Physiographical and sedimentological characteristics of submarine canyons developed upon an active forearc slope: The Kushiro Submarine Canyon, northern Japan

Abstract

Comprehensive geological surveys have revealed the physiographical and sedimentological characteristics of the Kushiro Submarine Canyon, one of the largest submarine canyons around Japan. The canyon indents the outer shelf along a generally straight, deeply excavated course of more than 230 km in length upon the active forearc slope of the Kuril Trench in the Northwest Pacifi c. The forearc slope has a convex-upward geometry that can be divided into upper and lower parts separated by an outer-arc high (3200-3500 m water depth). The upper slope consists of gently folded forearc sediments, and the lower slope is underlain by sedimentary rocks deformed by subduction-related processes. The upper reaches of the canyon (~3250 m of thalweg water depth) are developed on the upper slope, showing a weakly concave-upward longitudinal profi le with a gradual down-canyon increase in relief between the thalweg and the canyon rim. Although an infi ll of hemipelagic mud and the absence of turbidite deposits indicates that the upper part of the upper reaches of the canyon (~900 m thalweg water depth) is inactive, the lower part of the upper reaches (900-3250 m thalweg water depth) is considered to be an active conduit to the lower reaches, as determined from voluminous turbidites recovered in sediment cores (~76-yr intervals) and rockfalls observed in the canyon bottom by deep-sea camera. A number of gullies developed upon the northern slope of the lower part of the upper reaches might well provide a frequent supply of turbidity currents, giving rise to a down-canyon increase in the frequency of fl ow events. The down-canyon increase in fl ow occurrence is related to a gradual decrease in gradient, demonstrating an inverse power-law relationship between slope and drainage area. In contrast, the lower reaches of the canyon (3250-7000 m thalweg water depth) are characterized by a gradual decrease in relief, a high gradient, and extremely low sinuosity. The limited increase in drainage area down-canyon of the confl uence with the Hiroo Submarine Channel, which is the largest tributary of the main canyon, indicates that the erosional force of turbidity currents decreases down-canyon. The gradient of the lower reaches largely refl ects the morphology of the forearc slope along the canyon, which has been deformed by subduction-related tectonics. The lack of an inverse power-law relationship between gradient and drainage area in the lower canyon supports the hypothesis that the topography of the lower reaches is dominated by subduction-related tectonic deformation of the substrate rather than canyon erosion. Interrelationships between canyon erosion by currents and tectonic processes along the forearc slope are important in the development of the physiography of submarine canyons upon active forearc margins.

Interactions between submarine channel systems and deformation in deepwater fold belts: Examples from the Levant Basin, Eastern Mediterranean sea

“…Submarine channel systems are commonly described from such settings, examples include the Niger Delta (Deptuck et al, 2003;Adeogba et al, 2005;Heinio and Davies, 2007), the Gulf of Mexico (Posamentier, 2003;Pickering et al, 1986) the Nile Delta (Samuel et al, 2003), Brunei (Demyttenaere et al, 2000) and Offshore West Africa (Gee and Gawthorpe, 2006;Abreu et al, 2003). Submarine channels are also recognised from accretionary prisms located at subduction zones, examples include the Barbados Accretionay Prism (Huyghe et al, 2004), The Kuril Arc (Noda et al, 2008), the Central Chile Forearc (Hagen et al, 1994) and the Nankai Trough (Soh and Tokuyama, 2002).…”

Paleoseismicity along the southern Kuril Trench deduced from submarine-fan turbidites

“…Such Table 2. amalgamated turbidites have been reported previously from seismically active regions of Japan (Nakajima and Kanai, 2000;Noda et al, 2008) and Cascadia (Goldfinger et al, 2007). It is not possible to produce an amalgamated turbidite from a simple waning turbidity current of the type that produces a typical turbidite represented by the Bouma sequence.…”

“…The 14 C ages from benthic foraminifers were 820-870 yr older than those from planktonic foraminifers of the same horizon off Kushiro during the late Quaternary (Noda et al, 2008). We used a reservoir age of 386 ± 16 yr for the 14 C ages in this region (Yoneda et al, 2001).…”

“…Nanayama et al (2007) identified 13 tsunamigenic sand layers within marsh sediments, and calculated that the corresponding tsunami events had a recurrence interval of 365-553 yr over the past 4000 yr. Turbidites deposited upon the ocean floor also provide evidence of the recurrence intervals of earthquakes. Noda et al (2004Noda et al ( , 2008 reported an average recurrence interval of 68-85 yr for the deposition of turbidites off Kushiro over the past 2400 yr.…”

Key controls on submarine channel development in structurally active settings

“…Published examples include the Niger Delta (Pirmez et al, 2000;Deptuck et al, 2003Deptuck et al, , 2007Adeogba et al, 2005;Heinio and Davies, 2007), offshore West Africa (Broucke et al, 2004;Fonnesu, 2003;Ferry et al, 2005;Gee and Gawthorpe, 2006), the Austrian Tertiary Molasse foreland basin (Covault et al, 2009;Hubbard et al, 2009), the Nile Delta (Clark and Cartwright, 2009;Cross et al, 2009), the Barbados Accretionary Prism (Huyghe et al, 2004), the Hikurangi margin, New Zealand (Lewis et al, 1998;Mountjoy et al, 2009), the Kuril Trench (Noda et al, 2008) and the Central Chile forearc (Hagen et al, 1994;Laursen and Normark, 2002).…”