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SAMPLE INFO : 20_110-20_28
Sample ID:20_110-20_28
Station ID:Nayudu_core_20
Latitude:56.55
Longitude:-147.6355425
Datum:NAD83
Sample Type 1:Tephra Fall
Text Description:
Sample ID is the core number_cruise-and-sample-number_length (cm) from Table 1 in Nayudu (1964), which contains the list of the cores containing volcanic ash, their position, depth and length. Depth of 2,698 fathoms. Katmai ash is present in this core; the color of the ash varies from pale orange (10YR 8/2) to pale yellowish brown (10YR 6/2). Tephra has a maximum thickness of 7 cm. Mechanical analysis (0-3 cm) has the following size range: 1% fine sand, 13% very fine sand and 76% silt. Mean diameter of the ash is 22 microns, sorting coefficient is 1.82. Glass shards are irregular, thread-like, plate-like or splintered in shape. Gas bubble inclusions are restricted to large curved shards and are drawn out in elongate forms. The glass shards are unaltered. A middle basic ash is also present from 22.5-25 cm, and is brownish-black with a clearly defined base and poorly marked upper limit. Predominantly grayish-brown glass shards that are irregular and splintery with inclusions of gas bubbles and minerals, the most common being plagioclase, feldspar, and pyroxene. Shards show little to no alteration. Mechanical analysis has the following size fractions: 1.5% fine sand, 38% very fine sand, 50% silt. The median diameter is 41 microns and the sorting coefficient is 2.40. Glass content varies from 70-80% and the mineral and crystal fragments make up the rest. Hypersthene is the dominant mineral and some of the other important mineral constituents are basaltic hornblende, augite, magnetite and plagioclase (andesine and labradorite). The average refractive index of the glass is 1.562 +/- 0.002. Inferred to be 12,000-15,000 years old.

References:
Volcanic ash deposits in the Gulf of Alaska and problems of correlation of deep-sea ash deposits

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