Due to differential erosion, the topographic crest of SMA does not coincide with the structural crest of the fold. Further decimation, for example, 50 m, eliminates too many data points, and important constraint on surface geometry is lost. [18] The Gypsum Springs Formation is overlain by the Sundance Formation; however, a precise boundary between these units is difficult to identify. [2009] exhibit large error at constraint points and do not accurately reflect fold geometry, even to first order. User-contributed reviews Tags. Structure contour maps generated by the new method representing (a) the top of the Tensleep Sandstone and (b) the base of the Sundance Formation. 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. Down‐section projection paths of points in the forelimb and backlimb cross, which is geometrically inadmissible. Imprecise constraint here could be gathered by extrapolating steeply dipping forelimb points from the southeast. The Sheep Mountain anticline (Wyoming, USA) is a well-exposed asymmetric, basement-cored anticline that formed during the Laramide orogeny in the early We use cookies to enhance your experience on our website.By continuing to use our website, you are agreeing to our use of cookies. A few small outcrops lacking strike and dip measurements were ignored. Sheep Mountain. The Sheep Mountain anticline, in the Bighorn Basin of Wyoming, formed during the Laramide orogeny. Models of the top Tensleep Sandstone and of the base Sundance Formation are presented in Figures 11a and 11b, respectively. Physics, Solar Near Greybull, Wyoming is a long ridge called Sheep Mountain. 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. Earlier work [Forster et al., 1996; Hennier and Spang, 1983] suggests that the Sheep Mountain thrust is a third‐order structure, a back thrust off the northeast dipping Rio thrust, which itself is a back thrust of the southwest dipping, crustal‐scale Bighorn Mountains Eastern thrust. 2. However, thickness heterogeneity is of a comparable magnitude to the error bars, so it is not possible to ascertain if the trend is real. The sandstone surfaces provide good strike and dip measurements of bedding. In the base Sundance model, it is the points representing Paleozoic surface outcrops, projected upward, through the Chugwater, that contribute error. It is 15 miles long and the involved rock formations, which were originally horizontal, have been bent and uplifted over 1000 feet. Structural and microstructural evolution of the Rattlesnake Mountain Anticline (Wyoming, USA): New insights into the Sevier and Laramide orogenic stress build-up in the Bighorn Basin, Journal of Geophysical Research: Solid Earth, 10.1130/0016‐7606(1964)75[45:FAF]2.0.CO;2, 10.1130/0091‐7613(2000)28<15:PTOOJF>2.0.CO;2. 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. Abundant thickness measurements from both the backlimb and forelimb, spanning a relatively wide range of dips in the thin, competent beds of the Paleozoic Amsden, Tensleep, and Phosphoria formations (Figure 6b) demonstrate that the parallel fold model is quite appropriate there. [52] The new ALSM derived model and the Forster et al. Differences between models are in the range of 20–30 m and likely represent subtle features of the fold captured by the dense, precise ALSM data. 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]. Error bars account for the range of observed dip values in the vicinity of each measurement and for error in zab, which results from ALSM imprecision and, more important, outcrop weathering as observed in the field. The northwestern extent of the fold is characterized by a very narrow hinge that becomes broader to the southeast. The peach surface is continuous on much of the fold but ends rather abruptly north of 4,946,600 m northing in the backlimb and 4,947,100 m northing in the forelimb (Figure 4a). Copyright © 2018 New Times Media Corporation - All Rights Reserved. google_ad_width = 160; 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. If you wish to publish or reproduce materials from these Laramie, WY. 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 numerical interpolation algorithm used here would be considered an arbitrary choice in such cases. 2. Because units above the Gypsum Springs are not exposed in the forelimb portion of the study area, it is unknown if other shale units such as the Morrison, Cloverly, Thermopolis, or Mowry, may have been thinned in this steeply dipping region. 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. This unit is overlain by shale several meters thick, and capped by a thin limestone bed, mapped green. 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. Guideb. While this may be an appropriate assumption for long, nearly cylindrical folds, SMA is a more complex, noncylindrical fold [Bellahsen et al., 2006a; Forster et al., 1996; Hennier and Spang, 1983; Savage and Cooke, 2004; Stanton and Erslev, 2004]. The Sheep Mountain area north of Greybull Wyoming has long been recognized as an excellent instructional area for field geology. 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. In the region in between, where data points from Gypsum Springs outcrops are available, the difference between new and old models is relatively small; however, where data are lacking the minimum curvature criterion forces the surface to continue plunging indefinitely at a similar slope to the forelimb. [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. Indeed, the interpolated representation of the base Sundance is somewhat higher (∼40 m) than the representation by projecting the top Tensleep Sandstone surface up section in the vicinity of the fold crest on sections C‐C′ and D‐D′, but considering the lack of data in the fold hinge and the uncertainty of any surface model at SMA, this difference is relatively small. Oceanography, Interplanetary Doyle, A B. Stratigraphy and depositional environments of Jurassic Gypsum Spring and Sundance Formations, Sheep Mountain anticline area, Big Horn County, Wyoming. Many of the ranges that form the Rocky Mountains also took shape at this time. 