Microorganisms in marine subsurface sediments substantially contribute to global biomass. Sediments warmer than 40°C account for roughly half the marine sediment volume, but the processes mediated by microbial populations in these hard-to-access environments are poorly understood. We investigated microbial life in up to 1.2-kilometer-deep and up to 120°C hot sediments in the Nankai Trough subduction zone. Above 45°C, concentrations of vegetative cells drop two orders of magnitude and endospores become more than 6000 times more abundant than vegetative cells. Methane is biologically produced and oxidized until sediments reach 80° to 85°C. In 100° to 120°C sediments, isotopic evidence and increased cell concentrations demonstrate the activity of acetate-degrading hyperthermophiles. Above 45°C, populated zones alternate with zones up to 192 meters thick where microbes were undetectable.

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The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a multidisciplinary investigation of fault mechanics and seismogenesis along subduction megathrusts and includes reflection and refraction seismic imaging, direct sampling by drilling, in situ measurements, and long-term monitoring in conjunction with laboratory and numerical modeling studies. The fundamental objectives of NanTroSEIZE are to characterize the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout an active plate boundary system. As part of the NanTroSEIZE program, operations during Integrated Ocean Drilling Program (IODP) Expedition 348 were planned to extend and case riser Hole C0002F, begun during IODP Expedition 326 in 2010 and continued during Expedition 338 in 2012, from 860 to 3600 meters below the seafloor (mbsf).Riser operations during Expedition 348 were carried out and deepened the hole to 3058 mbsf, a new maximum depth record in scientific ocean drilling. Operations included installation and cementing of 13 3 ⁄8 inch casing to 2008.9 mbsf and an 11¾ inch liner to 2922.5 mbsf, stabilizing the borehole for future deepening. Reaching this depth required two sidetracking operations from the original Hole C0002F, resulting in the designation of Holes C0002N and C0002P for the successively deeper sidetracks. During drilling, a suite of logging-while-drilling (LWD) and measurement-while-drilling (MWD), mud-gas, and cuttings data were collected over the interval from 2162.5 to 3058.5 mbsf in Hole C0002P, and a partial suite was collected in Hole C0002N. The interval from 2163 to 2218 mbsf was cored with the rotary core barrel (RCB). Planned future riser drilling operations will deepen the hole to penetrate the plate boundary fault at ~4600-5200 mbsf.Additionally, a test hole for a prototype slimhole small-diameter RCB (SD-RCB) coring system, Hole C0002M, was drilled in riserless mode near Hole C0002F. The hole was advanced to 475 mbsf, where four cores were collected to 512.5 mbsf.Overall, Expedition 348 sampled and logged a deep interval in Holes C0002N and C0002P within the inner accretionary wedge, from 856 to 3058.5 mbsf, including a never-before sampled zone in the lowermost ~1 km of drilling. Cores were collected over a 55.5 m interval from 2163 to 2218.5 mbsf. The sampled sedimentary rocks are composed of hemipelagic sediment and fine turbi-

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X-ray computed tomography (XCT) can be used to identify lithologies and deformation structures within geological core, with the potential for the identification processes to be applied automatically. However, because of drilling disturbance and other artifacts, the use of large XCT-datasets in automated processes requires methods of quality control that can be applied systematically. We propose a new systematic method for quality control of XCT data that applies numerical measures to CT slices, and from this obtains data reflective of core quality. Because the measures are numerical they can be applied quickly and consistently between different sections and cores. This quality control processing protocol produces downhole radiodensity profiles from mean CT-values that can be used for geological interpretation. The application of this quality control protocols was applied to XCT data from International Ocean Discovery Program (IODP) Expedition 370 Site C0023 located at the toe of the Nankai accretionary complex. The evaluation of core quality based on this protocol was found to be a good fit to standard-evaluations based on the visual description of core, and could be used to select samples free from drilling disturbance or contamination. The quality-controlled downhole mean CT-value profile has features that can be used to identify lithologies within a formation, the presence and type of deformation structures and to distinguish formations.