Arid
DOI10.1016/j.quaint.2007.01.003
Th-230-U dating of surficial deposits using the ion microprobe (SHRIMP-RG): A micro stratigraphic perspective
Maher, K.; Wooden, J. L.; Paces, J. B.; Miller, D. M.
通讯作者Maher, K.
会议名称Conference on Dating Quaternary Sediments and Landforms in Drylands
会议日期MAR, 2005
会议地点Zzyzx, CA
英文摘要

We used the sensitive high-resolution ion microprobe reverse-geometry (SHRIMP-RG) to date pedogenic opal using the Th-230-U system. Due to the high-spatial resolution of an ion microprobe (typically 30 pm), regions of pure opal within a sample call be targeted arid detrital material can be avoided. In addition, because the technique is non-destructive, the sample can be preserved for other types of analyses including electron microprobe or other stable isotope or trace element ion microprobe measurements. The technique is limited to material with U concentrations greater than similar to 50ppm. However, the high spatial resolution, small sample requirements, and the ability to avoid detrital material make this technique a suitable technique for dating many Pleistocene deposits formed in semi-arid environments.


To determine the versatility of the method, samples from several different deposits were analyzed, including silica-rich pebble coatings from pedogenic carbonate horizons, a siliceous sinter deposit, and opaline silica deposited as a spring mound. U concentrations for 30-mu m-diameter spots ranged from 50 to 1000 ppm in these types of materials. The Th-230/(232) Th activity ratios also ranged from similar to 100 to 106, eliminating the need for cletrital Th corrections that reduce the precision of traditional U-Th ages for many milligram- and largersized samples. In pedogenic material, layers of high-U opal (ca. 500 ppm) are commonly juxtaposed next to layers of calcite with much lower U concentrations (1-2 ppm). If these types of samples are not analyzed using a technique with the appropriate spatial resolution, the ages may be strongly biased towards the age of the opal. Comparison with standard TIMS (Thermal Ionization Mass Spectrometry) measurements from separate microdrilled samples suggests that although the analytical precision of the ion microprobe (SHRIMP-RG) measurements is less than TIMS, the high spatial resolution results in better accuracy in the age determination for finely layered or complex deposits. The ion microprobe approach also may be useful for pre-screening samples to determine the age and degree of postdepositional alteration, analyzing finely layered samples or samples with complex growth histories, and obtaining simultaneous measurements of trace elements. Published by Elsevier Ltd.


来源出版物QUATERNARY INTERNATIONAL
ISSN1040-6182
EISSN1873-4553
出版年2007
卷号166
页码15-28
出版者PERGAMON-ELSEVIER SCIENCE LTD
类型Article;Proceedings Paper
语种英语
国家USA
收录类别SCI-E ; CPCI-S
WOS记录号WOS:000247166400003
WOS关键词AMINO-ACID RACEMIZATION ; IMPURE CARBONATES ; PEDOGENIC CARBONATE ; COSMOGENIC CL-36 ; YUCCA MOUNTAIN ; URANIUM ; NEVADA ; DISEQUILIBRIUM ; CALIBRATION ; U-234
WOS类目Geography, Physical ; Geosciences, Multidisciplinary
WOS研究方向Physical Geography ; Geology
资源类型会议论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/296795
作者单位(1)US Geol Survey, Palo Alto, CA 94301 USA;(2)US Geol Survey, Denver Fed Sci, Denver, CO 80225 USA
推荐引用方式
GB/T 7714
Maher, K.,Wooden, J. L.,Paces, J. B.,et al. Th-230-U dating of surficial deposits using the ion microprobe (SHRIMP-RG): A micro stratigraphic perspective[C]:PERGAMON-ELSEVIER SCIENCE LTD,2007:15-28.
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