Sedimentary Evolution of the Japan Fore-Arc Region off Northern Honshu, Legs 56 and 57, Deep Sea Drilling Project.

Arthur, M. A., von Huene, Roland and Adelseck, C. G. (1980) Sedimentary Evolution of the Japan Fore-Arc Region off Northern Honshu, Legs 56 and 57, Deep Sea Drilling Project. Open Access Initial Reports of The Deep Sea Drilling Project, 56/57 . pp. 489-503. DOI 10.2973/dsdp.proc.5657.114.1980.

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The evolution of Neogene and Quaternary sedimentation in the fore-arc region off northern
Honshu is evaluated using multichannel and single-channel seismic records in conjunction
with the drill holes of the Japan Trench Transect (DSDP/IPOD Legs 56-57). The outer forearc
region, which consisted of older sedimentary rocks and some calc-alkaline volcanic rocks,
was subaerially exposed and eroded during the Paleogene and part of the Neogene. The deep
sea terrace (fore-arc basin) region subsided below sea level in the early Miocene; most rapid
subsidence occurred during the early to middle Miocene. Submergence progressed seaward so
that the last vestige of the Oyashio landmass, which is now under the upper trench slope, was
below sea level in the latest Miocene. Sediment sources to the outer fore-arc basin changed
progressively from lithic, predominantly nonvolcanic material derived from the uplifted landmass
during the late Paleogene-early Neogene to volcanic, arc-derived sediment rich in
volcanic glass, Plagioclase, and volcanic lithic fragments. The volcaniclastic sediment was probably
derived both from Honshu to the west and Hokkaido to the northwest.
In response to subsidence the sedimentary depocenters in the fore-arc basin migrated generally
seaward through time; the greatest relative seaward migration occurred between the late
Miocene and Pliocene. Thick sediment sequences accumulated in slope basins on the trench
inner slope. Sediment from the arc moved seaward to spill over the slope via large channels.
An abrupt change in morphology and patterns of sedimentation apparently took place in
the late Pliocene, coincident with a peak in explosive volcanism recorded in the form of ash
layers and increased glass contents in sediment. The deep sea terrace was uplifted several hundreds
of meters and a major channel crossing the fore-arc region was tilted landward and
filled. At about the same time the midslope terrace basin was created and began rapidly accumulating
sediment. The older basins, lower on the trench inner slope, were destroyed, possibly
by steep seaward tilting, or filled. Large slump masses were sloughed-off downslope to
the trench. Little sediment now accumulates on the trench inner slope in the vicinity of the
sites, and older strata crop out on the slope. The locus of deposition has shifted northward off
Hokkaido where a large channel feeds sediment to the slope. Large slump masses now fill the
trench and are being accreted, creating a "toe" to the slope in this region.
The evolution of the fore-arc region off northern Honshu has not been steady state.
Tectonic accretion has been discontinuous, and tectonic erosion of the continental margin
edge may have occurred periodically. Slope basins have been both created and abruptly
destroyed at different points on the trench inner slope. There appears to be little possibility of
distinguishing most sediment "scraped off" the oceanic plate from hemipelagic sediment deposited
in the fore-arc region of Japan.

Document Type: Article
Keywords: Sediments, Sedimentary Evolution, Japan Fore-Arc Region, Northern Honshu, DSDP Leg 56, DSDP Leg 57
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.2973/dsdp.proc.5657.114.1980
Projects: DSDP
Date Deposited: 10 Oct 2016 13:20
Last Modified: 10 Oct 2016 13:20

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