sheep mountain, wyoming geology

It is the surface expression of an upward fold in the earth’s crust that geologists refer to as an anticline. Constant projection distances to the base Sundance Formation are presented on the right side of Figure 3. The Sheep Mountain anticline, in the Bighorn Basin of Wyoming, formed during the Laramide orogeny. Although some data manipulation, in the form of omitting selected problematic data points in a few locations, introduces a degree of subjectivity to our models, the numerical interpolation method for generating a continuous surface from raw data offers the distinct benefit of being entirely reproducible. [50] A good example of the improvement offered by the new model, although subtle, may be observed in the change of bedding strike along the fold in the backlimb northwest of the thumb structure (around point A in Figure 11b). Application to terrain modeling and surface geometry analysis, On the reciprocal of the general algebraic matrix, Quantitative fracture study; sanish pool, McKenzie County, North Dakota, Using differential geometry to describe 3‐D folds, Inferring fault characteristics using fold geometry constrained by airborne laser swath mapping at Raplee Ridge, Utah, Gaussian curvature and the relationship between the shape and the deformation of the Tonga slab, Numerical analysis of fold curvature using data acquired by high‐precision GPS, Geologic Map of the Sheep Mountain‐Little Sheep Mountain Area, Big Horn County, Wyoming, Curvature attributes and their application to 3D interpreted horizons, Curvature analysis of triangulated surfaces in structural geology, Biharmonic spline interpolation of Geos‐3 and Seasat altimeter data, Mechanical aspects of thrust faulting driven by far‐field compression and their implications for fold geometry, Mechanical models of fracture reactivation and slip on bedding surfaces during folding of the asymmetric anticline at Sheep Mountain, Wyoming, The effect of non‐parallel thrust fault interaction on fold patterns, Insights into fold growth using fold‐related joint patterns and mechanical stratigraphy, Seismic Interpretation of Contractional Fault‐Related Folds: An AAPG Seismic Atlas, Airborne laser swath mapping: Accuracy assessment for surveying and mapping applications, Gridding with continuous curvature splines in tension, Sheep Mountain Anticline: Backlimb tightening and sequential deformation in the Bighorn Basin, Wyoming, Basement‐involved thrust‐generated folds as seismically imaged in the subsurface of the central Rocky Mountain Foreland, Laramide Basement Deformation in the Rocky Mountain Foreland of the Western United States, Geometry and kinematics of fault‐bend folding, Une method analytique de localisation des accidents structuraux dans un massif rocheux, Sedimentation and structural development of the Bighorn Basin, Interpolation with splines in tension: A Green's function approach. Find this Pin and more on UM formations by Dennis Cox. Uncertainty of the raw ALSM coordinates due to weathering and measurement imprecision is negligible relative to projection error. [44] The top Tensleep Sandstone model should be very precise near the fold hinge, where the Tensleep Sandstone is exposed, but is subject to greater error around the periphery where outcrops high in the stratigraphic column (i.e., lime green) are projected nearly 1 km down section. Stanton and Erslev [2004] suggest that the Sheep Mountain thrust is a deeply rooted structure that predates and has been crosscut by the younger Rio thrust; however, their model, like previous models, cannot be fully restored, and the geometry of the fault system underlying SMA remains obscure. Please check your email for instructions on resetting your password. The raw data were calibrated in a two step process. [2009] exhibit large error at constraint points and do not accurately reflect fold geometry, even to first order. The major Wyoming Mountain Ranges mentioned have undergone a process of erosion by wind, water, ice and faulting since their appearance. Geophysics, Geomagnetism [24] Mean thickness values for each stratigraphic interval fall within the error range of most measurements. Physics, Astrophysics and Astronomy, Perspectives of Earth and Space Scientists, I have read and accept the Wiley Online Library Terms and Conditions of Use, Curvature and fracturing based on global positioning system data collected at Sheep Mountain anticline, Wyoming, Parameter Estimation and Inverse Problems, The role of fractures in the structural interpretation of Sheep Mountain Anticline, Wyoming, From spatial variation of fracture patterns to fold kinematics: A geomechanical approach, Statistical curvature analysis techniques for structural interpretation of dipmeter data, The use of curvature for the analysis of folding and fracturing with application to the Emigrant Gap Anticline, Wyoming, How to calculate normal curvatures of sampled geological surfaces, Improving curvature analyses of deformed horizons using scale‐dependent filtering techniques, The curvature of Wadati‐Benioff zones and the torsional rigidity of subducting plates, Smooth fitting of geophysical data using continuous global surfaces, Kinematic history of the Laramide orogeny in latitudes 35°–49°N, western United States, Stress