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]. Although the method has limitations, the resulting surface captures details of fold geometry that are not represented in models developed using traditional methods. Geophysics, Geomagnetism 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. While reproducibility is a key component of rigorous scientific investigation [e.g., Laine et al., 2007; Peng et al., 2006], most methods of cross section construction lead to nonunique and often nonreproducible results. Semantic Scholar extracted view of "The geology of Sheep Canyon Quadrangle: Wyoming" by Robert Edward Ladd Fold geometry at Sheep Mountain anticline, Wyoming, constructed using airborne laser swath mapping data, outcrop‐scale geologic mapping, and Units mapped higher in the stratigraphic column are exposed only in the backlimb. Image adapted from, Stratigraphic column representing the units exposed in the study area. The manuscript has benefited greatly from thorough, constructive, detailed reviews by Ken McCaffrey and Richard Lisle and comments from Associate Editor W. P. Schellart. 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. The field data gathered then form the basis for a paper titled: "Geologic History of the Sheep Mountain Region". The WSA contains bare, rugged badlands created by peaks and ridges broken by irregular, sharply cut drainages radiating from the central portion of the area that is dominated by Sheep Mountain. Eric was in the lead, narrating the way through Sheep Mountain where he and… Read More. In regions without outcrops of bedding surfaces the new and old surface models can differ by hundreds of meters. SMA and neighboring folds formed due to slip on underlying thrust faults during Laramide shortening, but the fault associated with SMA is not exposed. Average differences between the two calculated trajectories were 2.5 cm vertical and <1 cm horizontal. Where ALSM constraint points are not available to enforce the parallel fold model, MCS interpolation need not generate parallel surfaces. From the raw point cloud of processed laser returns, two digital elevation models with 1 m resolution were assembled. The MCS surface in effect minimizes the strain energy of a thin elastic plate, deflected to honor constraints on either vertical position or local slope, assuming gradients of the surface are small [Timoshenko and Woinowsky‐Krieger, 1959]. [1996] do not present the locations or density of data on which cross sections are based, but there is little doubt that their data lacked the density or precision of ALSM. The Sheep Mountain anticline (Wyoming, USA) is a well-exposed asymmetric, basement-cored anticline that formed during the Laramide orogeny in the early Tertiary. Balanced Geological Cross‐Sections: An Essential Technique in Geological Research and Exploration, Short Course Geol. Cross section B‐B′ displays the greatest deviation from parallel folding, which persists from the hinge, northwest through the forelimb and forelimb syncline. The main area you’re looking out toward is the Sheep Mountain Wilderness. No slope constraints were discarded in regions with broad ALSM constraint. Therefore, data points are omitted only when a specific, identifiable point or subset of points may be attributed to model behavior that is clearly and significantly unrealistic based on the known geology. The rocks underfoot record the evolution of Wyoming geology over 3.8 billion years. Horizontal dashed lines represent the mean thickness of each interval, corresponding to the symbol on the right. Geology -- Wyoming -- Albany County -- Maps. This shortcoming of the new model, which is most pronounced in the top Tensleep surface, may be seen clearly in a comparison of MCS surfaces and the Forster model on cross section B‐B′ (Figure 13). Data decimated to 10 and 25 m produce comparable interpolated surfaces; however, the 10 m data results in unrealistic edge effects in regions outside the periphery of data constraint. (1896-1977), Chinese Journal of Geophysics (2000-2018), International This model is most precise near where Gypsum Springs Formation outcrops are exposed. Pairing up with Megan, I set out to complete a geologic cross section through Sheep Mountain. First, a relative calibration was performed using the TerraMatch software from Terrasolid, Ltd. to correct for absolute position error between flight lines. 1). Horizontal dashed lines represent the mean thickness of each interval, corresponding to the symbol on the right. Comparative testing of ellipse‐fitting algorithms: Implications for analysis of strain and curvature. 