Integration of core and wireline data from Hole U1309D, Atlantis Massif, IODP Expeditions 304 and 305.

Core recovery is often poor in igneous successions however, in IODP Expeditions 304 and 305 excellent rock recovery enables the direct link between the rock record and key petrophysical properties. Here we examine data from IODP Site U1309. This site was drilled at the Atlantis Massif (western flank of Mid-Atlantic Ridge (MAR) 30°N), through a 1.5-2 Ma old oceanic core complex. The main hole, Hole U1309D, is the second deepest hole drilled into an intrusive slow-spread oceanic lithosphere: it penetrated 1415.5 mbsf. Of the 75% recovered core, 96% is gabbroic, comprising olivine-rich troctolites (>70% modal olivine), troctolites, olivine and troctolitic gabbros (5 to 50% modal olivine), gabbros (including gabbronorites) and oxide gabbros (>2% modal Fe-Ti oxides). Even though rock recovery levels for this expedition were consistently high, only by correlating the core with the down-hole logs can continuous information regarding the lithologies and mineralogy be obtained for the entire drilled hole, i.e. the logs can circumvent the issue that 25% of the rock was lost. Down-core mineral modal percentage changes reveal variations in the proportion of olivine, plagioclase and clinopyroxene. In particular below ~970mbsf the modal percentage values for olivine fluctuate strongly from a low (≤40%) - high (>40%) - low zone to the base of the hole. This zonation is highlighted by the gamma ray log, and the density log picks up the main mineralogical changes, i.e. potential mineral zone boundaries. Additionally, alteration which locally causes serpentinization can be identified in the logs, particularly with neutron porosity and resistivity logs. Being able to thoroughly investigate these core-log data linkages in regions of relatively high core recovery enables the transfer of knowledge to more problematic, challenging areas, particularly in sections of poor core recovery. The result is a continuous log based lithological profile which has been calibrated on core data.