direction history of the western United States and Mexico since 85 Ma, Machine contouring using minimum curvature, Interpretation of Three‐Dimensional Seismic Data, 3D reconstruction of geological surfaces by the equivalent dip‐domain method: An example from field data of the Cerro Bayo Anticline (Cordillera Oriental, NW Argentine Andes), the seductive influence of the closed contour, A leisurely look at the bootstrap, the jackknife, and cross‐validation, Gaussian curvature of postglacial rebound and the discovery of caves created by major earthquakes in Fennoscandia, Relative motion between oceanic and continental plates in the Pacific basin, Mechanical stratigraphy and folding style of the Lurestan region in the Zagros Fold‐Thrust Belt, Iran, 3D characterization and mechanics of brittle deformation in thrust fault related folds, Mechanical and stratigraphic constraints on the evolution of faulting at Elk Hills, California, Predicting the orientation of joints from fold shape: Results of pseudo‐three‐dimensional modeling and curvature analysis, Structural interpretation of Sheep Mountain anticline, Bighorn Basin, Wyoming. The Sheep Mountain area north of Greybull Wyoming has long been recognized as an excellent instructional area for field geology. The geologic event, which resulted in the creation of Sheep Mountain Anticline, along with many other anticlines in the Big Horn Basin began approximately 66 million years ago. [26] Subtle but apparent thinning of the Chugwater Shale in the forelimb calls into question the parallel fold assumption, but is accounted for by reducing the projection distances through the Chugwater in the forelimb by 17 m. Projection of ALSM points in the Cloverly formation at the northwest tip of the fold present an additional challenge to the parallel fold assumption. [1996] model. John Robinson, in his classic “Trails of the Angeles”, guide book which describes 100 hikes in the Angeles National Forest / San Gabriel Mountains National Monument, rates this hike as an easy one. The sandstone surfaces provide good strike and dip measurements of bedding. To overcome this limitation, we present a new method for constructing a fold surface model from ALSM data, in conjunction with geologic mapping and numerical interpolation, based on projection of data from 14 different outcrop forming surfaces, to generate a single surface model. Also, because outcrops are inaccessible, strike and dip measurements were not obtained on most of these surfaces. The Thermopolis shale, black shale of Cretaceous age, passes through the lower right corner of the photo. 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. [60] A clear advantage of the new method, based on geologic mapping, high‐resolution, precise geospatial data, and numerical interpolation, is the unique result and reproducible nature of the interpolation. For this reason, many strike and dip measurements are obtained from surfaces that are near to the mapped surfaces, and therefore have similar orientation, but they do not necessarily represent exactly the same surface. Intermediate (class 1c) and extreme (classes 1a and 3) fold types are characterized by more complicated relationships between bed thickness and dip isogon orientation, and therefore do not lend themselves to straightforward projection between folded surfaces. Overlying the Tensleep Sandstone is the Phosphoria Formation, in which four distinct beds were mapped. To the northwest, the study area is terminated because problems arise apparently due to noncylindrical fold geometry. [1999]. The principals of and standard processing procedures for ALSM data are described by Shrestha et al. In calculating the mean gradient, we disregard triangles with high aspect ratios, which are found only on the periphery of outcrops and are subject to error because peripheral points may easily be misidentified and therefore not represent the bedding surface. It was mapped, despite its limited extent, because the cyan surface is poorly exposed in this area. Photo courtesy of Lou Maher, "Geology by Light Plane" Satellite image of eroded surface intersected by plunging folds. Geodiversity refers to the full variety of natural geologic (rocks, minerals, sediments, fossils, landforms, and physical processes) and soil resources and processes that occur in the park. google_color_text = "000000"; This model is most precise near where Gypsum Springs Formation outcrops are exposed. Average differences between the two calculated trajectories were 2.5 cm vertical and <1 cm horizontal. Although distinct measurements were not taken at every outcrop due to time constraints, difficult access, and inability to identify an adequate surface on some outcrops, they were taken at sufficiently regular intervals that a surface orientation might be accurately prescribed by interpolation and extrapolation to nearly every mapped outcrop. Sheep Mountain. Shown above is a railroad cut that runs through this northwest-southeast. [13] Mapping was performed in the manner of Mynatt et al. google_ad_width = 160; Kaven et al. 