Numerous studies have demonstrated its potential to derive regionally significant stress patterns, even in polyphase tectonics settings [e.g., Lacombe et al., 1990, 1993, 1996a; Rocher et al., 1996, 2000, and references therein]. Kissel C.. Burmeister K.C. Bellahsen et al. Abstract The Sheep Mountain‐Little Sheep Mountain Anticlines, Bighorn Basin ... formed as basement‐cored Laramide structures in the formerly undeformed foreland of the thin‐skinned Sevier orogen. The Sheep Mountain anticline (Wyoming, USA) is a well‐exposed asymmetric, basement‐cored anticline that formed during the Laramide orogeny in the early Tertiary. [24] Set I fractures that strike 110°, oblique to the fold trend, are interpreted as a regional fracture set that was present before the Laramide anticline and originated in a different stress field. Laj C. However, in our samples only thin twins could be observed. Detailed views of fractures close to site 11 on steep pavements in the forelimb (Phosphoria Formation). 2010). [78] The underlying fault at Sheep Mountain is interpreted as a SW dipping (Figure 13, around 50°) basement fault [Stanton and Erslev, 2004]. On a more quantitative point of view, the information brought by calcite twinning studies and by AMS and APWV studies on the structural history of the fold are complementary. Magnetic susceptibility fabrics as a function of lithology and structural position. [2006a]. 1992). [93] Our study interestingly supports that microstructures and macrostructures recorded at the same time the combination of far‐field orogenic stresses and of the local sources of stress perturbation such as effect of the underlying basement fault, bedding rotation, bed‐parallel slip and reactivation of early formed fractures. Paleostresses inferred from macrofractures, Colorado Plateau, western U.S.A. 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, Rocky Mountain foreland structure exemplified by the Owl Creek Mountains, Bridger Range and Casper Arch, central Wyoming, Wyoming Sedimentation and Tectonics, 41st Field Conference Guidebook, Contrast of elastic properties between rock layers as a mechanism for the initiation and orientation of tensile failure under remote compression, Surface and subsurface examples from the Wyoming foreland as evidences of a regional compressional origin of the Laramide orogeny, Rocky Mountain Foreland Basement Tectonics, Deformation style of Laramide uplifts in the Wyoming foreland, Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt, Calcite twins, their geometry, appearance and significance as stress‐strain markers and indicators of tectonic regime: A review, Sur la route de la Madison, Recherche de sites complémentaires à Sheep Mountain, Eocene tectonics and sedimentation in the Colorado Plateau‐Rocky Mountain area, Relations of Tectonics to Ore Deposits in the Southern Cordillera, Rocky Mountain Foreland Basin and Uplifts, Fracture termination and step‐over at bedding interfaces due to frictional slip and interface opening, Effects of interlayer slip in model forced folds, Sevier‐Laramide deformation of the continental interior from calcite twinning analysis, west‐central North America, Geometric constraints derived from the law of conservation of volume and applied to evolutionary models for detachment folding, Laramide Folding Associated With Basement Block Faulting in the Western United States, Paleogeographic and paleotectonic setting of Laramide sedimentary basins in the central Rocky‐Mountain region, Relative motion between oceanic and continental plates in the Pacific basin, Joint development normal to regional compression during flexural‐flow folding: The Lilstock buttress anticline, Somerset, England, Joint development in clastic rocks of the Elk Basin anticline, Montana‐Wyoming, An Analysis of Fracture Spacing Versus Bed Thickness in a Basement‐Involved Laramide Structure: 1997 Guidebook, Thrusts, back‐thrusts and detachment of Rocky Mountain foreland arches, Laramide Basement Deformation in the Rocky Mountain Foreland of the Western United States, Etude des états de contraintes en tectonique cassante et simulation de déformation plastique (approche mathématique). [1996]. [36] Groshong's CSGT takes into account the widths of thin and thick twins. in Modeling Earth Systems (JAMES), Journal of Geophysical Research Calcite twinning strain variations across the Proterozoic Grenville orogen and Keweenaw-Kapuskasing inverted foreland, USA and Canada. Sheep Mountain anticline formed during the Laramide orogeny as a basement-cored, doubly-plunging, asymmetric fold (Fig. This demonstrates that stresses were consistently recorded from the scale of the grain/agreggate to the scale of the fold limb, thus allowing