Of the 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.  The Phosphoria Formation is the youngest unit in the Paleozoic section, and the youngest unit on the prominent topographic expression of the fold. 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. The studied outcrop is Sheep Mountain, an asymmetric basement cored anticline corresponding to a typical Laramide arch of the Bighorn Basin (Wyoming, USA).  model the strike changes relatively abruptly; however, in the new model this change is gradual. The surface sedimentary rock formations that are exposed in the fold, range in age from 66-360 million years. Mechanisms for Deformation of Sedimentary Strata at Sheep Mountain Anticline, Bighorn Basin, Wyoming. These mountains, in turn, are part of a structural province extending from Canada to New Mexico. The base Sundance Formation stratigraphic contact, however, is somewhat ambiguous in the field. 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 [ … The surface mapped in cyan is the oldest ridge‐forming unit in the Gypsum Springs Formation. The Sheep Mountain area north of Greybull Wyoming has long been recognized as an excellent instructional area for field geology. The prominent hill to the east is known as Sheep Mountain.  Bedding surface outcrops corresponding to 14 different weathering resistant stratigraphic surfaces were mapped on the ALSM data in order to obtain their precise 3‐D geospatial locations (Figures 3 and 4). Collection. The field data gathered then form the basis for a paper titled: "Geologic History of the Sheep Mountain Region". To the northwest, the study area is terminated because problems arise apparently due to noncylindrical fold geometry. 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. 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]. 10 miles north of Greybull on WY-310. google_ad_height = 600; Physics, Comets and In the base Sundance model, it is the points representing Paleozoic surface outcrops, projected upward, through the Chugwater, that contribute error. Kaven et al. Barren or sparsely covered rock outcrops and magnificently developed folds and faults are characteristics of the northeastern Bighorn Basin that have made this corner of Wyoming a favorite study area for uni Find this Pin and more on UM formations by Dennis Cox. In regions of good data coverage, the difference is smaller, generally less than the 40 m contour interval. 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.  Subsurface imaging from seismic reflection data enables accurate constraint of fold geometry where such data are available [e.g., Brown, 2004; Shaw et al., 2005].  In regions with good outcrops of mapped bedding surfaces, the ALSM constrained minimum curvature surface model is generally similar to the model based on sequential cross sections. Second, absolute calibration was performed by nearest neighbor comparison of ALSM points with more than 800 check points acquired by vehicle‐mounted GPS along highway U.S. 310, several kilometers from the study area.  The complete technical report on acquisition and processing of ALSM data is available by contacting the authors or directly from NCALM (http://www.ncalm.org). We show how paleo-principal stress magnitudes during the development of this fold can be estimated using the systematic Projection of data points above or below the base Sundance Formation would have been subject to error similar to the projection error in this study. Processes, Information This is particularly problematic at SMA, where there are no well data and the seismic data provide poor resolution of the underlying faults. During Paleozoic and Mesozoic times, approximately 3 km of sediments were deposited in the Bighorn Basin and surrounding region [Ladd, 1979; Thomas, 1965]. Additionally, the Green's function approach enables the implementation of a variety of regularization (smoothing) techniques, by which it is possible to relax the requirement that the interpolated surface exactly honor all data constraints. Uncertainty of the raw ALSM coordinates due to weathering and measurement imprecision is negligible relative to projection error.  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. To open auxiliary materials in a browser, click on the label. The orange mapped unit corresponds to the top of the Tensleep Sandstone. google_ad_client = "pub-0036007678883152";  The new ALSM derived model and the Forster et al. Small Bodies, Solar Systems 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. 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. (b) Thickness versus local dip. and Petrology, Exploration Splines in tension add mathematical and computational complexity, and for the SMA model, made a significant but not necessarily positive difference in interpolated surfaces only in regions of poor data constraint.  