Chronology of an oyster reef on the coast of Bohai Bay, China: Constraints from optical dating using different luminescence signals from fine quartz and polymineral fine grains of coastal sediments

Fossil oyster reefs are indicators of past sea levels, and their formation is usually dated by means of radiocarbon. However, radiocarbon dating of the shells from coastal areas may be complicated by the varying sources of carbon. Here we applied optical dating methods to date the samples from above and below a fossil oyster bed in a section on the coast of Bohai Bay, China. The optical ages of the sediments were used to constrain the oyster bed. Single-aliquot regenerative-dose procedures using the OSL signal from fine grain quartz, the IRSL and post-IR OSL signals from polymineral fine grains were employed to determine equivalent dose (D_e). The behaviors of the different luminescence signals from quartz and polymineral grains during D_e measurements were examined. The results showed that the quartz OSL signal is more reliable than the polymineral IRSL and post-IR OSL signals with respect to dating for these coastal samples. The optical ages indicated that the oyster reef formed between ca. 6.2 and 5.0 ka.     

Modeling the impact of climate change on sediment transport and morphology in coupled watershed-coast systems:A case study using an integrated approach

Climate change is an issue of major concern nowadays.Its impact on the natural and human environment is studied intensively,as the expected shift in climate will be significant in the next few decades.Recent experience shows that the effects will be critical in coastal areas,resulting in erosion and inundation phenomena worldwide.In addition to that,coastal areas are subject to ＂pressures＂ from upstream watersheds in terms of water quality and sediment transport.The present paper studies the impact of climate change on sediment transport and morphology in the aforementioned coupled system.The study regards a sandy coast and its upstream watershed in Chalkidiki,North Greece;it is based on：（a）an integrated approach for the quantitative correlation of the two through numerical modeling,developed by the authors,and（b）a calibrated application of the relevant models Soil and Water Assessment Tool（SWAT）and PELNCON-M,applied to the watershed and the coastal zone,respectively.The examined climate change scenarios focus on a shift of the rainfall distribution towards fewer and more extreme rainfall events,and an increased frequency of occurrence of extreme wave events.Results indicate the significance of climatic pressures in wide-scale sediment dynamics,and are deemed to provide a useful perspective for researchers and policy planners involved in the study of coastal morphology evolution in a changing climate.     

ESR dating of fluvial quartz: Estimate of the minimal distance transport required for getting a maximum optical bleaching

An ESR experimental study of artificial optical bleaching of sedimentary quartz has shown that the aluminum center was maximally bleached after a 6-month illumination equivalent to natural light. This duration seems too long to apply in natural conditions. Nevertheless, the measurement of the ESR intensity of aluminum centers in quartz extracted from modern sediments and deposited in sandy bars shows that the maximum bleaching has effectively been reached.

In order to determine the relationship between the bleaching and the distance covered by a quartz grain in a river, samples were collected along the Creuse River (France) from its spring to about 170 km downstream, where maximum bleaching levels were observed in previous studies. The ESR intensities of the aluminum and titanium centers in quartz were measured, using X-band spectroscopy, before and after artificial bleaching. The difference measured between these sub-samples shows that the maximum bleaching level is obtained in the course of the first kilometer. Hence, the assumption that ESR dating of fluvial sediment is based on the optical bleaching was validated.     

ESR dating of optically bleached quartz grains from Plio-Pleistocene to Holocene coastal dune deposits (Wilderness-Knysna area,South Africa): a comparison with luminescence

Five Plio-Pleistocene to Holocene aeolian quartz samples from the coastal dune deposits of the Wilderness-Knysna area (South Africa) previously dated by OSL were selected for ESR dating. Samples were processed following the Multiple Centre approach and using the Multiple Aliquot Additive dose method. Aluminium (Al) and Titanium (Ti) signals were systematically measured in all samples.Our study shows that ESR results obtained for Middle Pleistocene to Holocene samples may be strongly impacted by (i) the presence of a significant high frequency noise in the ESR spectra acquired for the Ti signals and (ii) the choice of the fitting function employed. In particular, if not taken into account, very noisy spectra can lead to a significant overestimation of the true ESR intensity measured for the Ti–H signal. These sources of uncertainty are however not sufficient to remove the ESR age overestimations. Consequently, our results indicate that the Al and Ti ESR signals of these quartz samples have not been fully reset during their aeolian transport.While this work contributes to improve our understanding of the ESR method applied to quartz grains, and especially of the potential and limitations of the Ti signals, it also provides additional baseline data to illustrate the existing variability among quartz samples of different origins or sedimentary context. Our results are consistent with previous studies by confirming that the Ti–H signal shows the best potential for the evaluation of low dose values (<100 Gy for these samples), whereas it becomes inappropriate for the higher dose range, and the Ti–Li–H (option D sensu Duval and Guilarte, 2015) should be used instead.Beyond the methodological outcome, this ESR dating study also provides a useful addition to the existing chronology of the aeolian deposits in this region. In particular, new (and possibly) finite numerical age results were obtained for the two oldest samples, constraining the aeolianite landward barrier dune and the coversand formations to the MIS 10-8 and Pliocene, respectively.     

Age determination for a Neolithic site in northeastern Qinghai-Tibetan Plateau using a combined luminescence and radiocarbon dating

The archaeological Shaliuheqiaodong site, located at the junction between the estuary of Shaliu River and the northeast bedrock terrace of Qinghai Lake, is one of the earliest Neolithic Age sites in the Qinghai-Tibetan Plateau (QTP), which is critical for understanding patterns of prehistoric human inhabitation in the high plateau extreme environments. There are only two published radiocarbon ages by far for chronological control. Recently, a new section (Gangcha section) was found, with abundant charcoals and fish bones well-preserved in the matrix of aeolian sediments, providing a good opportunity for a combined study of luminescence and radiocarbon dating. In the current study, we obtained three luminescence ages on aeolian sediment, six radiocarbon ages (three on charcoals and three on fish bones). Our results showed that the luminescence ages (average of 3.2 ± 0.2 ka) are in agreement with charcoal radiocarbon ages (3165–3273 cal a BP) where applicable, and that the lake reservoir effect age of radiocarbon dating was approximately 0.3–0.7 cal ka BP and an average of 0.4 cal ka BP at ∼3.2 cal ka BP (age difference between that of charcoals and fish bones). The prehistoric residence in Qinghai Lake area seemed to be sequenced from 15 ka BP to 3.1 ka BP, based on our data and previously published data altogether. The obvious baked vestiges on the bones of fish and animals, as well as a number of artifacts, indicate that naked carps had become a food resource for prehistoric people at least since 3.2 cal ka BP.