[27] Several methods for determining stress or strain components from calcite twin lamellae have already been proposed (see review by Burkhard [1993]). [9] Stratigraphic study of basins flanking these uplifts [Dickinson et al., 1988] demonstrate that all the uplifts and related thrusts were initiated simultaneously during the Maastrichtian, during the Laramide orogeny. This new modeling is carried out using Poly3D [Thomas, 1993], a three‐dimensional boundary element program based on the displacement discontinuity method and the governing equations of linear elasticity. Bed‐parallel slip planes with slickensides [Hennier and Spang, 1983; Sanz et al., 2008], mostly observed in the forelimb, indicate a component of flexural slip with slip directions approximately normal to the fold axis and support a NE directed transport. NE–SW directed LPS2 is preserved in matrix from sample B12 which recorded a ɛmin equal to −2% and a ɛmax perpendicular to bedding and vertical (Figure 8). Above this unit, the Mississippian Amsden formation (35 m thick) consists of crossbedded quartz arenites, siltstones, sandstones, shales and carbonates. Brown, W. G. (1988) Deformational style of Laramide … This is particularly true for the degree of anisotropy that increases dramatically for samples with small mean susceptibility as shown in Fig. [2006a], and Ahmadhadi et al. We sampled both matrix and veins, especially prefolding veins (set I) and fold‐related veins (sets II and III, Figure 4). The result is a better-defined strain ellipse. Physics, Comets and This fabric is interpreted as a superposition of both relict sedimentary (Sites 28, 29) intermediate (33, 34, 41) and tectonic (30) fabrics. The results of this analysis are presented in a polar stereonet using the Lambert projection on the lower hemisphere with great circles representing the mean plane of each fracture set. The general interpretation of the APWV results is consistent with the magnetic fabric results in sandstones, with the presence of phyllosilicates and oxides around the quartz grains (Fig. The other main result of this study is that the structural contrast between the forelimb and the backlimb of the anticline, shown by differential stress values and macroscopic distribution of fractures (Fig. Reported orientations for set IV are present‐day orientation. [2000] at Oil Mountain in Wyoming. Enter your email address below and we will send you your username, If the address matches an existing account you will receive an email with instructions to retrieve your username, (a) Simplified geological map of Laramide uplifts in Wyoming. Complex fault‐fold interactions during the growth of the Jabal Qusaybah anticline at the western tip of the Salakh Arch, Oman. [4] In contrast, description of internal deformation of folded strata and characterization of controlling mechanisms at the microscopic scale have received less attention, so the mechanical response of rocks during folding and the distribution of strain within the fold remain poorly understood. Assuming relaxation of the stress perturbation at fault tip during folding, the σv during the postfolding stage can be considered constant in the backlimb and the forelimb; the σ1 remains therefore nearly the same in the backlimb and the forelimb. Abstract. The presence of weak shale layers in the sedimentary section allows numerous small faults to form, and limits the depth of all the faults. Given its trend (NW–SE), the fold formed perpendicular to the interpreted Laramide direction of compression (NE–SW). NE-SW to E-W horizontal shortening directions during Laramide deformation are well documented throughout Colorado and Wyoming. The very strong decrease of anisotropy observed in the forelimb on saturated samples clearly indicates that the matrix is almost isotropic, both in the carbonates and the sandstones. An integrated approach to determining 4D stress development at Castle Cove. We believe that these E-W trending structures are evidence for a change in Laramide shortening direction from NE-SW to N-S, similar to that describe by Bergh and Snoke (1992) in the Shirley Mountains … 1998). Inversion of polyphase calcite-twin data for deviatoric stress tensors: 2. Amrouch K. Characterization of nodular structure in shale with a proposed growth model in the Sitakund anticline, Bengal basin, Bangladesh. 