Geomorphology and sequence stratigraphy due to slow and rapid base-level changes in an experimental subsiding basin (XES 96-1)
Geomorphology and sequence stratigraphy due to slow and rapid base-level changes in an experimental subsiding basin (XES 96-1)
复制标题
实验沉降盆地缓慢和快速基准面变化引起的地貌和层序地层学 (XES 96-1)
DOI：
10.1306/8626ca0f-173b-11d7-8645000102c1865d
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发表时间：
2001
期刊：
影响因子：
3.5
通讯作者：
R. Steel
中科院分区：
文献类型：
--
作者：
P. Heller;C. Paola;I. Hwang;B. John;R. Steel
沉降是自然盆地填料堆积和结构的主要因素。明尼苏达大学圣安东尼瀑布实验室最近建造的实验设施（实验地球景观设施 [XES]）首次在其设计中采用了灵活的沉降地板。因此，实验盆地可以模拟与沉积物供应、绝对基准面变化以及沉降速率和几何形状的独立变化相关的侵蚀和沉积。这里描述了在原型盆地 (1 × 1.6 × 0.8 m) 中进行的第一次实验的结果，其中分析了具有凹陷几何形状的盆地中与先慢后快的基准面旋回相关的地层发育。实验录像和随后对盆地中干燥地层的连续切片可以解释在精确已知的绝对基准面、沉降和沉积变化的条件下的层序发育。由于沉降的凹陷几何形状，相对基准面的变化在盆地中发生了很大的变化，尽管自循环变化也很重要，但它似乎对沉积模式发挥了主要控制作用。缓慢和快速基准面下降之间的序列边界样式不同。在基准面缓慢下降期间，一旦海岸线超出最大沉降区，就会形成下切山谷，这表明海岸线的下切可能对相对基准面的变化非常敏感。然而，一旦开始，山谷就迅速变宽，通过小点退缩，形成宽阔的、低起伏的侵蚀面，延伸到整个盆地。由于侵蚀发生在拐点处，沉积立即发生顺流，因此拐点和上游沉积界限一起向陆地迁移，产生强烈的时间海侵侵蚀和上超层序。该层序边界的地层（开始第 818 页）记录是一个单一但非常微妙的广泛不整合面，在下游变得整合，这在地层横截面中很难追踪。相比之下，在基准面快速下降过程中形成的切谷相对较窄、较深，并且随着时间的推移，谷口的沉积物逐渐暴露并切穿而变长。直到基准面快速上升开始，下切山谷的大规模回填才开始。因此，与缓慢的基准面变化相比，快速的基准面变化在地层记录中产生了更容易识别的切谷。通过孔隙度的灰度代理来评估地层内潜在的储层发育。盆地内出现了四个独特的储层质量增强区域：盆地的最近部分；以生长断层为界的沉积楔的上部；由颗粒流沉积物组成的深水强迫海退体系域；和海侵体系域是在基准面快速上升过程中形成的。相对多孔单元的这种分布表明，由于多种原因，快速的海平面循环可能会产生最好的储层单元。
Subsidence is a major factor in the accumulation and architecture of natural basin fills. A recently built experimental facility (Experimental Earthscape Facility [XES]) at St. Anthony Falls Laboratory of the University of Minnesota incorporates, for the first time, a flexible subsiding floor in its design. Thus the experimental basin can model erosion and deposition associated with independent variations in sediment supply, absolute base-level change, and rates and geometries of subsidence. The results of the first experiment in a prototype basin (1 × 1.6 × 0.8 m) are described here, wherein the stratigraphic development associated with first slow and then rapid base-level cycles in a basin that has a sag geometry has been analyzed. A videotape of the experiment and subsequent serial slicing of the dried strata in the basin allow interpretation of the sequence development under conditions of precisely known changes of absolute base level, subsidence, and sedimentation. Relative base-level changes, which strongly varied in the basin owing to the sag geometry of subsidence, seem to exert primary control on sedimentary patterns, although autocyclic changes were also important. Style of sequence boundaries differed between slow and fast base-level falls. During the slow base-level fall, an incised valley developed once the shoreline prograded out of the zone of maximum subsidence, suggesting that incision at the shoreline may be very sensitive to changes in relative base level. Once started, however, the valley quickly widened, by knickpoint retreat, into a broad, low-relief erosion surface that stretched across the entire basin. As erosion took place at the knickpoint, deposition occurred immediately downflow, so both the knickpoint and the upstream limit of deposition migrated landward together, producing a strong time-transgressive erosion and onlap sequence. The stratigraphic (Begin page 818) record of this sequence boundary is a single yet very subtle widespread unconformity that becomes conformable downstream, which is difficult to trace in stratigraphic cross section. In contrast, the incised valley that formed during the rapid base-level fall was relatively narrow, deep, and lengthened over time as deposits at the mouth of the valley were gradually exposed and incised through. Wholesale backfilling of the incised valley did not begin until the rapid base-level rise started. As a result, the rapid base-level change produced a more easily recognized incised valley in the stratigraphic record than did the slow base-level change. Potential reservoir development within the strata is evaluated by means of a gray-scale proxy for porosity. Four distinctive zones of enhanced reservoir quality occurred in the basin: the most proximal part of the basin; the upper part of growth-fault-bounded sedimentary wedges; deep-water forced regressive systems tract composed of grainflow deposits; and transgressive systems tract formed during the rapid base-level rise. This distribution of relatively porous units suggests that, for a variety of reasons, rapid sea level cycles may produce the best reservoir units.