Structures in Cretaceous strata in the Devils River Uplift of west Texas include folds, thrust faults, and bedding-parallel veins indicative of contractional deformation in a thrust faulting stress regime. In this study we analyze a series of small-wavelength (meters to tens of meters) folds in roadcut exposures northwest of Del Rio, Texas. The folds have WNW-ESE dominant trends, gently plunging axes, and are gentle to tight with upright to inclined axial surfaces of variable vergence. These structures are interpreted as detachment folds, with detachments within volcanic ash or mudrock beds. Observed thickening in anticline cores was by ductile flow of volcanic ash or mudrock, small-scale folding, and thrust or reverse faulting. Bed-perpendicular calcite veins are common and in some cases are offset by flexural slip on fold limbs, indicating that folding occurred after brittle failure and extension vein formation in lithified rock. Although rare, bed-parallel calcite veins are also present in the exposure and indicative of a thrust faulting stress regime. Occasional normal and reverse or thrust faults are also present in the exposures. Fluid inclusion analysis of vein cements from extension fractures and faults yielded homogenization temperatures of 71–101 °C, and estimated trapping depths of 2.2–3.5 km prior to and coeval with folding. We interpret these folds as having formed during NNE-SSW directed Laramide shortening (∼80–40 Ma) in a thrust-faulting stress regime with >2 km of overburden, rather than as either penecontemporaneous with deposition or after exhumation by caliche formation, as previously interpreted.

得克萨斯州西部魔鬼河隆起的白垩纪地层结构包括褶皱、逆冲断层和平行层理脉，表明逆冲断层应力状态下的收缩变形。在这项研究中，我们分析了德克萨斯州德尔里奥西北部道路切割暴露中的一系列小波长（米到几十米）褶皱。褶皱具有 WNW-ESE 主导趋势，轴平缓下沉，从平缓到紧密，具有可变辐合的直立到倾斜的轴向表面。这些结构被解释为分离褶皱，在火山灰或泥岩床内有分离。在背斜岩心中观察到的增厚是由于火山灰或泥岩的韧性流动、小规模褶皱以及逆冲断层或逆断层。垂直于床的方解石静脉很常见，在某些情况下被折叠肢上的弯曲滑动所抵消，表明在岩化岩石脆性破坏和伸展脉形成后发生褶皱。虽然罕见，但平行床的方解石脉也存在于暴露中，并表明逆冲断层应力状态。偶尔的正向和反向或逆冲断层也出现在暴露中。来自伸展裂缝和断层的脉状胶结物的流体包裹体分析得出均一化温度为 71-101 °C，估计圈闭深度为 2.2-3.5 km，与褶皱同时发生。我们将这些褶皱解释为在 NNE-SSW 定向拉拉胺缩短 (~80-40 Ma) 期间形成的，在具有 > 2 km 覆盖层的逆冲断层应力状态下，而不是与沉积同时期或在通过 caliche 形成折返之后形成，如以前解释过。