COLLABORATIVE RESEARCH: Integrated Biostratigraphy and K-Bentonite Chronostratigraphy in the Ordovician of the Northern Appalachian Basin: Geochemical and Geochrono......

合作研究：北阿巴拉契亚盆地奥陶系综合生物地层学和钾膨润土年代地层学：地球化学和地球年代学......

• 批准号: 9204931
• 负责人: John Delano
• 金额: $ 5.86万
• 依托单位: SUNY at Albany
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1992
• 资助国家: 美国
• 起止时间: 1992-06-15 至 1995-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9204931&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Integrated; Biostratigraphy; Bentonite

The late Middle and early Upper Ordovician carbonate and siliciclastic rocks of the Trenton Group in the northern Appalachian foreland basin enclose a large number of altered volcanic ash beds (K-bentonites) deposited from Plinian eruptions on an off-shore volcanic arc. These strata also form part of the standard reference section of the North American Ordovician time scale as well as the reference standard for the conodont and graptolite biozonations commonly used for temporal correlation in this interval. The goal of the research is to employ geochemical fingerprinting of unaltered phenocrysts within the K-bentonites together with new and detailed studies of the ranges of graptolite and conodont species to integrate these separate stratigraphies into a unified chronostratigraphic network. We propose to accomplish this by 1) establishing precise ties between the graptolite zones and the North Atlantic and midcontinent conodont zones based on detailed collecting of range data from numerous measured sections that each span the facies transition from Trenton Group carbonates into the Utica Shale and 2) establishing precise ties between the laterally equivalent siliciclastic and carbonate facies based on the identification of synchronous time planes through geochemical fingerprinting of the K-bentonites. The techniques to be employed for K-bentonite correlation include analysis of 1) major and trace element composition of melt inclusions within quartz phenocrysts. Additionally, we propose to use high precision U-Pb zircon geochronometry to calibrate our chronostratigraphy. The resulting chronostratigraphy will provide a temporal framework, calibrated in years, that will provide a direct test of the accuracy of the existing graptolite and conodont biostratigraphies as well as sequence stratigraphic and coenocorrelation studies of these rocks. This chronostratigraphy will constitute the temporal framework necessary for studies of the rate of evolution among graptolites and other organisms that occur in the studied sections. Simultaneously, the K-bentonite geochemical and geochronological data will provide unique insights about the tectonic provenance of these altered volcanic ash beds and the nature and duration of Taconic orogenic events.

阿巴拉契亚前陆盆地北部特伦顿群的中奥陶世晚期和上奥陶世早期碳酸盐岩和硅质碎屑岩包围着大量由近海火山弧上的普林尼式喷发沉积的蚀变火山灰层（K膨润土）。 这些地层还构成北美奥陶纪时间尺度标准参考部分的一部分，以及常用于该区间时间相关的牙形刺和笔石生物分区的参考标准。 该研究的目标是利用钾膨润土中未改变的斑晶的地球化学指纹，以及对笔石和牙形刺物种范围的新的详细研究，将这些单独的地层整合到统一的年代地层网络中。 我们建议通过以下方式实现这一目标：1）根据详细收集的大量测量剖面的范围数据，在笔石带与北大西洋和中部大陆牙形石带之间建立精确的联系，每个测量剖面都跨越从特伦顿群碳酸盐岩到尤蒂卡页岩的相过渡；2）根据同步时间平面的识别，在横向等效的硅质碎屑岩和碳酸盐岩相之间建立精确的联系 通过钾膨润土的地球化学指纹分析。 用于钾膨润土关联的技术包括分析 1) 石英斑晶内熔体包裹体的主要和微量元素组成。 此外，我们建议使用高精度 U-Pb 锆石地球测时法来校准我们的年代地层学。 由此产生的年代地层学将提供一个以年为单位校准的时间框架，这将为现有笔石和牙形刺生物地层学的准确性以及这些岩石的层序地层学和共相关研究提供直接测试。 这种年代地层学将构成研究笔石和发生在研究部分的其他生物体的进化速率所必需的时间框架。 同时，钾膨润土地球化学和地质年代学数据将为这些蚀变火山灰床的构造起源以及塔科尼造山事件的性质和持续时间提供独特的见解。