The climate of the Late Cretaceous: New insights from the application of the carbonate clumped isotope thermometer to Western Interior Seaway macrofossil
The climate of the Late Cretaceous: New insights from the application of the carbonate clumped isotope thermometer to Western Interior Seaway macrofossil
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DOI：
10.1016/j.epsl.2012.11.036
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发表时间：
2013-01-15
影响因子：
5.3
通讯作者：
Schrag, D. P.
中科院分区：
文献类型：
--
作者：
Dennis, K. J.;Cochran, J. K.;Schrag, D. P.
我们应用碳酸盐成团同位素温度计（Delta（47））对北美西部内陆航道（WIS）菊石带的Baculites compressus（类似于73.5 Ma）和Hoploscaphites nebrascensis（类似于67 Ma）以及附近同时代的陆地和开阔海洋环境中的宏体化石进行了研究。碳酸盐凝聚同位素温度计是基于单相同位素交换平衡，随着温度降低，该平衡促进两种重同位素在单个碳酸盐分子内“凝聚”在一起。由于温度计的同位素独立于水，三角洲（47）和碳酸盐（三角洲O-18（c））的主体氧同位素组成的耦合测量，使古温度和同位素组成的生物生长的水重建。在将该技术应用于化石海洋生物（主要是菊石，但也有一些腹足类，双壳类，和一个belemnite）的文石壳之前，我们测量了现代鹦鹉螺和墨鱼的聚集同位素组成，这两个最近的亲戚白垩纪菊石。现代头足类在δ（47）方面表现出不平衡同位素效应，而在δ O-18（c）方面则没有，因此，在重建古温度之前，对晚白垩世宏体化石数据进行了简单的校正。成岩作用也通过视觉保存和先前测量的Sr浓度来评估（Cochran等人，2003年）。晚白垩世西部内陆航道重建的温度范围为16.4 +/- 3.5摄氏度，适用于H。对于B，将nebrascensis区的温度降低到24.2 +/- 0.4 ℃。挤压菊石带海道本身的同位素组成约为千分之-1（相对于VSMOW），这是对无冰全球海洋平均值的预期，而附近的淡水环境的同位素组成接近千分之-20。我们比较重建的气候属性的预测晚白垩世气候模型和以前的重建的海道的基础上，也评估我们的结果的敏感性，现代头足类动物校正比较合适的现代类似物。最后，我们聚集的同位素数据是一致的晚坎帕尼亚和马斯特里赫特之间的冷却，也看到在底栖有孔虫三角洲O-18。(C)2012爱思唯尔有限公司版权所有。
We apply the carbonate clumped isotope thermometer (Delta(47)) to macrofossils from the Baculites compressus (similar to 73.5 Ma) and the Hoploscaphites nebrascensis (similar to 67 Ma) ammonite zones of the Western Interior Seaway (WIS) of North America, and nearby coeval terrestrial and open marine environments. The carbonate clumped isotope thermometer is based on a single-phase isotope exchange equilibrium that promotes the 'clumping' of two heavy isotopes together within a single carbonate molecule as temperature decreases. Due to the thermometer's isotopic independence from water, coupled measurements of Delta(47) and the bulk oxygen isotopic composition of a carbonate (delta O-18(c)) enable the reconstruction of both paleotemperature and the isotopic composition of the water in which the organisms grew. Before applying the technique to the aragonite shells of fossil marine organisms (mostly ammonites, but also some gastropods, bivalves, and one belemnite), we measure the clumped isotopic composition of modern nautilus and cuttlefish, two of the nearest living relatives to the Cretaceous ammonites. Modern cephalopods exhibit disequilibrium isotope effects with respect to Delta(47), but not delta O-18(c), therefore a simple correctional scheme is applied to the Late Cretaceous macrofossil data before reconstructing paleotemperatures. Diagenesis is also assessed by visual preservation and previously measured Sr concentrations (Cochran et al., 2003). Temperatures reconstructed for the Late Cretaceous Western Interior Seaway range from 16.4 +/- 3.5 degrees C for an offshore Interior Seaway environment from the H. nebrascensis zone to 24.2 +/- 0.4 degrees C for the B. compressus ammonite zone. The seaway itself has an isotopic composition of approximately -1 parts per thousand (relative to VSMOW), the expectation for an ice-free global ocean average, while a nearby freshwater environment has an isotopic composition approaching -20 parts per thousand. We compare the attributes of the reconstructed climate to predictions based on Late Cretaceous climate models and previous reconstructions of the seaway, and also assess the sensitivity of our results to the modern cephalopods correction by comparisons to suitable modern analogs. Finally, our clumped isotope data are consistent with cooling between the Late Campanian and Maastrichtian, as also seen in benthic foraminfera delta O-18. (C) 2012 Elsevier B.V. All rights reserved.