Ichthyoliths from Site 436, Northwest Pacific, Leg 56, Deep Sea Drilling Project

Doyle, P. S.; Riedel, W. R.

doi:10.2973/dsdp.proc.5657.127.1980

Cited by 6 publications

(4 citation statements)

References 4 publications

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“…Radiolarian microfossils are absent in the clay in core 17R so the age has not been precisely determined. Pelagic clay at DSDP Site 436 is Early Miocene to Eocene [Doyle and Riedel, 1980]. The pelagic clay in the Pacific Plate at the JFAST site (core 21R) is Cretaceous (see section 3.2).…”

Section: Composition Of the Décollementmentioning

confidence: 98%

Structure and lithology of the Japan Trench subduction plate boundary fault

et al. 2015

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The 2011 Mw9.0 Tohoku‐oki earthquake ruptured to the trench with maximum coseismic slip located on the shallow portion of the plate boundary fault. To investigate the conditions and physical processes that promoted slip to the trench, Integrated Ocean Drilling Program Expedition 343/343T sailed 1 year after the earthquake and drilled into the plate boundary ∼7 km landward of the trench, in the region of maximum slip. Core analyses show that the plate boundary décollement is localized onto an interval of smectite‐rich, pelagic clay. Subsidiary structures are present in both the upper and lower plates, which define a fault zone ∼5–15m thick. Fault rocks recovered from within the clay‐rich interval contain a pervasive scaly fabric defined by anastomosing, polished, and lineated surfaces with two predominant orientations. The scaly fabric is crosscut in several places by discrete contacts across which the scaly fabric is truncated and rotated, or different rocks are juxtaposed. These contacts are inferred to be faults. The plate boundary décollement therefore contains structures resulting from both distributed and localized deformation. We infer that the formation of both of these types of structures is controlled by the frictional properties of the clay: the distributed scaly fabric formed at low strain rates associated with velocity‐strengthening frictional behavior, and the localized faults formed at high strain rates characterized by velocity‐weakening behavior. The presence of multiple discrete faults resulting from seismic slip within the décollement suggests that rupture to the trench may be characteristic of this margin.

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Section: Composition Of the Décollementmentioning

confidence: 98%

Structure and lithology of the Japan Trench subduction plate boundary fault

et al. 2015

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“…The top of Unit 3 is composed of dark brown to nearly black early Miocene to Eocene pelagic clay underlain by Cretaceous chert, sampled as chert cobbles in the two lowermost cores (Langseth et al, 1977). The Miocene/Eocene pelagic clays are devoid of radiolaria but were dated using fish teeth fossils (Doyle and Riedel, 1980). Drilling at DSDP Site 436 Langseth et al, 1977) and ODP Site 1149 (b, Plank et al, 2000).…”

Section: Dsdp Site 436 Stratigraphymentioning

confidence: 98%

Multiple major faults at the Japan Trench: Chemostratigraphy of the plate boundary at IODP Exp. 343: JFAST

Rabinowitz

Savage

Plank

et al. 2015

Earth and Planetary Science Letters

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“…The chert sequence is overlain by brown pelagic clay 19 m thick. The age of the pelagic clay is estimated to range from Eocene to early Miocene based on fish teeth (Doyle and Riedel, 1980). No other fossils were recovered from the clay, presumably because it accumulated in a deep, chemically corrosive oceanic environment.…”

Section: Stratigraphy At Reference Site 436mentioning

confidence: 99%

Sediment provenance and controls on slip propagation: Lessons learned from the 2011 Tohoku and other great earthquakes of the subducting northwest Pacific plate

et al. 2015

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The ~50 m slip of the Tohoku earthquake occurred along a very fine grained red-brown smectitic clay horizon subducting in the Japan Trench. This clay, cored in the plate boundary fault at Integrated Ocean Drilling Program Expedition 345, Site C0019, correlates with similar pelagic clay recovered seaward of the trench at Deep Sea Drilling Project Sites 436 and 1149. Comparable clays occur throughout the northwest Pacific Basin. Backtracking of ocean drilling Sites 436, C0019, and 1149 indicates that they formed during the Early Cretaceous at the Kula-Pacific Ridge. These sites traveled northwestward through the equatorial zone, accumulating siliceous and calcareous oozes until ca. 100-85 Ma. Sites 436, C0019, and 1149 then entered the realm of pelagic clay deposition where they remained until ca. 15 Ma. From ca. 15 Ma to the present, Sites 436, C0019, and 1149 accumulated clays and silty clays with variable amounts of siliceous microfossils and volcanic ash, representing the transition from deep-sea conditions to a continental margin sedimentary environment. The predicted backtracked vertical sequence of sediments fits well with the cores at Sites 436, 1149, and C0019, after accounting for structural complications in the latter.Pelagic clay occurs in numerous boreholes penetrating the relatively smooth ocean floor of the Pacific plate north and northeast of the Tohoku earthquake. Here the widespread pelagic clay apparently fosters tsunami and tsunamigenic earthquakes. Seamounts rising above the normal oceanic crust accumulated sequences of calcareous sediments as their crests remained above the calcite compensation depth for most of their history. A seafloor including pelagic clay and carbonate-covered seamounts occurs south and southeast of the southern extent of the Tohoku earthquake rupture zone. This area has no historic tsunami or tsunamigenic earthquakes along the Japan and Izu-Bonin Trenches with the possible exception of the poorly located Enpo earthquake of A.D. 1677. We believe that the seamounts incoming on the oceanic plate to the south and southeast of the Tohoku rupture zone interfere with long-distance propagation of slip in the pelagic clay, limiting earthquake magnitude, shallow slip, and tsunami generation.

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Ichthyoliths from Site 436, Northwest Pacific, Leg 56, Deep Sea Drilling Project

Cited by 6 publications

References 4 publications

Structure and lithology of the Japan Trench subduction plate boundary fault

Structure and lithology of the Japan Trench subduction plate boundary fault

Multiple major faults at the Japan Trench: Chemostratigraphy of the plate boundary at IODP Exp. 343: JFAST

Sediment provenance and controls on slip propagation: Lessons learned from the 2011 Tohoku and other great earthquakes of the subducting northwest Pacific plate

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