Zeroing tests and application of thermoluminescence dating to Fraser River delta sediments

Abstract

Thermoluminescence (TL) systematics of known-age sediments from the Fraser River delta in southwestern British Columbia have been determined to test the hypothesis that "zeroing" of TL mineral clocks occurs in deltaic and fluvial environments. Analyzed sediments include suspended silt carried by the Fraser River, surface mud from three different environments on the modern Fraser River delta, and independently dated floodplain and prodelta sediments from two cores. Derived TL dating procedures were also applied to unknown-age proglacial muds from one of these cores. The suspended silt and surface muds yielded minimum, relict TL ages of about 300 years, with typical "zero-point" equivalent-dose values of 0.5–1 Gy. Zero-point-corrected TL ages of two samples of Holocene floodplain sediments from one core and two samples of latest Pleistocene – early Holocene prodelta sediments from a second core agree with independent age estimates. In contrast, the older proglacial deposits could not be dated by the TL methods used here because plateaus in equivalent-dose values were not observed.