Autogenic Hiatus in Fluviodeltaic Successions: Geometrical Modeling and Physical Experiments
Autogenic Hiatus in Fluviodeltaic Successions: Geometrical Modeling and Physical Experiments
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DOI：
10.2110/jsr.2011.19
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发表时间：
2011-03
影响因子：
2
通讯作者：
A. Tomer;T. Muto;Wonsuck Kim
中科院分区：
文献类型：
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作者：
A. Tomer;T. Muto;Wonsuck Kim
摘要海盆范围内的裂孔不连续性已被普遍认为是构造运动或一个完整的海平面升降旋回等独特的异源事件的有力证据。在这里，我们通过理论和实验模拟表明，在外部动力强迫没有变化的情况下，在河流三角洲序列中可以自生地产生大尺度的间断面，即，恒定的相对海平面上升率（rslr）和恒定的沉积物供应率（qS/单位宽度）。这种“自生间断”发生在（1）腹地坡度比三角洲的水下坡度更陡，以及（2）补给冲积河流的初始下游长度超过主要由qSlrslr指定的临界量级Lcrt。在这种地形背景下，现有的沉积体系成为海侵和非三角洲尽快海平面开始上升。现有的水下表面缺乏沉积物，并逐渐向陆地延伸，直到冲积长度减少到Lcrt。在退水河流达到这个临界长度后，海岸线仍在后退，但沉积体系恢复为三角洲沉积。正因为如此，水下表面，这是以前饥饿的沉积物，成为覆盖三角洲前积沉积物后，一个显着的时间间隔。因此，海平面的稳定上升可以产生以下所有的结果：a）裂孔下面的地层，B）裂孔本身，以及c）裂孔上面的地层。不需要rslr或qS的变化来解释这种特定类型的间隙的存在。数值模拟表明，如果发生晚更新世至全新世的海平面上升（即，0.01 km/kyr（10 kyr）。这进一步表明，在河流三角洲的地层记录中，特别是第四纪的地层记录中，很可能存在自生间断。当与海岸线自动后退理论相结合时，对自生间断的理解为某些地层间断的起源提供了另一种观点。
Abstract Basinwide hiatal discontinuity has been generally accepted as firm evidence of a distinctive allogenic event such as tectonic movement or a complete eustatic cycle. Here we show through theoretical and experimental modeling that a largescale, hiatal discontinuous surface can be produced autogenically in fluviodeltaic successions under no changes in external dynamic forcing, i.e., constant relative sea-level rise (rate rslr) and constant sediment supply (rate qS per unit width). This “autogenic hiatus” occurs where (1) the hinterland slope is steeper than the subaqueous slope of the delta, and (2) the initial downstream length of the feeding alluvial river exceeds a critical magnitude Lcrt that is specified primarily by qSlrslr. In this topographic setting, the existing depositional system becomes transgressive and nondeltaic as soon as sea level starts to rise. The existing subaqueous surface is starved of sediment and progressively extends landward until alluvial length is reduced to Lcrt. After the retreating river has attained this critical length, the shoreline still retreats but the depositional system is restored to deltaic sedimentation. Because of this, the subaqueous surface, which was previously starved of sediment, becomes overlain by delta foreset deposits after a significant time gap. Thus a steady sea-level rise can produce all of the following: a) the strata underlying the hiatus, b) the hiatus itself, and c) the strata overlying the hiatus. Changes in rslr or qS are not required to account for the presence of a hiatus of this particular type. Numerical simulations suggest that autogenic hiatuses are likely to be produced in most natural river deltas if a sea-level rise such as occurred during latest Pleistocene to Holocene (i.e., 0.01 km/kyr for 10 kyr) is available. This further implies that autogenic hiatuses may well exist in stratigraphic records of river deltas, especially of Quaternary age. An understanding of autogenic hiatuses, when combined with the theory of shoreline autoretreat, provides an alternative view of the origin of some stratigraphic breaks.