Shimokita-oki submarine landslides and feasibility studies for future scientific drilling
Presented by Dr. Sumito MORITA on 23 Sep 2013 from 17:15 to 19:15
Type: Poster presentation
Session: Poster session
Track: Poster presentations
By a high-resolution 3D seismic data analysis, a great number of buried submarine landslide deposits were identified off Shimokita Peninsula, NE Japan. The submarine landslide deposits are interpreted as slump deposits interbedded in the Pliocene and Quaternary formations in northern Sanrikuoki Basin. Some of the slump deposits are over size of the survey area and are likely more than 30 km in both length and width. The structure tells that the slumping is almost all layer-parallel slip on a very gentle continental slope, where sedimentary formations are very flat and parallel to the present seafloor of less than 1 degree in gradient. So, the slump deposits have avoided fatal collapse. They basically indicate block-supported structure containing regularly imbricated thrust sheets of slid ancient surface layers with little matrix of chaotic cover. Dewatering structure strongly dependent on the imbrication forms parallel dikes occurring from the base of the slid layers, i.e. from slip plane. The layers corresponding to the slip plane are easy to trace due to a typical reflection of low-amplitude having some thickness. In 2011, Integrated Ocean Drilling Program (IODP) raised submarine landslide as one of science targets on the new science plan for the next 10 years from 2013. So, we recognize that the large slump deposits off Shimokita Peninsula are appropriate target to determine submarine landslide mechanism because of the simple layer-parallel slip, ensuing regular re-depositional structure and the traceable slip planes. For that reason, we started various research activities to examine feasibility of future scientific drilling. Further detailed structural analysis is in progress using 2D and 3D seismic data to extract candidate site for scientific drilling. Since the area is known as high flux of temperature-sensitive methane, we performed detailed heat flow measurements, deploying a long-term bottom water temperature monitoring system for precise correction of heat flow values. Vitrinite reflectance analysis and Rock-Eval pyrolysis were carried out using sediment samples recovered by IODP Expedition 337, which is conducted just in a part of the study area in summer, 2012. Results of the analyses will be available to determine maturity of organic materials and to model thermal history in the basin. In September, 2012, we held a field excursion in Nichinan Group in Kyushu, Japan to observe typical geologic structures related to slumping and dewatering. The slumping and dewatering in the outcrops are also considered to have occurred in such low-angle slope where flute cast remarkably develops. The field excursion was a good opportunity to share general ideas about the slump deposits off Shimokita Peninsula among the science community. The seismic analysis, the vitrinite reflectance analysis, the Rock-Eval pyrolysis, and the field excursion and science meeting in Miyazaki were supported by the foundation of “Feasibility studies for future IODP scientific drillings” by JAMSTEC CDEX in 2012-2013. A part of organic materials analyses are supported by the CDEX’s fund for IODP post-expedition researches. The detailed heat flow analysis was funded by 2012 GREEN Grant, AIST. This study uses the 3D seismic data from the METI seismic survey “Sanrikuoki 3D” in 2008.
Shimokita-oki submarine landslide deposits led by layer-parallel slumping are typically characterized by very simple and comprehensible features. So, we started feasibility studies of scientific drilling in the slump deposits to determine submarine landslide mechanism. Detailed seismic analysis is kept going on, and sedimentary basin evaluation was set out in various methods. Community started discussion of the feasibility.
Location: GEOMAR East shore
Address: Wischhofstr. 1-3 / D-24148 Kiel