Heavy-mineral concentrations as proxies of high-energy events along sandy coasts
Buynevich, I. V.
Larchenkov, Yevhenii P.
Oakley, B. A.
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Sediment-rich coastal sequences have the potential of preserving long-term records of regional-scale erosional events. Among the most diagnostic features of erosion are steep berm and dune scarps, regional unconformities (discontinuities), layers of coarse sediment or shell hash, as well as extensive accumulations of heavy minerals (magnetite, ilmenite, garnet, zircon, hornblende, etc.). These heavy mineral concentrations (HMCs) are found in many parts of the world and occur in thin layers or thick placer deposits (Fig. 1A). Their formation is due primarily to selective density sorting during the waning stages of storms (Komar and Wang, 1984; Peterson et al., 1986; Kurian et al., 2001). The HMCs can therefore be used as proxies for high-energy events along sandy coastal regions, and have been attributed to storm or tsunami-induced erosion in a number of studies (Smith and Jackson, 1990; Nichol, 2002; Buynevich et al., 2004; Dougherty et al., 2004). Substantial contrast in electromagnetic properties between sands enriched in ferromagnesian heavy minerals and quartz-rich background sediments is responsible for the sharp nature of subsurface reflections (Meyers et al., 1996; Buynevich et al., 2004) making HMCs some of the most prominent horizons in ground-penetrating radar (GPR) profiles (Fig. 1B). By combining high-resolution geophysics for mapping subsurface erosional indicators with radiocarbon or optical dating of individual erosional horizons, it is possible to reconstruct the long-term history of coastal hazards in various parts of the world.
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