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doi:10.2204/iodp.proc.322.204.2013

Results

The amorphous silica content of sediment from Sites C0011 and C0012 are summarized in Figures F2 and F3 and Table T1. The amorphous silica content in all samples examined is ≤1.1 wt%. The amorphous silica content is higher in the shallow sediment than in the deeper sediment. At Site C0011, in lithologic Subunit IA, the sediment ranges from 0.75 to 1.11 wt% amorphous silica and averages 0.93 wt% amorphous silica. The Subunit IA/IB boundary at 252 meters below seafloor (mbsf) is defined at a sharp gradient in volcanic ash alteration; fresh volcanic glass is above the boundary and altered ash layers with little remaining glass are below the boundary (Expedition 333 Scientists, 2012). The measured amorphous silica content decreases sharply across the Subunit IA/IB boundary (Fig. F2). Below the boundary, sediment ranges from 0.13 to 0.59 wt% amorphous silica and averages 0.36 wt% amorphous silica (Fig. F2).

Similar to Site C0011, the amorphous silica content at Site C0012 is higher in the shallow sediment than in the deeper sediment. The four samples examined in Subunit IA average 0.63 wt% amorphous silica (standard deviation = 0.4 wt%) (Fig. F3). Samples below the Subunit IA/IB boundary average 0.26 wt% amorphous silica (standard deviation = 0.08 wt%) (Fig. F3). The Subunit IA/IB boundary at 72 mbsf is a transition below which ash layers are scarce and volcanic glass shards are more altered (Expedition 333 Scientists, 2012).

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