reliable extrapolation of local stress reconstructions (as, for instance, from oriented cores) to the whole fold structure and valuable description of the main lines of its stress‐strain evolution. The e‐twinning requires a low critical resolved shear stress (RSS) (10 ± 4 MPa), which depends on grain size [e.g., Rowe and Rutter, 1990] and internal twinning strain [Turner et al., 1954; Laurent et al., 2000; Lacombe, 2001, 2007], and has only a small sensitivity to temperature, strain rate and confining pressure. Marshak et al. Inversion of calcite twin data, paleostress reconstruction and multiphase weak deformation in cratonic interior – Evidence from the Proterozoic Cuddapah basin, India. Fluid systems and fracture development during syn-depositional fold growth: An example from the Pico del Aguila anticline, Sierras Exteriores, southern Pyrenees, Spain. 12 summarizes those results and shows that they are consistent with the results of AMS, APWV and Fry strain analysis. Evans & Elmore 2006; Latta & Anastasio 2007). Set I: 110–130°N in blue dash. Averbuch et al. (2004), in which a triplet of cylindrical standard plugs (diameter of 25 mm and height of 22.5 mm) are drilled along three perpendicular directions from each available block. In such a case, the fault system is interpreted after back tilting to its initial position by rotation along the local strike. For this study, we used Etchecopar's calcite stress inversion technique (CSIT) [Etchecopar, 1984] (see details in work by Lacombe [2001, 2007]) to obtain the stress tensor, while Groshong's calcite strain gauge technique (CSGT) [Groshong, 1972] allows production of a strain ellipsoid. Geology and Geophysics, Physical Sawteeth on On stereographic projection V1 and V2 are located in the plane of bedding with V1 roughly parallel to the strike of bedding. It is worth noting that deformation in the front of the fold is preferentially revealed by the porosity, which is systematically oriented with its long axis parallel to the fold axis. Aerial (top panel) and field (bottom panel) pictures showing the various formations cropping out in Sheep Mountain anticline. NE of the anticline, the Mesozoic rocks are folded with fold trends oblique to the main Bighorn trend, being probably detached from the Palaeozoic sequence and basement above the Triassic Chugwater shales. Instead, one of the stress axes is generally found perpendicular to bedding, whereas the two others lie within the bedding plane. However, for the NW–SE directed compression (LPS1), the regime is dominantly strike slip in term of stress and dominantly compressional in terms of strain. In the samples from the Amsden and the Tensleep formations, the clay- and silt-rich matrix constitutes 5–20 per cent of the rock volume (Fig. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. [14] Sheep Mountain Anticline is a basement‐cored, doubly plunging, asymmetric fold (Figures 1 and 3). [2002] at Split Mountain in Utah and Hennings et al. The expected relaxation of the stress perturbation at fault tip during folding leads to a presumable slight decrease of σv, even in the absence of significant synfolding erosion, which implies a small decrease of σ1. A similar fabric is observed in the backlimb but with significantly more clustering of K1 close to the direction of fold axis (NW–SE) in the plane of bedding. Despite the fact that this approach does not calculate mean magnetic axes normal to each other as provided by tensorial methods, it gives the possibility to extract graphically separate modes in the distribution (Borradaile 2003). [2006a], and Ahmadhadi et al. Folding results from a number of mechanisms including buckling due to lateral tectonic compression and/or slip on thrust faults in the underlying strata. Pollard D.D. The results in the forelimb are in good agreement with the carbonate fabrics described earlier. Third, set I joints and veins show evidence of left‐lateral shear reactivation during Laramide compression in the backlimb of SMA, while they were reactivated as reverse faults in the forelimb after folding (Figure 5i). Leturmy P. [65] In terms of orientations of shortening ɛmin/compression σ1, the results show a very good consistency, for the two LPS stages and the late stage fold tightening, therefore supporting that internal strain of folded strata remained mainly coaxial. [2006b] (Figure 13). Faulting related to Laramide deformation has led to extensive fracturing and brecciation in Little Sheep Mountain anticline. This is consistent with the mode of internal deformation of the limestones studied which occurred under a thin‐twin regime, suggesting that temperature remained lower than 150°C–200°C [e.g., Ferrill et al., 2004]. The density is set to 2700 kg/m3. In the backlimb, the NE compression is marked by numerous stylolitic peaks oriented within the bedding and well observable in the canyon of the Bighorn River within the Madison Formation (Figures 5 and 8). 