Anatomy and dynamics of a mixed contourite sand sheet, Ryukyu Island Arc, northwestern Pacific Ocean

Naohisa Nishida, Takuya Itaki, Atsuko Amano, Hajime Katayama, Taichi Sato, Dorrik Stow, Uisdean Nicholson

Research output: Contribution to journalArticlepeer-review

Abstract

Contourites are well-known from many continental margins under the influence of bottom currents but have been little reported from the Pacific Ocean. This paper documents a new area of contourite-controlled sedimentation in the NW Pacific Ocean, which we call the Ryukyu Sand Sheet. This contourite sand sheet has an area of around 35,000 km2 and extends from the narrow island shelves to over 1500 m water depth. It comprises mainly moderate to well-sorted fine-grained sands, with current ripples and giant sediment waves and is also associated with small drifts. It is formed under the influence of three principal current systems – the Kuroshio Current, the Kuroshio Countercurrent and the Ryukyu Current. The interaction of these currents with each other and with a complex seafloor topography, spawns a series of meso-scale gyres, eddies and vortices that shape the seafloor and lead to deposition of an extensive sandy substrate, locally with gravels and exposed seafloor. Strong surface currents, as well as deep-water thermohaline circulation, both influence the depositional and erosional processes of deep-sea sediments. The role of the modern Kuroshio Current in this context supports earlier work that proposed an ancestral Kuroshio Current for the deposition of Miocene contourites onshore Japan. Sediment supply to the Ryukyu Sand Sheet is by a mixed process of seafloor polishing and sand spillover that involves combined oceanographic and gravitational processes.
Original languageEnglish
Article number106707
JournalMarine Geology
Volume444
Early online date23 Dec 2021
DOIs
Publication statusPublished - Feb 2022

Keywords

  • Kuroshio Current
  • Okinawa Trough
  • Ryukyu sand sheet
  • Sandy contourite
  • Sediment waves

ASJC Scopus subject areas

  • Oceanography
  • Geology
  • Geochemistry and Petrology

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