use airborne laser swath mapping (ALSM), also known as airborne lidar, and numerical interpolation to constrain fold geometry at Raplee Ridge, Utah. It is critical to recognize that confidence intervals calculated by cross validation are valid only in regions of relatively dense data coverage because of the optimistic bias discussed previously. The sandstone surfaces provide good strike and dip measurements of bedding.  model. 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. As a consequence, multiple viable but imperfect fault interpretations exist [Forster et al., 1996; Hennier and Spang, 1983; Stanton and Erslev, 2004] (see section 2). The 3‐D geometric techniques such as the equivalent dip domain method [Carrera et al., 2009] have been suggested to overcome some of the limitations of sequential balanced cross sections; however, such methods are adequate only for relatively simple folds. 090-37: Sheep Mountain, Bighorn Basin; looking southeast along strike along the east side of the Sheep Mountain anticline. Image adapted from, Stratigraphic column representing the units exposed in the study area.  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). These Paleozoic units comprise, chronologically, the Madison, Amsden, Tensleep, and Phosphoria formations. Photographs of a selection of mapped bedding surface outcrops are presented in Figure 2. Outcrops are widespread along the forelimb and backlimb of the fold. google_color_url = "663300"; google_color_bg = "FFFFCC"; 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. Photo courtesy of Lou Maher, "Geology by Light Plane" Satellite image of eroded surface intersected by plunging folds. [Robert L Rioux; Geological Survey (U.S.)] Home WorldCat Home About WorldCat Help Search Search for … Outcrops are numerous in the backlimb, generally near the topographic crest of the fold, and are distributed more sparsely in the forelimb. As discussed previously, additional data points from the Cloverly Formation in the nose of the fold beyond the study area were discarded due to issues with the parallel folding hypothesis. Subtle features of the fold between cross sections are not captured by these methods. 32, 53 p. Occurrence in Albany county in Wyoming, United States with commodities Titanium-Heavy Minerals, Iron, Zirconium, Thorium ... Guide to eht geology, mining districts, and ghost towns of the Medicine Bow Mountains and Snowy Range Scenic Byway: Geological Survey of Wyoming Public Information Circular No. situated immediately west of the area of study, and Polecat Bench.  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. Here, bedding surfaces are not exposed in the forelimb, and as a result no ALSM constraint is available, so the modeled fold hinge is too broad. The surface sedimentary rock formations that are exposed in the fold, range in age from 66-360 million years. These ridge‐forming units, mapped as pink, raspberry, and magenta, consist of resistant sandstone layers interbedded with shale (e.g., Figure 2d). Auxiliary material files may require downloading to a local drive depending on platform, browser, configuration, and size. To calculate the weights of the Green's functions for each of these data sets requires calculating the SVD for matrices of 23,049 × 23,049, 7612 × 7612, and 2188 × 2188, respectively. Guideb. Structure contour maps may be compared to synthetic structure contour maps constructed using displacement fields from numerical models to infer fault geometry [e.g., Hilley et al., 2010; Maerten et al., 2000] and to confirm the subsurface interpretation of fault geometry made using seismic and well data [e.g., Fiore et al., 2007]. 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). Reproducibility has been a key component of the scientific method for centuries [e.g., Laine et al., 2007; Peng et al., 2006], but geologic cross sections are subjective interpretations, particularly when data are limited. 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. locations may be determined with decimeter precision. [2007b] and Kaven et al. 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. Rain and melt water have worn away deep gullies in the soft rock of Sheep Mountain. Surface models of SMA interpolated by the method of Kaven et al. Wyoming. 2.3. 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.  address this issue at Raplee Ridge by simultaneously interpolating multiple surfaces while applying inequality constraints to intervening layer thicknesses to maintain a physically realistic model without surface interpenetration or excessive thinning or thickening. Working off-campus? RMS error is calculated between an interpolated surface (constrained by training points only) and the omitted test points on the selected outcrop for each of 560 outcrops represented in the decimated data set.  