[18] The Gypsum Springs Formation is overlain by the Sundance Formation; however, a precise boundary between these units is difficult to identify. These data, supplemented by several hundred strike and dip measurements constraining local orientation of folded strata, are projected to the stratigraphic position of a single surface and used as constraint for a smoothed minimum curvature spline interpolation to generate a continuous representation of fold geometry. Also, the cross sections rely on interpretation of the fault structure underlying the Thumb fold, which is poorly understood. (c) Structure contour map of the base Sundance Formation from, Cross sections of SMA along transects identified in. [59] The moderate uncertainty values presented by the cross validation analysis and applicable to areas of SMA where dense ALSM constraint is available should be considered an improvement over the Forster model. The highway was nicknamed “Sweet 16” because it presents the modern traveler with a scenic and safe route across this 90 mile long and 30 mile wide mountain range. White vectors represent the normal to each triangle, the mean of which is taken to represent local bedding orientation. Journal of Advances Thickness there should be equal to the stratigraphic thickness (366 m, Figure 3), but comparison of contours in Figure 11 suggests thickness in excess of 400 m. Isopach contours representing the thickness between modeled surfaces are difficult to comprehend due to steeply dipping strata across much of the fold, so we use cross sections of the fold (Figure 13) to evaluate whether we successfully interpolate two parallel surfaces. It is particularly interesting that there is no trend toward thinning in regions of greatest dip because such an observation might suggest nonparallel folding. [13] Mapping was performed in the manner of Mynatt et al. Models of folded surfaces are necessary input for curvature analysis, which has been used to describe folded surfaces geometrically [Bengtson, 1981; Bergbauer and Pollard, 2003; Bergbauer et al., 2003; Lisle, 1992; Lisle and Robinson, 1995; Lisle and Martinez, 2005; Mynatt et al., 2007a; Pearce et al., 2006; Roberts, 2001], and as a proxy for strain [Bevis, 1986; Ekman, 1988; Lisle, 1994, 1999; Nothard et al., 1996; Samson and Mallet, 1997; Wynn and Stewart, 2005] and for fracture density and orientation [Allwardt et al., 2007; Bergbauer, 2002; Fischer and Wilkerson, 2000; Hennings et al., 2000; Lisle, 1994; Murray, 1968; Thomas et al., 1974]. google_color_border = "FFFFFF"; Black letters show the locations of outcrops in Figures 2b–2e. Major lithologic formations are labeled in white. If you wish to publish or reproduce materials from these collections, please attribute each item to University of Wyoming. Sheep Mountain The Sheep Mountain Anticline is situated between the towns of Lovell and Greybull in the northwest part of Wyoming; its long, narrow, and perfectly straight crest is an easily recognizable sight from many areas around the Big Horn Basin. This mountain range pushed through ancient western sea beds to tower above the landscape. Surface models of SMA interpolated by the method of Kaven et al. [1996] model differ most dramatically around the periphery of the observation area, and in other areas where data constraint is limited. This study focuses only on that part of SMA northwest of Sheep Canyon (Figure 1) because outcrop quality is poor to the southeast. User-contributed reviews Tags. These mountains, in turn, are part of a structural province extending from Canada to New Mexico. Much of the difference between models in areas of dense data coverage may be attributed to increased resolution and accuracy of the ALSM constrained MCS method. Outcrops are sparse, but generally good quality, occurring along the hinge of the fold. 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. Filtered and unfiltered digital elevation models with 1 m pixel resolution were generated from the raw point cloud with a kriging algorithm in Surfer® Version 8.04, from Golden Software, Inc. Kriging was performed using a linear variogram with a nugget variance of 0.07 m, microvariance of 0.00 m, search radius of 40 m, minimum points per quadrant of 5, and maximum points per quadrant of 10. Histograms show the distribution of model misfit, represented by RMS error, for (a) leave‐one‐out (outcrop‐by‐outcrop) cross validation of the interpolated surface and (b) the smoothed (truncated SVD) interpolation using the complete decimated data set, also on an outcrop‐by‐outcrop basis. Even if the specific data points used by Forster et al. [11] An ALSM survey at SMA, covering approximately 86 km2, was flown by the National Center for Airborne Laser Mapping (NCALM) in July 2007. It is the surface expression of an upward fold in the earth’s crust that geologists refer to as an anticline. The Sheep Mountain mining claims cover a total area of approximately 4,475 acres, out of which private lease lands account for 630 acres. [29] The difference between bed orientation as measured with a Brunton compass in the field, and as calculated from the ALSM data, is plotted versus outcrop size in Figure 10. In the Forster et al. Auxiliary material for this article contains a high‐resolution version of Figure 4a. Omitting points from the training set one outcrop at a time reduces this bias; however, cross validation results likely remain optimistically biased because outcrops tend to be clustered. Learn about our remote access options, Department of Geological and Environmental Science, Stanford University, Stanford, California, USA, Department of Geology and Geophysics, University of Minnesota‐Twin Cities, Minneapolis, Minnesota, USA. To the northwest, the study area is terminated because problems arise apparently due to noncylindrical fold geometry. Contours of the difference between new and old models of the base Sundance Formation are presented in Figure 12. Down‐plunge view (6° plunge at N34°W) of the fold on cross section A‐A′ (, Triangulated surfaces are generated from ALSM points representing each outcrop to calculate local surface orientation. Because many outcrops are represented by multiple data points (up to 51) in the decimated data set, a cross validation scheme in which only some points representing a given outcrop were omitted from the training data set would result in an optimistic bias in uncertainty estimates. adshelp[at]cfa.harvard.edu The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative Agreement NNX16AC86A Comparison of these two representations of the base Sundance Formation enables a qualitative evaluation of how parallel the fold profile is between the two modeled surfaces; if the fold were perfectly parallel, the two surface representations should be identical. NCALM researchers have verified these accuracy specifications in a study which suggests that RMS error of elevation measurements by ALSM is only 6–10 cm [Shrestha et al., 1999]. 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