IODP Proceedings    Volume contents     Search



We analyzed the particle size distribution of 208 sediment samples from the seven Expedition 329 drill sites. Particle size distributions are given in Tables T1, T2, T3, T4, T5, T6, and T7. We plot the downcore profile of mean grain size (e.g., graphic mean: ϕ = (ϕ16 + ϕ50 + ϕ84)/3) and sorting (e.g., standard deviation: σϕ = [(ϕ84 – ϕ16)/4] + [(ϕ95 – ϕ5)/6.6]), along with the summary of lithologic units and mineral composition for Sites U1365–U1371 in Figures F2, F3, F4, F5, F6, F7 and F8. In this study, we used the well-established size boundaries of 63 µm separating sand and silt and 4 µm separating silt and clay. The sediment collected during Expedition 329 is dominantly fine-grained clay and silt with negligible sand. Typical fine fraction contents are >99 wt%, with some samples having >95 wt% of particles finer than 1.5 µm, in particular at Sites U1365 and U1370 (Tables T1, T6; Figs. F2, F7). Samples with >75 wt% of particles finer than 1.5 µm were attributed an arbitrary mean particle size of 1.5 µm (9.4 ϕ) and no sorting. Site U1365 grains are mostly coarse clay with some very fine silt (Table T1). Sites U1366 and U1367 are mostly very fine silt (Tables T2, T3), as are the deeper parts of Sites U1368 and U1369 (Tables T4, T5). The upper part of Sites U1368 and U1369 consist of coarse clay. Site U1370 is mostly medium clay (Table T6). Site U1371 grains vary between coarse clay and very fine silt (Table T7). In most samples, the particle size distribution is negatively skewed to very negatively skewed and moderately sorted (poorly sorted at Site U1371; Table T7). However, a number of samples at the sites further offshore (Sites U1368 and U1369) are very well sorted (Tables T4, T5).