The Marine 234U/238U Record and the Timing of the Marine 18 O/ 16 O Record

Marine 234U/238U 记录和 Marine 18 O/ 16 O 记录的计时

• 批准号: 9402693
• 负责人: Richard Edwards
• 金额: $ 44.16万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-06-15 至 1998-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9402693&HistoricalAwards=false
• 关键词: Marine; 234U; 238U; Record; Timing

9402693 EDWARDS Direct dating of the marine S18 O record has been a classic problem for the last four decades, and is still largely unsolved. Interest in this problem has increased in the wake of improvements in analytical capabilities for measurement of 234 U/ 238 U (Chen et al., 1986) and 230 Th/238 U (Edwards et al., 1987 a,b) and further analytical refinements (Edwards et al., 1993). However, attempts to use 230 Th techniques to date deep-sea marine carbonates will be faced with at least one major, perhaps insurmountable, obstacle: separation of contaminant 230 Th produced by uranium in the overlying water column from 230 Th produced by uranium in the carbonate (Delaney and Boyle, 1983). Consequently, two alternate approaches will be investigated to constrain the timing of the marine S18 O record: 234 U/238 U dating of carbonate-rich sediments (Ku, 1965; Ludwig et al., 1991) and 230 Th dating of tropical-island speleothems. The 234U/238U ratio is measured with a precision of +1 per mil (Edwards et al., 1993), which corresponds to an error in 234U/238U age of +4Ka. Thus high-resolution 234U/238U ages are in principle, possible. Bulk carbonate will be analyzed from cores that have high primary uranium contents and are close to 100% carbonate. Also, dating of speleothems from tropical islands will be dated with TIMS 230 Th techniques (Li et al., 1989; Dorale et al., 1992; Baker et al., 1993; Richards et al., in press) and may have S18 O values that mimic marine values, thereby providing a means of dating the marine record. These two approaches will place direct constraints on the timing of the marine S18 O record (over the past 350,000 years) and will help to understand the fundamental causes of Quaternary climate change.

9402693 爱德华兹 在过去的四十年里，海洋S18 O记录的直接测年一直是一个经典的问题，而且在很大程度上仍然没有解决。 随着用于测量234 U/238 U的分析能力的改进，对该问题的兴趣增加（Chen等人，1986）和230 Th/238 U（Edwards等人，1987 a，B）和进一步的分析改进（Edwards等人，1993年）。 然而，试图利用230 Th技术测定深海海洋碳酸盐的年代将面临至少一个主要的、也许是无法克服的障碍：将上覆水柱中铀产生的污染物230 Th与碳酸盐中铀产生的230 Th分离（Delaney和波义耳，1983年）。因此，将研究两种替代方法来限制海洋S18 O记录的时间：富含碳酸盐沉积物的234 U/238 U测年（Ku，1965年; Ludwig等人，1991）和230 Th测年。234U/238U比率以每密耳+1的精度测量（Edwards等人，1993），这对应于+4Ka的234U/238U年龄误差。 因此，高分辨率的234U/238U年龄在原则上是可能的。将从原生铀含量高且接近100%碳酸盐的岩心中分析块状碳酸盐。 此外，来自热带岛屿的洞穴沉积物的年代测定将采用TIMS 230 Th技术（Li等人，1989; Dorale等人，1992; Baker等人，1993;理查兹等人，正在印刷中），并且可能具有模拟海洋值的S18 O值，从而提供了一种确定海洋记录日期的方法。 这两种方法将直接限制海洋S18 O记录的时间（过去35万年），并将有助于了解第四纪气候变化的根本原因。