Site C0018

,

doi:10.2204/iodp.proc.333.103.2012

Cited by 25 publications

(11 citation statements)

References 12 publications

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“…1), along which mega-thrust earthquakes are known to occur (Tobin and Kinoshita, 2006). Sites C0011 and C0012 were drilled in order to characterize the pre-subduction inputs to the Nankai subduction zone (Saito et al, 2010;Henry et al, 2012a). They are located ~10 km apart in the Shikoku Basin, Japan, ~100 km southeast of the Kii Peninsula and ~160 km west of the Izu-Bonin Arc on the Kashinosaki Knoll, a prominent bathymetric high-as in its current configuration or as an off-axis volcanic seamount (Ike et al, 2008).…”

Section: Sources Of Volcanic Ash To the Nankai Regionmentioning

confidence: 99%

“…2). Shipboard smear slide analyses of the bulk sediment (note, not of the ash layers) estimate that volcanic ash constitutes an average of ~25-30 wt% of the bulk sediment through Units I and II, and decreases to ~7-15 wt% in Unit III (Saito et al, 2010;Henry et al, 2012a). In Unit IV, the smear slide values vary from ~1% to ~40%, and average ~11% with an increase in Unit V to ~50% on average.…”

Section: Sedimentology and Stratigraphymentioning

confidence: 99%

“…In Unit IV, the smear slide values vary from ~1% to ~40%, and average ~11% with an increase in Unit V to ~50% on average. The smear slide estimates differentiate between "volcanic glass" and "volcanic lithics" in the bulk sediment, but they do not yield further compositional information and have wide uncertainties, making specific interpretations based on smear slides correspondingly uncertain as well (Saito et al, 2010;Henry et al, 2012a).…”

Section: Sedimentology and Stratigraphymentioning

confidence: 99%

“…Dry bulk-density values were calculated from shipboard moisture and density measurements (Saito et al, 2010;Henry et al, 2012a). Depositional ages were calculated by fitting linear segments to the respective age-depth models (Henry et al, 2012a), solving for the slope of each line segment, and then computing the age for each depth point on that segment.…”

Section: Shikoku Basin Paleogeographymentioning

confidence: 99%

“…Depositional ages were calculated by fitting linear segments to the respective age-depth models (Henry et al, 2012a), solving for the slope of each line segment, and then computing the age for each depth point on that segment.…”

Section: Shikoku Basin Paleogeographymentioning

confidence: 99%

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Sedimentary inputs to the Nankai subduction zone: The importance of dispersed ash

et al. 2018

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We examine the importance of dispersed volcanic ash as a critical component of the aluminosilicate sediment entering the Nankai Trough, located south of Japan's island of Honshu, via the subducting Philippine Sea plate. Multivariate statistical analyses of an extensive major, trace, and rare earth element data set from bulk sediment and discrete ash layers at Integrated Ocean Drilling Program (IODP) Sites C0011 and C0012 quantitatively determine the abundance and accumulation of multiple aluminosilicate inputs to the Nankai subduction zone. We identify the eolian input of continental material to both sites, and we further find that there are an additional three ash sources from Kyushu and Honshu, Japan and other regions. Some of these ash sources may themselves represent mixtures of ash inputs, although the final compositions appear statistically distinct. The dispersed ash comprises 38 ± 7 weight percent (wt%) of the bulk sediment at Site C0011, and 34 ± 4 wt% at Site C0012. When considering the entire sediment thickness at Site C0011, the dispersed ash component supplies 38000 ± 7000 g/cm 2 of material to the Nankai subduction system, whereas Site C0012 supplies 20000 ± 3000 g/cm 2 . These values are enormous compared to the ~2500 g/cm 2 (C0011) and ~1200 g/cm 2 (C0012) of ash in the discrete ash layers. Therefore, the mass of volcanic ash and chemically equivalent alteration products (e.g., smectite) that are dispersed throughout the stratigraphic succession of bulk sediment appears to be up to 15-17 times greater than the mass of discrete ash layers. The composition of the dispersed ash component at Site C0011 appears linked to that of the discrete layers, and the mass accumulation rate for dispersed ash correlates best with discrete ash layer thickness. In contrast, at Site C0012 the mass accumulation rate for dispersed ash correlates better with the number of ash layers. Together, the discrete ash layers, dispersed ash, and clay-mineral assemblages present a complete record of volcanism and erosion of volcanic sources; and indicate that mass balances and subduction factory budgets should include the mass of dispersed ash for a more accurate assessment of volcanic contributions to large-scale geochemical cycling.