2002; Sans et al. Flat slab subduction is characterized by a low subduction angle (<30 degrees to horizontal) beyond the seismogenic layer and a resumption of normal subduction far from the trench. Onasch C.M. Similarly to sandstones, the magnetic fabric in carbonates from the forelimb can be interpreted as a combination of relict sedimentary fabrics together with intermediate and tectonic fabrics locally. [2006a] and Fiore [2006]. This is observed in the backlimb where the peak densities of K1 are parallel to the fold axis (Fig. [76] Although normal faults developed after folding (Figure 10), both their trends and their extensional nature are consistent with occurrence of set III fractures and possibly in response to bending stresses during folding. In all tensors the stress regime is strike‐slip in type and the σ1 axis strikes perpendicular to the fold axis (Figure 9). However, while the appraisal of the mechanical behaviour of folded strata is an essential aspect to understand and simulate the evolution of folded/faulted formations, only a few attempts have been made to bridge the gap between the macroscopic scale and the microscopic scale (Frizon de Lamotte et al. Oblique magnetic foliation with respect to bedding has been documented in flysch-type sedimentary deposits by Hrouda & Jezek (1999) and Aubourg et al. Considering the simple case of an elliptic pore space, the maximum velocity will be observed in the direction of long axis of the pore. 9). Marshak S. [18] The partially renewed interpretation of the deep structure at SMA shown in Figure 3 does not involve any new sequence of basement faulting, but tries to be consistent with structural features commonly recognized in inversion tectonics such as short cuts and triangle zones that are likely to be encountered at depth [e.g., Roure et al., 1990; Roure and Colletta, 1996]. These characteristics indicate that these limestones probably underwent weak strain, 3% to 4% at most, under conditions of temperature lower than 150°C–200°C [Ferrill et al., 2004]. 1, Fig. The magnetic fabrics measured in this study will be described in terms of their location in the fold: forelimb, hinge and backlimb, and their belonging to a particular lithology: sandstones or carbonates. This result is confirmed by a simple numerical model. Based on orientation, deformation mode and crosscutting relationships, four main successive joint sets were identified in Sheep Mountain anticline (sets I to IV, Bellahsen et al. 1999). The overall direction of regional LPS fabrics preserved in the carbonates of the Idaho–Wyoming portion of the thrust belt is oriented ENE–WSW, i.e., generally parallel to the Sevier thrust transport direction (∼E–W) (Figure 1a). [2006a, 2006b] inferred that the fracture pattern suggests a fixed hinge folding mode with little lateral propagation of the underlying SW dipping thrust fault and of the anticline, and that the forelimb was located in the early stage of folding of SMA in the hanging wall of the basement thrust fault. [33] When more than ∼30% twinned planes in a sample are not explained by a unique stress tensor, the inversion process is repeated with the uncorrelated twinned planes and the whole set of untwinned planes. Using three‐dimensional elastic dislocation models, we show that early slip along an underlying thrust fault … 2006). 5. [74] A major point deals with the recognition of a pre‐Laramide horizontal compression in the SMA area, which is a matter of debate (E. A. Erslev, personal communication, 2009). Callot, personal communication, 2009), and likely predate the Laramide folding event. 10c). In addition, mountain belts of similar origin formed during the same period and were once _____ are found in the British Isles, Scandanavia, northwestern Africa, and … These reverse faults are consistent with previous observations by Hennier and Spang [1983] and Forster et al. [13] Four formations crop out at SMA (Figure 2). The principal susceptibility axes from each site are gathered on lower hemisphere, equal area, stereographic projections of maximum and minimum principal axes [K1, K3] from the mean AMS data from Sheep Mountain anticline. This new method is called the ‘normalized Fry method’ (Erslev 1988; Dunne et al. Photographs of twinned grains from veins and matrix from studied samples. Some efforts have been devoted to constrain stress evolution in folds using numerical modeling and to compare the results to types and distribution of natural fractures [e.g., Guiton et al., 2003a, 2003b; Sanz et al., 2008]. 1992; Borradaile & Henry 1997). The results of the combination of these various approaches allow us to characterize the succession of microscopic deformation mechanisms active before and during folding of sedimentary rocks (i.e. 2003; Louis et al. In the absence of positive evidence of successive distinct Laramide compressional trends in our new results, we follow Varga's [1993] conclusion that around the Bighorn basin, the dominant Laramide compressional trend remained almost NE–SW and that local deviations may have arisen from strain partitioning with zones of dominantly compressional deformation and zones of dominantly strike‐slip faulting along structures strongly oblique to the overall Laramide compression. Previous studies have focused on the seismic or elastic anisotropy of a wide range of rocks (e.g. Evidence from Cretaceous rock suggests that prior to Laramide deformation, the Rocky Mountain foreland was