Coarse versus fine-grain quartz optical dating of the sediments related to the 1985 Ms7.1 Wuqia earthquake, northeastern margin of the Pamir salient, China

Abstract

Optical dating of earthquake related sediments were investigated including one modern sample and three samples from a trench excavated across the 1985 Ms7.4 Wuqia Earthquake surface rupture. The results indicated that equivalent dose (D e ) values vary with grain size and the method used for D e determination. The residual dose of the modern sample is 0.1 ka (0.2 +0.2 -0.1 Gy) for the quartz single grain measurements. Only 1.5-3.6% of the grains have a detectable OSL signal. Single grain quartz ages are similar to the expected ages. Fine grain quartz results overestimate the D e values and are much older than single grain quartz and coarse grain quartz small aliquot standardized growth curve (SA-SGC) ages. Single grain quartz OSL dating may be optimal for dating earthquake related deposits, but SA-SGC can save measurement time and has potential for dating some poorly bleaching samples.

Dose dependency of aliquot sizes and age models from modern alluvial fan deposits of Helan Mountain, China

“…The ratios of the IEU D e s with small aliquots (~30 grains) to the expected dose are consistent with unity within two standard errors for paleoflood deposits (Medialdea et al, 2014). In addition, it is proven by modern earthquake-related deposits of 1-mm aliquots with MAM (Yang et al, 2017).…”

“…The minimum age model (MAM, Galbraith et al, 1999;Arnold et al, 2009) assumes that only a proportion of the D e values belong to the burial dose distribution and that the other D e values are part of a normal distribution truncated at the burial dose. This statistical method has been applied to modern earthquake-related sediments to identify the lower D e s, which is related to the true ages (Fattahi et al, 2016;Yang et al, 2017). The internal/external consistency criterion (IEU, Thomsen et al, 2003Thomsen et al, , 2007 was used to identify the lowest normal dose population, which is presumed to be the population of grains most likely to have been well-bleached at deposition (Zhao et al, 2015(Zhao et al, , 2017.…”

“…The OSL signal from quartz is reset more quickly than the infrared-stimulated luminescence from feldspar when the minerals are exposed to sunlight (Godfrey-Smith et al, 1988;Yang et al, 2012). In addition, in many cases, coarser grains are generally better bleached than finer fractions (Olley et al, 1998;Hu et al, 2010;Yang et al, 2017). Moreover, D e could decrease with increasing transport distance due to the longer time to bleach (Alexanderson, 2007;Vandenberghe et al, 2007;Hu et al, 2010;Zhao et al, 2015).…”

“…It now becomes possible to measure the luminescence from a single grain of quartz to distinguish between well-bleached grains (Thomas et al, 2005;Duller, 2008;Wu et al, 2010;Zhao et al, 2015;Zhao et al, 2017). However, the single grain technique requires considerable time, labor, and specific equipment, which restricts its wide application (Tooth et al, 2007;Yang et al, 2017). Many studies have shown that the application of a specific aliquot size can identify well-bleached populations of sediments with different D e values (Olley et al, 1999;Tooth et al, 2007;Duller, 2008) and obtain accurate burial doses for modern and old sediments (Medialdea et al, 2014).…”

“…In addition to the impact of the aliquot sizes, studies on statistical methods have shown that some different age models can be used for the analysis of D e values to obtain the true deposition ages. The application of statistical methods is essential for incomplete bleaching sediments to identify well-bleached populations (Duller, 2006(Duller, , 2008Wu et al, 2010;Yang et al, 2017;Zhao et al, 2015Zhao et al, , 2017.…”