JA Daily Science Report for Expedition 309, 20 August 2005

LOCATION: Site 1256

SCIENCE UPDATE: A 150 barrel mud sweep was pumped before pulling the final core barrel, which was retrieved at 1100 hr on 20 August. The bit was then pulled to the casing shoe and lowered back to bottom.  No fill was encountered.  Another 150 barrel mud sweep was pumped to clean the hole.  The bit was then pulled out of the hole and cleared the cone at 2025 hr. After Core 170R was retrieved the bit had accumulated 53.1 hours of rotation. Bit #9 had cored 51.3 m with a recovery of 37.57 m (73%) and an ROP of 0.97 m/hr. The bit was in very good condition and the bearings were effective. Four gauge cutters and some inserts from the cones were damaged or missing. Logging operations are currently underway.

The last two cores of Expedition 309 (Cores 169R and 170R) recovered 6.17 m of basalt from 1247.0 to 1255.1 mbsf at the impressive recovery rate of 76%. Three lithological units consisting of aphyric microcrystalline basalt (63, 64, and 65) were identified based on systematic changes in grain size. Piece 17 of Section 169R-1 shows an intrusive contact with a cryptocrystalline dike. The dike material is present in numerous brecciated angular to subangular pieces (0.1-1 cm size), which seem to be embedded in a chloritic matrix. Some phenocrysts form glomerocrysts in Unit 65.

Hole 1256D has now been deepened into basement by 503 m on Expedition 309 to a total depth of 1255 mbsf or 1005 msb.