Dating Deglaciation

The assumptions with cosmogenic nuclide dating method is "(1) that nuclides from previous periods of exposure were removed by erosion of at least several meters during the most recent glaciation (Briner et al., 2016), (2) that surfaces were not shielded by snow or sediment following deglaciation (Heyman et al., 2016; Schildgen et al., 2005), and (3) that surfaces have not been eroded following deglaciation (Zimmerman et al., 1994)" (1.) For radiocarbon dating methods, the assumptions are "the unknown lag time between ice margin retreat and the onset of organic matter deposition may make minimum age limits too young (Davis and Davis, 1980). The scarcity of organic material in postglacial sediments because of cold conditions also limits the utility of basal radiocarbon ages for developing accurate deglaciation chronologies (Cotter et al., 1986; Stone and Borns, 1986; Balco and Schaefer, 2006). Additionally, carbon unrelated to the material being dated can contaminate the sample, especially in the case of bulk sediments or concretions (Grimm et al., 2009)." (2.) "Bulk lake sediment ages are often too old because they contain recycled carbon (Davis et al., 1995) or are subject to hard water effects (Shotton, 1972). Several studies in Vermont have shown organic macrofossil ages to be hundreds of years younger than bulk sediment ages (Brown, 1999; Noren, 2002; Parris, 2003), likely because of carbon recycling." (1.)