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界层序在地质年代学和理解沉积过程中的重要意义。通过对中泥盆世（Hamilton群）事件地层学的广泛细致研究，我们发现了许多小型和大型旋回、有界包，其中一些具有广泛的可追溯性，在性质上表现为异旋回。我们还假设：1)至少在大尺度旋回中，上浅基序并不普遍，旋回在盆地中心附近是次对称的，但在边缘渐变为不对称的浅-上浅序；2)包裹体的边界面可能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性；4)连续旋回层序沉积中心规律性地向西迁移，与当前前陆盆地逆冲加载模式一致。为了检验这些模式的普遍性，我们将全面记录纽约州中部汉密尔顿群的小规模粗化向上序列的沉积学、地层学、古生物学和区域分布，以及它们在其他地区的相关序列。特别是，我们将重点关注a)陆架-盆地剖面上有界旋回的相关性；B)环内横向对称变化；C)小尺度旋回包体内部相解剖；d)边界面的性质和时间尺度。这项研究将有助于更好地了解泥泞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型。

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.