LS deposits are deposited over a period of centuries but they are time transgressive because initiation as well as peak rates may occur at different times within a basin and at largely different
times between regions. Production of LS may be polycyclic with multiple events over time, such as when failed mill dams or collapsed gully walls produce a second cycle of anthropogenic sediment. Thus, LS cascades may occur in space as reworking of LS moves sediment down hillslopes, into channels, and see more onto floodplains (Lang et al., 2003 and Fuchs et al., 2011). LS may have a distinct lithology and geochemistry or it may be highly variable down-valley or between subwatersheds and indistinguishable from underlying sediment. Non-anthropic sediment will usually be mixed with anthropic sediment, so LS is usually diluted and rarely purely of anthropic origin. In regions with deep LS deposits the anthropogenic proportion is likely to be high. Several studies have shown greatly accelerated sediment deposition rates after disturbance and relatively slow background sedimentation rates (Gilbert, 1917 and Knox, 2006). Although there are important exceptions to the assumptions of low pre-settlement and high post-settlement sedimentation rates in North America (James, 2011), pre-Columbia
sediment accumulation rates were generally an order of magnitude lower than post-settlement rates. Thus, PSA is likely www.selleckchem.com/products/nu7441.html to contain a high proportion of anthropogenic sediment, and the assumption of substantial proportions of anthropic sediment in such a deposit is often appropriate. The definition of LS should extend to deposits generated over a wide range of geographic domains and from prehistory to recent time. For example, vast sedimentary deposits in Australia and
New Zealand have been well documented as episodic responses to land-use changes following European settlement (Brooks and Brierley, 1997, Gomez et al., 2004 and Brierley et al., 2005). These deposits are in many ways similar to those in North America and represent a legacy of relatively recent destructive land use superimposed on relatively stable pre-colonial land surfaces. Moreover, LS can also be used to describe Old World tuclazepam sedimentary units that were in response to episodic land-use changes. Sedimentation episodes have been documented in Eurasia for various periods of resource extraction or settlement (Lewin et al., 1977, Lang et al., 2003, Macklin and Lewin, 2008, Houben, 2008 and Lewin, 2010). Older periods of episodic erosion and sedimentation associated with human settlement in Europe have been documented as far back as the Neolithic, Bronze Age, and Iron Age in parts of Europe and Britain (Macklin and Lewin, 2008, Dotterweich, 2008, Reiß et al., 2009 and Dreibrodt et al., 2010).