Distribution of the Trace Elements in Fossil Teeth: Implication for Uranium Mobilization
| Autor: | Min-Lin Shen, 沈敏琳 |
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| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 In the Quaternary research, a precise chronological controlling method plays the most significant role in connecting the evolution processes of environment, climate and human being. The U-series dating is the most powerful method to apply in Quaternary, especially the radiogenic pairs of 234U and 230Th. The 234U-230Th method can be used to provide precise age up to 450 thousand years. At present, there are many geological samples dated with U-series including carbonates, corals, speleothems and fossil teeth. In order to obtain an accurate age, one has to assure all samples were in a closed system, otherwise, it is necessary to correct the artifacts by applying proper model calibration. Especially for the fossil teeth dating, it is still a series problem whether the obtained age is accurate or not. Hence, it is important to study how uranium migrated into the fossil teeth and how to create a proper model to calibrate these ages. Aimed to check the instrumental parameters, we have analyzed several international carbonate standards, including three coral ( RKM-4、RKM-5 and JCp-1 ) and three speleothems ( 76001、GBW04412 and GBW04413 ) standards. We used standard addition method to quantify these standards using a high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). There is no trace element composition available in these standards, except for JCp-1. A comparison of JCp-1 results with previous measurements allows us to evaluate systematically of the ICP-MS technique. On the other hand, a new database of trace element compositions can be certified for these international standards. For the fossil teeth, major, minor and trace elements were pre-scanned using laser ablation before HR-ICP-MS analyses. According to the Diffusion-Adsorption Model suggested by Millard and Hedges, the uranium distribution patterns in the fossil teeth provide information on preservation status and if is worthy of efforts for dating. The trace elements distribution also can be used to evaluate the artifacts after buried. The preliminary results indicate that uranium was enriched in the dentine compared with enamel. There is low thorium in the teeth except where fracture located. This indicates the overestimation of ages due to uptake of 230Th is unlikely. Moreover, Fe, Mn, Al, and Pb shows similar distribution in the crack or certain spots of the teeth, probably relatd to diagenesis. In summary, the uranium distribution is concentrated in the dentine, and is apparently saturated and therefore an accurate age is likely can be obtained. |
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