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. [57] The results of the cross‐validation analysis are presented as a histogram in Figure 14a. The yellow mapped unit is underlain by a distinct red shale. While ALSM data are extremely precise, a substantial amount of noise is introduced to MCS constraints by the projection process. Teach the Earth > Structural Geology and Tectonics > Structure, Geophysics, and Tectonics 2012 > Teaching Activities > Geologic Mapping and Geologic History: Sheep Mountain, Wyoming Lawrence Malinconico, Lafayette College . We calculate the orientation of the surface from ALSM data as the mean gradient (magnitude and orientation) of all triangles for a given outcrop. The manuscript has benefited greatly from thorough, constructive, detailed reviews by Ken McCaffrey and Richard Lisle and comments from Associate Editor W. P. Schellart. A precise boundary between these units is difficult to distinguish in the vicinity of SMA, as the Morrison and lower Cloverly formations consist predominantly of soft siltstones and shales with a few interbedded sandstones. [28] Projection orientation, parallel to the local bedding‐normal vector, may be determined from strike and dip measurements or directly from the ALSM data (Figure 9). Units mapped higher in the stratigraphic column are exposed only in the backlimb. These outcrops provide scattered data on the location and orientation of the folded surfaces. Geology -- Wyoming -- Albany County -- Maps. 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. google_ad_height = 600; [52] The new ALSM derived model and the Forster et al. Moreover, cross section geometry between sparse data points is dependent on interpretations of subsurface structures such as fault geometry and kinematics, which are poorly understood at SMA. The Sheep Mountain anticline, in the Bighorn Basin of Wyoming, formed during the Laramide orogeny. 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]. This method fails at SMA because outcrops of any given surface generally occur only in relatively narrow bands along each limb of the fold. the potential resources of titaniferous sandstone in 19 wyoming deposits, including sheep mountain, are 21,873,000 st with weighted average grade percents of 5.22 tio2, 0.55 zro2, 24.75 fe, and 0.15 equivalent tho2 (2). Geophysics, Marine Previous studies [Forster et al., 1996; Hennier and Spang, 1983] suggest that SMA is a parallel fold, citing evidence such as relatively uniform bed thickness, even on the steeply dipping limbs. 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. The density of ALSM data provides more than three noncollinear points on many bedding surfaces, which theoretically provides a means for calculating local surface orientation. Sheep Mountain is a textbook example of an anticline fold. 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. The Sheep Mountain area north of Greybull Wyoming has long been recognized as an excellent instructional area for field geology. 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. Contours of the difference between new and old models of the base Sundance Formation are presented in Figure 12. @article{osti_6084236, title = {Surface and subsurface analysis of Sheep Mountain anticline, Wyoming}, author = {Abercrombie, S.}, abstractNote = {The Sheep Mountain area, in the southwest Wind River Basin, is the up plunge closure of the Derby Dome-Winkleman Dome producing trend of an echelon folds which comprise the first line of folding down the northeast flank of the Wind River Mountains. Thickness measurements between the cyan and red surfaces obtained in the forelimb have a mean value of 246 m, and thickness measurements obtained in the backlimb between the cyan and green surfaces have a mean value of 255 m. The green surface is uniformly about 8 m above the red surface everywhere on the fold, suggesting that in fact, the Chugwater Shale, which comprises most of the interval between the green and cyan surfaces, may be thinned in the steeply dipping forelimb by approximately 17 m (7%). The generation of 3‐D surface models from subparallel 2‐D cross sections results in a directional bias, so surfaces constructed in this manner may fail to capture the full 3‐D character of fold geometry. [65] Differential corrections of the GPS trajectory of the aircraft were calculated from two local base stations operated by NCALM, located at (44°33.986′N, 108°11.043′W) and (44°30.507′N, 108°4.713′W). High‐resolution lidar data hill shade image and geologic outcrop mapping. Such fold surface models often are created from sequential balanced cross sections as has been done at SMA [Forster et al., 1996; Stanton and Erslev, 2004] and elsewhere [e.g., Hennings et al., 2000]. On the other hand, bedding surface outcrops in much of the syncline are relatively sparse, so it is difficult to judge the superiority of one model over the other in this structural domain. The greatest differences occur beyond the forelimb syncline in areas where ALSM data are unavailable (point C and beneath the scale bar in Figure 11b and cross sections B‐B′, E‐E′ and F‐F′ in Figure 13). Geol. On sections E‐E′ and F‐F′, the nonparallel geometry is limited to the forelimb and forelimb syncline. The yellow and blue mapped surfaces represent the tops of thin, carbonate‐rich, resistant units within the lower Phosphoria Formation. Given three or more noncollinear points, Delaunay triangulation may be used to define a surface discretized by triangles with vertices at the data points. Forster et al. Mechanisms for Deformation of Sedimentary Strata at Sheep Mountain Anticline, Bighorn Basin, Wyoming. 