| The formation and change of climate, environment, geology and topography during the Quaternary are closely associated with the development of human evolution and civilization. To describe those processes more accurate, developing the framework of chronology is very important. In recent years, with the continuous progresses on measurement methods, the range and reliability of dating and suitable dating materials are widening. However, in the region where is lack of volcanic minerals and older than20million years, accurate dating is still one of the difficult problems in present. Electron Spin Resonance (ESR) dating becomes the hotspot of research and is widely used in geological dating (e.g., archaeological site, river terrace, fault and et al). The reliability of sediment ESR age is directly based on whether the quartz paramagnetic centers can be resetting before the last bury event or not. Recently, studies have shown that heat and nature light are the main reasons for resetting in Quartz. However, during the river transportation process, especially in the river with high turbidity, the above effects are not obvious. While, plenty of dating results indicate that the paramagnetic centers in fluvial sediments are resetting to their largest extent. Therefore, some researchers proposed that river mechanical movement results in the resetting.In this study, to explore the ESR signal and resetting characteristics of quartz, fluvial sediments are used in simulation experiments. First of all, the relationship between ESR intensity during the fluvial movement and resuspended effect is analyzed. As the previous researches had reported, the abrasion of quartz surface causes the decline of ESR signal intensity. We utilize hydrofluoric acid to etch the sediment samples with different time, and therefore to exam if it is the influencing factor as previous reports. After all laboratory experiments, sediment samples were collected along a tributary of Minjiang River (upstream) to verify the results drew before. Besides, we present detailed ESR dating of the Donggutuo Paleolithic site in Nihewan basin. Overall, the conclusions are obtained:(1) Fluvial mechanical movement can result in resetting of ESR intensity in Al center and Ti center of quartz. Besides, the reduction of ESR intensity in Al center and Ti center in sediments with the grain size of100-150μm is greater than200-250μm part. According to the tumbler experiment, after relatively short tumbling times, the ESR intensity of OHC center small grain-size quartz cannot reset. Therefore, OHC center is not suitable for dating.(2) The hydrofluoric acid etching experiment shows that the ESR intensity of quartz centers is decreased with etching time. Therefore, particle surface abrasion is one of the reasons in signal resetting.(3) The ESR intensity of sediment samples from Minjiang river show significant correlation with the change of grain sizes. Specifically, in landslide area, the grain sizes and ESR intensity have positive correlation. The reason may be that the sediment from landslide had not experienced fluvial movement, and thus the signal had not been reset fully. While in other areas, the relationship changes to negative, which is consistent with the results of simulation experiments.(4) The four archaeological layers A, B, C and E of the Donggutuo site yield ESR ages ranging from1057±160ka to1264±171ka with a mean of1187±120ka. The ages are well consistent with the paleomagnetic finding, which show that the Donggutuo Paleolithic site lies just below the onset of the Jaramillo normal subchron(0.99-1.07Ma). |
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