Optical dating of Holocene sediments from the Yangtze River (Changjiang) Delta, China

Establishing a reliable chronology is essential for understanding delta evolution, which is normally performed using radiocarbon (14C) dating and the recently emerging technique of optically stimulated luminescence (OSL). The application of the latter one to the Holocene Yangtze River (Changjiang) Delta deposit is still quite limited. In this study, two 60.9-m-long cores were collected from Taizhou (TZ) and Nantong (NT) within the paleo-incised valley of the Yangtze River, and a total of seven and nine OSL samples were collected from the TZ and NT cores, respectively. In addition, ten accelerator mass spectrometry (AMS) 14C ages of the TZ core were presented with eight AMS 14C ages that were previously obtained from the NT core. The single-aliquot regenerative-dose (SAR) protocol was applied to coarse silt-sized (45-63 μm) and fine sand-sized (90-125 μm) quartz. The results showed that the grains in the 45-63 μm size fractions appeared to be better bleached than those in the 90-125 μm size fractions, and the detection of insufficiently bleached sediments is required in order to obtain accurate age estimates. The ages adopted for the samples range from 3 ka to 9 ka for the TZ core, and from 1 ka to 14 ka for the NT core, which were in general internally coherent within the limits of experimental errors and with respect to their stratigraphic order. The AMS 14C age of the TZ core were significantly older than their OSL ages, while those from the NT core generally showed good agreement with their OSL ages. One should be cautious when using AMS 14C to date deltatic deposits. Based on the OSL ages, two periods of rapid accumulation rates can be found in both cores, which are linked to the rapid sea level rise in early Holocene and migration of delta front facies in late Holocene. These investigations indicate that OSL technique is an effective method with which to date Holocene deltaic deposits, especially in coarse sedimentary layers where organic carbon material is sparse.