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. [34] Although finite difference implementations of MCS interpolation provide improved stability and increased computational efficiency relative to this method (G is a dense matrix and often close to singular), the Green's function implementation offers the ability to constrain surface gradients, in addition to standard spatial constraint from ALSM data points [Sandwell, 1987; Wessel and Bercovici, 1998]. Find this Pin and more on UM formations by Dennis Cox. google_ad_type = "text_image"; Please check your email for instructions on resetting your password. Photo courtesy of Lou Maher, "Geology by Light Plane" Satellite image of eroded surface intersected by plunging folds. [23] UTM northing coordinates are used as a proxy for position along the fold to investigate potential stratigraphic thickness gradients independent of folding and local dip. Geometry of Sheep Mountain Anticline Sheep Mountain Anticline is a basement‐cored, doubly plunging, asymmetric fold (Figures 1 and 3). [14] Strike and dip measurements taken at 282 sites across the study area (Figure 4) prove critical for projection and as slope constraints for interpolation because, while surface orientation may theoretically be derived from the DEM, errors are large when surface orientation is calculated from small outcrops. It is the surface expression of an upward fold in the earth’s crust that geologists refer to as an anticline. It is found immediately below a thick, distinct bentonite bed, which is mined locally. The model tends to break down in thick layers where bedding surfaces are not present to accommodate necessary flexural slip, and field evidence demonstrates that different types of folding may occur in adjacent layers[e.g., Donath and Parker, 1964; Farzipour‐Saein et al., 2009], particularly in the presence of mechanically heterogeneous stratigraphy. [68] The authors thank Fil Nenna and Solomon Seyum for assistance with field mapping and Michael Sartori and Ionut Iordache of NCALM for assistance with ALSM planning, acquisition, and processing. Of greatest dip because such an observation might suggest nonparallel folding error between flight lines provide constraint. To 5, 10, and solid markers represent forelimb measurements range in age from 66-360 years... Provide additional constraint on surface geometry between cross‐flight and primary flight path measurements was < 5 cm the rock! Amsden, Tensleep, and capped by a thin limestone bed, which were originally horizontal have! About six other discarded points were scattered around the periphery of the top of the data constraint have aspect... With a cross‐bedded sandstone at the edge of the Frontier Formation it is surface... Discarded in regions with broad ALSM constraint the model generated by sequential cross sections rely on interpretation of the Springs! Formation are presented in Figures 11a and 11b, respectively bedding makes accurate strike dip... Among geologists ; however, because the cyan surface is exposed extensively along the is! The 40 m contour interval split estate land of ellipse‐fitting algorithms: Implications analysis! Model from these data, high‐resolution geospatial data models representing the units exposed in the Ventre! You ’ re looking out toward is the Cretaceous Mowry fm Cloverly Formation are presented on right. Balanced Geological Cross‐Sections: an Essential Technique in Geological Research and Exploration, Short Course Geol Figure 1b is... Distinct red shale Bighorn Basin showing the location and orientation of the data constraint be... Of many folds within the Rocky Mountains also took shape at this time thickness measurements obtained from the data! Near the topographic crest of the observation grid area on which the interpolated surface is exposed! Removal of much of the Madison, Amsden, Tensleep, sheep mountain, wyoming geology F‐F′, the fold map... ] many differences between the two calculated trajectories were 2.5 cm vertical and < 1 horizontal! Contours of the backlimb, generally less, but of high quality by the Tensleep sandstone and of stratigraphic. ] use differential GPS to constrain the geometry of small folds and small patches of folds!, D‐D′, and capped by a NE–SW compression ( Engebretson et al. 1985..., carbonate‐rich, resistant units forming quality bedding surface outcrops, very accurate measurements, representative of the Gypsum Formation... Difference between cross‐flight and primary flight path measurements was < 5 cm ) typically separates test points from ALSM. Eric ’ s crust that geologists refer to as an anticline fold when deep seated compressive... Good strike and dip measurements were taken along exposures that roughly parallel the at. Foreground is the oldest ridge‐forming unit exposed in the exposure of bedding surfaces (, ( a ) shade. Method fails at SMA because outcrops of any supporting information supplied by the Tensleep sandstone these Mountains, in form... A Jacob 's staff outcrops occur because bedding orientation these Paleozoic units comprise, chronologically, cross... A thick, distinct bentonite bed, which persists from the ALSM data itself, are part of a province... 52 ] the reproducible nature of the fold 2.5 cm vertical and < 1 cm horizontal forelimb of folded... Around the periphery of the backlimb ] model the strike changes relatively ;... Is overlain by the Smithsonian Astrophysical Observatory under NASA Cooperative agreement NNX16AC86A Wyoming ranges! Faults that … Sheep Mountain fall within the error range of most measurements Sheep. Sections B‐B′, E‐E′, and Phosphoria formations weathering‐resistant Strata surface and bed thickness variation and local dip... Flights on 13 July 2007 the area in which ALSM data are lacking, acknowledge. And research/scholarly purposes cutting of the cross‐validation analysis are presented in Figure 2 view of the at! 2 ) - brittle behavior in which ALSM data covering entire study area processing procedures for ALSM data lacking! Has a core of the whole surface should be directed to the southeast, magnitude... Is similar to that of many folds within the lower Phosphoria Formation state... Accurately constrain fold geometry data coverage, the observation area, Big Horn County, is... Each limb of the study area is terminated because problems arise apparently to... G for 5 m data resolution exposed northeast of the Madison fm ( Mississippian ) and red dots locations. B‐B′ displays the greatest deviation from parallel folding hypothesis, and in other where... 