Mid-Quaternary decoupling of sediment routing in the Nankai Forearc revealed by provenance analysis of turbiditic sands

Abstract

funnelled to this site through the Suruga Canyon. However, sands in the forearc basin show persistent presence of blue sodic amphiboles across the 1 Ma boundary, indicating continuous flux of sediments from the Kumano/Kinokawa River. This implies that the sands in the older turbidites were transported by transverse flow down the slope. The slope basin facies then switched to reflect longitudinal flow around 1 Ma, when the turbiditic sand tapped a volcanic provenance in the Izu-Honshu collision zone, while the sediments transported transversely became confined in the Kumano Basin. Therefore, the change in the depositional systems around 1 Ma is a manifestation of the decoupling of the sediment routing pattern from transverse to long-distance axial flow in response to forearc high uplift along the megasplay fault.

Sediment flow routing during formation of forearc basins: Constraints from integrated analysis of detrital pyroxenes and stratigraphy in the Kumano Basin, Japan

“…Volcanic fragments found in the modern Nankai Trough clearly indicate a detrital input from the Collision Zone through the Suruga Canyon (De Rosa et al, 1986). The existence of a similar process earlier during evolution of the margin has been suggested based on the framework grain composition of sand/sandstone (e.g., Fergusson, 2003;Underwood and Fergusson, 2005;Usman et al, 2014) but could not be confirmed by recent analysis of detrital zircons (Clift et al, 2013). Pyroxenes from site C0001 are therefore the first unequivocal evidence for long-distance axial transport from the Collision Zone along the Nankai Trough in the early Quaternary.…”

“…The initiation of the Kumano Basin created a large accommodation space in the upper forearc, which is expected to have strongly modified sediment routing along the margin (e.g., Underwood and Moore, 2012;Takano et al, 2013;Usman et al, 2014). Determining the time of basin initiation, therefore, is critical in reconstructing sedimentation patterns in the forearc region.…”

“…Similarly, igneous, metamorphic and sedimentary fragments reworked from the Inner and Outer Zones have been significant components of turbidites in the lower forearc (i.e., trench slope, trench-slope basins and trench) since the Miocene (De Rosa et al, 1986;Fergusson, 2003;Underwood et al, 2003;Underwood and Fergusson, 2005;Underwood and Moore, 2012;Clift et al, 2013;Usman et al, 2014). However, to date, constraints on the provenance of turbidites have been restricted to the modal composition of sandstones (e.g., Fergusson, 2003;Usman et al, 2014) and one zircon study (Clift et al, 2013). Although there is evidence that the morphology of the trench slope controlled distribution of turbidites during the Neogene (e.g., Underwood et al, 2003), patterns of detrital sedimentation associated with formation of the forearc basin remain to be determined.…”

“…Sediment provenance studies along the Nankai margin have been essentially constrained based on the framework grain composition of sandy sediments (i.e., quartz, feldspars and lithic fragments) using a Gazzi-Dickinson point counting technique (e.g., Ferguson, 2003;Usman et al, 2014). Although this approach can give valuable insight into source effects controlling the composition of detrital sediments (e.g., Dickinson and Suczek, 1979;, hydrodynamic sorting during transport and deposition, and preferential preservation of some mineral species during transport and diagenesis are equally significant in controlling sediment composition (Morton and Hallsworth, 1999;Garzanti et al, 2009).…”

Possible climate preconditioning on submarine landslides along a convergent margin, Nankai Trough (NE Pacific)

“…There is no direct sediment source into the basin and the main depocenters nearby are located in the Kumano basin and downslope in the Nankai Trough (Buchs et al 2015;Usman et al 2014). There is possibly sediment input from the NNE, from the Tenyu or Fuji rivers (Usman et al 2014), but as the sediments deposited in the studied basin are very fine grained, this represents only the very distal to pelagic part of the supplied sediment. The sedimentation rates at C0018A determined in this study vary by~100 cm/kyr (which is the same order of magnitude as estimated by Henry et al 2012).…”