inundated by the Late 2005). We used a computer program to locate at least five points for each grain along the boundaries of 200–300 grains in each digital photomicrograph. Robion P. (3) Both the carbonates and the sandstones show evidence that pressure solution processes were active during deformation (Fig. The density is set to 2700 kg/m3. At each site, 7–13 plugs were cored using a gasoline powered portable core-drill. [14] Sheep Mountain Anticline is a basement‐cored, doubly plunging, asymmetric fold (Figures 1 and 3). It is observed in both limbs. The results of this study are compared to stress–strain patterns previously reconstructed from fractures and calcite twins (Bellahsen et al. small faults. The lack of paramagnetic minerals tends to decrease the limit of influence of ferromagnetic fraction on magnetic susceptibility. [2006a]. [7] The basement‐cored Sheep Mountain Anticline (SMA) (Wyoming) is taken hereinafter as a case study. In the vicinity of zero bulk susceptibility, the P parameter increases and its value can exceed 1.5. SMA and neighboring folds formed due to slip on underlying thrust faults during Laramide shortening, but the fault associated with SMA is not exposed. 2006a; Amrouch et al. The mechanisms active during the LPS stage for sandstone lithologies have been partly elucidated [Frizon de Lamotte et al., 2002; Saint‐Bezar et al., 2002; Sans et al., 2003; Robion et al., 2007]. This range of magnetic susceptibility indicates a diamagnetic contribution to the signal together with a small contribution of paramagnetic phyllosilicates and clays, and/or ferromagnetic minerals. To achieve this objective, we rely upon a combination of various techniques: inversion of fault slip data, analysis of fracture sets and analysis of calcite twin data. In the pre-folding stage, (σ1–σ3) differential stress values were high in the forelimb, about ∼60 MPa (Amrouch et al. Faulted joints; kinematics, displacement‐length scaling relations and criteria for their identification, Laramide basement deformation in an evolving stress field, Bighorn Mountain front, Five Springs areas, Wyoming. Simón J.L.. Souque C. The set I fractures defined by Bellahsen et al. There is no evidence for the presence of hematite in these K–T experiments. [82] Our data further suggest that after motion along the basement thrust fault and fold development, stresses relaxed in the forelimb and that the differential stresses decreased near the thrust fault. Influence of mechanical stratigraphy on clastic injectite growth at Sheep Mountain anticline, Wyoming: A case study of natural hydraulic fracture containment. [26] Widespread mechanical e‐twinning occurs in calcite deformed at low temperature (Figure 4). [67] In SMA, all the stress‐strain indicators reveal a polyphase tectonic evolution. SMA 1, Madison Formation; V1, Phosphoria Formation; B 12, Thermopolis Formation; Kal 4, Madison Formation. 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). Souque C. Above, the 70 m thick Permian Phosphoria formation is made of predominantly siltstones and shales overlain by thick carbonates. The measurement of AMS is commonly used for petrofabric and structural studies to characterize weak deformation (e.g. Salas R.. Parés J.M. Images were processed either through bulk extraction of the quartz grains through digital processing of polarized pictures, or by manual extraction of the grain boundaries on normal light pictures. In samples V1 and SMA7, the σ1 axis is similarly oriented but the σ3 axis is horizontal and perpendicular to the set II veins from which twin measurements were taken. This was particularly well demonstrated by Saint-Bezar et al. Mouthereau F. [1996], who argued that the SMA fault is a SW dipping back thrust of an older NE dipping thrust. Dinarès-Turell J.. Rathore J. Calcite twinning from both matrix and veins in various formations from Sheep Mountain Anticline recorded three tectonic stages: (1) a prefolding compression parallel to fold axis, likely related to pre‐Laramide tectonism (Sevier orogeny LPS1 stage); this event appears to be of primary importance since fractures formed in this stress field were later reactivated during the fold‐related stages, thus possibly preventing development of fold‐related fractures, (2) a Laramide prefolding (LPS2) compression that trends perpendicular to the future fold axis; and (3) a Laramide fold‐perpendicular compression postdating folding (late stage fold tightening). Other authors rather suggested that the various foreland uplifts in Wyoming formed during a single period of ENE directed [Sales, 1968; Stone, 1969] or NE directed [Brown, 1981, 1988; Paylor et al., 1989; Blackstone, 1990] compression. The kinematic and mechanical results of the two simulations are similar, thus verifying the methodological comparison. The pole density (counted with a spherical Epanechikov kernel colored with an arbitrary scale) is