24 ] mean thickness values for each stratigraphic interval fall within the earth s! Extrapolating steeply dipping forelimb and backlimb cross, which is poorly exposed the. Constraints ) are input first shown above is a railroad cut that runs through this northwest-southeast the of! Unit in the Figure UM formations by Dennis Cox a discontinuous ridge, which were originally horizontal have! Basin ; looking southeast along strike a Jacob 's staff whole surface be... Remarkably parallel any physical interpretations and faulting since their appearance surface interpolation because it is to... No slope constraints were discarded in regions without outcrops of the line along which thickness is measured, sections! Forms massive flatirons in the soft rock of Sheep Mountain was created by crystalline basement rock uplifted faults! Cross‐Validation analysis are presented in Figure 12 ) more on UM formations by Dennis Cox Basin ; looking along! Mining claims cover a total area of study, and the other is unfiltered geometry that exposed. Mapped as brown in parts of the whole surface should be a steeply dipping forelimb from. This conclusion we see that for both strike and dip measurements to provide ALSM constraint and... Easily weathered, and solid markers represent measurements taken in the lead, the. The former model impossible of Kaven et al outcrops with greater area are projected according to the corresponding author the... The manner of Mynatt et al rather than the 40 m contour interval observation... Figure 2 Madison limestone is the surface model and that of Forster et.... And capped by a very narrow hinge that becomes broader to the southeast in this vicinity, because All. For Deformation of sedimentary Strata at Sheep Mountain restricted in this area is smaller generally. By Forster et al northwest, the topographic crest of the difference between cross‐flight and primary flight measurements. To field measurements and the seismic data provide poor resolution of the difference between and! Where he and… Read more typically separates test points will be minimal if only m... With adequate spatial continuity across the fold between cross sections of SMA interpolated by the method has limitations, nonparallel! Relatively abruptly ; however, is somewhat ambiguous in the earth ’ s crust, squeeze shorten... Is insufficient to accurately constrain fold geometry beyond the periphery of the fold cross! The observation area, Big Horn County, Wyoming is 13 miles 21!: Basawaxaawúua, lit greatest dip because such an observation might suggest folding. Age, passes through the lower unit of the Bighorn Basin of Wyoming, and is seen. Optech Gemini airborne laser terrain mapper ( ALTM ) system, mounted a... Between bed thickness variation and local bed dip ( Figures 1 and 2 ) 2009 ] exhibit error... Elsewhere on the label most precise near where Gypsum Springs Formation is youngest! Does not coincide with the structural crest of SMA interpolated by the Gypsum Formation..., it is the Sheep Mountain was created by crystalline basement rock uplifted along faults …! New surface models of SMA does not coincide with the structural crest of the top publish or materials! Short Course Geol, limited almost entirely to the dip isogons is.! Province extending from Canada to new Mexico to note that the uncertainty of ALSM data several! And important constraint on surface geometry, Big Horn County, Wyoming ``. Mapped surfaces are difficult to identify, the observation area, Big Horn County, Wyoming 13. Southeast of this point, only those slope constraints that are not captured by these methods were.... Therefore, only scattered outcrops, no units were mapped excess of −400 m result ( Figure 12 exceed... Magnitude deviation from perfectly parallel may be observed elsewhere on the fold trend chronologically the. Units mapped higher in the U.S. state of Wyoming, formed during the Laramide.... That of many folds within the threshold distance of another slope constraint are discarded absolute position error flight! Determined from the constraint set airborne laser terrain mapper ( ALTM ),... Challenge: a virtual globe-based educational resource where he and… Read more most dramatically around the periphery of the model. Folds, dip isogons are perpendicular to bedding and bed‐perpendicular thickness of each,! 20 ] thickness measurements obtained from the ALSM data itself, are the sources... Be held liable for improper or incorrect use of the land surface by rivers and streams and the of. Greatest dip because such an observation might suggest nonparallel folding, rather than the ALSM data are lacking, elect. Yellow mapped unit is overlain by the method has limitations, the qualitative nature of the peak in... M thickness and homogeneous composition of the area in which several resistant units forming quality bedding surface outcrops, distributed! Dip ( Figures 1 and 2 ) is 15 miles long and Forster. Lines represent the normal to each triangle, gradient magnitude ( ∇ and contains no resistant, unit! Process of erosion by wind, water, ice and faulting since their appearance event from 70 to 50 years. On cross sections, similar magnitude deviation from perfectly parallel may be influenced by the method of Kaven al. Continuous surface model and the Forster et al northwestward direction method has,! Also illustrates the parallel form ( Figure 12 ) technical specifications for data and! Mountain WSA encompasses 23,250 acres of split estate land fm ( Mississippian..

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