High Resolution Sequence and Event Stratigraphy of Mid Silurian Strata in Eastern Laurentia and Avalonia

越来越多的证据表明，从构造和生态进化事件的角度来看，长期被视为“静止”的志留纪实际上是一个非常动态的时期。然而，即使在研究充分的地区，地层和事件的相关性，特别是在志留纪中期，仍然模糊不清。本项目拟基于偶联k -膨润土、层序地层学和生物地层学标准，建立北美东部（Laurentia）的theNiagaran （Llandovery-Wenlock晚期）的区域地层格架、古地理和海平面历史。我们还将通过比较北美和阿瓦洛尼亚新发现的k -膨润土层来评估国际相关性的潜力。这项研究将：a)对北美东部的这一区间进行更精确的关联和分类，重点是辛辛那提拱门地区；B)对以前的层序地层解释进行检验和扩展；c)有助于记录盐碱造山早期（晚特利契—温洛克）火山活动和盆地动力学的存在和潜在位置；d)提供尼亚加拉系列（北美）和llanddovery /Wenlock系列（英国）部分锆石放射性定年；e)探索在Laurentia和Avalonia之间匹配k -膨润土层位或基因相似的灰层间隔的可能性。高分辨率的相关性将允许区分区域海平面和劳伦斯东部llandover - wenlock晚期地层的构造历史，并为区域和全球各种物理和生物事件的明显同向性提供测试。本研究的具体成果可总结如下：1)如果能在每个古地理区域内识别和追踪k -膨长岩和其他事件层（似乎是确定的），这将允许a)对Laurentia东部和Avalonia东部的Llandovery-Wenlock地层进行高分辨率的地层对比；B)反过来，这将有助于将稳定的台地区与构造活跃的盆地详细联系起来；c)在这两种情况下，但特别是在北美东部（那里不可能有精细的笔石生物地层学）。这样的相关性将允许对各种物理和生物事件的明显同步性进行测试。例如，层序地层学重建的相对海平面曲线的相似性表明了海平面上升的控制（Brett et al., 1990,1998; Johnson et al.,1991）；k -膨润土可能提供独立的高分辨率地层控制，这将使这一推论得到明确的检验。膨脱土相关性还可以测试构造事件的同步性，例如前陆的沉降脉冲和Findlay/Algonquin拱的间歇隆起，以及辛辛那提拱的前兆（Ettensohn和Brett， 1998）。最后，精细的相关性可以提供对生物事件的共时性与历时性的检验，例如在阿巴拉契亚盆地（Brett and Baird, 1995）和其他地方分隔相对稳定的动物群（或生态进化亚单位）间隔的更替脉冲。(2)至少，如果能确定各区域内地层层序的同时性，并且这些模式看起来相似，那么就会加强异旋和可能的涨落的情况，而不是严格地局部自旋回控制相波动。此外，如果成群的k -膨长岩（相对于单一指纹层）在Laurentia和Avalonia大致重合（在牙形石生物地层分辨率范围内），这可能证实了共同构造历史的模型，与其他构造证据一致（Torsvik et al. 1996）。各古大陆钾质膨润土的扩散和厚度模式有助于火山源地体的定位和古风向和古地理的重建。3)最后，建立了trans-Iapetus k -膨润土和层序地层对比：a)首次将温洛克层型与北美东部经典的尼亚加拉省系列进行了真正详细的对比；b)对johnson等人（1991）最近提出的全球海平面上升曲线进行检验；C)为可能的全球生物事件的同步性提供测试。该项目将为Michael DeSantis提供博士后职位，并为他提供与博士研究相关但不同的领域的进一步研究经验。此外，我们打算雇用一名或多名本科生。这些学生将受益于实地和实验室研究的培训，并可能发展“顶点”项目，从而产生高级论文和/或发表摘要和论文。

Increasing evidence indicates that the Silurian, long viewed as "quiescent", was actually a very dynamicperiod from the standpoint of tectonics and ecological evolutionary events. However, correlations of strataand events, particularly during the mid-Silurian, remain ambiguous even in well-studied areas. This projectproposes to establish a regional stratigraphic framework, paleogeography, and sea level history for theNiagaran (late Llandovery-Wenlock) in eastern North America (Laurentia), based on coupled K-bentonites,sequence stratigraphic, and biostratigraphic criteria. We will also evaluate the potential for internationalcorrelation by comparisons of newly discovered K-bentonite beds in North America and Avalonia. Thisresearch will: a) yield more precise correlation and bracketing of this interval in eastern North America,with emphasis on the Cincinnati Arch region; b) provide a test and extension of previous sequencestratigraphic interpretations; c) help to document the presence of and potentially, the position of volcanicactivity and basin dynamics during early phases of the Salinic Orogeny (late Telychian-Wenlock); d)provide zircon-based radiometric dating of parts of the Niagaran Series (North American) andLlandovery/Wenlock Series (Britain); and e) explore the possibility of matching K-bentonite horizons orintervals of genetically similar ash beds, between Laurentia and Avalonia. High-resolution correlations willpermit discrimination of regional sea level and tectonic history of late Llandovery-Wenlock strata withineastern