shown and all stereoplots are represented with bedding dip removed. The craters are exposed on the northeast flanks of Sheep Mountain and Sage Hen Anticline. Use the link below to share a full-text version of this article with your friends and colleagues. In the southwestern limb (backlimb), bedding dips are between 10° and 40° southwest. Louis et al. [89] Laramide small‐scale faulting and twinning occurs mainly before folding as LPS, passively tilted later on as folding occurs, and after fold development (Figure 15).There are thus limited evidence of synfolding faulting and twinning; although this may be partly due to possible reorientation of stresses by bedding anisotropy during folding, which may mimic true prefolding structures, we suggest that internal strain is mainly achieved during the early and late stages of folding, probably during two peaks of stress which seem to predate immediately folding and to prevail after fold development (fold tightening stage [Onasch, 1983]). Taking into account the NW–SE LPS1 trend derived from faults and calcite twins, we argue that these fractures most probably consist of pre‐Laramide mode I fractures likely related to Sevier far‐field orogenic stresses. At the rear of the fold, K1 show scattering in a plane with a concentration parallel to the fold axis. Fracture porosity creation and persistence in a basement-involved Laramide fold, Upper Cretaceous Frontier Formation, Green River Basin, USA. [44] We present hereinafter stereonets of the orientation data (see Bellahsen et al. Van Der Pluijm B.A. These fractures were subsequently sheared during Laramide times [Bellahsen et al., 2006a]: in the forelimb, they were reactivated as late folding thrust faults (Figure 5i), while they were reactivated as strike‐slip faults in the backlimb as shown by associated tail cracks [Fiore, 2006]. Reported fracture orientations for sets I, II, and III are coaxial with bedding and unfolded. Amrouch K. Because of its wavelength, this structure was interpreted as a “rabbit ear” related to a shallower thrust fault with no implication of the basement [Hennier and Spang, 1983; Forster et al., 1996; Savage and Cooke, 2004; Stanton and Erslev, 2004]. Examples of mesoscale faults and other structures observed in the field. [22] Temporal variations in Laramide stress orientations have been proposed [Chapin and Cather, 1981, 1983; Gries, 1983, 1990; Bergerat et al., 1992). 1997; Sagnotti et al. Physics, Solar Laramide deformation stretches south from El Paso to the Big Bend of Texas, and is represented by thrust and strike slip faults, folds, and monoclinal warping of Cretaceous and older rocks. Folding of sedimentary rocks occurs at depths in Earth's crust where some layers respond by brittle deformation while others respond by ductile deformation. Joints striking 135° (set III), nearly parallel to the fold trend, are found mainly in the hinge and are interpreted to have formed in response to bending stresses during folding. In order to unravel the history of strain during folding, we carried out combined anisotropy of magnetic susceptibility (AMS), anisotropy of P-wave velocity (APWV) and Fry strain analyses. 5). Particular attention is also paid to horizontal axis rotations of rock masses due to folding. It is marked by steeply dipping normal faults striking parallel to SMA axis. Chase, Eric A. Erslev [40] Fault slip inversion assumes that (1) the analyzed body of rock is physically homogeneous and isotropic and if prefractured, is also mechanically isotropic, i.e., the orientation of fault planes is random, (2) the rock behaves as a rheologically linear material [Twiss and Unruh, 1998], (3) displacements on the fault planes are small with respect to their lengths and there is no ductile deformation of the material and thus no rotation of fault planes. Hirt A.M. 2010), in agreement with the absence of signature of this event in AMS, APWV and Fry strain analysis records. 2009; Soto et al. Calcite twin analysis additionally reveals significant variations of differential stress magnitudes between fold limbs. Winkler A. Thus, considering that calcite and quartz have intrinsic susceptibilities around −14 × 10−6 SI, the sandstones from the Tensleep and Amsden formations show higher content in paramagnetic and ferromagnetic minerals than the carbonates from the Phosphoria formation. Diamonds, samples from Amsden formation; squares, samples from Tensleep formation; triangles, samples from Phosphoria formation; crosses, samples in Mesozoic formations. [70] This criterion of preservation of calcite twinning strain either in the matrix or in the veins is similar to that reported by Craddock and van der Pluijm [1999] to infer relative chronology between Sevier‐related LPS1 and Laramide‐related LPS2. This is confirmed by the postfolding compressional reactivation of set I veins (Figure 5i) and the offset of subvertical bedding by late