Tectonic Significance of Lower Cretaceous Gravels, Western Interior: Quantitative Modeling of Subsidence and Paleo- topography

西部内陆的下白垩统砾石传统上被用来确定塞维尔造山带的逆冲作用的开始时间。然而，这些砾石分布异常广泛，从最近的逆冲板块的前缘延伸了500多公里。相比之下，现代和古代前陆盆地中的同造山砾岩通常局限在冲断带70公里以内。该项目的目标是确定这些下白垩统砾石是否真的来自塞维尔冲断带或其他构造事件。怀俄明大学将使用一种新的多学科方法，将地层学和沉积学观察与既定的古水力和地球物理模拟技术相结合。这些技术将被用来区分关于下白垩统砾石成因的四种假说：(1)在逆冲侵位时形成一个小型的早期前陆盆地，但被砾石充填和覆盖；(2)砾石是在逆冲开始后立即沉积的，但在前陆盆地可能发育之前；(3)砾石是在紧接冲断前的广泛隆升事件中沉积的；(4)砾石来自冲断带以西，与冲断带无关。通过检验这四个假说，我们希望确定广泛分布的下白垩世砾石是否来自Sevier带的早期隆升，以及这些砾石是否独立地沉积在前陆盆地中或在其形成之前。因此，这一研究成果将有助于我们通过定量的盆地分析来理解新生的Sevier造山作用的时间和机制。此外，将各种独立的建模技术与地面实况观测相结合，以约束沉积-构造模型，可能是回答有关盆地如何以及何时在冲断带系统附近和其他构造环境中发展的问题的有力办法。

Lower Cretaceous gravels of the western interior have traditionally been used to date the initiation of thrusting in the Sevier orogenic belt. However, these gravels are anomalously widespread, extending over 500 km from the leading edge of the nearest thrust sheet. In contrast, synorogenic conglomerates in modern and ancient foreland basins are usually confined to within 70 km of the thrust belt. The goal of this project is to determine if these Lower Cretaceous gravels were indeed derived from the Sevier thrust belt or from some other tectonic event. The University of Wyoming will use a new multidisciplinary approach combining stratigraphic and sedimentologic observations with established paleohydraulic and geophysical modelling techniques. These techniques will be used to distinguish among four hypotheses for the origin of the Lower Cretaceous gravels: (1) a small incipient foreland basin developed as the thrust was emplaced but was filled and overtopped by the gravel; (2) the gravels were deposited immediately after thrusting began but before a foreland basin could develop; (3) the gravels were deposited during a broad uplift event that immediately preceded thrusting; and (4) the gravels were derived from west of, and are unrelated to, the thrust belt. By testing these four hypotheses we hope to determine if the widespread Lower Cretaceous gravels were derived from the early uplift of the Sevier belt and, independently, if the gravels were deposited in, or preceded formation of, a foreland basin. Thus the results of this study will advance our understanding of the timing and mechanics of the nascent Sevier orogeny by using quantitative basin analysis. In addition, the integration of diverse and independent modelling techniques with ground truth observations in order to constrain sedimentary-tectonic models is a potentially powerful approach to answering questions concerning how and when basins develop adjacent to thrust-belt systems and in other tectonic settings.