Climatic Temperature Record of Cherts

燧石气候温度记录

• 批准号: 9417874
• 负责人: L. Paul Knauth
• 金额: $ 11.01万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-02-01 至 1997-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9417874&HistoricalAwards=false
• 关键词: Climatic; Temperature; Record; Cherts

9417874 Knauth The oxygen and hydrogen composition of ancient cherts will be investigated to explore the idea that the earth's climatic temperature history is imprinted in isotopic data for these rocks. A large secular variation exists in the isotopic composition of cherts, and this has been attributed to either climatic temperature changes, variations in isotopic composition of the oceans, or later alteration of the isotopic record. Mounting evidence that the isotopic composition of the oceans cannot account for the observed variations warrants a new look at whether the secular variations are recording the earth's climatic temperature history. New samples from key time periods and different geologic settings will be analyzed to build up the currently limited data base and to test whether later alteration is responsible for the observed secular variations. Samples from existing collection of Precambrian cherts made by various groups over the last 10 years for paleontological and sedimentological investigations will be analyzed. Preliminary data suggest a major warming around the Precambrian-Cambrian boundary, and new samples from localities bracketing this boundary will be collected and analyzed. Hydrogen isotope analyses can provide additional constraints on interpretations, and these will be used on suitable cherts such as those from paleokarst horizons. The effects of metamorphism and the field/petrographic criteria used to select least-altered samples will be evaluated by analyzing bedded and modular cherts that have been metamorphosed in vary degrees to higher grades than would ever be sampled for secular variation studies. Later alteration by meteoric ground waters will be evaluated by isotopic analyses of coexisting carbonates. Existing data on the Miocene Monterey Formation will be augmented to confirm that even chert which form during deep burial leave isotopic signatures characteristic of the local climate. The anticipated result of this work is a new data base for che rts over geologic time which can be meaningfully evaluated as an indicator of past climatic temperatures.

9417874 Knauth将研究古代硅质岩的氧和氢组成，以探索地球气候温度历史印记在这些岩石的同位素数据中的想法。硅质岩的同位素组成存在很大的长期变化，这要么归因于气候温度变化，要么是海洋同位素组成的变化，要么是后来同位素记录的改变。越来越多的证据表明，海洋的同位素组成不能解释观测到的变化，因此有必要重新审视长期变化是否记录了地球的气候温度历史。将对来自关键时期和不同地质环境的新样品进行分析，以建立目前有限的数据库，并测试后来的变化是否对观察到的长期变化负责。将分析过去10年来由不同团体为古生物学和沉积学研究而采集的现有前寒武纪硅质岩样本。初步数据显示，前寒武纪-寒武纪边界附近出现了重大变暖，将收集和分析这一边界周围地区的新样本。氢同位素分析可以为解释提供额外的约束，这些分析将用于合适的硅质岩，如来自古岩溶层的硅质岩。变质作用的影响和用于选择变化最小的样品的野外/岩石学标准将通过分析层状和模块化硅质岩进行评估，这些硅质岩已经以不同程度的变质到比用于长期变化研究的样品更高的等级。未来大气地下水的变化将通过共存碳酸盐的同位素分析来评估。关于中新世蒙特雷组的现有数据将得到补充，以证实即使是在深埋过程中形成的硅质岩也会留下当地气候特有的同位素特征。这项工作的预期结果是为地质时期的CHE RTS建立了一个新的数据库，该数据库可以作为过去气候温度的指标进行有意义的评估。