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doi:10.2204/iodp.proc.333.103.2012

Site C0018¹

Expedition 333 Scientists²

Background and objectives

During Integrated Ocean Drilling Program (IODP) Expedition 333, the slope basin seaward of the megasplay that is characterized in 3-D seismic data by stacked mass transport deposits (MTDs) (Strasser et al., 2011) (Fig. F1) was drilled and sampled at Site C0018. The primary goals of drilling at Site C0018 were

1. To establish a well-dated Quaternary mass-movement event stratigraphy and

2. To sample the distal part of an exceptionally thick MTD and analyze its rheological behavior to constrain sliding dynamics and tsunamigenic potential.

These goals aim at providing answers to the following questions:

1. What is the frequency of submarine landslides?

2. What is the source material of MTDs?

3. What is the importance of accretionary wedge remobilization versus surficial processes?

4. What controls the type, size, and magnitude of turbidites and MTDs and how do they change through time?

5. How do large MTDs relate to the timing of splay fault activity as inferred from Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Stage 1 drilling (Strasser et al., 2009)?

6. What are the dynamics of large submarine landslides and can we infer their tsunamigenic potential?

By addressing these questions, we aimed to isolate tectonic processes influencing magnitude and occurrence of submarine landslides along active subduction zone margins and to understand their potential for triggering catastrophic events in terms of both hazards (tsunamigenic landslides) and sediment mass transfer within the context of margin evolution.

Site C0018 (proposed Site NTS-1A) (water depth = 3084.35 m) is located on a margin-perpendicular transect 4.5 km southwest of the NanTroSEIZE Stage 1 drilling transect (Fig. F2). It is located 5 km south-southwest of IODP Site C0008, which was drilled into a small slope basin seaward of the megasplay fault (Kinoshita, Tobin, Ashi, Kimura, Lallemant, Screaton, Curewitz, Masago, Moe, and the Expedition 314/315/316 Scientists, 2009). Site C0008 results showed the utility of using the ages of MTDs to reconstruct slope failure activity and to relate it to megasplay fault movements (Strasser et al., 2009). Apart from the deepest section, Site C0008 lacks clear evidence for MTDs because of a significant hiatus, suggesting erosion related to a prominent slope collapse structure seaward of the megasplay fault (Strasser et al., 2011; Conin et al., 2011). Site C0018 is located within a lower slope basin that (1) better represents the depocenter for downslope mass transport, (2) is clearly characterized by stacked MTDs as seismically imaged by acoustically transparent to chaotic bodies with ponded geometries (Fig. F1), and (3) includes a large, as thick as 182 m, MTD (Strasser et al., 2011). Expedition 333 drilled at a location where the MTD bodies wedge out and basal erosion is minimal. Continuous coring with hydraulic piston coring system (HPCS) and extended shoe coring system (ESCS)/extended punch coring system (EPCS) to ~314.15 meters below seafloor (mbsf) allowed sampling of the MTDs across this stratigraphic succession.

¹ Expedition 333 Scientists, 2012. Site C0018. In Henry, P., Kanamatsu, T., Moe, K., and the Expedition 333 Scientists, Proc. IODP, 333: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.333.103.2012

² Expedition 333 Scientists’ addresses.

Publication: 18 May 2012
MS 333-103

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