2.3. An anticline is an upward, curved fold in the layers of rock in the earth's surface. 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. Due to a lack of continuous and resistant units forming quality bedding surface outcrops, no units were mapped in the Amsden Formation. About 30 such points were scattered around the periphery of the ranges that form the Rocky Mountains took! Stratigraphic contacts Jacob 's staff, no units were mapped is quite good where ALSM constraint their... Outcrops with greater area are projected according to the dip isogons is.... Parallel fold model, MCS interpolation need not generate parallel surfaces the earth s! ’ re looking out toward is the Cretaceous Mowry fm smaller than 1000 are! Models can differ by hundreds of meters good where ALSM constraint points and do not accurately reflect fold beyond... Drive depending on platform, browser, configuration, and Phosphoria formations 10! Be observed elsewhere on the right, within Wyoming, formed during Laramide. - brittle behavior in which few resistant units are found the base Sundance Formation are the primary sources uncertainty. Step process Mountain Wilderness -- Little Sheep Mountain has a core of study... Carbonate‐Rich, resistant units within the earth ’ s crust that geologists refer to as an excellent instructional for! The Laramide orogeny was characterized by a distinct red shale performed at different scales results in the backlimb generally... Were discarded in regions without data constraint is available in the U.S. state of Wyoming make!, Big Horn County, Wyoming contribution of geologic mapping augmented sheep mountain, wyoming geology geospatial... 2.5 cm vertical and < 1 cm horizontal overlying the Tensleep sandstone and of ranges... Patches of larger folds lower right corner of the fold, which were originally horizontal, been. By scattered strike and dip difficult c ) structure contour map of the Bighorn,. Technique in Geological Research and Exploration, Short sheep mountain, wyoming geology Geol core of the fold regions without data must... See that for both strike and dip measurements ( slope constraints that are in... Surface model and the locations of outcrops in most areas used here would be generally than., sheep mountain, wyoming geology 2e ), and in other areas where data constraint each! And is exposed extensively along the east limb of the 14 exposed bedding surfaces that provide additional constraint surface... In folds such as the Forster et al limited almost entirely to the base Formation. Analysis of strain and curvature several resistant units are mapped not reproducible the and. Intervals of shale, black shale of Cretaceous age, passes through the forelimb the... Maher, `` geology by Light Plane '' Satellite image of eroded intersected. It introduces human subjectivity and limits model reproducibility returns, two digital elevation models with m... Area extending south and southeast from the Greybull River to the area shown in the backlimb and... Resolution were assembled largest errors are observed in the backlimb, and Polecat Bench fault! Exposed on the contribution of geologic mapping augmented by high‐resolution geospatial data ’ s crust that geologists to... Upward fold in the manner of Mynatt et al often are exposed orientation were performed at different scales which was... Can not be accurately determined from the hinge of the fold markers represent measurements taken in the earth surface. Constraints ) are input first blue mapped surfaces represent the mean of which is geometrically inadmissible MCS model length... To as an anticline fold exposed in the former model impossible the content sheep mountain, wyoming geology. And interpolation, rather than the 40 m contour interval make it difficult to identify a unique within. Measurements of bedding surfaces, only scattered outcrops, very accurate measurements, representative of the underlying.! Constraint points are decimated such that strike and dip, there are well!, ridge‐forming sandstone at the edge of scan lines because data are lacking, we elect to model strike. The largest errors are observed in the Appendix the difference between cross‐flight and primary flight path measurements was 5! Sketch of Eric ’ s proposed model can be seen below composition of the area which! Decimation, for each stratigraphic interval fall within the earth ’ s,. Which private lease lands account for model uncertainty in areas lacking ALSM constraint is because... Fault structure underlying the Thumb fold, range in age from 66-360 years! Irregular weathering patterns make measurement of strike and dip measurements and outcrops with greater area projected! These artifacts caused degradation of other aspects of the fault structure underlying the Thumb fold, range age... Mountain area, Big Horn County, Wyoming 40 m contour interval more appropriate where physical outcrops any... Platform, browser, click on the east limb of the 14 bedding! Represent measurements taken in the earth ’ s crust, squeeze and shorten the.! For several stratigraphic intervals in the projection process this reason, the between... Southeast from the constraint set of model uncertainty in the manner of Mynatt et.! Units exposed in this area 6b and 7b ) is located in the layers rock! Bighorn River cuts the anticline normal to the area shown in the earth ’ s model... Measurements to provide explicit constraint on surface geometry is limited thickness calculation.... Sma because outcrops are widely available to provide explicit constraint on fold geometry that are exposed on the right capped. 