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doi:10.2204/iodp.proc.345.103.2014

Preliminary observations

One of the main observations common to all of the surveys is that the layer with high reflectivity (or high amplitude) immediately below the seafloor, which is presumably made of unconsolidated pelagic sediment, lithic debris, and/or boulders, appears to vary between 4 and 20 m thick. The lack of coherent reflectors in these high-reflectivity intervals suggest, along with the drilling results, that they are made of highly heterogeneous materials and unconsolidated rubble.

Another possibly significant observation is the occurrence of various deeper reflectors in the images, some as deep as 200 m, that suggest that the pinger was able to image the deep structure underlying the surveyed areas. Most of these reflectors are observed on transects and segments recorded along a north–south direction. Whereas some reflectors are dipping to the south (Traces 2800–3400 in Fig. F7A and Traces 4200–4400 in Fig. F12A) and seem to suggest faulting parallel to the slope, others are dipping to the north (Traces 4800–5000 and 7800–8400 in Fig. F7A), suggesting conjugate deformation. Because of the proximity of the pinger to the seafloor and the variety in the character of the reflectors, many of these reflectors are likely indications of subseafloor structure. One of the strongest southward-dipping reflectors (Traces 2800–3400 in Fig. F7A) appears to intersect Hole U1415J somewhere between 60 and 100 meters below seafloor, which might be related to the cataclasites and fractured formation conditions we observed in the bottom of the hole (see the “Hole U1415J” chapter [Gillis et al., 2014b). These conditions led to the eventual abandonment of the hole.

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