Climatic Temperature Record of Cherts

小行星9417874 将研究古代硅质岩的氧和氢成分，以探索地球气候温度历史在这些岩石的同位素数据中留下印记的想法。 硅质岩的同位素组成存在很大的长期变化，这是由于气候温度的变化，海洋同位素组成的变化，或后来的同位素记录的改变。 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，这就需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背景的新样本进行分析，以建立目前有限的数据库，并测试后期蚀变是否是观测到的长期变化的原因。 将对过去10年来不同研究组为古生物学和沉积学调查采集的前寒武纪硅质岩样品进行分析。 初步数据表明，在前寒武纪-寒武纪边界附近有一个主要的变暖，将收集和分析来自该边界附近地区的新样本。 氢同位素分析可以提供额外的限制解释，这些将被用于适当的硅质岩，如那些从古岩溶层。 变质作用的影响和用于选择蚀变最小的样品的现场/岩相学标准将通过分析层状和模块化硅质岩进行评估，这些硅质岩已经变质到比长期变化研究所取样的等级更高的不同程度。 后期由大气地面沃茨造成的蚀变将通过共存碳酸盐的同位素分析来评价。 中新世蒙特利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燧石也会留下当地气候特征的同位素特征。 这项工作的预期结果是一个新的数据库，可以有意义地评估作为过去的气候温度的指标，在地质时期的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.