Mass transport deposits and gas hydrate occurrences in the Ulleung Basin, East Sea – Part 1: Mapping sedimentation patterns using seismic coherency.

Scholz, N.A., Riedel, Michael , Bahk, J.-J., Yoo, D.-G. and Ryu, B.-J. (2012) Mass transport deposits and gas hydrate occurrences in the Ulleung Basin, East Sea – Part 1: Mapping sedimentation patterns using seismic coherency. Marine and Petroleum Geology, 35 (1). pp. 91-104. DOI 10.1016/j.marpetgeo.2012.03.004.

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Abstract

Seismic coherency measures, such as similarity and dip of maximum similarity, were used to characterize mass transport deposits (MTDs) in the Ulleung Basin, East Sea, offshore Korea. Using 2-D and 3-D seismic data several slope failure masses have been identified near drill site UBGH1-4. The MTDs have a distinct seismic character and exhibit physical properties similar to gas hydrate bearing sediment: elevated electrical resistivity and P-wave velocity. Sediments recovered from within the MTDs show a reworked nature with chaotic assemblage of mud-clasts. Additionally, the reflection at the base of MTDs is polarity reversed relative to the seafloor, similarly to the bottom-simulating reflector commonly used to infer the presence of gas hydrates. The MTDs further show regional seismic blanking (absence of internal reflectivity), which is yet another signature often attributed to gas hydrate bearing sediments. At the drill site UBGH1-4, no gas hydrate was recovered in sediment-cores from inside a prominent MTD unit. Instead, pore-filling gas hydrate was recovered only within thin turbidite sand layers near the base of the gas hydrate stability zone. With the analysis of seismic attributes, the seismic character of the prominent MTD (Unit 3) was investigated. The base of the MTD unit exhibits deep grooves interpreted as gliding tracks from either outrunner blocks or large clasts that were dragged along the paleo-seafloor. Similar seismic features were identified on the seafloor although the length of the gliding tracks on the seafloor is much shorter (a few hundred meters to ∼1 km), compared to over 10 km long tracks at the base of the MTD. The seismic coherency attributes allowed to estimate the volume of the failed sediment as well as the direction of the flow of sediment. Tracking the MTD and extrapolating its spatial extent from the 3-D seismic volume to adjacent 2-D seismic profiles, a possible source region of this mass failure was defined ∼50 km upslope of Site UBGH1-4.

Document Type: Article
Keywords: Mass transport deposits; Seismic coherency attribute; Outrunner blocks; Gliding tracks; Pressure ridges; Gas hydrate; Depositional environments
Refereed: Yes
DOI etc.: 10.1016/j.marpetgeo.2012.03.004
ISSN: 0264-8172
Date Deposited: 17 Nov 2015 10:22
Last Modified: 17 Nov 2015 10:22
URI: http://oceanrep.geomar.de/id/eprint/30072

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