hyaloclastite hosts many small (lapilli-size), irregular-shaped fragments of aphyric vesicular basalt in a matrix containing fresh volcanic glass particles. Intervals that stretch over several cores are surprisingly well preserved. Meanwhile more results from shipboard measurements from samples of the conglomerate/breccia succession between Core U1372A-4R and -8R (between the young, pelagic sediment cover and the beginning of the igneous “basement”) got generated. It appears that the clasts that make up this succession exhibit a large contrast in p-wave velocity that varies between the different clast types (between 3.5 to almost 6.5 km/sec). This might explain the distinct seismic reflectors of this interval in the seismic side-survey data.
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