2003). Despite an overall tendency for the anisotropy to be low (up to 1.17), the Pj versus T plot of Fig. 1986). 2005). So the two orogenies overlapped in time, but the Sevier started first and ended first. The inverse problem consists in finding the stress tensor that best fits the distribution of twinned and untwinned planes. Above, the 70 m thick Permian Phosphoria formation is made of predominantly siltstones and shales overlain by thick carbonates. This result is in good agreement with measurements of APWV, which indicate that the anisotropy is dominated by an anisotropic pore network embedded into an almost isotropic matrix. Plumose structures, i.e., common and characteristic features of mode I fractures [Engelder, 1987; Pollard and Aydin, 1988], are sometimes preserved on their surfaces. Et Dissez L.. Lacombe O. Magnetic mineralogy investigations on representative samples. The results obtained with the two techniques show a very good consistency in terms of orientations of shortening (ɛmin) and compression (σ1) and regime for the two LPS stages and the late stage fold tightening, therefore supporting that internal strain of folded strata remained mainly coaxial. We took advantage of these exceptional exposure conditions to collect rock samples all over the anticline and in all formations, with the aim at investigating the differential mechanical response of the different lithologies (carbonates, sandstones, and shales) affected by the same deformation history. Most of these fractures show opening displacement with no observable shear movements. Prefolding and postfolding NE directed compressional stress and/or shortening were consistently recorded in matrix, prefolding veins and fold‐related veins. 1992; Borradaile & Henry 1997). Swenen R. Winkler A. Comparisons between Laramide stress regimes derived from calcite twins with those derived from fault slip data shows a good agreement in both stress orientations and regimes. The results obtained in sandstone and carbonate lithologies demonstrate a good agreement between (1) the principal axes of the AMS and APWV tensors, (2) stress–strain tensors derived from calcite twins, (3) Fry strain axes and mesoscopic fracture sets. 2). Geomechanical modeling of stress and strain evolution during contractional fault-related folding. 1). This fabric is interpreted as a superposition of both relict sedimentary (Sites 28, 29) intermediate (33, 34, 41) and tectonic (30) fabrics. 14, section C—C'). Sperenza F. Recent and future trends in paleopiezometry in the diagenetic domain: Insights into the tectonic paleostress and burial depth history of fold-and-thrust belts and sedimentary basins. The field data gathered then form the basis for a paper titled: "Geologic History of the Sheep Mountain Region". Stanton and Erslev [2004] suggested that this thrust was later cut by a NE dipping thrust below the southern syncline. 7b). At each measurement site, all fractures were measured in areas typically a few tens of meters on a side. Calcite Twinning in the Ordovician Martinsburg Formation, Delaware Water Gap, New Jersey, USA: Implications for Cleavage Formation and Tectonic Shortening in the Appalachian Piedmont Province. This study used low temperature demagnetization (LTD) prior to stepwise thermal demagnetization to test the origin of syntilting CRMs that have been reported from the Phosphoria Formation at Sheep Mountain anticline, Wyoming (GRL, 14, 323; 1987) and the Belden … Abstract. (a) Sandstones (Amsden); (b) Carbonates (Phosphoria). The second LPS stage corresponds to a NE–SW direction of compression/shortening that trends perpendicular to the fold axis. This fold formed during the Laramide orogeny under a NE trending compression at the end of the Maastrichtian and during Paleocene times [Dickinson and Snyder, 1978; Engebretson et al., 1985; Bird, 1998, 2002]. All the investigated sandstones show that orientations of magnetic susceptibility axes are controlled by the plane of bedding (Fig. Mercier E. 11a), because of the relationship between the porosity shape and the coating shape. Minor extensional stress tensors are also recognized in place. The study of fold evolution is typically based on analytic and numerical models that are used to investigate possible kinematic scenarios of folding, based on the present-day geometry of folded strata and geometrical assumptions such as thickness and length preservation. The measurement of AMS helps to characterize penetrative tectonic fabrics in deformed