Optically Stimulated Luminescence Dating Of Sediments Research Articles

Optical dating of sediments affected by post-depositional mixing: Modelling, synthesizing and implications

One of the biggest challenges in optically stimulated luminescence (OSL) dating is to deal with sediments that are affected by post-depositional mixing. Equivalent dose (De) distributions of such samples are commonly analysed using the finite mixture model (FMM), which can statistically identify dose components of grains derived from sedimentary layers with different ages. The FMM has been increasingly applied in OSL dating of sediments from key geological and archaeological sites that are critical for understanding the evolution of Quaternary environment and human history. The burial age of the dated layer is commonly determined by dividing the De value of the target dose component estimated using the FMM by the total dose rate of the bulk sample. However, a systematic investigation of the reliability of this method for different post-depositional mixing situations has not been conducted. This study aims to investigate the reliability of the burial ages so obtained, using simulated mixed single-grain De distributions. We assess the performances of two different protocols—a user-specified or an automatically estimated between-grain dispersion value, σb. A number of factors influencing the reliability of the determined burial age are investigated, including the inherent dispersion in different dose populations, the proportion of grains associated with the target layer, the sample size used, the difference in dose rates and burial ages between the mixing components, and the time when mixing occurred. Published single-grain samples affected by post-depositional mixing are synthesized and their FMM results are assessed. Our results show that the reliability of FMM is controlled by the analytical and the intrinsic errors and depends critically on the proportion of grains for the target layer. The simulation and synthesized results caution against using an arbitrarily specified σb as input for the FMM. The intrinsic accuracy of the burial age is controlled by multiple factors for both synchronously and asynchronously mixed samples. The FMM ages derived from sediment samples affected by serious post-depositional mixing should be constrained by independent chronological information.

Tectonic Uplift of the Yili Basin during the Last Stage of the Late Pleistocene: Evidence from ESR and OSL Dating of Sediments in the Huocheng Area, Xinjiang

The Quaternary sediments in the Yili Basin can serve as archives for studying the Cenozoic basin–mountain relationship. In this study, based on typical natural sections and boreholes, the surficial sediments of the Huocheng area were studied, and their sedimentary ages were obtained using the optically stimulated luminescence (OSL) and electron spin resonance (ESR) dating methods. These dates, combined with changes in the sedimentary facies, provided details of the neotectonic movement in the Yili Basin and adjacent areas. By dating sediments from five sections and three boreholes, we determined that the surficial sediments of the Huocheng area were mainly formed in the Late Pleistocene, with scattered instances of Holocene sediments. The surficial sediments mainly consisted of alluvial fan facies, fluvial facies, lacustrine facies, and desert facies. Based on the activity on the Hongshanzui fault and the northern margin fault of the Wusun Mountains, the Huocheng area was uplifted synchronously with the Tianshan Mountains during the last stage of the Late Pleistocene, causing the desert facies sediments to be superimposed on the former paleo–lake sediments.

OSL dating of sediments from a mountainous river in southeastern Brazil: Late Cenozoic tectonic and climatic implications

The upper Das Velhas River basin is located in the central portion of the Quadrilátero Ferrífero in southeastern edge of São Francisco Craton, southeastern Brazil. Its drainage network has a strong lithostructural influence and mountainous river segments crossing different tectonic blocks. The neotectonic activity in this cratonic edge is associated with epirogenetic Brazilian Shield uplift and with local and regional differential movements of crustal blocks due to WNW migration of South-American plate. This process cause an intraplate transfer of tectonic efforts, forcing the reactivation of old faults (NW-SE and NE-SW) and the generation of recent ones (E-W). Using optically stimulated luminescence (OSL) dating and fluvial deposit data, this paper focuses on the late Cenozoic evolution of this mountainous river basin, relating it to tectonic and climatic forcing. Even with few records of ancient alluvial deposits as a result of intense dissection, three levels of river terraces were identified in some sites along the valley: a higher terrace level (T3), a cut-in-bedrock terrace of ~ 48 ka; an intermediate terrace level (T2) of ~ 7.5 ka; and a lower terrace level (T1), of ~ 1 ka. The T2 is found along the valley as a cut-in-bedrock terrace or as a fill terrace, and is found T1 as a cut-in-bedrock terrace or as a nested fill terrace or even overlapping T2 sediments. The diverse relation between these terraces may be related to unequal fluvial downcutting. We identified three main downcutting periods: (i) before T3; (ii) from T3 to T2, related to Late Pleistocene regional tectonics; and (iii) from T2 to T1, which was a response to tectonics and climate change in the early Holocene. These stages of more intense downcutting should be a response to uplift pulses. In the most active blocks, cut-in-bedrock terraces show a greater unevenness in relation to lower levels, while in the most stable blocks, T1 is found as a nested fill terrace or overlapping T2.

OSL dating of sediments from deserts in northern China

Aeolian samples from deserts in northern China were studied using the optically stimulated luminescence (OSL) of quartz and potassium (K) feldspar separates. K-feldspar has shown advantages over quartz for dating samples younger than 100 years, due to its more homogeneous equivalent dose ( D e) values, higher internal dose rate and higher luminescence sensitivity to dose. Without additional measurements, the luminescence characteristics of quartz obtained in D e determination procedures can be used to reveal the source material and/or quartz thermal history for the deserts in northern China. The results indicated that the duration of paleosol formation in desert areas reflects regional paleoenvironments.