Abstract The interpretation of fracture networks in contractional folds is challenging due to the range of factors that control fracture formation. We use outcrop-based analysis of fractures in plan-view pavements and in a 9-bed cross-sectional exposure to evaluate the fracture system within Cretaceous limestone layers of a Laramide fold in west Texas, the Stillwell anticline. Opening-mode extension fractures (veins) at high angles to bedding dominate the fracture population, although shear fractures and faults cut bedding at low angles within the forelimb. Analysis of extension fractures reveals NW-striking axial parallel and NE-striking axial-perpendicular fracture sets interpreted to have formed during contractional folding, a third N-striking fracture set formed during subsequent Basin and Range extension, and a fourth ESE-striking fracture formed due to unloading during exhumation. Fracture fill textures suggest that many fracture apertures increased during exhumation. The relative abundances of the four fracture sets and the intensity of each set vary from bed to bed in cross section. Because beds display no significant differences in mechanical strength and there is no correlation between bed thickness and fracture intensity, we attribute this bed-to-bed variability to differences in cohesion between beds. Bed decoupling, when combined with low extensional (

中文翻译：

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层间黏聚力对褶皱相关裂缝发育的影响，静井背斜，西德克萨斯（美国）

摘要 由于控制裂缝形成的因素范围广泛，对收缩褶皱中裂缝网络的解释具有挑战性。我们对平面视图路面和 9 层横截面暴露中的裂缝进行基于露头的分析，以评估德克萨斯州西部拉拉米德褶皱（Stillwell 背斜）白垩纪石灰岩层内的裂缝系统。尽管剪切裂缝和断层在前肢内以低角度切割层理，但与层理成高角度的张开模式延伸裂缝（脉）在裂缝群中占主导地位。对伸展裂缝的分析揭示了 NW 走向的轴向平行和 NE 走向的轴向垂直裂缝组被解释为在收缩折叠期间形成，第三个 N 走向的裂缝组在随后的盆地和范围扩展期间形成，由于挖掘过程中的卸载而形成了第四个 ESE 冲击裂缝。裂缝填充结构表明，在折返过程中许多裂缝孔径增加。四个裂缝组的相对丰度和每组裂缝的强度在横截面中因层而异。由于床层在机械强度方面没有显着差异，并且床层厚度和断裂强度之间没有相关性，我们将这种床间变异性归因于床层之间的凝聚力差异。床分离，当结合低拉伸（由于床层在机械强度方面没有显着差异，并且床层厚度和断裂强度之间没有相关性，我们将这种床间变异性归因于床层之间的凝聚力差异。床分离，当与低拉伸结合时（由于床层在机械强度方面没有显着差异，并且床层厚度和断裂强度之间没有相关性，我们将这种床间变异性归因于床层之间的凝聚力差异。床分离，当与低拉伸结合时（