IODP Proceedings    Volume contents     Search


Expedition 314 Site C00041

Expedition 314 Scientists2

Background and objectives

Integrated Ocean Drilling Program (IODP) Site C0004 (proposed Site NT2-01I) targets the uppermost 400 meters below seafloor at the seaward edge of the Kumano Basin uplift (outer arc high) where the megasplay fault system branches and approaches the surface (Figs. F1, F2). The Site C0004 summary log diagram is shown in Figure F1. Both inline and cross-line three-dimensional (3-D) seismic lines crossing Site C0004 are shown in Figure F2. Locations of drill holes at Site C0004 are plotted in Figure F3 with 3-D seismic profile coverage.

The primary objective of drilling at the NT2-01 series of proposed sites was to access the shallow portion of the megasplay fault system and the thrust sheets uplifted by it, as well as a thin overlying slope sediment cover sequence. The nature of the material in these thrust sheets is unknown. The acoustically nonreflective nature of this section suggests that it may be composed of chaotically deformed accretionary wedge sedimentary mélange transported from significantly greater depth. After drilling at Site C0003 failed to reach the fault reflector objective, Site C0004 was selected for a second attempt to drill and log across the fault zone and associated hanging wall and footwall structures.

The principal objective was to obtain in situ density, resistivity, gamma ray, porosity, P-wave velocity, and photoelectric factor data through logging while drilling (LWD) and seismic while drilling at this site. Together with later core samples, logs from this zone will verify our initial interpretations and provide data on physical properties, strength, composition, and structure of the megasplay fault zone and adjacent domains.

At Site C0004, we drilled into the toe of a thrust wedge in the hanging wall of the megasplay fault system along Inline 2675 of the Kumano 3-D seismic volume (Moore et al., 2007). The thrust wedge is draped by a ~70 m thick cover of hemipelagic slope sediments and is thrust over older slope sediments (Fig. F2A, F2B). The upper boundary of the wedge is a continuous reflection in the inline direction but is less continuous in the cross-line direction. Faint low-amplitude northwest-dipping reflections within the wedge are interpreted as thrust faults that intersect the thrust splay. A ~40 m thick zone below and parallel to the splay fault is interpreted as a fault zone. A strong reflection separates the fault zone from the underlying slope sediment section.

1 Expedition 314 Scientists, 2009. Expedition 314 Site C0004. In Kinoshita, M., Tobin, H., Ashi, J., Kimura, G., Lallemant, S., Screaton, E.J., Curewitz, D., Masago, H., Moe, K.T., and the Expedition 314/315/316 Scientists, Proc. IODP, 314/315/316: Washington, DC (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/​iodp.proc.314315316.116.2009

2 Expedition 314/315/316 Scientists’ addresses.

Publication: 11 March 2009
MS 314315316-116