Sedimentary characteristics and processes of submarine mass-transport deposits in the Ulleung Basin and their relations to seismic and sediment physical properties

Each MTD unit is characterized in the logging-while-drilling (LWD) data by a gradual increase in bulk density, P-wave velocity, and resistivity values at the basal part and an abrupt decrease at the lower boundary. Nine sedimentary facies are identified in the MTD units, which indicate a variety of mass-transport processes such as sliding with brittle to plastic deformations and high-to low-viscosity debris flows. Vertical distribution of sedimentary facies shows a repeated generalized pattern in all MTD units. The pattern is interpreted to represent initial deep failures involving sand-prone consolidated sediments near the shelf break and successive shallow failures involving soft heterogeneous muddy sediments that were deposited in a deeper downslope area. The presence of sand-prone mass-transport deposits accounts for the basal densification and strong-amplitude negative basal reflections. Absence of such sand-prone basal parts in MTDs at other locales implies unpredictability of lithologic characteristics in MTDs with similar seismic reflection signatures.