Abstract

This report describes the mineral assemblages from four sites in the Canterbury Basin, eastern South Island, New Zealand. Coring was completed during Expedition 317 of the Integrated Ocean Drilling Program. A total of 838 unlithified samples of continental margin lithologies (mud, sand, shell hash, and marl) were analyzed by X-ray diffraction (qXRD) using random powder mounts of bulk samples. Sample analyses primarily targeted seismic sequences S16–S19 at all four sites (U1351–U1354), with secondary emphasis on samples with complementary downhole petrophysical data. The primary minerals observed above analytical confidence limits (3% by weight) were, in order of relative abundance, plagioclase (albite + oligoclase + labradorite; ~25 wt%), illite + muscovite (~24 wt%), quartz (~17 wt%), chlorite (~13 wt%), and calcite + aragonite (~7 wt%). Also observed above detection limits were K-feldspar (orthoclase + microcline), epidote, amphiboles (hornblende), and biotite. Total carbonates vary the most at all four sites, ranging in relative abundance from 0 to 77 wt%, with the largest variability at Site U1352. Comparison of carbonate concentrations measured by coulometer and qXRD on co-located samples resulted in an R2 value of 0.96 (n = 194) over the full range of values. Spatially, the feldspars (plagioclase and K-feldspar) and quartz were on average the most abundant at the innermost shelf Site U1353 (~50 wt%) but were still significant components at the upper slope Site U1352 (~47 wt%). Average illite + muscovite + chlorite concentrations were highest at Site U1352 (~44 wt%) but were still a significant component (~35 wt%) at Site U1353. Prominent changes in mineralogy were not observed across lithostratigraphic unit boundaries, attesting to the gradual transition in lithofacies during progressive seaward margin development. Within lithostratigraphic units, notable changes in mineralogy, primarily between siliciclastic and carbonate minerals, are observed at the projected depths of seismic sequence boundaries. Transitions in the relative abundances of each mineral are often seen within seismic sequence intervals and are the largest in the uppermost two to four sequences (S16–S19).