Laurentia and provide tests for apparent synchroneity of various physical and biotic eventsregionally and globally.The specific benefits expected to emerge from this study can be summarized as follows:1) If K-bentonites and other event beds can be identified and traced within each paleogeographic area, asseems definite, this will permit a) high resolution stratigraphic correlation of late Llandovery-Wenlock stratawithin both eastern Laurentia and Avalonia; b) in turn, this will facilitate detailed linkage of stable platformareas with tectonically active basins; c) in both cases, but particularly in eastern North America (for whichrefined graptolite biostratigraphy is impossible). Such correlations will then permit tests for apparentsynchroneity of various physical and biotic events. For example, similarities of relative sea level curvesreconstructed from sequence stratigraphy suggest eustatic controls (Brett et al., 1990, 1998; Johnson et al.,1991); K-bentonites may provide independent high-resolution stratigraphic controls that will enable adefinitive test of this inference. Bentonite correlations can also test for synchroneity of tectonic events, suchas pulses of subsidence in the foreland and episodic uplift of the Findlay/Algonquin arch, and precursors ofthe Cincinnati arch (Ettensohn and Brett, 1998). Finally, refined correlations may provide a test of thecoeval vs. diachronous nature of bioevents, such as the turnover pulses that separate intervals of relativelystable faunas (or ecological-evolutionary subunits) in the Appalachian Basin (Brett and Baird, 1995), andelsewhere.2) At the very least, if synchroneity of stratigraphic sequences within each area can be established,and those patterns appear similar, then it will strengthen the case of allocyclic and probably eustatic, asopposed to strictly local autocyclic controls of facies fluctuations. Furthermore, if clusters of K-bentonites(as opposed to single fingerprinted beds) coincide approximately (within conodont biostratigraphicresolution) in Laurentia and Avalonia, this may corroborate models of shared tectonic histories, consistentwith other tectonic evidence (Torsvik et al. 1996). Patterns of K-bentonite dispersal and thickness in eachpaleocontinent will aid in location of the volcanic source terranes and reconstruction of paleowind directionsand paleogeography.3) Finally, the establishment of trans-Iapetus K-bentonite and sequence stratigraphic correlations: a)permit the first really detailed correlation of the Wenlock stratotype with the classic Niagaran provincialseries of eastern North America; b) provide a test for global eustatic sea level curve recently proposed byJohnson and others (1991); c) provide a test for synchroneity of possible global bioevents.This project will provide a post-doctoral position for Michael DeSantis and give him furtherresearch experience in an area related to, but distinct from his doctoral studies. In addition, we intend toemploy one or more undergraduates. These students will benefit from the training in field and laboratoryresearch and may develop "capstone" projects resulting in senior theses and/or published abstracts andpapers.