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

传统上，下白垩世西部内陆的砾石被用来确定塞维尔造山带逆冲运动的起始年代。然而，这些砾石分布异常广泛，从最近的逆冲板的前缘延伸超过500公里。相比之下，现代和古代前陆盆地的同造陆砾岩通常局限于逆冲带70 km范围内。该项目的目的是确定这些下白垩纪的砾石是否确实来自塞维尔冲断带或其他一些构造事件。怀俄明大学将采用一种新的多学科方法，将地层学和沉积学观测与已建立的古水力和地球物理建模技术相结合。这些技术将用于区分下白垩统砾石起源的四种假说：(1)一个小型的早期前陆盆地随着冲断构造的就位而发育，但被砾石填满和覆盖；(2)逆冲作用开始后，前陆盆地发育前，砾石立即沉积；(3)砾石沉积于逆冲作用之前的广泛隆升事件；(4)砾石产于逆冲带以西，与逆冲带无关。通过测试这四个假设，我们希望确定广泛分布的下白垩世砾石是否来自塞维尔带的早期隆起，以及独立地确定这些砾石是否沉积在前陆盆地中或在形成之前。因此，本研究结果将通过定量的盆地分析促进我们对早期塞维尔造山运动的时间和机制的理解。此外，为了约束沉积构造模型，将多种独立的建模技术与地面真实观测相结合，是回答有关盆地如何以及何时与冲断带系统相邻以及在其他构造环境中发育的问题的潜在有力方法。

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.