RUI: Terrane Analysis of Silurian Reefal Carbonates, Alaska

小行星9417907 许多地质学家认为，“外来的”地壳碎片或碎屑在大陆边缘的增生是过去6 000万至1亿年间北美西部沿着大陆增长的构造过程。 由于加积构造所产生的复杂地质关系，北美西部这种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出现在这个复杂的加积动物区，并占据了北美动物区系与环太平洋和环北极地区之间的地理位置。 为了更好地了解阿拉斯加的古生物的起源和地质历史，古生物学家一直在寻求识别独特的化石套件，这些化石套件基于占据相似栖息地的动物群的共同亲缘关系，将某些古生物联系在一起或与大陆源区建立地理联系。 以这种方式使用古生物地理数据具有巨大的潜力，可以解决在描述北美西部构造演化的竞争模型中所反映的争议，特别是阿拉斯加。 拟议的项目旨在通过调查阿拉斯加东南部的志留纪珊瑚礁和与珊瑚礁有关的碳酸盐沉积物，以确定它们与阿拉斯加西南部志留纪石灰岩的地质关系，建立PI以前的研究。 阿拉斯加东南部出露的岩石属于亚历山大河，它在早古生代至中古生代期间作为火山活动岛屿存在于古太平洋的一个未知地点，而阿拉斯加西南部（尼克松福克河）的沉积物代表了北美大陆的一个原始部分，尽管被肢解了。 在这两个地区的地层中，志留纪海绵动物群有着共同的特征，它们保存在不寻常的叠层石中。 在阿拉斯加东南部，志留纪的碳酸盐岩曾在零星的地方被详细研究过，但主要是在亚历山大海南部的一个相对较小的地区。 拟议中的研究将使志留纪岩石的详细调查，暴露在其他部分的亚历山大湖，特别是在那里的勘察研究已经揭示了保存完好，但尚未研究生物。 涉及本科研究生的实地工作将侧重于描述岩石和收集化石系统地从测量和拍摄地层剖面。 样品将从现场运来提取化石，并在实验室制备成薄片和抛光板，用于岩相学目的。 岩石学、岩相学和古生物学数据的汇编将构成确定保存的生物化石的古生态学、环境背景和动物群亲缘关系的基础，并确定阿拉斯加西南部志留纪岩石和化石组成的相似程度。 证明阿拉斯加东南部一个以上相对较小的地区的化石多样性与阿拉斯加西南部有共同之处，将代表我们对亚历山大化石早期地质历史的理解的重要进展。 这些数据将有助于文件支持的假设，即亚历山大是在靠近北美西北部，使动物群之间的沟通两个地方的证据。 这些数据对于提供亚历山大海与北美之间的古地理联系非常重要。 由于类似的志留纪海绵沉积物也发生在俄罗斯乌拉尔山脉，因此拟议的研究将为探索以下想法奠定重要基础：在志留纪晚期，一条海道使生物沿着北美（劳伦蒂亚）和欧洲（波罗的海）的北方边缘迁移。

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.