DEEPWATER DEBRITES AND LINKED MEGATURBIDITES IN CONFINED BASINS: AN EXAMPLE FROM THE ONNURI BASIN, EAST SEA OF KOREA

摘要

We analyzed data from seven piston cores, multi-channel seismic-reflection (MCS) and chirp profiles, and multibeam echosounder (MBES) data to study the distribution, emplacement time, sedimentary fades, and depositional processes of sediment-gravity-flow deposits in the Onnuri Basin, a confined basin in the East Sea. These data reveal that debris flows have traveled ca. 30 km downslope, forming a seismic fades consisting of stacked, wedgeshaped, transparent units separated by high-amplitude continuous reflectors. Analysis of piston cores shows three distinct sedimentary units, throughout the basin. The lowest unit, 1, is a debrite containing numerous mud clasts of varying size and color distributed in a mud-rich matrix; it is absent over elevated basinal highs or ridges, such as the Onnuri Ridge, suggesting that local topography controls its distribution. The debrite forms a recognizable acoustically transparent layer on subbottom chirp profiles (av. 7 m thick), covers approximately 500 km(2), and has an estimated volume of similar to 3.5 km(3).