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Section: Sources Of Volcanic Ash To the Nankai Regionmentioning

confidence: 99%

Section: Sedimentology and Stratigraphymentioning

confidence: 99%

Section: Sedimentology and Stratigraphymentioning

confidence: 99%

Section: Shikoku Basin Paleogeographymentioning

confidence: 99%

Section: Shikoku Basin Paleogeographymentioning

confidence: 99%

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Sedimentary inputs to the Nankai subduction zone: The importance of dispersed ash

et al. 2018

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Flow dynamics of Nankai Trough submarine landslide inferred from internal deformation using magnetic fabric

Kanamatsu

Kawamura

Strasser

et al. 2014

Geochem. Geophys. Geosyst.

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Submarine landslide deposits in an active subduction zone were investigated by Integrated Ocean Drilling Program Expedition 333 as the ''Nankai Trough Submarine Landslides History.'' The expedition recovered a Pleistocene to Holocene sequence of stacked mass-transport deposits at Site C0018, located within a slope basin on the footwall of the megasplay fault in the Nankai Trough off the Kii Peninsula, southwest Japan. Six mass-transport deposit units intercalated with coherent intervals were recovered from the upper 190 m of the drilled succession. Anisotropy of magnetic susceptibility variations within mass-transport deposit units was used to ascertain their rheology. Shape parameters and magnetic fabric orientation reveal inhomogeneity through the sequences, indicating that different compaction and shear occurred within individual units. The upper intervals of younger units generally represent a magnetic fabric formed under vertical compression. However, the lower intervals involve magnetic fabrics indicating lateral shear with in-depth gradual change. In the older mass-transport deposit, a distribution of magnetic foliation forms tightly folded strata, indicating different sliding patterns from the younger mass-transport deposit units. Using available paleomagnetic data, the shear directions of basal intervals of units are reoriented, producing two different sliding orientations. Variation in the flow type and supply route is interpreted to reflect the slope condition (e.g., slope gradient and susceptibility to ground motion), which has been controlled by local tectonic evolution of the accretionary wedge.

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Rapid sedimentation and overpressure in shallow sediments of the Bering Trough, offshore southern Alaska

et al. 2017

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Pore pressures in sediments at convergent margins play an important role in driving chemical fluxes and controlling deformation styles and localization. In the Bering Trough offshore Southern Alaska, extreme sedimentation rates over the last 140 kyr as a result of glacial advance/retreats on the continental shelf have resulted in elevated pore fluid pressures in slope sediments overlying the Pamplona Zone fold and thrust belt, the accretionary wedge resulting from subduction of the Yakutat microplate beneath the North American Plate. Based on laboratory experiments and downhole logs acquired at Integrated Ocean Drilling Program Site U1421, we predict that the overpressure in the slope sediments may be as high as 92% of the lithostatic stress. Results of one‐dimensional numerical modeling accounting for changes in sedimentation rate over the last 130 kyr predicted overpressures that are consistent with our estimates, suggesting that the overpressure is a direct result of the rapid sedimentation experienced on the Bering shelf and slope. Comparisons with other convergent margins indicate that such rapid sedimentation and high overpressure are anomalous in sediments overlying accretionary wedges. We hypothesize that the shallow overpressure on the Bering shelf/slope has fundamentally altered the deformation style within the Pamplona Zone by suppressing development of faults and may inhibit seismicity by focusing faulting elsewhere or causing deformation on existing faults to be aseismic. These consequences are probably long‐lived as it may take several million years for the excess pressure to dissipate.

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Site C0018

Cited by 25 publications

References 12 publications

Sedimentary inputs to the Nankai subduction zone: The importance of dispersed ash

Sedimentary inputs to the Nankai subduction zone: The importance of dispersed ash

Flow dynamics of Nankai Trough submarine landslide inferred from internal deformation using magnetic fabric

Rapid sedimentation and overpressure in shallow sediments of the Bering Trough, offshore southern Alaska

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