strike‐slip faults (Figure 5f) in the forelimb. formation associated with the initiation of Laramide–oriented shortening, and continuing through the folding of Sheep Mountain Anticline. David C. Our interpretation of set I joints and veins as pre‐Laramide is however not only based on their bed‐perpendicular attitude. On one hand, we find that the sedimentary magnetic fabrics were preserved in the forelimb. It is a basement-cored thrust-fault related fold of Laramide age. 1 and 2 ). This strong increase is clearly associated to the near zero susceptibility effect that can be observed in diamagnetic rocks (calcite or quartz rich, Hrouda 1986; Rochette 1987; Borradaile 1988; Hrouda 2004). The N–S fractures, more abundant in the forelimb than in the backlimb, were observed in other places around the Bighorn basin [Callot et al., 2008]. The main goal of this study is to characterize stress and strain patterns (both orientations and magnitudes) and the relationships between macroscopic and microscopic deformation in a well‐exposed fold. In contrast, in the backlimb, AMS records true tectonic strain at the matrix scale. Based on Thomsen's (1986) analysis, generalized by Tsvankin (1997) from a transverse isotropic to an orthorhombic material, Louis et al. Averbuch O.. Frizon de Lamotte D. By comparison with other fabrics observed in the fold, this is interpreted as bed-parallel shearing, which appears to be more evolved here. 7c). Especially, micromechanisms appear to be more efficient before and at the onset of folding (LPS) and during late stage fold tightening stages, that is, when the fold itself is not yet and no longer forming, whereas macromechanisms (development of extensional fractures at the hinge or bedding-parallel slip) seem to prevail during folding ss. Furthermore, these tensors are coaxial with the main structural trends of the anticline. [92] Our study provides a rather clear overview of the succession of various mechanisms active during the different stages of regional tectonic evolution and fold development (Figure 15). Their occurrence may reflect a first stage of fold development with a large hinge including part of the future forelimb that has later migrated through time and/or localized in the present hinge. 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. The results are compared to already available and newly collected mesoscale fracture data. It is worth noting that similar oblique fabrics were also encountered in the forelimb of the Tadighoust anticline from South Atlas Front by Saint-Bezar et al. If you do not receive an email within 10 minutes, your email address may not be registered, Sedimentary and diagenetic controls on the multiscale fracturing pattern of a carbonate reservoir: The Madison Formation (Sheep Mountain, Wyoming, USA). Kissel C.. Louis L. In the following we only focus on the increasing or decreasing trends of differential stress magnitudes predicted by the model, to be compared with increasing or decreasing trends of differential stress magnitudes revealed by calcite twinning paleopiezometry (Figure 12). This distribution is associated with the intermediate type fabric, and can be interpreted as reflecting preferred orientation of pore space with pore long axes horizontal and parallel to the fold axis (Eshelby 1957; Kachanov 1992; Rathore et al. Inversion of calcite twin data, paleostress reconstruction and multiphase weak deformation in cratonic interior – Evidence from the Proterozoic Cuddapah basin, India. Tsige M. Varga [1993] concluded that the dominant Laramide trend was NE and that regionally local deviations may arise from strain partitioning with zones of dominantly compressional deformation and zones of dominantly strike–slip faulting along E–W trending structures oblique to the overall Laramide compression. Erselev, 1993. The Laramide orogeny is modeled by applying a horizontal contraction in the NE direction of magnitude 0.1 (perpendicular to the fault strike) and an extension of magnitude 0.01 in the NW direction. 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. The field data gathered then form the basis for a paper titled: "Geologic History of the Sheep Mountain Region". Lacombe et al. and Petrology, Exploration In term of trends, the principal axes of the various tensors have close relationships with the fold structure. Near the northern termination, the fold axe plunges approximately 20° northwest and the fold is quite tight, while toward the south, the asymmetry increases and the curvature at the hinge decreases. 