Oxygen isotopic ratios in quartz as an indicator of provenance of dust

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Abstract
Quartz was isolated in the fine silt fraction (1 to 10 μm in diameter) from atmospheric aerosols, wind-erosive and loessial soils, shales, and Pacific pelagic sediments of the Northern and Southern Hemispheres. Its oxygen isotopic ratio (18O/16O) was determined by mass spectrometry to trace provenance or origin in a study of dust sequestering of 137Cs and other nuclear fission products. Quartz origin from two sources was established: (1) weathered igneous and metamorphic rocks and (2) low-temperature authigenic sources such as chert. High-temperature quartz preferentially accumulates in beach sands, while it decreases in finer particle sizes and in deposits farther from shore. Low-temperature authigenic quartz (for example, chert) increases in fine silt in central marine basin sediments, with δ18O= 17 to 24‰. Glacial and fluvial erosion carried predominantly igneous and metamorphic quartz from the suture highlands of the South Polar supercontinent, Gondwanaland, onto continental shelves during late Paleozoic-early Mesozoic time. Quartz of aerosol dust of these uplifted shelves (continents that drifted northward in Cretaceous time) and in the South Pacific pelagics has mainly δ18O = 13 ± 2‰. Concurrently, present Northern Hemisphere continents moved across tropical and equatorial climates under which weathering caused great desilication of soils, leaching of soluble Si(OH)4 into rivers and seas, and accumulation of biogenic silica. The latter subsequently was crystallized into fine quartz silt of chert and other authigenic materials. A high proportion of low-temperature, high-δ18O (mainly 19 ± 2‰) quartz occurs in North Pacific pelagic sediments and in sediments and soils of the plains of now Northern Hemisphere continents, in contrast to the situation in the mid- and high-latitudes of the Southern Hemisphere.

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