Integrated Ocean Drilling Program (IODP) Expedition 322 is part of the Nankai Trough Seismogenic Zone Experiment (NanTro-SEIZE) and was designed to document characteristics of incoming sedimentary strata and upper igneous basement prior to their arrival at the subduction front. To accomplish these objectives, coring was conducted at two sites in the Shikoku Basin on the subducting Philippine Sea plate. Site C0011 is located on the northwest flank of a prominent bathymetric high (the Kashinosaki Knoll), whereas Site C0012 is located near the crest of the knoll. The resulting data, which include logging while drilling during IODP Expedition 319, provide a wealth of new information on presubduction equivalents of the seismogenic zone. Unfortunately, coring at Site C0011 began at 340 m core depth below seafloor (CSF) and failed to reach the total depth target because of premature destruction of the drill bit at 876 m CSF. Coring at Site C0012, however, penetrated almost 38 m into igneous basement and recovered the sediment/basalt interface intact at 537.81 m CSF. The age of basal sediment (reddish brown pelagic claystone) is >18.9 Ma. This recovery of basement was a major achievement, as was the comprehensive integration of core-logseismic data at Site C0011. The correlation of lithofacies and agedepth models from the two sites within the Shikoku Basin shows changes from an expanded section (Site C0011) to a condensed section (Site C0012) and captures all of the important ingredients of basin evolution, including a previously unrecognized interval of late Miocene tuffaceous and volcaniclastic sandstone designated the middle Shikoku Basin facies. An older (early to middle Miocene) turbidite sandstone/siltstone facies with mixed detrital provenance occurs in the lower Shikoku Basin; this unit may be broadly correlative with superficially similar Miocene turbidites on the western side of the basin. When viewed together, the two sites around the Kashinosaki Knoll not only demonstrate how basement relief influenced rates of hemipelagic and turbidite sedimentation in the Shikoku Basin, but also build the complete lithostratigraphic template on which all of the postexpedition laboratory results can be placed. Those forthcoming details will include mineral and volcanic ash composition, geotechnical properties, frictional properties, and hydrological properties. Another triumph came from geochemical analyses of interstitial water and hydrocarbons at Site C0012. Unlike other so-called reference sites in the Nankai Trough, interstitial water on top of the

The location of the Integrated Ocean Drilling Program's (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) was based on regional two-dimensional seismic reflection surveys carried out by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Final site locations were chosen based on a three-dimensional (3-D) seismic reflection survey acquired across the seaward margin of Kumano Basin and the accretionary prism from the basin to the deformation front. This survey covered a region 12 km wide (approximately parallel to the regional structural strike) and 56 km long (approximately perpendicular to the regional strike) and provided detailed images of the structure and seismic stratigraphy of the drill sites. Sites were drilled in the frontal thrust zone at the toe of the accretionary prism, the frontal region of the megasplay fault zone, and the forearc basin. The 3-D seismic data volume images a main frontal thrust at the prism toe with the hanging wall thrust at least 7.5 km seaward over the trench. This configuration is different from that in other parts of the Nankai prism. At the shallow end of the megasplay, the data images a complex thrust system that truncates older structures in the underlying accretionary prism and shows that the hanging wall block has overridden more than 1250 m of young slope sediments. At the forearc basin site, we interpret landward-dipping forearc basin strata onlapping older slope sediments, which in turn overlie an older part of the accretionary prism.

Seismostratigraphy, coring, and logging while drilling during Integrated Ocean Drilling Program Expeditions 319, 322, and 333 (Sites C0011/C0012) show three Miocene submarine fans in the NE Shikoku Basin, with broadly coeval deposits at Ocean Drilling Program Site 1177 and Deep Sea Drilling Project Site 297 (NW Shikoku Basin). The sediment dispersal patterns have major implications for paleogeographies at that time. The oldest, finer‐grained (Kyushu) fan has sheet‐like geometry; quartz‐rich flows were fed mostly from an ancestral landmass in the East China Sea. During prolonged hemipelagic mud deposition at C0011‐C0012 (~12.2 to 9.1 Ma), sand supply continued at Sites 1177 and 297. Sand delivery to much of the Shikoku Basin halted during a phase of sinistral strike slip to oblique plate motion, after which the Daiichi Zenisu Fan (~9.1 to 8.0 Ma) was fed by submarine channels. The youngest fan (Daini Zenisu; ~8.0 to 7.6 Ma) has sheet‐like geometry with thick‐bedded, coarse‐grained pumiceous sandstones. The pumice fragments were fed from a mixed provenance that included the collision zone of the Izu‐Bonin and Honshu Arcs. The shift from channelized to sheet‐like flows was favored by renewal of relatively rapid northward subduction, which accentuated the trench as a bathymetric depression. Increased sand supply appears to correlate with long‐term eustatic lowstands of sea level. The stratigraphic position and 3‐D geometry of the sandbodies have important implications for subduction‐related processes, including the potential for focused fluid flow and fluid overpressures above and below the plate boundary fault: In sheet‐like sands, pathways for fluid flow have greater horizontal permeability compared with those in channel sands.

