Origin, structure and evolution of submarine canyons on central and
southern continental slopes of Okinawa Trough and its potential genetic
mechanism related to methane seepage
Abstract
Submarine canyons are of great significance to understand the transport
mechanism of terrigenous clastic materials to deep sea and the deep-sea
sedimentary dynamic process. In this study, the spatiotemporal framework
of stratigraphic sequence in the central and southern slopes of the
Okinawa Trough was established, and the geomorphological and
erosional-depositional features of submarine canyons were analyzed
detailedly. The submarine canyons on the continental slope of Okinawa
Trough began to develop in the early Pleistocene (< 1.8 Ma),
and continued to develop even today. The canyons could be divided into
three parts along the axial direction: head, upstream, and downstream.
The head of the canyon was mostly inherited from the ancient incised
valley developed on the outer continental shelf during the last glacial
maximum (LGM). The canyon channel was filled with multi-stage turbidites
and mass transport deposits (MTDs). The seismogeologic characteristics,
such as the MTDs associated with the bottom simulating reflectors
(BSRs), the imbricated, twisty or chaotic seismic reflections, the
liquefaction deformation structures, the fluid transport channels, and
the gaps that indicate methane escaping on the side walls, and the
truncated relationship between the BSRs and the submarine canyons all
indicate that there is a complex relationship between the submarine
canyons and the methane seepage associated with gas hydrate in the
Okinawa Trough. Finally, a coupled model with four evolutional stages
for the submarine canyons was established.