Stable Isotopic Constraints on The Paleoclimate of a High- Latitude Cretaceous Terrestrial Basin

稳定同位素对高纬度白垩纪陆盆地古气候的约束

• 批准号: 9106073
• 负责人: Robert Gregory
• 金额: $ 11万
• 依托单位: Southern Methodist University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1991
• 资助国家: 美国
• 起止时间: 1991-06-15 至 1993-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9106073&HistoricalAwards=false
• 关键词: Stable; Isotopic; Constraints; Paleoclimate; Latitude

The Cretaceous has long been considered a time of equable climate while the cenozoic is regarded as a time of ice ages. Recent work suggests that the concept of an ice free Cretaceous may need to be re-examined. The best place to look for the extremes of Cretaceous climate is within a high latitude terrestrial sedimentary basin. Such rocks exist within the Otway and Strzelecki groups, southeastern Australia, which were deposited at high latitude (70 degrees S) during the lower Cretaceous. Stable isotopic measurements provide a vehicle for inferring the surface temperature. Previous work on the carbonate concretions recovered from terrestrial sandstones revealed extremely O-depleted values for calcite, and these data indicate precipitation from low O meteoric fluids and annual temperatures on the order of 0 degrees C. In addition, isotopic profiling of individual concretions and cemented beds indicates that secular changes in the O values of calcite cements can be correlated on three different scales: within an individual concretion, within a relative age sequence in a composite concretion, or over meter scales in a vertical section by comparing the isotopic compositions of concretion cores. This type of detailed isotopic work in conjunction with textural studies indicate that it is possible to differentiate in these rocks the near surface primary meteoric water signature from complications arising from subsequent diagenetic events. Interpreted in terms of temperature change, the maximum O change would correspond to about a 5 degree C change in mean annual surface temperature. In this study, we propose to further constrain the carbonate oxygen isotope data with O/ O data on phosphate from fossil bones, and with D/H and O/ O data from paleosols. Because of the high paleolatitude of this site and because of its terrestrial character, any Cretaceous global climatic changes should be amplified and easily detected in sequential samples in stratigraphic sections. The changes already detected in limited stratigraphic sampling suggest that it may be possible to recognize Milankovitch climatic forcing in the isotopic record of the Cretaceous, southeastern Australia.

白垩纪一直被认为是一个 新生代被认为是冰河时期。 最近的研究表明，无冰白垩纪的概念可能 需要重新检查。 寻找极端的最佳地点 白垩纪的气候是在一个高纬度陆地 沉积盆地 这种岩石存在于奥特威， 澳大利亚东南部的Strzelecki群，沉积于 在白垩纪早期高纬度地区（南纬70度）。 稳定 同位素测量提供了一种工具， 温度 以前对碳酸盐结核的研究 从陆地砂岩中发现了极度贫氧的值 方解石，这些数据表明降水从低O 大气流体和年平均温度 C. 此外，个别结核的同位素分布， 胶结层表明， O值 方解石胶结物的含量可以在三个不同的尺度上进行关联： 在一个单独的结核中，在一个相对的年龄序列中， 一个复合结核，或在垂直截面超过米的规模 通过比较结核芯的同位素组成。 这 一种详细的同位素工作，结合纹理研究 这表明，在这些岩石中， 近地表大气水特征 由随后的成岩作用引起。 解释在 温度变化的最大值 O变化将对应于 年平均地表温度变化约5摄氏度。 在 在这项研究中，我们建议进一步限制碳酸氧 同位素数据， 化石骨骼中磷酸盐的O/ O数据，以及 利用古土壤的D/H和O/ O数据。 由于高 古纬度的这个网站，因为它的陆地 任何白垩纪的全球气候变化都应该是 在连续样本中扩增并容易检测， 地层剖面 已检测到的更改有限 地层取样表明， 米兰科维奇同位素记录中的气候强迫 白垩纪，澳大利亚东南部。