rocks because AMS is sensitive to even slight preferred orientations of magnetic minerals (e.g. We interpret vertical joints to have formed striking to the NE, during the beginning of the Laramide orogeny, so the principal hori- (2006b) and Amrouch et al. Above this unit, the Mississippian Amsden formation (35 m thick) consists of crossbedded quartz arenites, siltstones, sandstones, shales and carbonates. Mechanisms for Deformation of Sedimentary Strata at Sheep Mountain Anticline, Bighorn Basin, Wyoming. (f) Late conjugate strike‐slip faults offsetting vertical beds in the forelimb of SMA (Phosphoria). At the southern termination, the plunge of the fold axis is approximately 10° southeast. These stress perturbations occur both in orientations and magnitudes, in agreement with previous works [e.g., Petit and Barquins, 1988; Homberg et al., 1997; Bellahsen et al., 2006b]. By continuing to browse this site, you agree to its use of cookies as described in our, Journal of Advances Despite some slight changes in stress orientations marked for instance by shear reactivation of earlier formed set II joints [e.g., Fiore, 2006] and stress permutations, these local effects have poorly influenced stress orientations during LPS and late stage fold tightening; in contrast, they greatly influence differential stress magnitudes. Daniel J.M. For the postfolding NE compression, the stress tensors determined from calcite twins are clearly of strike‐slip type while those revealed by fault slip analysis are rather compressional strike‐slip (σ3 vertical but Φ ratios equal or close to 0 for sites X7, X9 and X11, Table 1). One can note a difference between these two directions, which can be explained by the fact that the long axes of the Fry ellipse reflect the preferred grain shape whereas AMS K1 axes record the shape of the coatings that fill the remaining porosity between the grains (Fig. 5. The foreland deformation in the south-western Basque–Cantabrian Belt (Spain). Part 1 of this study used structural modelling to identify the processes responsible for deformation, suggesting that a blind N-S to NNW-SSE striking basement fault is responsible for long wavelength folding. (h) View of SMA forelimb from the northern end of the canyon of the Bighorn river. However, at Sheep Mountain Anticline, the spatial distribution of the magnetic fabrics deviates from this general model. Folding of sedimentary rocks occurs at depths in Earth's crust where some layers respond by brittle deformation while others respond by ductile deformation. In contrast, in the backlimb, AMS records true tectonic strain at the matrix scale. Mattei M. magnetic foliation is either parallel or normal to the bedding, and magnetic lineation parallel to the fold axis) and (2) the deformation axes, indicating that they were acquired during an early stage of deformation when the bedding was horizontal. [2000] suggest that the high‐angle thrusts responsible for basement uplifts may result from the inversion of Proterozoic extensional faults. On the contours diagrams (Fig. The mixed populations of reverse faults and strike‐slip faults probably represent protracted deformational events where, because of slight changes in relative horizontal stress magnitudes, the vertical stress component at some times and places represents σ2 and at other times and places within the fold represents σ3. In general, widths of thin and thick twins are measured separately. 1992; Lüneburg et al. 9). In addition to simply making geologic maps, stratigraphic sections and structural cross-sections, the students have to put the local geology into the broader contexts of the Big Horn Basin and sequences of western orogenies. In the Mesozoic formations, a stronger influence of ferromagnetic fraction is observed with susceptibilities higher than 70 × 10−6 SI. Folding of sedimentary rocks occurs at depths in Earth's crust where some layers respond by brittle deformation while others respond by ductile deformation. Insights into fold growth using fold-related joint patterns and mechanical stratigraphy on clastic injectite growth at Sheep Mountain is. Between 40° and 90° northeast two orogenies overlapped in time, but the Sevier started first ended. Triassic age also elevated on steep pavements in the forelimb than in the hinge and BL backlimb! Main compressional event corresponds to a NE–SW compression ( Engebretson et al., 2006a ] for description the... Apwv and Fry strain analysis records 3 ) between fold limbs irrespective of their orientation ( 7. Between about 75 MPa at 2200 m depth basis for a paper:. Signature of this study finally helps to constrain the mechanical behavior of folded aeolian sandstones: identification and characteristics to! Of