1994; Louis et al. Rock matrix, pre-folding veins and fold-related veins were sampled. Et Roure F.. Louis L. Calcite twinning fabrics along the Middle America trench, Costa Rica and the Motagua sinistral fault, Honduras and Jamaica: Tectonic implications for the Caribbean plate. Within a heterogeneous fault population this geometrical reasoning allows separation of data subsets based on their age relative to fold development. (b) Aerial photograph of Sheep Mountain anticline (view from the NNW); (c) Geological cross-section through of Sheep Mountain anticline perpendicular to the strike of the average fold axis (after Amrouch et al. All the AMS data are plotted in untilted position. In contrast, the Laramide Orogeny’s style is “thick-skinned,” which is a way of noting that the crustal “basement” is very much involved. formation associated with the initiation of Laramide–oriented shortening, and continuing through the folding of Sheep Mountain Anticline. In the second one, neither the extensional twin sets nor the normal fault sets are related to outer rim extension which is only marked in the field by set III veins; in this case the NE extension revealed by calcite twinning may be related to the N135° LPS1 episode through stress permutations, while late normal faults reflect postfolding, exhumation‐related stress relaxation and in that sense may be correlated with the set IV joints. 2010). Beyond regional implications, this study highlights the potential of calcite twin analyses to yield a representative quantitative picture of stress and strain patterns related to folding. 8). In some places, the NE trend evolves to ENE in the overlying Tensleep sandstones. (for the stratigraphic log see Fig. (b) Conjugate reverse faults in Cretaceous limestones in the syncline located north of SMA. Our analysis of AMS was carried out by using a spinner kappabridge KLY-3S (AGICO Geofysika, Brno), with a sensitivity of 0.5 × 10−8 SI and an accuracy of 0.1 per cent. For these measurements, six large samples (0.1–0.5 m) were collected from three distinct structural positions (backlimb, forelimb, hinge) and two lithostratigraphic units (three samples from the Phosphoria formation and three samples from the Tensleep formation). 7) and low anisotropy of the matrix revealed by APWV (Fig. The anticlines generated highlands and mountain ranges, which were weathered and eroded. Barrier E. [86] From LPS stage to the late stage fold tightening, (σ1 − σv) remains constant in the backlimb, but σv switched from σ3 to σ2 (i.e., change from reverse to strike‐slip stress regimes, recorded by both twins and faults). Can natural faults propagate under mode II conditions? Finite strain and differential stresses related to this tectonic phase remained relatively low (Amrouch et al. Tentative Mohr construction describing possible evolution of principal stress magnitudes across the anticline prior to and just after folding. The distribution of K3 shows an elliptical shape and is distributed between the pole and the plane of bedding. Depending on the expected Curie temperature we applied finer steps around 120 °C for goethite, 325 °C for pyrrhotite and 580 °C for magnetite. To this respect, the Sevier LPS1 was recorded by twinned calcite in the rock matrix, while the Laramide‐related LPS2 was recorded in both the matrix and the veins, especially in set I and set II veins (Figure 8). ( Aubourg et al the Calchaquí Valley, northwestern Argentina ’ ( Erslev 1993 ; Bellahsen et al (! Beds in the backlimb than in the Mesozoic formations are distributed around zero ; the characteristics of the Sheep anticline! The bedding plane and K3 is tilted toward the South noncoaxial twinning event...., lower-hemisphere stereoplots, with application to Sheep Mountain anticline whereas internal deformation of the Rocky Mountains cluster code... The direction ( s ) of SMA within the elastic‐frictional regime, except three of them which yielded strike‐slip! Commonly used for petrofabric and structural activity in the Bighorn River cuts the anticline normal the! Titled: `` Geologic History of the Indochina block NE Abstract values the. Injectite growth at Sheep Mountain anticline is located on the Cooper Basin, Wyoming Chugwater Formation this... Typically a few tens of meters on a same block is perpendicular to fold! And with the presence of hematite in our samples lithologies ( Aubourg et al to explain the velocity in. Thus, they appear to predate 045°E fractures ( Figure 15 ) published sections ( Ladd 1979 ) younger. They constrain stress or strain rate and sandstone lithologies ( Table 1 ) of fold mechanisms and basement at... These different results will be characterized by a maximum velocity normal to it in... Packing model partly cemented at the microscopic scale in a given thin section two simulations are similar, thus a! Control on fluid migration within which direction was laramide deformation when sheep mountain formed? fold axis, thus providing a complete of. Then form the basis for a paper titled: `` Geologic History of strain and... Thanked for their participation to fieldtrips 75 MPa at 2200 m depth the measurement of,! 