RUI: Terrane Analysis of Silurian Reefal Carbonates, Alaska

RUI：阿拉斯加志留纪珊瑚礁碳酸盐岩的地体分析

• 批准号: 9417407
• 负责人: Constance Soja
• 金额: $ 12.59万
• 依托单位: Colgate University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-06-01 至 2000-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9417407&HistoricalAwards=false
• 关键词: RUI; Terrane; Analysis; Silurian; Reefal

9417907 Soja The accretion of "exotic" crustal fragments, or terranes, to continental margins is the tectonic process believed by many geologists to have been responsible for continental growth along western North America in the last 60-100 million years. Because of the complex geologic relationships produced by accretionary tectonics, the complete geologic history of this tectonic collage in western North America is still unknown. Paleobiogeographic research is of critical importance in Alaska because fossils preserved there occur within this complex zone of accreted terranes and occupy a present geographic position intermediate between the faunal provinces of North America and the circum-Pacific and circum-Arctic regions. To gain a better understanding of the origins and geologic histories of terranes in Alaska, paleontologists have been seeking to identify distinctive suites of fossils that, on the basis of shared affinities in faunas which occupied similar habitats, link certain terranes together or establish biogeographic connections with continental source areas. Using paleobiogeographic data in this way has enormous potential for resolving the controversies reflected in competing models that describe the tectonic evolution of western North America, in general, and Alaska, in particular. The proposed project aims to build upon the PI's previous research by investigating Silurian reef and reef-related carbonate deposits in southeastern Alaska to determine their geologic relationship to Silurian limestones in southwestern Alaska. Rocks exposed in southeastern Alaska belong to the Alexander terrane, which existed during the Early-Middle Paleozoic as volcanically active islands at an unknown site in the ancient Pacific Ocean, whereas deposits in southwestern Alaska (Nixon Fork terrane) represent an original, although dismembered part of the North American continent. Strata in these two areas share in common distinctive Silurian sponge faunas preserved in unusual stromatolite ree fs. In southeastern Alaska, Silurian carbonates have been examined in detail at scattered localities but principally only in one relatively small area in the southern part of the Alexander terrane. The proposed research will enable detailed investigations of Silurian rocks that are exposed in other parts of the Alexander terrane, especially where reconnaissance studies have revealed well-preserved, but as yet unstudied biotas. Field work involving undergraduate research students will focus on describing rocks and collecting fossils systematically from measured and photographed stratigraphic sections. Samples will be shipped from the field for the extraction of fossils and to be prepared in the lab as thin-sections and polished slabs for petrographic purposes. Compilation of petrologic, petrographic, and paleontolgic data will form the basis for determining the paleoecology, environmental setting, and faunal affinities of the preserved biotas and for identifying the degree of similarity in rock and fossil composition with Silurian rocks in southwestern Alaska. Demonstrating that a diversity of fossils from more than one relatively small part of southeastern Alaska is shared in common with southwestern Alaska will represent an important advancement in our understanding of the early geologic history of the Alexander terrane. These data will help to document supporting evidence for the hypothesis that the Alexander terrane was in close proximity to northwestern North America allowing faunal communication between the two localities. Such data would be important in providing a definitive paleogeographic link between the Alexander terrane and North America proper. Because similar Silurian sponge deposits also occur in the Ural Mountains, Russia, the proposed study will lay critical groundwork for exploring the idea that a seaway enabled migration of organisms along the northern rims of North America (Laurentia) and Europe (Baltica) in the Late Silurian.

9417907 Soja 许多地质学家认为，“外来”地壳碎片或地体向大陆边缘的增生是过去 60-1 亿年中北美西部大陆生长的原因。 由于增生构造产生的复杂地质关系，北美西部这一构造拼贴的完整地质历史仍然未知。 古生物地理学研究在阿拉斯加至关重要，因为那里保存的化石发生在这个复杂的增生地体区域内，并且目前的地理位置介于北美动物区系和环太平洋和环北极地区之间。 为了更好地了解阿拉斯加地体的起源和地质历史，古生物学家一直在寻求识别独特的化石套件，这些化石基于占据相似栖息地的动物群的共同亲缘关系，将某些地体连接在一起或与大陆源区建立生物地理联系。 以这种方式使用古生物地理数据具有解决描述北美西部（特别是阿拉斯加）构造演化的竞争模型中所反映的争议的巨大潜力。 拟议的项目旨在以 PI 之前的研究为基础，通过调查阿拉斯加东南部的志留纪珊瑚礁和与珊瑚礁相关的碳酸盐矿床，以确定它们与阿拉斯加西南部志留纪石灰岩的地质关系。 阿拉斯加东南部暴露的岩石属于亚历山大地体，它存在于早中古生代，作为古太平洋未知地点的火山活动岛屿，而阿拉斯加西南部的沉积物（尼克松福克地体）代表了北美大陆的原始部分，尽管已被肢解。 这两个地区的地层拥有共同的独特的志留纪海绵动物群，这些动物群保存在不寻常的叠层石礁中。 在阿拉斯加东南部，志留纪碳酸盐岩已在分散的地点进行了详细检查，但主要仅在亚历山大地体南部的一个相对较小的区域进行。 拟议的研究将能够对亚历山大地体其他部分暴露的志留纪岩石进行详细调查，特别是在勘察研究发现保存完好但尚未研究的生物群的地方。 本科生的实地工作将侧重于描述岩石并从测量和拍摄的地层剖面中系统地收集化石。 样品将从现场运出用于提取化石，并在实验室中制备成用于岩相学目的的薄片和抛光板。 岩石学、岩相学和古生物学数据的汇编将为确定保存的生物群的古生态、环境背景和动物亲缘关系以及确定岩石和化石成分与阿拉斯加西南部志留纪岩石的相似程度奠定基础。 证明阿拉斯加东南部多个相对较小地区的化石多样性与阿拉斯加西南部有共同之处，这将代表我们对亚历山大地体早期地质历史的理解取得了重要进展。 这些数据将有助于记录支持这一假设的证据，即亚历山大地体靠近北美西北部，允许两地之间的动物群交流。 这些数据对于提供亚历山大地体和北美本土之间明确的古地理联系非常重要。 由于类似的志留纪海绵沉积物也出现在俄罗斯乌拉尔山脉，因此拟议的研究将为探索海道使志留世晚期生物体沿着北美（劳伦西亚）和欧洲（波罗的海）北缘迁移的想法奠定重要基础。