Alluvial Architecture and Floodplain Paleosols: Field Evaluation of Theoretical Models

小行星9706115 河流沉积学最重要的进展之一是冲积结构模型的发展。 这些模型的一个重要组成部分是信道撕脱，最近的两项研究提供了新的和更现实的见解的影响，撕脱冲积建筑。 Mackey和Bridge（1995年）的新模型预测了“撕脱层序”，其中主要砂岩在剖面上部逐渐变薄。 Heller和保拉（1996年）提出了一个简单的几何模型，探讨了撕脱频率和沉积速率之间的关系如何影响冲积物结构。 尽管它们有解释岩石记录的潜力，但模型的有效性和实用性取决于现代和古代冲积层序的现场测试。 因此，这里提出的研究是检查冲积建筑的始新世冲积矿床的新模式。 本研究的创新之处在于，将河漫滩古土壤分析与更典型的砂体特征分析相结合，建立了冲积体系结构以及对河流系统的内在和外在控制。 该项目有两个主要目标：（1）实地测试撕脱和冲积结构的新概念，并为完善这些新模型提供实地数据;（2）进一步开发古土壤，作为冲积结构研究（包括实地和定量研究）的一个组成部分。 为了只关注沉降速率和撕脱频率对冲积层结构的影响，将研究一个暴露异常良好的古代实例中的时间等效上游和下游横截面。 要分析的地层单位，威尔伍德组，是特别适合这项研究，因为它有很好的生物地层和古地磁地层记录，可用于时间对比和计算沉积物积累率。 前人对该盆地其他地区威尔伍德古土壤的研究为分析古土壤提供了一个框架。 野外研究的重点是描述主要的砂岩体及其周围的古土壤。 将描述两个研究区主要砂岩的外部几何形状、内部特征和相互联系。 古土壤将在实验室中描述和进一步研究，以确定不同类型的古土壤及其成熟度。 对砂岩体和古土壤的分析将被整合，以测试和改进计算机模型。 将对这两个剖面进行检查，以确定砂体尺寸和相互连接性以及古土壤成熟度的向上剖面变化，以检验是否存在Bridge和Mackey（1995年）预测的撕脱序列。 将对两个研究区的冲积结构进行比较和对比，以了解沉积物积累速率的增加对冲积结构的影响，并检验Heller和保拉（1996）的结果对地层记录的适用性。 无论是新的冲积结构模型和整合古土壤分析到冲积结构研究的方式冲积过程和由此产生的存款理解有重要的影响。 它们一起提供了一个基本的新的评估如何冲积矿床可以被描述和解释，他们提供了巨大的潜力，更好地预测冲积层结构在地下资源，如含水层和石油和天然气田。

9706115 Kraus One of the most important advances in fluvial sedimentology has been the development of alluvial architecture models. An important component of these models is channel avulsion, and two recent studies provide new and more realistic insights on the influence of avulsion on alluvial architecture. The new model of Mackey and Bridge (1995) predicts "avulsion sequences" in which major sandstones become progressively thinner up-section. Heller and Paola (1996) have presented a simple geometric model that explores how the relationship between avulsion frequency and sedimentation rate can influence alluvial architecture. Despite their potential for interpreting the rock record, the validity and usefulness of the models depend upon field testing in both modern and ancient alluvial sequences. Consequently, the research proposed here is to examine the alluvial architecture of Eocene alluvial deposits in light of the new models. This research is innovative in that the alluvial architecture and the intrinsic and extrinsic controls on the fluvial system will be established by integrating the analysis of floodplain paleosols with the more typical analysis of sandstone body characteristics. This project has two major goals: (1) to field test the new concepts of avulsion and alluvial architecture and provide field data for refining these new models and (2) to further develop paleosols as an integral part of alluvial architecture studies (both field and quantitative studies). To focus on only the effects of subsidence rate and avulsion frequency on alluvial architecture, time-equivalent upstream and downstream cross-sections in an exceptionally well-exposed ancient example will be examined. The stratigraphic unit to be analyzed, the Willwood Formation, is especially appropriate for this study because it has excellent biostratigraphic and paleomagnetostratigraphic records that can be used for time correlation and calculating sediment accumulation rates. Previous studies of Willwood paleosols in other parts of the basin provide a framework for analyzing the paleosols. Field study will focus on describing the major sandstone bodies and the paleosols surrounding them. The external geometry, internal characteristics, and interconnectedness of the major sandstones in the two study areas will be described. Paleosols will be described and further studied in the lab to determine the different the different kinds of paleosols and their maturity. The analyses of the sandstone bodies and the paleosols will be integrated to test and refine the computer models. The two cross sections will be examined for up-section changes in sandstone body size and interconnectedness and in paleosol maturity to test for the presence of avulsion sequences predicted by Bridge and Mackey (1995). The alluvial architectures in the two study areas will be compared and contrasted to see what effect increasing rates of sediment accumulation had on alluvial architecture and to test how applicable the results of Heller and Paola (1996) are to the stratigraphic record. Both the new alluvial architecture models and the integration of paleosol analysis into alluvial architecture studies have important implications for the way alluvial processes and the resulting deposits are understood. Together they provide a fundamental new assessment of how alluvial deposits can be described and interpreted, and they offer enormous potential for better prediction of alluvial architecture in subsurface resources such as aquifers and oil and gas fields.