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    201601201601

    Geochemical approaches to the quantification of dispersed volcanic ash in marine sediment

    Scudder R P, Murray R W, Schindlbeck J C, Kutterolf S, Hauff F, Underwood M B, Gwizd S, Lauzon R, McKinley C C

    Dispersed ash, Caribbean Sea, Equatorial Pacific Ocean, Northwest Pacific Ocean, Ash layers, Volcanic eruptions, DSDP, ODP, IODP

    Top: Global distribution of subaerial volcanoes in different tectonic settings. Map has been modified after http://d-maps.com and volcano positions are taken from the Smithsonian Global Volcanism Program (http://www.volcano.si.edu).

    Bottom: Locations of sites highlighted in this paper. Data from GeoMapApp (http://www.geomapapp.org; GMRT-Global Multi-Resolution Topography; Ryan et al., 2009)

    Volcanic ash has long been recognized in marine sediment, and given the prevalence of oceanic and continental arc volcanism around the globe in regard to widespread transport of ash, its presence is nearly ubiquitous. However, the presence/absence of very fine-grained ash material, and identification of its composition in particular, is challenging given its broad classification as an “aluminosilicate” component in sediment. Given this challenge, many studies of ash have focused on discrete layers (that is, layers of ash that are of millimeter-to-centimeter or greater thickness, and their respective glass shards) found in sequences at a variety of locations and timescales and how to link their presence with a number of Earth processes. The ash that has been mixed into the bulk sediment, known as dispersed ash, has been relatively unstudied, yet represents a large fraction of the total ash in a given sequence. The application of a combined geochemical and statistical technique has allowed identification of this dispersed ash as part of the original ash contribution to the sediment. In this paper, we summarize the development of these geochemical/statistical techniques and provide case studies from the quantification of dispersed ash in the Caribbean Sea, equatorial Pacific Ocean, and northwest Pacific Ocean. These geochemical studies (and their sedimentological precursors of smear slides) collectively demonstrate that local and regional arc-related ash can be an important component of sedimentary sequences throughout large regions of the ocean.