lieh, obwohl der Vorgang geographisch diachron ist. Sein Verschwinden aus dem Südatlantik ist frühzeitig, grob korrelierbar mit Schätzungen aus tropischen Regionen. Kurze Intervalle starker Häufigkeit von C. reticulatum und C. protoannula können darauf hindeuten, daß ihr letztes Erscheinen (jeweils 37.86 Ma und 38.18 Ma) einen begrenzeten biochronologischen Wert hat. Für die Eozän/Oligozän-Grenze wird anhand des Hole 522 und des Aussterbens von Hantkenina ein Alter von 36.15 Ma bis 36.20 Ma vorgeschlagen. Das nächstliegende Nannofos-Silienereignis ist das erste häufige Erscheinen von E. obruta (36.07 Ma) oder, regional (?), der scharfe Umschlag im Verhältnis R. umbilicus/C. formosus (36.10 Ma).

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Drilling operationsThe advanced piston corer (APC), extended core barrel (XCB), and rotary core barrel (RCB) systems were used during Expedition 344. The APC and XCB systems were used to recover the sedimentary section in Holes U1381C, U1412A, U1412B, U1413A, U1413B, and U1414A and the sediment/basement interface at Hole U1381C. The RCB system was used to recover sediment and basement sections in Holes U1380C, U1412C, U1412D, U1413C, and U1414A.The APC system cuts soft-sediment cores with minimal coring disturbance relative to other IODP coring systems. After the APC core barrel is lowered through the drill pipe and lands above the bit, the drill pipe is pressured up until the two shear pins that hold the inner barrel attached to the outer barrel fail. The inner

During IODP Expedition 322, an interval of Late Miocene (7.6 to 9.1 Ma) tuffaceous and volcaniclastic sandstones was discovered in the Shikoku Basin (Site C0011B), Nankai region. This interval consists of bioturbated silty claystone including four 1-7 m thick interbeds of tuffaceous sandstones (TST) containing 57-82% (by volume) pyroclasts. We use major and trace element glass compositions, as well as radiogenic isotope compositions, to show that the tuffaceous sandstones beds derived from single eruptive events, and that the majority (TST 1, 2, 3a) came from different eruptions from a similar source region, which we have identified to be the Japanese mainland, 350 km away. In particular, diagnostic trace element ratios (e.g., Th/La, Sm/La, Rb/Hf, Th/Nb, and U/Th) and isotopic data indicate a marked contribution from a mantle source beneath continental crust, which is most consistent with a Japanese mainland source and likely excludes the Izu-Bonin island arc and back arc as a source region for the younger TST beds. Nevertheless, some of the chemical data measured on the oldest sandstone bed (TST 3b, Unit IIb) show affinity to or can clearly be attributed to an Izu-Bonin composition. While we cannot completely exclude the possibility that all TST beds derived from unknown and exotic Izu-Bonin source(s), the collected lines of evidence are most consistent with an origin from the paleo-Honshu arc for TST 1 through 3a. We therefore suggest the former collision zone between the Izu-Bonin arc and Honshu paleo-arc as the most likely region where the eruptive products entered the ocean, also concurrent with nearby (200 km) possible Miocene source areas for the tuffaceous sandstones at the paleo-NE-Honshu arc. Estimating the distribution area of the tuffaceous sandstones in the Miocene between this source region and the 350 km distant Expedition 322, using bathymetric constraints, we calculate that the sandstone beds represent minimum erupted magma volumes between 1 and 17 km 3 (Dense Rock Equivalent (DRE)). We conclude that several large volume eruptions occurred during the Late Miocene time next to the collision zone of paleo-Honshu and Izu-Bonin arc and covered the entire Philippine Sea plate with meter thick, sheet-like pyroclastic deposits that are now subducted in the Nankai subduction zone.

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