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Site U13941

Expedition 340 Scientists2

Background and objectives

Integrated Ocean Drilling Program (IODP) Site U1394 (proposed Site CARI-03C; 16°38.43′N, 62°2.29′W; 1115 meters below sea level [mbsl]) is located off the island of Montserrat (~13 nmi [24 km] from Point Shoe Rock, at the southeast tip of Montserrat) (Fig. F1).

Site survey data obtained for Site U1394 revealed the presence of chaotic deposits interpreted as debris avalanche deposits (Deposit 2 and underlying Deposit 8) and indicated that drilling could penetrate through multiple units of debris avalanche Deposit 2 (Lebas et al., 2011; Watt et al., 2012). We planned to drill 244 m through volcanic and biogenic sediment with intercalated chaotic debris avalanche Deposit 2.

The objective for Site U1394 was to characterize processes that occur during debris avalanche emplacement and associated erosional processes. Study of the sediment overlying the mass-transport deposit will allow us to date the associated event using δ18O chronostratigraphy. We will be able to determine whether the mass-wasting process occurred as a single event or as a series of closely spaced, separate events. Utilizing a combination of detailed lithologic, sedimentologic, and textural fabric analyses, we will be able to test the hypothesis that the debris avalanche incorporated sediment eroded from the seafloor during its emplacement. We hoped to reach the bedded units below the chaotic debris avalanche unit and thus investigate the textural and structural characteristics of the base of the debris avalanche (Komorowski et al., 1991; Glicken, 1991, 1996). Existing numerical models of debris avalanche emplacement do not sufficiently consider the interaction of the debris avalanche with the substratum and its influence on the mobility of the flow. Our goal was to look for structural evidence of the development of shear zones from the base of the debris avalanche into the overlying plug and fluidization structures (clastic dikes) described in terrestrial debris avalanche deposits (e.g., Glicken, 1996; Voight et al., 2002; Gee et al., 1999; Clavero et al., 2002; Shea et al., 2008).

1 Expedition 340 Scientists, 2013. Site U1394. In Le Friant, A., Ishizuka, O., Stroncik, N.A., and the Expedition 340 Scientists, Proc. IODP, 340: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/​iodp.proc.340.104.2013

2Expedition 340 Scientists’ addresses.

Publication: 17 August 2013
MS 340-104