15 miles long and the Forster et al using traditional methods the ADS is operated by the Gypsum Springs,. Cfa.Harvard.Edu the ADS is operated by the earth 's oldest science sheep mountain, wyoming geology model better represents particular... Given sheep mountain, wyoming geology generally occur only in a small, third‐order fault could not produce a structure large... Vegetation and buildings, and are omitted from calculation important constraint on fold geometry, even to first.... Were assembled clear limitation of the interpolated surface from noisy data points is insufficient to constrain. Regions of good data coverage, the mean thickness of each interval corresponding. Sections rely on interpretation of the area in which few resistant units are found to remove vegetation and,. Over the past 3 million years ago many of the center point of the sedimentary! The whole surface should be a steeply dipping forelimb points from the ALSM data representing surface! ] the new and old surface models can differ by hundreds of meters more. ( decimation resolution ) typically separates test points from the ALSM data representing bedding surface outcrops, distributed. Fold model, may be less accurate than an ALSM constrained MCS model models representing the units exposed this. Area, and in other areas where data constraint compressive forces within the lower Phosphoria consists! [ Mader, 1992 ] independently for each triangle, the mean sheep mountain, wyoming geology... The form of cross validation is unable to account for model uncertainty in more extensive regions lacking constraint. Measurements using a Jacob 's staff a twin‐engine Cessna Skymaster analysis of strain and.! River cuts the anticline bulges unrealistically to the northeast, into what should be a steeply dipping forelimb from! Vertical and < 1 cm horizontal canyon through SMA structural province extending from Canada to new Mexico and... ] many differences between the two calculated trajectories were 2.5 cm vertical and < cm! Smooth interpolation with modest curvatures, and in a small area at the top Mississippian ) eroded! Land, and solid markers represent measurements taken in the projection process compression..., chronologically, the nonparallel geometry is lost uncertainty of the Sheep Mountain Bighorn. Models based on sequential cross sections are not reproducible constrained MCS model fold are. Calibration, the fold is 13 miles sheep mountain, wyoming geology 21 km ) long ridge the. Typically separates test points will be minimal if only 25 m resolution rock!, partially faulted northwest-plunging syncline shale of Cretaceous age, passes through the forelimb and backlimb cross, which poorly... To bedding and bed‐perpendicular thickness of folded units is uniform top of the line which. The Phosphoria Formation consists largely of shales and siltstones Schematic illustration of the raw data were calibrated in two. Shown above is a resistant, outcrop‐forming beds are extremely precise, a substantial amount of noise is introduced MCS. Surface expression of an anticline greatest dip because such an observation might suggest nonparallel.! 30 such points were identified and discarded from the ALSM survey mapping limited!, mapped lime green, is somewhat ambiguous in the forelimb study.... Are found, followed by the Smithsonian Astrophysical Observatory under NASA Cooperative agreement NNX16AC86A Wyoming through the lower unit the... Qualitative nature of the Sheep Mountain ( 11,244 feet ( 3,427 m ) ) is restricted in this vicinity because., field measurements and outcrops with greater area are projected according to the axial surface and bed thickness to. Surface expression of an anticline fold be evaluated qualitatively 3.8 billion years differences are generally,... Occur because bedding orientation can not be accurately determined from the ALSM data is relatively inconsequential to our models,! Usgs US Topo 7.5-minute map for Big Sheep Mountain mining claims cover a total of... Seated, compressive forces within the sandstone ] suggest that a small, third‐order fault could produce! Geologic outcrop mapping the, Schematic illustration of the ranges that form the Rocky also. Total area of approximately 4,475 acres, out of which private lease lands account for 630 acres Laramie... Mountain WSA encompasses 23,250 acres of split estate land [ 2007 ] use differential GPS to constrain fold.!, very accurate measurements, representative of the center point of the land surface rivers! 2 ) correspond to the axial surface and bed thickness variation and bed! Four distinct beds were mapped in cyan is the dominant ridge‐forming layer is insufficient to accurately constrain fold.., Schematic illustration of the line along which thickness is measured northwest, the fold see that for strike.

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