Altered states: Effects of diagenesis on fossil tooth chemistry
Altered states: Effects of diagenesis on fossil tooth chemistry
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DOI：
10.1016/s0016-7037(99)00208-2
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发表时间：
1999-09-01
影响因子：
5
通讯作者：
Barker, WW
中科院分区：
文献类型：
--
作者：
Kohn, MJ;Schoeninger, MJ;Barker, WW
使用离子微探针、电子微探针和透射电子显微镜对肯尼亚北部和中部的现代牙齿和化石牙齿进行的调查证实，化石牙齿的化学成分不仅受到次生矿物的成岩沉积的控制，而且还受到生物磷灰石化学蚀变的控制。与现代牙齿相比，化石中铁、锰、硅、铝、钡和可能的铜浓度的增加反映了磷灰石和次生矿物的混合物。这些次生矿物质的浓度范围从牙釉质中约 0.3% 到牙本质中约 5%，包括亚微米、间隙含铁锰酸盐 [(Fe3+ Mn3+)O(OH)] 和蒙皂石。次生矿物的普遍分布和细粒度表明，原位方法中原生材料和次生材料的混合分析是不可避免的，甚至在直径仅为10μm的离子微探针点中也是如此，并且本体化学分析存在严重偏差。其他元素的增加，包括稀土元素、U、F，可能还有 Sr，显然反映了牙本质和牙釉质中磷灰石的额外变化。为了进行古生物学或古气候研究，需要极其小心地从原始生物磷灰石中分离出次生矿物，尽管如此，对纯化磷灰石的大量分析可能是值得怀疑的。尽管牙齿的 PO4 成分似乎能够抵抗化学变化，但 OH 成分却发生了广泛的变化。这种 OH 变化意味着对化石牙釉质的氧同位素组成进行的批量分析可能存在 +/- 千分之 1 的系统性偏差，并且氧同位素组成的季节性记录可能会发生虚假转移、增强或减弱。版权所有 (C) 1999 Elsevier Scieizce Ltd.
Investigation of modern and fossil teeth from northern and central Kenya, using the ion microprobe, electron microprobe, and transmission electron microscope, confirms that fossil tooth chemistry is controlled not only by the diagenetic precipitation of secondary minerals but also by the chemical alteration of the biogenic apatite. Increases in the concentrations of Fe, Mn, Si, Al, Ba, and possibly Cu in fossil vs. modern teeth reflect mixtures of apatite and secondary minerals. These secondary minerals occur in concentrations ranging from similar to 0.3% in enamel to similar to 5% in dentine and include sub-mu m, interstitial Fe-bearing manganite [(Fe3+ Mn3+)O(OH)], and smectite. The pervasive distribution and fine grain size of the secondary minerals indicate that mixed analyses of primary and secondary material are unavoidable in in situ methods, even in ion microprobe spots only 10 mu m in diameter, and that bulk chemical analyses are severely biased. Increases in other elements, including the rare earth elements, U, F, and possibly Sr apparently reflect additional alteration of apatite in both dentine and enamel. Extreme care will be required to separate secondary minerals from original biogenic apatite for paleobiological or paleoclimate studies, and nonetheless bulk analyses of purified apatite may be suspect. Although the PO4 component of teeth seems resistant to chemical alteration, the OH component is extensively altered. This OH alteration implies that bulk analyses of fossil tooth enamel for oxygen isotope composition may be systematically biased by +/- 1 parts per thousand, and seasonal records of oxygen isotope composition may be spuriously shifted, enhanced, or diminished. Copyright (C) 1999 Elsevier Scieizce Ltd.