Collaborative Research: Geochemistry and Paleontology of Precabrian Exposure Surfaces

结合野外、岩相学和同位素工作， 在前寒武纪碳酸盐岩地层（800百万年）中确定了2个层位。 Beck Spring Dolomite，CA. 1200米梅斯卡尔石灰石，亚利桑那州） 在前寒武纪侵蚀事件中被硅化。 在这些燧石样品中发现了微化石， Horodyski的地平线，代表了第一个化石记录， 生活在前寒武纪陆地表面的生物。 碳 相关碳酸盐的同位素测量显示， 陆地表面被一种陆地生物广泛占据 光合群落 燧石中的微化石 因此可能不是孤立的例子， 广泛的社区。 将尝试建立 前寒武纪陆地的第一个古生物记录 环境 野外、同位素和岩相学工作将确定 古岩溶层位的古环境条件及 详细地确定了前寒武纪期间形成的硅相 风化作用与早期成岩作用形成的风化作用相反 原始的海洋碳酸盐。 具有强烈纹理和 指示陆上形成的地球化学特征将 在厚的岩石切片中检查是否存在 微化石 微结构的生物原性将是 评估，并将努力建立生物学 任何微化石发现的亲和力。特别注意将 比较与暴露有关的微化石， 与海底硅质岩中的硅质岩进行对比， 发现的微体化石与暴露面有关 真实地代表了生活在陆地上的微生物 设置.

A combination of field, petrographic, and isotopic work has identified 2 horizons in Precambrian carbonate strata (800 m.yr. Beck Spring Dolomite, CA. and 1200 m.yr. Mescal Limestone, AZ) which were silicified during Precambrian erosion events. Microfossils have been discovered in chert samples from these horizons by R Horodyski and represent the first fossil record of organisms that inhabited the Precambrian land surface. Carbon isotope measurements in the associated carbonate reveal that the land surface was extensively occupied by a terrestrial photosynthesizing community. The microfossils in the chert are therefore probably not isolated examples but are elements of this extensive community. An attempt will be made to establish the first paleontologic record for the Precambrian terrestrial environment. Field, isotopic, and petrographic work will establish the paleoenvironmental conditions of the paleokarst horizons and will establish, in detail, which silica phases formed during Precambrian weathering as opposed to those which formed during early diagenesis of the original marine carbonates. Cherts with strong textural and geochemical characteristics indicative of subaerial formation will be examined in thick petrographic sections for the presence of microfossils. The biogenicity of microstructures will be evaluated, and an effort will be made to establish biologic affinities for any microfossils found. Particular attention will be given to comparing microfossils associated with the exposure surfaces with those in the underlying marine cherts to establish that the microfossils found associated with the exposure surfaces truly represent microorganisms that were living in a terrestrial setting.