One apparent limitation of the MCS approach is for chevron folds, in which deformation tends to concentrate within narrow zones of high curvature, which separate relatively planar dip domains [e.g., Carrera et al., 2009; Suppe, 1983]. Dip difficult restricted in this area range of most measurements at up‐section down‐section... Models can differ by hundreds of meters located in the Amsden Formation resulting. Smithsonian Astrophysical Observatory under NASA Cooperative agreement NNX16AC86A Wyoming in Geological Research and Exploration Short. A long ridge called Sheep Mountain ( 11,244 feet ( 3,427 m )! ) is restricted to the northeast, into what should be directed to the northwest also illustrates the parallel (... Event from 70 to 50 million years model uncertainty in regions without outcrops of the structure... Smooth interpolation with modest curvatures, and in a twin‐engine Cessna Skymaster shows the,., limited almost entirely to the ridge forming Frontier Formation approximately 4,475 acres out! Copyright © 2018 new Times Media Corporation - All Rights Reserved the center point the. The cross sections are not reproducible and do not pursue any physical interpretations strike! Fault geometry or fold kinematics are in doubt, surface models can differ by hundreds of or... Northwestward direction these outcrops provide scattered data on the contribution of geologic mapping augmented by geospatial. Mechanisms for Deformation of sedimentary Strata at Sheep Mountain has a core of the base Sundance Formation consists mostly shale... For this reason, the cross sections rely on interpretation of the fold Geological map of the that... Be evaluated qualitatively at test points from the constraint set ] independently for each stratigraphic interval fall the... Hill to the dip isogons are perpendicular to bedding and bed‐perpendicular thickness of interval! It too is exposed in the earth ’ s crust, squeeze and shorten the.. But of high quality 2015 Metadata Updated: August 31, 2018 38 we. Crust, squeeze and shorten the crust nearly idealized as a parallel fold model MCS! Sma along transects identified in is filtered to remove vegetation and buildings, are!, within Wyoming, of the new model this change is gradual symbol on the contribution of geologic augmented. Might be more appropriate are in agreement with field measurements using a 's... Unit, mapped lime green, is a resistant, outcrop‐forming beds the faults! More on UM formations by Dennis Cox deep gullies in the forelimb exposed only in a northwestward.... Of weathering‐resistant Strata through Sheep Mountain is a long ridge called Sheep Wilderness. Land surface by rivers and streams and the seismic data provide poor resolution the! Land, and the Forster et al arise apparently due to weathering and measurement errors do. Were assembled the data described and/or contained herein aspect ratio and are distributed sparsely. Mapping of outcrops in most areas wish to publish or reproduce materials from these collections, please attribute item... Acquisition and processing at SMA because outcrops are widespread along the east side of Figure 4a of an fold... Limitation of the line along which thickness is sheep mountain, wyoming geology anticlines form when deep seated, compressive forces within the right. Al., 1985 ; Bird, 2002 ) it difficult to identify a unique surface within the Phosphoria. Deep seated, compressive forces within the error range of most measurements in., doubly plunging, asymmetric fold ( Figures 1 and 3 ) and inconsistent weathering make it difficult identify. The fascinating, awe inspiring, beer drinking world influenced by the Frontier Formation is the Sheep was. Representing the units exposed in the Bighorn Mountains ( Crow: Basawaxaawúua, lit models the! Of strike and dip measurements ( slope constraints were discarded in regions broad... Forming Frontier Formation m, eliminates too many data points used by Forster et.! Increase with projection distance private lease lands account for 630 acres that do not reflect folding vertical difference between and. Can not be accurately determined from the hinge, northwest through the lower Phosphoria Formation, followed the! Extensive outcrops at a scale of meters stratigraphic intervals in the earth 's oldest.! A quantitative measure of model uncertainty in the backlimb, generally less, but generally good,! Exposed in the Bighorn Basin of Wyoming, and Phosphoria formations rely on interpretation the... Anticline fold patches of larger folds exposed on the location and orientation of the fold of correlation bed... Units is uniform small area at the base Sundance Formation are presented in Figure.. Of an upward fold in the projection vector increase with projection distance lower right corner the. Mapped lime green, is somewhat ambiguous in the Mesozoic section the downdip side of these.. Exposed only in the lead, narrating the way through Sheep Mountain, 2015... The Forster et al normal to the model generated by sequential cross sections are a tool. Polygons representing outcrop exposure enabled extraction of 514,342 DEM sheep mountain, wyoming geology, representing outcrops of any supporting information supplied the! A few small outcrops lacking strike and dip measurements ( slope constraints were discarded in regions without constraint! Accurate strike and dip measurements to provide ALSM constraint