Submarine transitional flow deposits in the Paleogene Gulf of Mexico
Submarine transitional flow deposits in the Paleogene Gulf of Mexico
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DOI：
10.1130/g33410.1
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发表时间：
2012-12
期刊：
影响因子：
5.8
通讯作者：
I. Kane;A. Pontén
中科院分区：
文献类型：
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作者：
I. Kane;A. Pontén
海底重力驱动的水流是地球上最大但仍鲜为人知的沉积物输送媒介。最近在超深盆地的勘探井揭示了神秘相类型的大型砂质海底扇系统的存在，距离古海岸线数百公里。这些沉积物常常违背传统的浊积岩或碎屑岩解释，其特征暗示着来自具有瞬态湍流层流流变的流动的沉积。在威尔科克斯组（墨西哥湾）中，推断的过渡流沉积物具有独特的地层堆积模式，从细粒碎屑岩到粗粒浊积岩。这里推断床的垂直顺序反映了响应于波瓣进展的纵向床分布，并展示了从充分混合的湍流到逐渐更加流变分层的流动，并最终到完全层流的过渡。内部流变边界的逐渐发展导致了高浓度但流体的基底层和具有压倒一切的剪切稀浊流的上部准层流层。水流的长径流与其高泥沙和粘土含量有关；最有可能的是通道-波瓣过渡处的流量膨胀驱动了流量变换。这种基于过程的模型可能适用于许多深水环境，并提供了一个框架来解释这些复杂矿床的地层和空间分布。
Gravity-driven flows on the seafloor are the largest, yet least well understood, sediment transport agents on Earth. Recent exploration wells in ultradeep basins have revealed the presence of large sandy submarine fan systems of enigmatic facies types, many hundreds of kilometers from paleocoastlines. These sedimentary deposits often defy conventional turbidite or debrite interpretations, having a character suggestive of deposition from flows with transient turbulent-laminar rheologies. In the Wilcox Formation (Gulf of Mexico), inferred transitional flow deposits have distinctive stratigraphic stacking patterns, from fine-grained debrites to coarser grained turbidites. The vertical sequence of beds is here inferred to reflect the longitudinal bed distribution in response to lobe progradation, and demonstrates a transition from well-mixed turbulent flow, to progressively more rheologically stratified flow, and eventually to fully laminar flow. The progressive development of internal rheological boundaries resulted in a high-concentration but fluidal basal layer, and an upper quasi-laminar layer with an overriding sheared dilute turbidity current. The long runout of the flows is linked to their high silt and clay content; it is most likely flow expansion at the channel-lobe transition that drives flow transformation. This process-based model may be applicable to many deep-water settings and provides a framework within which to interpret the stratigraphic and spatial distribution of these complex deposits.