Multi-Scale Heterogeneity of the Stream-Dominated Alluvial Fan: New Perspective and Implications for Transport

尽管河流为主的冲积扇构成了重要含水层系统的很大比例，但文献中明显缺乏对这些沉积物的详细三维描述。层序地层学概念在石油研究中预测地下相分布的成功应用有力地表明，当对纯陆相地层进行修正时，层序地层学可以用于描述冲积扇系统。该项目涉及几个学科的融合，包括水文学、地质学、地球物理学和土壤学，以开发一个层序地层框架，从这个框架中可以为典型的河流为主的冲积扇产生更先进、更容易处理的非均质性模型。本研究的意义有三个方面。首先，它将通过陆相层序地层学概念的发展，为我们理解许多冲积扇地下水系统的非均质性创造一些必要的“秩序”。第二，这项研究将提供一种方法，将地质统计模拟纳入层序地层框架，从而提供含水层系统的详细特征。最后，这项研究将使我们在描述和模拟许多类型冲积沉积物中的区域地下水流动和运移的能力方面向前迈进一大步。这一进展对于估计农业和城市污染对地下水质量可持续性的长期影响是非常必要的。拟议研究的核心是认识到与第四纪气候循环有关的序列，其边界是横向广泛的成熟古土壤。这些古土壤标志着间冰期扇体的暴露，并在含水层系统中形成横向广泛的含水层。层序中的地层代表了在冰期扇上发生的沉积，当时由于增加了流量和沉积物供应，提供了可容纳的空间。在这些层序中，在岩心、钻探测井和国王河扇地貌填图中也发现了体系域(例如，在气候周期的一个时期内沉积的岩相的相互联系的组合)。建议在特定的系统区域(例如，切割的山谷充填沉积物)收集额外的连续岩心，以检查这些差异。通过环境磁学、相形态和岩相学分析对体系域进行对比。在国王河冲积扇的其他部分已经成功地完成了对岩心数据的相对丰富的钻探测井的校准，这将提供一种在地下确定系统域几何形状的方法。将使用一种新的马尔可夫链技术对具有更高地质严格性的沉积单元的空间分布进行地质统计模拟(Carle和Fogg，1996a，1997)，以产生层序地层框架内的结构单元的随机模拟。

9870342FoggThough stream-dominated alluvial fans comprise a large percentage of important aquifer systems, detailed three-dimensional characterizations of these deposits are notably lacking in the literature. Successful application of sequence stratigraphic concepts in petroleum research to predict subsurface facies distributions strongly suggests that, when modified for purely continental strata, sequence stratigraphy can be applied to characterize alluvial fan systems. This project involves the fusion of several disciplines, including hydrology, geology, geophysics, and soil science, to develop a sequence stratigraphic framework from which a more advanced, tractable model of heterogeneity can be produced for typical, stream-dominated alluvial fans. Significance of this research is three-fold. First, it will create some needed "order" in our understanding of heterogeneity in many alluvial fan groundwater systems through development of continental sequence stratigraphic concepts. Second, the research will provide a method to incorporate geostatistical simulation into a sequence stratigraphic framework, thus providing a detailed characterization of the aquifer system. Finally, the research will provide a large step forward in our ability to characterize and model regional groundwater flow and transport in many types of alluvial deposits. Such an advance is sorely needed for estimating long-term impacts of agricultural and urban pollution on sustainability of groundwater quality.Central to the proposed research is the recognition of sequences, related to Quaternary climate cycles, bounded by laterally extensive, mature paleosols. These paleosols mark fan exposure during interglacial periods, and form laterally extensive aquitards in the aquifer system. Strata within the sequences represents deposition that occurred on the fan during glacial episodes, when accommodation space was made available by increased discharge and sediment supply. Within these sequences, systems tracts (e.g., linked assemblage of lithofacies deposited during one time period of the climatic cycle) have also been recognized in core, driller's logs, and geomorphic mapping of the Kings River fan. It is proposed that additional continuous core will be collected specific systems tracts (e.g., incised valley fill deposits) to examine these differences. The systems tracts will be compared through use of environmental magnetism, facies morphology, and petrographic analysis. Calibration of relatively abundant drillers logs to the core data, already successfully accomplished in other portions of the Kings River alluvial fan, will provide a means to define systems tract geometry in the subsurface. A new Markov-chain technique for geostatistical modeling of spatial distribution in sedimentary units with greater geologic rigor (Carle and Fogg, 1996a, 1997) will be used to produce stochastic simulations of textural units within the sequence stratigraphic framework.