Fossil fish teeth as proxies for seawater Sr and Nd isotopes
Fossil fish teeth as proxies for seawater Sr and Nd isotopes
复制标题
DOI：
10.1016/s0016-7037(99)00376-2
复制
发表时间：
2000-03
影响因子：
5
通讯作者：
E. Martin;B. Haley
中科院分区：
文献类型：
--
作者：
E. Martin;B. Haley
本文分析了太平洋两个地点新近系鱼齿化石的Nd和Sr同位素组成，以确定清洗方案和埋藏成岩作用对海水同位素值保存的影响。Sr在牙齿生长时就被吸收到牙齿中；因此，锶同位素对化学地层学具有潜在的价值。Nd同位素是古环流的潜在保守示踪剂；然而，Nd是在死后加入的，可能记录成岩孔隙水而不是海水。我们对两个地点（Ontong爪哇高原807A和伊豆-波宁弧786A）的样品进行了评价，这两个地点暴露于相似的底部水，但具有不同的岩性和孔隙水化学。鱼齿的锶同位素值似乎准确地反映了两个地点同时期的海水。两个地点牙齿的Nd同位素值之间的良好相关性表明，当牙齿与海水处于化学平衡时，Nd被合并，并且该信号在地质时间尺度和随后的埋葬中被保存下来。这些数据也证实了从相似水深回收的太平洋锰铁地壳中提取的古海水Nd同位素组成（Ling et al., 1997）。这一佐证有力地表明，这两种材料都保留了海水中的Nd同位素值。太平洋深水ε ndvalue的变化与巴拿马地峡的浅滩化和随后通过南极环极流进入太平洋的非放射性成因北大西洋深水的开始的预测相一致。
We analyzed Nd and Sr isotopic compositions of Neogene fossil fish teeth from two sites in the Pacific in order to determine the effect of cleaning protocols and burial diagenesis on the preservation of seawater isotopic values. Sr is incorporated into the teeth at the time of growth; thus Sr isotopes are potentially valuable for chemostratigraphy. Nd isotopes are potential conservative tracers of paleocirculation; however, Nd is incorporated post-mortem, and may record diagenetic pore waters rather than seawater. We evaluated samples from two sites (site 807A, Ontong Java Plateau and site 786A, Izu-Bonin Arc) that were exposed to similar bottom waters, but have distinct lithologies and pore water chemistries. The Sr isotopic values of the fish teeth appear to accurately reflect contemporaneous seawater at both sites. The excellent correlation between the Nd isotopic values of teeth from the two sites suggests that the Nd is incorporated while the teeth are in chemical equilibrium with seawater, and that the signal is preserved over geologic timescales and subsequent burial. These data also corroborate paleoseawater Nd isotopic compositions derived from Pacific ferromanganese crusts that were recovered from similar water depths (Ling et al., 1997). This corroboration strongly suggests that both materials preserve seawater Nd isotope values. Variations in Pacific deepwater εNdvalues are consistent with predictions for the shoaling of the Isthmus of Panama and the subsequent initiation of nonradiogenic North Atlantic Deep Water that entered the Pacific via the Antarctic Circumpolar Current.