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doi:10.2204/iodp.proc.314315316.221.2012

Methods and materials

Samples of unconsolidated sand (10 cm³ samples) were collected during routine shipboard sampling with a sampling density of ~1 sample/core, limited by the availability of sand-size sediment. A total of 87 sand samples, 81 of Pleistocene age and 6 of Pliocene age, were obtained. A correlated set of mud samples, 166 Pleistocene, 53 Pliocene, and 3 Miocene, was also collected and used in a study by Milliken and Reed (2010). This report describes 35 sand samples distributed across the depth ranges available in the cores (Fig. F2). The time available for the senior honors project on which this report is based did not allow for a larger number of samples to be examined.

The fine fraction (detrital clay and silt) was removed from the samples by wet-sieving on a 62 µm screen to isolate clean sand-size material. Sand was dried, made into grain mounts using blue-dyed epoxy, thin sectioned, and stained for identification of Ca-plagioclase and K-feldspar. Staining follows the procedure of Houghton (1980).

Thin sections were point-counted using the Gazzi-Dickinson method (Dickinson, 1970; Ingersoll et al., 1984). A total of 500 grains were counted using a Swift automatic point-counter in order to achieve “maximum grid spacing to cover the entire slide” (Ingersoll et al., 1984). A total of 22 grain categories were chosen based on categorizations established in previous studies (Marsaglia, 1992; Marsaglia et al., 1992; Fergusson, 2003). These categories include monocrystalline quartz and feldspars, volcanic lithic grains, metamorphic lithic grains, sedimentary lithic grains, and accessory grains including biogenic grains, micas, and heavy minerals (Table T1). Local cementation of ash beds by carbonate minerals is reported in this volume (see the “Expedition 316 Site C0004,” “Expedition 316 Site C0006,” “Expedition 316 Site C0007,” and “Expedition 316 Site C0008” chapters [Expedition 316 Scientists, 2009a, 2009b, 2009c, 2009d]), but cementation, grain replacement, or grain dissolution evident by transmitted light microscopy is very minor in the samples described here. No authigenic components evident by transmitted light microscopy are included among the point-count categories. Ternary plots are made using the spreadsheet of Zahid and Barbeau (2011).

Grain size estimation (Φ) was made by comparison of thin sections to a visual comparator (¼ Φ intervals) using a light table and a hand lens.

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