Temperature, d18O, d13C, K, Rb, and Sr concentrations and 87Sr/86Sr values of calcites from DSDP Site 92-597 and fish teeth from DSDP Sites 15-149, 68-502, and 98-576 and from sediment cores AMPH-116 and DODO-111

Calcites from the basaltic basement at Deep Sea Drilling Project Site 597, containing 3.4 to 4.4 mol % MgCO3, were analyzed for d13C, d18O, 87Sr/86Sr, K, Rb, and Sr concentrations. The d13C values range from 1.9 to 2.4 per mil (relative to PDB) and are typical for calcites from the extrusive layer of the oceanic crust. The d18O values of calcites are very uniform and unusually high (2.33 to 2.77 per mil, PDB), which suggest temperatures of formation of 1.5 to 2.9°C and 0.03 to 1.7°C using the calibrations of O'Neil et al. (1969) and Epstein et al. (1953), respectively (after correction for MgCO3), and assuming - l per mil for the late Oligocene/early Miocene bottom water. Paleogene bottom waters are thought to have been warmer than those of present day, and hence the calibration of Epstein et al. (1953) yields more reasonable temperatures for late Oligocene/early Miocene bottom waters. K and Rb concentrations are very low, which is consistent with their incompatible character. Sr/Ca ratios of calcites from sub-basement depths less than 35 m are typical for calcites precipitated from pure seawater, whereas the lowermost sample, from a sub-basement depth of 78 m, appears to contain substantial amounts of basaltic Ca. The 87Sr/86Sr ratios of seawater calcites range from 0.708192 to 0.708349, suggesting that they precipitated from 20 to 28 Ma seawater, or within 8 m.y. after formation of the oceanic crust at Site 597. Our data for calcites from Site 597, drilled on fast-spreading oceanic crust, are similar to data for carbonates from slowspreading crust, except that the high d18O values of the former suggest low temperatures of formation. The low temperatures of calcite formation apparently indicate that the oceanic crust at Site 597 was unusually permeable, allowing rapid circulation of seawater.

采自深海钻探计划（Deep Sea Drilling Project, DSDP）597站位玄武质基底的方解石，其MgCO₃含量为3.4至4.4 mol%，研究者对其δ¹³C、δ¹⁸O、⁸⁷Sr/⁸⁶Sr比值以及K、Rb、Sr元素浓度开展了分析。其δ¹³C值介于1.9至2.4‰（相对于Pee Dee Belemnite，PDB标准），符合洋壳喷出层方解石的典型同位素特征。该批方解石的δ¹⁸O值均一性极强且异常偏高（2.33至2.77‰，PDB标准），分别采用奥尼尔等人（O'Neil et al., 1969）与爱泼斯坦等人（Epstein et al., 1953）的同位素温度校准公式（经MgCO₃组分校正后），并假设晚渐新世-早中新世底层水的δ¹⁸O值为-1‰，可推算出其形成温度分别为1.5至2.9℃与0.03至1.7℃。古近纪底层水被认为较现代海水更为温暖，因此爱泼斯坦等人（1953）的校准公式所得到的形成温度，对于晚渐新世-早中新世的底层水环境而言更为合理。样品中的K与Rb浓度极低，这与其作为不相容元素的地球化学特性相符。亚基底深度小于35m处的方解石Sr/Ca比值，符合纯海水沉淀成因方解石的典型特征；而采自78m亚基底深度的最下层样品，则似乎含有大量玄武质来源的钙。海水成因方解石的⁸⁷Sr/⁸⁶Sr比值范围为0.708192至0.708349，表明其沉淀于20至28 Ma的海水中，即该站位洋壳形成后的8百万年以内。本研究针对597站位（位于快速扩张洋壳之上）方解石的分析数据，与慢速扩张洋壳碳酸盐的相关数据集具有相似性，仅前者偏高的δ¹⁸O值指示了更低的形成温度。方解石形成温度偏低这一现象，表明597站位的洋壳具有异常高的渗透性，使得海水得以在其中快速循环。