Collaborative Research: Fold Form, Strain, and Mechanics at the Whaleback Anticline: New Approaches to a Classic Field Locality

褶皱岩层是最基本、最有启发性和最有魅力的地质构造之一。研究褶皱是为了调查造山，了解岩石的工程性质，预测水或碳氢化合物的地下运动，并深入了解褶皱本身的基本过程。这些应用依赖于对褶皱内岩石变形的精确解释。各种概念和数学模型预测褶皱相关的变形。为了评估这种预测模型的能力，需要来自自然例子的数据。这可能具有挑战性，因为地球表面的大多数地质褶皱只是部分暴露出来，褶皱的主要部分要么埋在地下，要么被侵蚀掉。在熊谷的鲸背背斜，宾夕法尼亚州中东部，是一个独特的地方，一个完整的大规模褶皱暴露；上个世纪早期的露天采煤详细地揭示了这一点。这种突出的暴露允许观察褶皱表面的完整三维形式，并提供了非常详细的褶皱变形记录。该项目将使用尖端的数字成像技术和传统的地质实地调查来产生一个全面的数据集，以测试关于折叠的假设。除了该项目的科学目标外，该研究还有助于在科学、技术、工程和数学（STEM）教育领域取得与社会相关的成果，包括通过研究生和本科生培训培养多样化、具有全球竞争力的STEM劳动力；三所高校科研基础设施建设研究扩大代表性不足群体对科学的参与；提高公众的科学素养和公众对科学技术的参与。鲸背背斜是美国东部数十所大学地质系的重要教育实地考察地点，也是当地社区经常使用的娱乐场所。作为这个拟议项目的一部分，我们将保存、扩大和整理从鲸背岛进行的地质观测，供研究人员、教育工作者和社区使用。与折叠相关的变形由分布应变和离散次级结构记录。这些特征对于认识褶皱演化机制和演化顺序具有重要意义，同时作为流体在褶皱内和褶皱周围运移的记录和寄主具有重要的实际意义。来自自然例子的不完整数据限制了评估几何和基于物理的折叠模型的能力。在数字成像和分析方面的最新进展，现在可以对非圆柱形褶皱进行定量的三维描述，并评估这些形式与褶皱相关应变的分布和演化之间的关系。该项目有以下目标：1)制作一个标志性褶皱的高分辨率数字表面模型，即宾夕法尼亚州中东部熊谷的鲸背背斜；2)通过新的颗粒尺度应变观测、磁化率各向异性观测和褶皱层中尺度结构详细制图，记录褶皱周围应变的空间变异性；3)验证表面曲率控制褶皱周围观测应变的空间变化和类型的假设；4)通过有限元分析，评价地层和流变学对褶皱应变的影响；5)展示动态结构摄影测量作为构造地质学研究工具的效用；6)生产教育资源，以保护和扩大进入世界级实地地点的机会，并吸引当地社区。

Folded rock layers are among the most fundamental, instructive and charismatic geologic structures. Folds are studied to investigate mountain building, to understand the engineering properties of rock, to predict the underground movement of water or hydrocarbons, and to give insight into the fundamental processes of folding itself. These applications rely on the accurate interpretation of rock deformation within a fold. Various conceptual and mathematical models predict fold-related deformation. To assess the capabilities of such predictive models, data from natural examples are required. This can be challenging, because most geologic folds at Earth's surface are only partially exposed, with major portions of the fold either buried underground or eroded away. The Whaleback Anticline in Bear Valley, east-central Pennsylvania, is a unique locale where a complete large-scale fold is exposed; strip mining for coal early in the last century revealed it in exquisite detail. This outstanding exposure permits observation of the complete three-dimensional form of the folded surface and provides a highly detailed record of deformation across the fold. This project will use cutting-edge digital imaging techniques and traditional geologic fieldwork to produce a comprehensive data set against which to test hypotheses about folding. In addition to the scientific goals of the project, the research is contributing to achievement of societally relevant outcomes in the areas of science, technology, engineering, and mathematics (STEM) education, including the development of a diverse, globally competitive STEM workforce through graduate and undergraduate student training; the development of research infrastructure of three universities; the broadening of participation of underrepresented groups in science; and increased public scientific literacy and public engagement with science and technology. The Whaleback Anticline is an important educational field trip location for dozens of university geology departments throughout the eastern United States, and it is a well-used recreation site for the local community. As part of this proposed project we will preserve, expand and curate geological observations from the Whaleback, for use by researchers, educators and the community. Deformation associated with folding is recorded by distributed strain and discrete secondary structures. These features are of fundamental importance to understanding mechanisms and sequence of fold evolution and are of practical importance as records and hosts for fluid migration in and around folds. Incomplete data from natural examples limits the ability to evaluate geometric and physics-based models of folding. Recent advances in digital imaging and analysis now make it possible to produce quantitative three-dimensional descriptions of noncylindrical folds and evaluate the relationships of these forms to the distribution and evolution of fold-related strain. This project has the following objectives: 1) to produce a high-resolution digital surface model of an iconic fold, the Whaleback Anticline in Bear Valley, east-central Pennsylvania; 2) to document the spatial variability of strain around the fold with new observations of grain-scale strain, anisotropy of magnetic susceptibility, and detailed mapping of mesoscale structures in the folded layer; 3) to test the hypothesis that surface curvature controls the spatial variation and style of observed strain around a fold; 4) to evaluate stratigraphic and rheological influences on fold strain, through finite element analysis; 5) to demonstrate the utility of structure-from-motion photogrammetry as a tool for structural geology research and 6) to produce educational resources that will preserve and expand access to a world-class field locality and engage the local community.