Small Scale Depositional Sequences in a Middle Devonian Foreland Basin

许多作者强调了小尺度地层旋回和不连续有界层序在地质年代学和理解沉积过程中的重要性。作为对中泥盆世(汉密尔顿群)事件地层学广泛而详细的研究的结果，我们已经识别出许多小型和大型旋回、有界的包裹，其中一些是广泛可追踪的，似乎是异旋回性质的。我们还假设：1)至少在更大规模的旋回中，向上变浅的母题不是普遍存在的，而是在盆地中心附近呈次对称的旋回，而是逐渐边缘地进入不对称的浅升序列；2)包体的边界面可以记录海平面的下降或上升，但3)它们代表了相当大的不连续；4)连续旋回层序的沉积中心表现出规则的向西迁移，这与目前的前陆盆地逆冲加载模式一致。作为对这些模式通用性的检验，我们将详细记录纽约州中部哈密尔顿群小规模向上粗化层序的沉积学、挖掘学、古生物学和区域分布，以及其他地区的相关资料。特别是，我们将侧重于a)陆架到盆地剖面上的有界旋回的相关性；b)旋回内的横向对称性变化；c)小尺度旋回包的内部相解剖；以及d)边界表面的性质和时间尺度。这项研究将有助于更好地了解泥质前陆盆地的相对海平面波动和沉积动力学，并可作为解释整个地质记录中类似背景的模式。

Many authors have stressed the significance of small-scale stratigraphic cycles and discontinuity bounded sequences in geochronology and in understanding depositional processes. As a result of extensive detailed studies of event stratigraphy of the Middle Devonian (Hamilton Group), we have recognized numerous small- and large-scale cyclic, bounded packages, some of which are widely traceable and appear to be allocyclic in nature. We also postulate that: 1) an upward-shallowing motif, at least in larger-scale cycles, is not pervasive, rather cycles are subsymmetrical near basin centers, but grade marginward into asymmetrical shallowing-upward sequences; 2) that the bounding surfaces of packages may record either sea level fall or rise, but 3) that they represent discontinuities of considerable magnitude; 4) depocenters of successive cyclic sequences display a regular westward migration that is consistent with current models of thrust loading in foreland basins. As a test of the generality of these patterns we will thoroughly document the sedimentology, taphonomy, paleontology and regional distribution of small-scale coarsening-upward sequences of the Hamilton Group in central New York State, and their correlatives in other areas. In particular, we will focus on a) correlation of bounded cycles across a shelf-to-basin profile; b) lateral symmetry changes within cycles; c) internal facies anatomy of small scale cyclic packages; and d) the nature and temporal scale of bounding surfaces. This research will lead to better understanding of relative sea-level fluctuations and depositional dynamics of a muddy foreland basin and could serve as a model for interpreting similar settings throughout the geologic record.