Wyniki wyszukiwania - BazTech

1

ESR dating of fossil teeth: In which extent the thickness of adjacent tissues should be taken into account in the external beta dose rate evaluation?

Duval Mathieu, Martin Loïc

Geochronometria

|

2019

|

Vol. 46, no. 1

102--110

EN

We used DosiVox to evaluate the impact of cement thickness on the dose effectively absorbed by the enamel layer. Until now, the thickness of the dental tissues adjacent to the enamel layer was not considered by any of the most widely used combined US-ESR dating programs (DATA and USESR). Instead, if adjacent tissues are present, their thickness is by default assumed to be sufficient to fulfill the infinite matrix conditions. Our result suggest that such an assumption may represent in first instance a fair approximation of the reality, as even with a thickness of only 1 mm, the cement contributes to at least 98% of the beta dose rate coming from the outer side of the enamel layer. However, when cement is < 1 mm thick, DATA or USESR would overestimate the external beta dose rate and the value should be corrected accordingly by considering the relative contribution of the sediment. The impact of this correction on the total dose rate may vary, as it is directly dependent on the radioactivity of the cement itself, as well as of the sediment or dentine. Our results show that a very thin cement layer (0.1 mm-thick) can significantly contribute to the beta dose rate and should therefore not be neglected. Consequently, based on these results, we recommend the systematic measurement of the thickness of the dental tissues adjacent to the enamel layer during sample preparation, in order to proceed to beta dose rate corrections if necessary. Although this work has been especially focused on the case of fossil teeth showing cement, the conclusions stand for any other geometry involving different dental tissues adjacent to the enamel layer dated by ESR.

2

Application of long time artificial optical bleaching of the E1’ centre to sediment ESR dating

Wei Chuan-Yi, Liu Chun-Ru, Li Chang-An, Yin Gong-Ming, Zhang Yu-Fen, Li Wen-Peng, Yu Lu-Peng

Geochronometria

|

2019

|

Vol. 46, no. 1

79--86

EN

Three quartz samples extracted from different origins were collected for ESR evaluation to appreciate the optical bleaching characteristics of the E1’ centre in a long time scale. After exposure of about 400 hours to artificial sunlight, the E1’ centre were bleached to a steady increasing level, about 2.5 times of its natural level, and the increase level also exhibit a small variability among different sample origins. The constant increasing level provide a significantly evidence for the potential use of the natural signal intensities of quartz E1’ centre in tracing sediment provenance. The results show that the signal intensity of E1’ centre increased within beginning 84 h and decreased after 202 h as previous researches have partly predicted. After long time exposed to sunlight, there is no correlation between irradiated samples’ dose rate and its E1’ centre ESR signal intensity. Thus, no new convenient indication shed light on the possible use of the E1’ centre for ESR sediment dating.

3

ESR geochronology of the Minjiang River terraces at Wenchuan, eastern margin of Tibetan Plateau, China

Liu C.-R., Yin G.-M., Zhang H.-P., Zheng W.-J., Voinchet P., Han F., Wang D., Song W.-J., Bahain J.-J.

Geochronometria

|

2013

|

Vol. 40, no. 4

360--367

EN

The Minjiang River terrace along the Longmen Shan fault zone near Wenchuan, at the eastern margin of the Tibetan Plateau, China, provides archives for tectonic activity and quaternary climate change. However, previous studies were not able to provide ages older than 100 ka due to the limitations of dating material or/and methods applied to date the fluvial sediments. In this study, we used the ESR signal of the Ti-Li center in quartz to obtain the ages of four higher terraces (T3-T6). According to the results, the terraces T3 to T6 were formed at 64±19 ka, 101±15 ka, 153±33 ka, and 423±115 ka, respectively. Combined with previous studies, these results indicate that the formations of all terraces correspond to glacial/interglacial transition periods, such as, T1-T5 being correlated to MIS2/1, MIS4/3, MIS5d/5c, and MIS6/5e respectively, while T6 probably to MIS12/11. According to these data, it is found that the average incision rate was significantly higher over the last 150 ka than that previous 100 ka (250 to 150 ka). As both tectonics and climate have affected the formation of these terraces, in addition to the overall uplifting of Tibetan Plateau, the regional uplift due to isostasy would be an additional tectonic factor in the formation of river terraces in the eastern margin of Ti-betan plateau.

4

ESR dating of the Donggutuo Palaeolithic site in the Nihewan Basin, northern China

Liu C.-R., Yin G.-M., Fang F., Voinchet P., Deng C.-L., Han F., Li J.-P., Song W.-J., Wang D., Bahain J.-J.

Geochronometria

|

2013

|

Vol. 40, no. 4

348--354

EN

The fluvio-lacustrine sequences in the Nihewan Basin, northern China, provide important terrestrial archives about Palaeolithic settlements and, therefore, about early human occupation in high northern latitude in East Asia. Here we present detailed ESR dating of the Donggutuo Palaeo-lithic site, located in this basin. Four levels A, B, C and E of the Donggutuo archaeological layer yield ESR ages ranging from 1060±129 ka to 1171±132 ka with a mean of 1119±132 ka. The ages are con-sistent with the paleomagnetic data, which show that the Donggutuo Palaeolithic site lies just below the onset of the Jaramillo normal subchron (0.99-1.07 Ma). Furthermore, our results indicate that the reliable ESR dating range of bleached quartz using Ti-Li centre can be effectively extended to 1100 ka and the Ti-Li centre was zeroed before the last deposition, which requires improvement of the understanding of the bleaching mechanism conditions.

