The green mapped unit forms smooth flatirons in the backlimb (e.g., Figure 2f), on which good strike and dip measurements were taken, but it forms few outcrops in the forelimb. Oceanography, Interplanetary These oscillations are characterized by a dominant fold‐parallel waviness, in the forelimb of the interpolated surface. Constant projection distances to the base Sundance Formation are presented on the right side of Figure 3. Its NW–SE trend (Figure 1) is similar to that of many folds within the Rocky Mountains, although some others formed at acute angles to the regional compression [ … Many of these points were located to the northwest, beyond the extent of the observation grid, where the fold appears to become less cylindrical and where ALSM data constraint was limited to sparse points from the Frontier Formation. Open markers represent measurements taken in the backlimb, and solid markers represent forelimb measurements. google_ad_width = 160; Auxiliary material for this article contains a high‐resolution version of Figure 4a. If slope constraints were distributed randomly throughout the data or at the end of the decimation input, the interpolation would be dominated by spatial constraint with very few, if any, slope constraint points surviving the decimation process. Geometry of Sheep Mountain Anticline [14] Sheep Mountain Anticline is a basement‐cored, doubly plunging, asymmetric fold (Figures 1 and 3). A series of parallel or subparallel cross sections are created, and a smooth surface is interpreted, which honors the location of the selected stratigraphic contact on each cross section. Open markers represent measurements taken in the backlimb, and solid markers represent forelimb measurements. Abstract The Sheep Mountain anticlinal complex between Lovell and Greybull, Wyoming, in the Bighorn basin provides exposure suitable for three-dimensional stratigraphic studies of Mesozoic rocks. The anticline bulges unrealistically to the northeast, into what should be a steeply dipping forelimb and synclinal hinge. Although the fold has less topographic relief in the Mesozoic section, these units were folded with the underlying strata and resistant beds crop out in distinctive ridges. [7] Abundant outcrops at SMA have motivated numerous structural studies focusing on fault‐related folding [Forster et al., 1996; Hennier and Spang, 1983; Sanz et al., 2007; Savage and Cooke, 2004; Stanton and Erslev, 2004] and fold‐related fracturing [Allwardt et al., 2007; Bellahsen et al., 2006a, 2006b; Harris et al., 1960; Johnson et al., 1965; Sanz et al., 2008; Savage et al., 2010]. The largest errors are observed in the Mesozoic section where dips at up‐section and down‐section outcrops differ significantly. The surface mapped in cyan is the oldest ridge‐forming unit in the Gypsum Springs Formation. Also, balanced cross sections assume plane strain deformation, but deformation of complex folds such as SMA has not occurred under plane strain conditions. All slope constraints are applied in all models. Average differences between the two calculated trajectories were 2.5 cm vertical and <1 cm horizontal. We acknowledge that multilayer folding to nearly vertical limb dips is a more complex physical process than the small deflection of a single elastic layer. This unit forms a consistent, identifiable ridge in the backlimb and most of the forelimb of the fold, and is exposed again beyond the syncline northeast of the forelimb. Geologically speaking, Sheep Mountain is an anticline which is a type of folded bedrock that has an arch-like shape with its oldest rocks at its core. [51] The two models clearly differ in the syncline between the thumb and the main fold (point B in Figure 11b, cross section F‐F′ in Figure 13), a feature that is more accentuated in the Forster et al. The principals of and standard processing procedures for ALSM data are described by Shrestha et al. Pink and raspberry beds are mapped consistently south of 4,946,400 m northing, but, similar to the peach unit in the Gypsum Springs Formation, abruptly end to the north (Figure 4a). The length is restricted to the southeast by the Bighorn River, where it cuts a canyon through SMA. The large fold seen in the sedimentary rocks at Sheep Mountain was created by crystalline basement rock uplifted along faults that … [2] Three dimensional surface models of folded geologic strata, often portrayed as structure contour maps, are a fundamental tool for geologists and geophysicists. This artificial, fold‐parallel waviness is prevented in the final surface models by omitting forelimb data points mapped in the Gypsum Springs, above the Chugwater Shale. [2007b], by printing hill shade images generated from the 1 m DEM on a 42 inch plotter at a scale of roughly 4000:1, on which individual outcrops more than 2–3 m across may be identified. We present a new method for modeling the geometry of kilometer‐scale folds using dense, precise topographic data available from airborne laser swath mapping (ALSM), outcrop‐scale geologic mapping, and a reproducible numerical interpolation method that is free of subjectivity. In the Forster et al. The balanced cross section approach is limited in this region because the two folds with nonparallel axial surfaces exhibit deformation that is not plane strain. [18] The Gypsum Springs Formation is overlain by the Sundance Formation; however, a precise boundary between these units is difficult to identify. Geologic setting and fracture data Sheep Mountain Anticline, located on the eastern edge of the Bighorn Basin, Wyoming, is a well known NW–SE trending, asymmetric Laramide fold (Fig. 2. Major lithologic formations are labeled in white. Where ALSM constraint points are not available to enforce the parallel fold model, MCS interpolation need not generate parallel surfaces. Location, geology, and mineralisation The Sheep Mountain uranium project is located in Fremont County, approximately 13km south of Jeffrey City, at the northern edge of the Great Divide Basin in Wyoming, US. [30] We implement a two‐dimensional minimum curvature (biharmonic) spline (MCS) interpolation method [Briggs, 1974; Sandwell, 1987; Wessel and Bercovici, 1998] constrained by ALSM data points and strike and dip measurements. Mechanisms for Deformation of Sedimentary Strata at Sheep Mountain Anticline, Bighorn Basin, Wyoming. After GPS processing, a Kalman filter algorithm, implemented in the Applanix™ software POSProc™, was used to integrate 1 Hz differential GPS data and 200 Hz IMU recordings to produce a smoothed and blended solution for aircraft position and orientation at 200 Hz. However, thickness heterogeneity is of a comparable magnitude to the error bars, so it is not possible to ascertain if the trend is real. Other important sources of data to constrain fold geometry are geological mapping [e.g., Groshong, 2006; Woodward et al., 1989] and well logging [e.g., Serra, 1984]. No significant trend is observed in the Paleozoic section (Figure 6a), but in the Mesozoic section (Figure 7a), subtle thinning to the southeast is suggested by measurements in the backlimb. Here we focus on the contribution of geologic mapping augmented by high‐resolution geospatial data. The method uses data from a flight path perpendicular to the primary flight lines, and optimizes aircraft heading, roll, pitch, and scanner mirror scale to minimize the deviation between flight paths. The 25 m decimation is selected for the optimal model in preference to greater decimation because it maintains sufficient resolution to capture fold details resolvable above noise, and in preference to lesser decimation because it produces a model that is less sensitive to noisy data and because the increased decimation reduces computational time from hours to minutes. [Stevens, E. H.] on Because the DEM consists of a 1 m × 1 m grid, triangles on the interior of any outcrop are, in map view, isosceles right triangles. The surface sedimentary rock formations that are exposed in the fold, range in age from 66-360 million years. google_ad_client = "pub-0036007678883152"; [27] Projection distances are calculated from mean stratigraphic thickness measurements presented in section 4, and supplemented by measurements of Rioux [1994]. The prominent hill to the east is known as Sheep Mountain. In regions of dense data coverage, an MCS surface will capture such zones of greater and lesser curvature in order to honor constraints; however, where data are limited, the MCS method, by definition, creates a broad hinge region in which curvature is distributed to the greatest extent possible. Throughout this region, few outcrops are available to provide ALSM constraint. The yellow mapped unit is underlain by a distinct red shale.