Evidence from Paleosols for Acid Rain at the Cretaceous- Tertiary Boundary

这项建议是为探索性研究(SGER)提供一小笔赠款：对埋藏的土壤进行试点研究，试图发现重金属痕量的迁移、脱钙和泥灰化，这些应该伴随着一些外星人对白垩纪-第三纪边界的影响预测的硝酸雨。在蒙大拿州东部的Bug Creek，已经找到并采样了跨越这一地质边界的适当完整的埋藏土壤序列。对选定的古土壤的分析将采用AA(常量和微量元素)、同位素稀释质谱分析(铅)和沃克莱-布莱克(有机碳)技术。还将进行岩石学研究，以完成对地下粘土(BT)层位和古土壤的其他古环境重要特征的记录。与在岩石学、化学和埋藏史上相似的边界上和边界下的古土壤中这些元素的深度函数相比，边界上的古土壤中铅和其他重金属微量元素的强烈亏损将指示硝酸雨。如果这项研究证明是酸雨，那么跨越白垩纪-第三系界线的其他古土壤序列的全面搜索将是有必要的。如果这项研究不能成功地指示酸雨，它仍然可能增加古环境信息，以重建地球历史上这个地点和时间的事件。

This proposal is for a small grant for exploratory research (SGER): a pilot study of buried soils to attempt to detect mobilization of heavy trace metals, decalcification and podzolization that should have accompanied the nitric acid rain predicted by some scenarios of extraterrestrial impact at the Cretaceous-Tertiary boundary. A suitably complete sequence of buried soils across this geological boundary has been located and sampled in Bug Creek, eastern Montana. Analyses of selected paleosols will be performed by AA (major and trace elements), isotopic dilution mass spectrometry (for Pb) and Walkley-Black (for organic carbon) techniques. Petrographic studies also will be undertaken in order to complete documentation of the subsurface clayey (Bt) horizons and other paleoenvironmentally significant features of the paleosols. Nitric acid rain would be indicated by strong depletion of the paleosol at the boundary in Pb and other heavy metal trace elements, compared to the depth function for these elements in paleosols above and below the boundary that are otherwise similar petrographically, chemically and in burial history. Should this research prove to indicate acid rain, then full scale search of other sequences of paleosols across the Cretaceous-Tertiary boundary would be warranted. Should this research be unsuccessful indicating acid rain, it may nevertheless add paleoenvironmental information for reconstructing events at this place and time in Earth history.