Collaborative Research: A Test of Eustatic and Local Tectonic Controls on Lithofacies Development

米切尔9627978层序地层学相发育解释已得到广泛应用。然而，这一模型很少与一组独立的高精度年代地层对比进行测试。这项拟议的研究试图直接检验层序地层学的两个核心假设：不整合边界的上覆/下覆旋回在大范围区域内是同步的，旋回内的最大洪泛面可以作为区域等时线。我们建议通过比较北美东部两个区域广泛断面的中奥陶世晚期沉积序列的时间来检验这些预测(图1)。第一个将在塔科尼克前陆盆地内向西南延伸，从纽约海角到宾夕法尼亚州再进入弗吉尼亚州海角。沿着这条横断面，我们将考察宾夕法尼亚州中东部、弗吉尼亚州西部、田纳西州东部和阿拉巴马州北部的部分地区。第二个横断面将从塔科尼克前陆盆地延伸到肯塔基州中北部的杰萨明穹顶，进入克拉通内陆，在那里我们将检查爱荷华州、伊利诺伊州和密苏里州的部分。这些地区在地理上相距甚远，并在此期间经历了不同的构造历史。沿着这两条断面，我们将研究中奥陶统最上三级层序相对于独立构建的高精度年代地层学的时空分布。我们将特别关注1)在纽约塔肯盆地美洲科里诺斯纪期发育的特伦顿组下部-尤蒂卡页岩海侵和高水位体系域，以及2)随后的低位扇(Dolgeville组)，它是在Orthogus ruedemanni Chron时期发育的。这个循环的预测序列等价物将取自已发表的文献。我们之前对纽约州中部的中奥陶世Ian Trenton群和Utica页岩的研究已经产生了高分辨率年代地层学，它将钾膨润土的地球化学指纹数据与笔石和牙形石生物地层学数据相结合。我们建议通过1)笔石和牙形刺生物地层学研究和2)高精度电子探针分析从研究地点的钾膨润土中获得的石英斑晶中的磷灰石斑晶和玻璃包裹体来扩展这一年代地层框架。该系统内基于图形对比的年代地层分辨率应该很高(远远超过单独的生物地层学或放射性测年)，并足以提供对快速超覆的海侵体系轨迹、上覆最大洪泛面/海平面和上层序界面/低水位扇的同步性的明确测试。通过将这组时间线延伸到相对稳定的克拉通内部和南部，延伸到在塔科造山运动早期的Bountain阶段经历碰撞加载的地区，将有可能1)获得北美东部这一时期记录的海侵-海退旋回之间精确和独立的同步性测量，因此，2)利用这一对比系统来研究海平面变化和区域构造事件对中奥陶世晚期地层层序形成的相对贡献。这项工作将提供有关克拉通和沿主要造山带的地质事件之间的物理和时间联系的重要信息，否则无法获得。

Mitchell 9627978 Sequence stratigraphic interpretations of facies development have come into wide application. Yet this model has seldom been tested against an independent set of high precision chronostratigraphic correlations. The proposed research seeks to directly examine two of the central assumptions of sequence stratigraphy: that unconformity bounded onlap/offlap cycles are synchronous across broad regions, and that maximum flooding surfaces within cycles can serve as regional isochrons. We propose to test these predictions by comparing the timing of late Middle Ordovician depositional sequence along two regionally extensive transects across eastern North America (Fig 1). The first will extend to the southwest within the Taconic foreland basin, from the New York Promontory through the Pennsylvania Reentrant to the Virginia Promontory. Along this transect, we will examine sections in east central Pennsylvania, western Virginia, eastern Tennessee, and northern Alabama. The second transect will extend from the Taconic foreland basin through the Jessamine Dome, in North central Kentucky, and into the cratonic interior, where we will examine sections in Iowa, Illinois, and Missouri. These areas are widely separated geographically and are known to have experienced different tectonic histories during this interval. Along these two transects, we will examine the time-space distribution of the upper-most Middle Ordovician third order stratigraphic sequence relative to an independently constructed high-precision chronostratigraphy. We will focus in particular on the equivalents of 1) the lower Trenton Group-Utica Shale transgressive and highstand systems tract that developed in the Taconic basin of New York during the Corynoides americanus Chron and 2) the succeeding lowstand fan (Dolgeville Formation), which developed during the Orthographus ruedemanni Chron. Predicted sequence equivalents of this cycle will be taken from published literature. Our previous research on the Middle Ordovic ian Trenton Group and Utica Shale in central New York State has produced a high resolution chronostratigraphy that integrates data from geochemical fingerprinting of K-bentonites with data from graptolite and conodont biostratigraphy. we propose to extend this chronostratigraphic framework by a combination of 1) graptolite and conodont biostratigraphic studies, and 2) high precision electron microprobe analysis of apatite phenocrysts and glass inclusions within quartz phenocrysts obtained from K-bentonites at the study sites. Chronostratigraphic resolution based on graphic correlation within this system should be high (greatly exceeding that of biostratigraphy alone or of radiometric dating) and sufficient to provide a definitive test of the synchroneity of the rapidly onlapping transgressive system track, the overlying maximum flooding surface/marine hiatus, and the upper sequence boundary/lowstand fan. By extending this set of time lines into the relatively stable cratonic interior and south into regions that experienced collisional loading during the earlier, Blountain Phase, of the Taconic Orogeny, it will be possible 1) to gain a precise and independent measure of synchroneity among the transgressive-regressive cycles documented in this interval in eastern North America and, therefore, 2) to use this system of correlations to examine the relative contributions of changing eustatic sea-level and regional tectonic events to the formations of late Middle Ordovician stratigraphic sequences. The work will provide important and otherwise inaccessible information about he physical and temporal connections between geological events on the craton and those along a major orogenic belt.