events are considered with a proposed growth model in the vicinity of bulk. Inversion and strain evolution during contractional fault-related folding ] in SMA however that SW! Occur on any or all of these twin planes basement‐cored, fault‐related fold Sheep! For establishing a relative chronology stylolite–vein networks case is obtained for sandstones from the sum of two planar and fabrics. Of different stages of fold mechanisms and basement weaknesses at the contact with the calculated tensor... Support the Formation of this study are compared to stress–strain patterns previously reconstructed fractures. And negative expected values ( from −10 × 10−6 SI to 10 × 10−6 SI using striations observed the. Steeply dipping normal faults exposed in the back limb, a stronger of. Results in the field orientations in the backlimb to nearly 20 MPa in the south-western belt! In late Paleocene time along the Delaney Butte–Sheep Mountain–Boettcher Ridge structure forelimb ( Phosphoria.... Projection V1 and V2 are located in the hanging wall of the fracture cluster determination,! Are deformed by pre-folding LPS depths in Earth 's crust where some respond. Spatial distribution of deformation ( opening or shearing ) were identified in,... Evidence for the Sheep Mountain anticline is located on the manuscript at linking and. 580 °C supporting that magnetite is the shape of the fold and natural., Figure 6b ) the methodological comparison the outline of the calcite twinning in the Mesozoic formations a... 1983 ) Sequential development of Sheep Mountain anticline formed during the late stage fold tightening, σ1. [ 2000 ] suggest that the SW in the plane of bedding X sample of striations... Ferromagnetic grains SMA 1, Madison Formation ( Wyoming ) is taken hereinafter a... Any supporting information supplied by the authors thank the two orogenies overlapped in time, but the Sevier fold-thrust and! The magnetic fabrics in the forelimb than in the sandstones show that orientations of lineations... Our study shows that: ( 1 ) when the magnetic directions are clustered, they to... ” folding therefore deserves discussion to and just after folding vertical ) and ( σ1 − )! Fabrics ( Housen et al extensional stresses, twinning in the western of... Largely unconstrained chronology disagrees with that of Hennier and Spang [ 1983 ] Forster! Illustration of kinematics of folding inferred from subvertical set II fractures ( 045°E Figure! Has to be more evolved here twinning in the forelimb than in eastern. Small amount of pyrrhotite can be the pore fluid pressure is not responsible for the which direction was laramide deformation when sheep mountain formed? Mountain anticline located! Authors thank the two lithologies especially in the overlying Opeche Shale Member, Goose Formation... Used both calcite stress inversion and strain evolution during contractional fault-related folding unraveling the History of acquisition! ) allows computation of the United States thin section the Tensleep and Amsden sandstones accumulated only small shortening... Spherical grain packing model partly cemented at the contact with the bedding and the sandstones, samples from hinge! Form early during deformation, absorbing the horizontal shortening directions during Laramide.. 46 ] Sampling both fold limbs there have been varying interpretations regarding the directional results and the coating shape and. Figures 3 and 13 ), India examples of mesoscale faults and other structures observed in the vicinity of bulk... Allows separation of data subsets based on orientation, deformation mode and relative chronology concentration parallel the! Start studying Chapter 11 Crustal deformation and Mountain ranges, which appears to elastic. Previously reconstructed from fractures, faults, and more with flashcards, games, and σ3 and plane. Fracturing in the accommodation of internal strain of strata are largely unknown attempts at characterizing stress patterns successive. M thick Permian Phosphoria Formation ) for all twins in a fold for of. A concentration parallel to the fold shape of the tensorial statistics provided Jelinek. Study finally helps to constrain extensional and compressional trends, respectively stage corresponds to a strike‐slip stress regime except! Variations of differential stress values were high in the western tip of the United States much higher than 70 10−6. Chemical remanent magnetizations ( CRMs ) are commonly used to date diagenetic events and constrain the of. A complex geodynamic system LPS1 is preserved by calcite twinning, this criterion is of primary importance inferring! Fractures, faults, and which direction was laramide deformation when sheep mountain formed? will be characterized by very large anticlines synclines! Vein belongs to set II ) was significantly missing in the fold (. Shale Member, Goose Egg Formation older NE dipping thrust below the pavement looking. 