5

Detailed protocol for an accurate non-destructive direct dating of tooth enamel fragment using Electron Spin Resonance

Joannes-Boyau R.

Geochronometria

|

2013

|

Vol. 40, no. 4

322--333

EN

In the context of human evolution, fossil remains are too valuable to be destroyed and any alteration should be kept to a minimum. The newly developed protocol on fossil fragments has open the gate for ‘virtually’ non-destructive ESR (Electron Spin Resonance) direct dating of human re-mains. The method allows the separation of unstable and interfering signals that were responsible for large dose underestimation. While a complete investigation of the ESR signal remains a complex task and requires numerous hours of manipulations, a rapid dose assessment protocol can be achieve with-out compromising the accuracy nor the integrity of the sample. The new protocol should be used for future dating regardless of the possibility of measuring powder.

6

ESR dating of marine barite in chimneys deposited from hydrothermal vents

Okumura T., Toyoda S., Sato F., Uchida A., Ishibashi J., Nakai S.

Geochronometria

|

2010

|

Vol. 37

57-61

EN

Electron Spin Resonance (ESR) dating of marine barite in chimneys deposited from hydrothermal vents was attempted to determine the time since hydrothermal activity occurred. In this study, we used Barite (BaSO4) precipitated in icroenvironments in the chimneys deposited from the hydrothermal vents at the Archaean site in South Mariana spreading centre (12°56.4'N, 143°37.9'E) and at Hakurei site in the Izena caldron (27°15‘N, 127°04‘E) for ESR measurements. ESR spectrum of marine barite is characterized by an electron-type centre with g values of 2.0034, 2.0022 and 1.9995 attributed to SO3 –. The signal intensity increased with gamma ray dose. The dose rates of hydrothermal chimneys from the Archaean site and from the Hakurei site were calculated using a model that assumed a grain size and that incorporation of radionuclides after 226Ra in U series into the chimney, and assuming the efficiency of the defect formation by alpha particles to be the same as that for OSL. The ESR ages were estimated to be 470 years old for barite from the Archaean site and 5670 years old for one from the Hakurei site, although there is a considerable difference between the present ESR ages and the 210Pb/226Ra disequilibrium ages previously reported.

7

ESR dating of sedimentary quartz from two pleistocene deposits using Al and Ti-centers

Tissoux H., Toyoda S., Falgueres C., Voinchet P., Takada M., Bahain J-J., Despriée J.

Geochronometria

|

2008

|

Vol. 30

23-31

EN

One sample from a fluvial terrace of Loir river (France) deposited during isotopic stages 7-8 and two samples from isotopic stage 5 marine sediments of Echizen Coast (Japan) were dated by ESR of quartz grains. Both additive and regenerative techniques were used on Ti-Li and Ti-H centers of quartz. No change of sensitivity of the centers was observed during regeneration which significantly reduced the errors on the equivalent doses. Bleaching experiments indicated that the Ti-Li center is less sensitive to UV(ultra-violet)-A (365-412 nm) than to the full sun spectrum whereas UVA alone is sufficient to reset the bleachable component of the Al-center. This effect could be the origin of the strong overestimation of the ages determined using the Ti-Li center in this study. The comparison of the equivalent doses determined by the two Ti-centers indicated that bleaching before deposition of the fluvial sediment was apparently better than for the marine sample.

8

The last Middle Pleistocene interglacial in Lithuania : insights from ESR-dating of deposits at Valakampiai, and from stratigraphic and palaeoenvironmental data

Molodkov A., Bolikhovskaya N., Gaigalas A.

Geological Quarterly

|

2002

|

Vol. 46, No 4

363-375

EN

The penultimate (Snaigupele, oxygen isotope stage (OIS) 7) interglacial has proved controversial in Lithuania because of palynological similarities between Holsteinian, SnaigupĹlĹ and Eemian interglacial deposits in the Lithuanian terrestrial record. Furthermore, no warm interglacial period has been recognised between the Holsteinian (OIS 11) and Eemian (OIS 5) in the neighbouring Baltic countries, Estonia and Latvia. In this study, we provide electron spin resonance (ESR) dates of two freshwater mollusc shell samples collected from lacustrine sediments at the Valakampiai site which are thought to be Snaigupele in age. Shells analysed gave mutually consistent dates of 116.0 š 10.8 and 110.0 š 12.1 ka with an average age of about 113.3 ka. These dates are thus significantly younger than OIS 7, and more closely correspond to OIS 5 (Eemian). The possible occurrence of this late Middle Pleistocene OIS 7 interglacial episode in Lithuania and other Baltic countries is evaluated with reference to the nearest and most complete long terrestrial sequences from the central and southeastern parts of the East-European Plain.

9

Symbiosis between geochronologists and quaternary geoscientists

Geyh M. A.

Geochronometria

|

2001

|

Vol. 20

1-8

EN

There is an apparent conflict between the high output of absolute dates of automated devises installed in geochronological laboratories and the growing need of an individual and thorough interpretation of absolute physical dates determined for geoscientists and archaeologists. This conflict can only be solved by a symbiotic co-operation with universal geochronologists. The benefit will be an increase of the reliability and precision of the geochronological time marks, an improvement of the dating methods and an extension of the fields of application for the many absolute dating methods based on cosmogenic isotopes, radiation damage or uranium-series disequilibrium.