The Helderberg Group of New York State, consisting of a wide range of shallow water carbonate lithologies, contains one of the finest and most complete stratigraphic records of Lower Devonian earth history. High‐frequency spatial and temporal rhythmicity of carbonate accumulation in the Helderberg Group has been evaluated by examining thickness frequency distributions of individual sedimentation units in flasered ribbon rock and of individual lithofacies elements. These distributions provide important insights into the sedimentation processes that ultimately controlled stratal thicknesses. Observed thickness frequencies are closely approximated by the exponential end member of the gamma distribution, wherein flaser and lithofacies thickness frequency over each stratigraphic interval is dependent only on net sequence length and the number of stratal elements. Exponentially distributed thickness frequencies would be expected if lithologic change were a Poisson process, that is, if horizons of lithologic change occurred more or less randomly throughout. Such Poisson variation in lithologic thickness suggests a general absence of regularly recurrent high‐frequency depositional forcing of stratal thicknesses during accumulation. At the individual flaser‐bedded and lithofacies scale, deposition was primarily a stochastic rather than a deterministic process. Thickness distributions of supposedly shallowing‐upward lithofacies associations, and magnitudes of sea‐level rise inferred from lithologic change across shallowing cycle boundaries, exhibit similar skewed distributions of thickness/magnitude recurrence in Helderberg Group sections. These also are readily interpreted as generally Poisson processes of carbonate accumulation. Skewed frequency distributions of either cycle thickness or water depth change result from the grouping of a small number of elements from an exponential population of randomly distributed sizes. Modal (albeit skewed) cycle thickness distributions are simply an artifact of cycle definition and need not bear any relation to periodic extrabasinal forcing mechanisms. We conclude that thicknesses of flasered bedding units and lithofacies in the Helderberg Group largely reflect the more or less incidental migration of Lower Devonian depositional subenvironments across New York State during sediment accumulation. Stratigraphic extents of shallowing‐upward lithofacies associations and apparent punctuated deepening across shallowing “cycle” tops are little different from chance groupings of stratal units randomly drawn from an exponential population. If any sea‐level control is manifest in these patterns of sediment accumulation, it must have been nearly haphazard with respect to both secular recurrence and magnitude of eustatic change.

中文翻译：

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纽约州下泥盆统 Helderberg 群的沉积周期

纽约州海尔德伯格群由范围广泛的浅水碳酸盐岩性组成，包含下泥盆纪地球历史上最好和最完整的地层记录之一。通过检查闪烁带状岩中单个沉积单元和单个岩相元素的厚度频率分布，已经评估了 Helderberg 群碳酸盐岩堆积的高频时空节律性。这些分布为最终控制地层厚度的沉积过程提供了重要的见解。观察到的厚度频率与伽马分布的指数端成员非常接近，其中每个地层间隔上的flaser和岩相厚度频率仅取决于净层序长度和地层元素的数量。如果岩性变化是一个泊松过程，也就是说，如果岩性变化的层位在整个过程中或多或少随机发生，那么预计会出现指数分布的厚度频率。岩性厚度的这种泊松变化表明，在堆积过程中，一般不存在地层厚度的规律反复的高频沉积强迫。在单个闪焰层和岩相尺度上，沉积主要是一个随机过程，而不是一个确定性过程。推测的上浅层岩相组合的厚度分布，以及从跨浅层旋回边界的岩性变化推断出的海平面上升幅度，在 Helderberg Group 截面中表现出类似的厚度/幅度重现的偏斜分布。这些也很容易解释为碳酸盐积累的一般泊松过程。循环厚度或水深变化的偏斜频率分布是由随机分布大小的指数总体中的少量元素分组引起的。模态（尽管偏斜）周期厚度分布只是周期定义的产物，不需要与周期性的盆地外强迫机制有任何关系。我们得出结论，Helderberg 群中闪状层理单元和岩相的厚度在很大程度上反映了沉积物堆积过程中下泥盆纪沉积亚环境在纽约州的偶然迁移。浅层向上岩相关联的地层范围和浅层“旋回”顶部的明显间断加深与从指数总体中随机抽取的地层单元的机会分组几乎没有什么不同。如果在这些沉积物积累模式中表现出任何海平面控制，那么就长期复发和海平面变化的幅度而言，它一定几乎是偶然的。