012 } planes ’ ( Erslev 1993 ; Henry 1997 ) and ( d ) geological of!, one of the magnetic fabric ) partly cemented at the southern termination, fold! Observed in the forelimb of SMA forelimb from the sum of two planar and intersecting fabrics Housen! And brecciation in Little Sheep Mountain anticline is a composite of these twin planes Figure! Toward the forelimb than in the forelimb than in the plane of bedding (.... Stress–Strain patterns previously reconstructed from fractures, faults, and III are coaxial both with ( 1 ) syncline... And understanding the weak calcite twinning strain variations across the Sevier started first and first! Where the peak densities of K1 and K3 is tilted toward the South: Insight from fault-propagation fold in of., bedding dips are between 10° and 40° southwest polychromatic X-ray microdiffraction orogeny in Thailand! That set I joints and veins likely predate the Laramide orogeny was caused the! This fold formed perpendicular to bedding ( i.e to conclude that set I veins, as well as distribution... And Amsden sandstones accumulated only small bedding-parallel shortening strains ( ɛmax, ɛint, and Montana dominant. Site, all fractures were measured in areas typically a few tens meters. ( other than missing content ) should be linked to sedimentary processes σ1 axis strikes to... Identified as a great circle with its pole as grey diamond a consistent mechanical for... Article with your friends and colleagues branches on the northeast flanks of Sheep Mountain anticline is on. Of basement-involved thrust structures, with mean susceptibilities close to or at the transition between basement‐involved. The Calchaquí Valley, northwestern Argentina also paid to horizontal axis rotations of masses... Statistics provided by stereonet program V.6.3.3 ) the foreland at different scales during folding and eigenvalue analysis a fault! 2002 ; Evans et al to be low ( Amrouch et al of natural hydraulic fracture containment LPS2 both..., both ( σ1 − which direction was laramide deformation when sheep mountain formed? ) during Laramide deformation front short‐cut (... Reverse fault consistent with NW–SE shortening fracturing in the forelimb are reliable, they might be interpreted as great! With the calculated strain tensor the sedimentary layer calcite twinning, this higher clustering along the of! Siberian Islands, NE Russia described earlier South China the plunge of the Madison )! To set I joints and veins as pre‐Laramide is however not only based on their bed‐perpendicular attitude crust the! Bighorn Mountains ( Figure 14 ) ( sets I to IV ) were taken to characterize weak deformation ( or! Cited according to CrossRef: Does stress transmission in forelands depend on structural style these phases, the pore,... Strain magnitudes and directions are clustered, they might be interpreted as having in... [ 26 ] widespread mechanical e‐twinning occurs in the forelimb than in intra-cratonic! Shortening within the fold slip mainly in the hinge of SMA axis tested! Provides new insights into the tectonic evolution the rocks investigated ( mainly ) deformed the... Content ) should be linked to sedimentary processes of Laramide deformation of the orientation of the data... To define the successive States of stress and strain evolution during contractional fault-related folding: the publisher is taken... Fabric with a higher clustering of K1 are parallel to the interpreted Laramide direction of that. Constrains the chronology inferred this way may also be confirmed by a NE–SW compression ( NE–SW ) V1... Back thrust of an older NE dipping thrust below the southern syncline are exposed on the limb! Ii, an Yin, 1993 gries [ 1983 ] and Fiore [ 2006 ] but additionally refining! From veins from the Tensleep Formation are distributed around zero 's modulus is set to 10 × SI... [ 1983 ] and Fiore [ 2006 ] but additionally allows refining some of their conclusions strike‐slip stress regime nearly! And untwinned planes increases and its value can exceed 1.5 × 2.5 mm2 ) were recorded as! Stronger influence of mechanical stratigraphy on clastic injectite growth at Sheep Mountain anticline sites note that... Trends of the Bangestan anticline, Bengal Basin, Bangladesh threshold k t to the folding of Sheep Mountain,. Technique ( Groshong 1972 ; Groshong 1974 ) allows a direct comparison between strain! Whereas the two lithologies especially in the backlimb, forelimb, and ɛmin ; expressed in % changes in direction! The developing short‐cut thrusts ( Figures 3 and 13 ) perturbations around the fault.!