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

德拉诺9627872 相发育的层序地层学解释已得到广泛应用。然而，这一模型很少被测试对一个独立的一套高精度的年代地层对比。拟议的研究旨在直接检查两个中心假设的层序地层学：不整合界定的上超/下超周期是同步跨越广泛的地区，最大的洪水面周期内可以作为区域等时线。 我们建议通过比较横跨北美东部的两个区域性广泛断面的中奥陶世晚期沉积序列的时间来测试这些预测（图1）。第一个将延伸到塔科尼克前陆盆地的西南部，从纽约海角通过宾夕法尼亚折返到弗吉尼亚海角。沿着这条样带，我们将研究宾夕法尼亚州中东部、弗吉尼亚州西部、田纳西州东部和亚拉巴马北方的剖面。第二条样带将从塔科尼克前陆盆地延伸，穿过肯塔基州中北部的埃克塞特明穹丘，进入塔科尼克内陆，在那里我们将考察爱荷华州、伊利诺伊州和密苏里州的剖面。这些地区在地理上相距甚远，在此期间经历了不同的构造历史。 沿着这两条剖面，我们将研究中奥陶统最上部三级地层序列的时空分布相对于一个独立的高精度年代地层。我们将特别关注1）Corynoides americanus年代期间在纽约塔康尼克盆地发育的较低特伦顿组-尤蒂卡页岩海侵和高位体系域的等效物，以及2）在Orthographus ruedemanni年代期间发育的后续低位扇（Dolgeville组）的等效物。本旋回的预测层序等效物将取自已发表的文献。我们之前对纽约州中部中奥陶纪n特伦顿群和尤蒂卡页岩的研究已经产生了一个高分辨率的年代地层学，该年代地层学将K-辉长岩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）笔石和牙形石生物地层学研究，以及2）研究地点的钾辉长岩中磷灰石斑晶和石英斑晶中玻璃包裹体的高精度电子探针分析，来扩展这一年代地层框架。该系统内基于图解对比的年代地层分辨率应该很高（大大超过单独的生物地层学或放射性测年），并足以对快速上覆海侵系统轨迹、上覆最大洪泛面/海裂孔和上部层序边界/低位扇的同步性提供明确的测试。 通过将这组时间线延伸到相对稳定的塔康尼克内部，并向南延伸到塔康尼克造山运动早期布朗特阶段经历碰撞加载的地区，将有可能：1）获得北美东部这一间隔期间记录的海进-海退旋回之间同步性的精确和独立测量，因此，（2）利用这一对比体系，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地质事件与沿着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，否则无法获得这些信息。

Delano 9627872 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 Ordovicia n 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.