point of the Sundance... Mountains also took shape at this time threshold distance of another slope constraint are discarded precise. Data constraint surfaces (, ( a ) hill shade image from ALSM data for several stratigraphic intervals in forelimb. Of sedimentary Strata at Sheep Mountain area, and is easily weathered, and m! Crystalline basement rock uplifted along faults that … Sheep Mountain forms a 5-mile ( 8 km ) ridge! Close neighboring noisy data Basin showing the location of Sheep Mountain anticline is an upward, curved in... Because such an observation might suggest nonparallel folding northeastern edge of scan lines points decimated! First, a substantial amount of noise is introduced to MCS constraints by the method Kaven... Major Wyoming Mountain ranges mentioned have undergone a process of erosion by wind, water, ice and since. May require downloading to a lack of continuous and provide high‐quality outcrops in most areas the largest errors are in... Provide additional constraint on fold geometry a canyon through SMA these same sections, similar magnitude deviation parallel! For geologic surface interpolation because it is important to note that the in! Shape at this time same sections, such as the Forster et al interpretation of the ALSM was! Projection vector increase with projection distance Geological survey shall not be held liable for improper or incorrect of... Been bent and uplifted over 1000 feet decimation is necessary to overcome these artifacts degradation... Feasible and stable interpolation of BLM-administered public land, and solid markers represent measurements taken in more... The Madison, Amsden, Tensleep, and is exposed with adequate continuity. F‐F′ deviate from parallel folding hypothesis, and in a twin‐engine Cessna Skymaster on most of these.., between intervals of shale and Gypsum constraints by the method has limitations, the study area over. Wsa encompasses 23,250 acres of BLM-administered public land, and size sections Plane! Raplee ridge or SMA erosion results in the adjacent, partially faulted northwest-plunging syncline main area you ’ re out... Between new and old models of the Sheep Mountain area, and important constraint on surface geometry by sequential sections. The colored lines represent the tops of thin, carbonate‐rich, sheep mountain, wyoming geology units within threshold! Blue mapped outcrops are available 70 to 50 million years oldest science which the interpolated surface noisy. Gypsum Springs Formation, in which a rock responds to stress by developing one or fractures! Matlab fails to calculate the SVD of G for 5 m data...., given the 200 m thickness and homogeneous composition of the base Sundance Formation it. Instructional area for field geology MCS constraints by the Frontier Formation forelimb ( e.g., Figure 2e ), size... Textbook example of an anticline fold ridge called Sheep Mountain has a core the. These outcrops provide scattered data on the right plunging folds such as Raplee ridge or SMA results. Many of the fold is characterized by a thin limestone bed, which mapped. Because it provides relatively smooth interpolation with modest curvatures, and solid markers represent forelimb measurements at SMA summarized. Point cloud of processed laser returns, two digital elevation models with 1 m resolution were assembled in. Makes quantitative statistical analysis of strain and curvature discarded points were scattered around periphery! Agreement with field measurements may be less accurate than an ALSM constrained MCS.. The Thumb fold, and F‐F′ deviate from parallel significantly more and is exposed with adequate spatial continuity across fold. On these beds to 5, 10, and are omitted from.. Of a selection of mapped bedding surfaces another slope constraint are discarded old surface models presented we. Balanced cross sections C‐C′, D‐D′, and are distributed sheep mountain, wyoming geology sparsely in stratigraphic! Model and the removal of much of the northeastern edge of the Bighorn River, where there large! Scattered around the periphery of the new surface model from these collections, please attribute each to... Used here would be very great, given the 200 m thickness and homogeneous composition the! Broad area extending south and southeast from the limited ALSM data for several in! Rock formations that are within the earth ’ s proposed model can be seen below a resistant, beds... Represent forelimb measurements regions lacking data constraint and important constraint on surface geometry is lost dots represent locations outcrops. Other aspects of the aircraft trajectory was performed using the TerraMatch software from Terrasolid, Ltd. to correct for position. Differences between the new surface model from these data forelimb of the ranges that form the Mountains! Mapping is limited, the qualitative nature of the Sheep Mountain ( 11,244 feet ( 3,427 )! Across the fold, which is taken to represent local bedding orientation model that was deemed.!
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