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

越来越多的证据表明，志留纪，长期以来被视为“静止”，实际上是一个非常动态的时期，从构造和生态演化事件的角度来看。然而，地层和事件的相关性，特别是在中志留世，仍然模糊不清，即使在充分研究的地区。该项目拟以耦合钾镁矾岩、层序地层学和生物地层学标准为基础，建立北美东部（劳伦蒂亚）的尼亚加拉（Llandovery-Wenlock晚期）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隆尼亚新发现的钾基膨润土床来评估国际相关性的潜力。本研究将：a）对北美东部的这段地层进行更精确的对比和划分，重点是辛辛那提拱区; B）对以前的层序地层解释进行测试和扩展; c）有助于记录在盐成造山运动早期阶段火山活动和盆地动力学的存在和可能的位置（Telychian-Wenlock晚期）; d）提供尼亚加拉系列部分地区的锆石放射性测年（北美）和兰多弗里/文洛克系列（英国）;以及e）探索在Laurentia和Avalonia之间匹配K-膨润土层位或遗传上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晚Llandovery-Wenlock地层在北劳伦特的构造历史，并提供测试的各种物理和生物事件的明显的同步性区域和全球。1）如果在每个古地理区域内都能识别和追踪到钾镁矾岩和其他事件层，似乎是确定的，这将有助于a）在东劳伦蒂亚和阿瓦隆尼亚范围内对Llandovery晚期-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地台区与构造活动盆地详细联系起来; c）在这两种情况下，但特别是在北美东部（其中精细笔石生物地层学是不可能的）。这样的相关性将允许测试各种物理和生物事件的表观同步性。例如，从层序地层学重建的相对海平面曲线的相似性表明海平面变化控制（Brett等人，1990，1998;约翰逊等人，1991）; K-辉长岩可能提供独立的高分辨率地层控制，这将使adefinitive测试的这一推断。膨润土的相关性还可以检验构造事件的同步性，例如前陆的沉降脉冲和芬德利/阿尔冈昆拱的幕式隆起，以及辛辛那提拱的前兆（Ettensohn和Brett，1998年）。最后，精细的相关性可以提供一个测试的coecoeval与历时性质的生物事件，如周转脉冲，分离间隔的相对稳定的动物群（或生态进化亚单位）在阿巴拉契亚盆地（Brett和Baird，1995），andelsewhere.2）至少，如果每个区域内的地层序列的同步性可以建立，并且这些模式看起来相似，那么它将加强异旋回和可能的海平面升降的情况，而不是严格的局部自旋回控制相波动。此外，如果在劳伦蒂亚和阿瓦隆尼亚的K-辉长岩群（而不是单一的指纹层）大致重合（在牙形石生物地层学分辨率内），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等，1996）。各古大陆中钾基膨润土的分布和厚度模式将有助于确定火山源岩的位置和重建古风向及古地理。3）最后，建立了跨Iapetus钾基膨润土和层序地层对比：a）首次将Wenlock层型与北美东部的经典Niagaran省级层系进行了真正详细的对比; B）对Johnson等（1991）提出的全球海平面变化曲线进行检验; c）对可能的全球生物事件的同步性进行检验。此外，我们打算雇用一名或多名本科生。这些学生将从实地和实验室研究的培训中受益，并可能开发“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.