Collaborative Research: Geochemistry and Paleontology of Precabrian Exposure Surfaces

合作研究：前寒武纪暴露面的地球化学和古生物学

• 批准号: 9105534
• 负责人: L. Paul Knauth
• 金额: $ 9.02万
• 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: 1991
• 资助国家: 美国
• 起止时间: 1991-07-15 至 1994-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9105534&HistoricalAwards=false
• 关键词: Collaborative; Research; Geochemistry; Paleontology; Precabrian

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.

结合野外、岩石学和同位素工作，确定了前寒武纪（800万年）碳酸盐岩地层中的2个层位。贝克泉白云石，加州和1200年。Mescal石灰岩，AZ)，在前寒武纪侵蚀事件中硅化。R Horodyski在这些地层的燧石样本中发现了微化石，代表了居住在前寒武纪陆地表面的生物的第一个化石记录。伴生碳酸盐的碳同位素测量表明，陆生光合群落广泛地占据了陆地表面。因此，燧石岩中的微化石可能不是孤立的例子，而是这个广泛群落的组成部分。将尝试建立前寒武纪陆地环境的第一个古生物记录。野外、同位素和岩石学工作将确定古岩溶层位的古环境条件，并将详细确定在前寒武纪风化期间形成的硅相，而不是在原始海相碳酸盐的早期成岩作用期间形成的硅相。具有强烈构造和地球化学特征的燧石将在厚岩相剖面中检查微化石的存在。将评估微结构的生物原性，并努力为发现的任何微化石建立生物亲和性。将特别注意比较与暴露面有关的微化石与下面的海洋燧石中的微化石，以确定与暴露面有关的微化石确实代表了生活在陆地环境中的微生物。