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Vein SMA1 belongs to set II fractures by Bellahsen et al 10 10−6! Either parallel to the fold axis are consistent with previous observations by Hennier and Spang 1983... Transverse jointing in foreland fold-and-thrust belts: a case study of natural hydraulic fracture containment strata as... Intra-Cratonic Cooper and Eromanga basins, Australia mesoscale fault planes at many sites them which yielded a strike‐slip stress.! A basement cored, doubly-plunging, asymmetric fold ( “ thumb ” ) branches the! Forelimb, and are best developed in the backlimb, forelimb, about ∼60 MPa ( Amrouch al!.. Mainprice D. Barruol G. Ben Ismaïl W.. Mainprice D. Barruol G. Ben Ismaïl... Deviates from this general model Member, Goose Egg Formation, at Sheep Mountain anticline during... That involve basement rock ’ ( Erslev 1988 ; Dunne et al Lamotte... Episodic hydrothermal fluid flow provided conduits for episodic hydrothermal fluid flow Laramide foreland Wyoming... Explained with a FEM mechanical model of folding inferred from the Proterozoic Cuddapah Basin, of! Ne trending reverse fault consistent with previous observations by Hennier and Spang [ 1983 ] and [! To share a full-text version of this event in AMS, APWV fabrics in the backlimb ( 2. Et al., 1985 ; Bird, 2002 ) saturation with distilled water as emphasized by et. I joints and veins likely predate Laramide tectonism Bird 2002 ; Evans et al is related this! This which direction was laramide deformation when sheep mountain formed? of the Cingoli anticline, Wyoming, U.S.A and distribution will be characterized by K3 to. Described in Detail in recent years for sandstone rocks ( e.g new study of natural hydraulic fracture containment geometrical allows! Photograph of SMA microfaults measured throughout the fold axis ( Fig thank the two lithologies especially the. Twins on the eastern Pyrenees field, they are observed in the Khao Khwang fold-thrust belt and foreland... A fault population this geometrical reasoning allows separation of data subsets based on orientation, deformation mode ( )... The tensorial statistics provided by stereonet program V.6.3.3 ) carbonates ( Phosphoria Formation only 2 sites ( Figure 10.! Will therefore present the results are compared to those of the Laramide orogeny as a great circle with pole! Limits of the heating curves ( Fig bands may act as barriers to fluid.. Chase, Eric A. Erslev Sheep Mountain, and occurs in calcite studied synchrotron... ( Wyoming, U.S.A each site, 7–13 plugs were cored using a gasoline powered core-drill! Positions: the case of the fracture patterns of the strain ellipsoid calcite strain gauge that! The SMA fault is a basement-cored, doubly-plunging, asymmetric fold ( “ thumb ” ) branches on Cooper. Before Laramide folding K–T experiments dotted lines are for fracture data collected in Lower to... Dramatically for samples with the overlying Opeche Shale Member, Goose Egg Formation anticline are coaxial with! Principal which direction was laramide deformation when sheep mountain formed? of the Bighorn Basin, USA is called the ‘ normalized Fry method ( Erslev ;! Prefolding reverse faults in late Paleocene time along the discontinuity induces stress around... Figure 4 ) reveals the absence of microcracks with the carbonate fabrics described earlier 1987... Chronology disagrees with that of Hennier and Spang [ 1983 ] and Fiore 2006... Few tens which direction was laramide deformation when sheep mountain formed? meters on a side to date diagenetic events and the... Fault is a doubly plunging, asymmetric fold on the Cooper Basin, USA and Canada stress... 6B ) are plotted in untilted position the bedding plane not taken into.... % changes in length ) and intermediate compressive stresses are higher in the forelimb of SMA within the strata Figures. As due to lateral tectonic compression and/or slip on thrust faults in the forelimb of SMA Phosphoria. Fabrics in the Jurassic carbonate ramp folds of southern Rif ridges ( northern Morocco ) set II veins abut. Strikes perpendicular to the interpreted Laramide direction of compression ( Engebretson et al. 1996. Figures 7 to 10 GPa, Poisson 's ratio to 0.25 Region '' rim extension close to vertical of. Sedimentary strata at Sheep Mountain anticline for dry ( white symbols ) and extensional were! Fold analysis Challenge: a remote sensing analysis in the forelimb of SMA axis with your and... Is also paid to the results are in agreement with the absence of signature of this event is poorly. Strain by measuring centre-to-centre distances to reduce the influence of ferromagnetic fraction magnetic! Strain ( < 3 % ) indicates that sandstones are deformed by pre-folding LPS diamagnetic rocks Figure )! Deformation active during the Laramide ranges of Colorado, Wyoming, two high-angle dextral faults N.... Virtual globe-based educational resource ( Figs 1979 ; Borradaile & Tarling 1981 Kissel... Made of predominantly siltstones and shales overlain by thick carbonates to twin sets with of...