Stratigraphy of a Cretaceous Coastal-Plain Fluvial Succession: The Campanian Masuk Formation, Henry Mountains Syncline, Utah, U.S.A.
Stratigraphy of a Cretaceous Coastal-Plain Fluvial Succession: The Campanian Masuk Formation, Henry Mountains Syncline, Utah, U.S.A.
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白垩纪沿海平原河流序列的地层学：美国犹他州亨利山向斜坎帕尼亚马苏克地层
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发表时间：
2011
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通讯作者：
L. Birgenheier
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作者：
M. Corbett;C. Fielding;L. Birgenheier
沿海平原河流序列的内部结构和成因地层分析，既可用于大陆边缘地层学的学术理解，也可用于地下油气和水储层的经济评价。尽管有大量的暴露的古代例子，这样的沿海平原浅海过渡，但是，横向相变和地层叠加模式的这种过渡仍然在很大程度上没有得到解决的细节。本文对美国西部犹他州亨利山向斜坎帕尼亚期马苏克组进行了沉积学和地层学分析，并提出了一个层序地层模型来解释该单元中发现的河流-河道岩性体的几何形状。在其标准剖面上，Masuk组是一个~ 220 m厚的砂岩、泥岩和煤互层序列，具有少量层内角砾岩。定义了六个相：相1为煤和碳质页岩，记录了海岸平原沼泽中有机沉积物的堆积，相2为泥岩，记录了海岸平原洪泛盆地环境，相3为砂岩和粉砂岩薄互层，代表了具有一段海泛的河口盆地沉积，相4为粉砂岩-砂岩混合层内角砾岩，代表了混乱充填的海岸平原河道;相5，砂岩-粉砂岩互层，具有倾斜的杂岩分层（IHS），记录了具有可变沉积物供应的海岸平原通道的沉积物;相6，槽交错层砂岩，记录了以砂为主的海岸平原通道沉积物。相4，5和6都显示了海岸和潮汐对沉积物积累的影响（IHS，低多样性的痕迹化石组合，双峰到双极古水流分布，小规模沉积结构上的泥披覆）在不同程度上的证据。相分析和关键表面（如区域性广泛侵蚀面（层序边界）和洪水面）的追踪表明，整个Masuk组（和下伏Muley峡谷砂岩的最上部）是一个单一的沉积层序。典型的多边河道体在沉积走向方向上可追踪的距离远大于经验计算的河道带宽度估计值。这种模式表明，堆积模式的同种异体控制。多层和多边河道主体通常在底部具有相4单元，被相5的一个或多个层覆盖，并且依次被相6覆盖。这种叠加模式可以反映出海侵过程中的下切、初始低位河道充填和随后的河口河道沉积的循环。这种模式进一步暗示了在长期序列中嵌套的高频序列保存的可能性。这项研究提供了新的见解的堆积模式的沿海平原河流的继承和解释。
Abstract The internal architecture and genetic-stratigraphic analysis of coastal-plain fluvial successions has applications to both academic understanding of continental-margin stratigraphy and to the economic evaluation of subsurface hydrocarbon and water reservoirs. Despite the abundance of exposed ancient examples of such coastal-plain to shallow marine transitions, however, the lateral facies changes and stratigraphic stacking patterns of such transitions remain largely unresolved in detail. This study presents a sedimentological and stratigraphic analysis of the Campanian Masuk Formation in the Henry Mountains syncline of Utah, western USA, and proposes a sequence-stratigraphic model to explain the geometries of fluvial-channel lithosomes found in the unit. At its type section, the Masuk Formation is an ~ 220-m-thick succession of interbedded sandstone, mudstone, and coal with minor intraformational breccias. Six facies are defined: Facies 1, coal and carbonaceous shale, records accumulation of organic sediments in coastal-plain mires; Facies 2, mudrock, records coastal-plain floodbasin settings; Facies 3, thinly interbedded sandstone and siltstone, represents estuarine-basin deposits with one interval of marine flooding; Facies 4, admixed siltstone-sandstone with intraformational breccia, represents chaotically filled coastal plain channels; Facies 5, interbedded sandstone-siltstone with inclined heterolithic stratification (IHS), records deposits of coastal-plain channels with variable sediment supply; and Facies 6, trough-cross-bedded sandstone, records sand-dominated coastal-plain channel deposits. Facies 4, 5, and 6 all show evidence of coastal and tidal influence on sediment accumulation (IHS, low-diversity trace-fossil assemblages, bimodal to bipolar paleocurrent distributions, mud drapes on small-scale sedimentary structures) to varying degrees. Facies analysis and tracing of key surfaces such as regionally extensive erosion surfaces (sequence boundaries) and flooding surfaces suggest that the entire Masuk Formation (and the uppermost part of the underlying Muley Canyon Sandstone) is a single depositional sequence. The typically multilateral channel bodies are traceable in a depositional strike direction over distances much greater than empirically calculated estimates of channel-belt width. This pattern suggests an allogenic control on stacking patterns. Multistory and multilateral channel bodies typically have a Facies 4 unit at the base, overlain by one or more stories of Facies 5, and in turn capped by Facies 6. This stacking pattern could reflect cycles of incision, initial lowstand channel filling, and subsequent backfilling of estuarine channels during transgressions. This pattern further hints at the possibility of preservation of high-frequency sequences nested within the longer-term sequence. This study provides new insights into the stacking patterns of coastal-plain fluvial successions and their interpretation.