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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >δ~(18)O of carbonate, quartz and phosphate from belemnite guards: implications for the isotopic record of old fossils and the isotopic composition of ancient seawater
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δ~(18)O of carbonate, quartz and phosphate from belemnite guards: implications for the isotopic record of old fossils and the isotopic composition of ancient seawater

机译：钙镁橄榄石保护层中碳酸盐，石英和磷酸盐的δ〜（18）O：对古化石同位素记录和古代海水同位素组成的影响

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Belemnite guards of Cretaceous and Jurassic age were found to contain varying amounts of quartz deposited both on the external surface and inside the rostrum. The oxygen isotopic composition of coexisting carbonate, quartz and phosphate from the same rostrum was measured according to well-established techniques. None of these compounds showed isotopic values in equilibrium with one another. Assuming δ~(18)O values of the diagenetic water within the range of meteoric waters, the δ~(18)O(SiO_2) yield temperatures in agreement with the apparent secondary origin of this phase. Theδ~(18)O(CO_3~(2-)) range, with a certain continuity, between -10.8 and +0.97 PDB-1 with most of the intermediate values being within the range of the carbonate isotopic values of Mesozoic fossils. The most positive isotopic results obtained from phosphate are close to +23/+24‰ (V-SMOW). They can hardly be related to a secondary origin of the phosphate, or to the presence of diagenetic effects, since these results are among the most positive ever measured on phosphate. As far as we know there is no widespread diagenetic process determining an ~(18)O enrichment of phosphate. The very low concentration of phosphate did not allow the determination of its mineralogical composition. All the available δ~(18)O(PO_4~(3-)) values from belemnite and non-belemnite fossils; (2) the δ~(18)O(PO_4~(3-)) of belemnite rostra seems to be, at least in the case of the most positive results, in isotopic equilibrium with environmental water because of the similarity between the results from Cretaceous belemnites and the results from Cretaceous and Lower Tertiary pelecypods and fish teeth; 3) if so, the only feasible interpretation that can be suggested for the ~(18)O enriched data is the possibility of a relatively large variation of the oxygen isotopic composition of ocean paleowater from Jurassic to recent time.
机译：发现白垩纪和侏罗纪的贝伦陨石护层在其外表面和讲台内部均沉积有数量不等的石英。根据公认的技术测量来自同一表皮的碳酸盐，石英和磷酸盐共存的氧同位素组成。这些化合物均未显示出彼此平衡的同位素值。假设成岩水的δ〜（18）O值在流域水的范围内，则δ〜（18）O（SiO_2）的产生温度与该相的表观次生起点相符。 δ〜（18）O（CO_3〜（2-））范围具有一定的连续性，PDB-1在-10.8和+0.97之间，大多数中间值在中生代化石的碳酸盐同位素值范围内。从磷酸盐获得的最阳性同位素结果接近+ 23 / + 24‰（V-SMOW）。它们几乎与磷酸盐的次要来源或成岩作用无关，因为这些结果是有史以来对磷酸盐测量最积极的结果之一。据我们所知，没有广泛的成岩过程确定磷酸盐的〜（18）O富集。磷酸盐浓度极低，无法确定其矿物组成。钙云母和非贝母石化石的所有可用δ〜（18）O（PO_4〜（3-））值; （2）至少在最阳性结果的情况下，贝伦石rostra的δ〜（18）O（PO_4〜（3-））似乎与环境水处于同位素平衡状态，因为白垩纪贝母和白垩纪及下第三纪脾脏和鱼齿的结果; 3）如果是这样，那么对于〜（18）O富集的数据，唯一可以建议的解释是，从侏罗纪到最近，海洋古水体的氧同位素组成有较大变化的可能性。

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