Data report: clay mineral assemblages within and beneath the Tuaheni Landslide Complex, IODP Expedition 372A Site U1517, offshore New Zealand

Abstract

The Tuaheni Landslide Complex is thought to have originated through multiple slip events offshore the Hawke’s Bay region, North Island (New Zealand). Cores were obtained from within and beneath the interpreted landslide complex to a maximum depth of ~188 meters below seafloor (mbsf) in Hole U1517C during International Ocean Discovery Program Expedition 372. This data report provides the results of 99 X-ray diffraction analyses of the clay-sized fraction (<2 µm spherical equivalent); sampling focused on the background lithology of hemipelagic mud. Normalized weight percent values for common clay-sized minerals (where smectite + illite + undifferentiated [chlorite + kaolinite] + quartz = 100%) do not vary markedly among the five lithostratigraphic units. Overall, the mean and standard deviation (σ) values are smectite = 47.1 wt% (σ = 5.2), illite = 34.0 wt% (σ = 3.4), chlorite + kaolinite = 8.8 wt% (σ = 1.9), and quartz = 10.2 wt% (σ = 4.0). Mineral proportions within the clay-sized fraction do change somewhat across the boundaries between units and near inferred slip surfaces (e.g., at ~31 mbsf), but those excursions are within the normal range of statistical scatter for the site. Likewise, indicators of clay diagenesis are relatively monotonous throughout the cored interval. The average value of illite crystallinity index is 0.53Δ°2θ (σ = 0.027). Smectite expandability averages 77.4% (σ = 4.9), and the average proportion of illite in illite/smectite mixed-layer clay is 8.7% (σ = 5.6).