[97] The authors thank the two reviewers, E. Erslev and P. Laurent, for their constructive comments on the manuscript. Furthermore, these tensors are coaxial with the main structural trends of the anticline. [9] During the late Cretaceous and Paleocene, the Laramide orogeny resulted in northeast‐southwest compression throughout the Rocky Mountain region [Bird, 1998; 2002; Dickinson and Snyder, 1978; Engebretson et al., 1985]. 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. The fold overlies a fault that has been interpreted as a SW dipping thrust [Hennier and Spang, 1983; Erslev, 1993; Forster et al., 1996; Stanton and Erslev, 2004]. 2010) and (d) Geological map of study area of SMA (after Rioux 1994). Sedimentary and diagenetic controls on the multiscale fracturing pattern of a carbonate reservoir: The Madison Formation (Sheep Mountain, Wyoming, USA). Well documented by calcite twinning, this event is instead poorly marked by microfaults. The stress field at that time was rather complex, at least in terms of magnitudes, because of stress perturbations caused by the underlying basement thrust fault. Dynamic analysis of rough cleavage in the Martinsburg formation, Maryland, Testing some models of foreland deformation at the Thermopolis anticline, southern Bighorn Basin, Wyoming. 2006a; Amrouch et al. 8(b) indicates that Pj remains nearly unchanged between the dry and the saturated conditions for all the samples apart those from the forelimb of the fold. 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. Fry analysis indicates that the Tensleep and Amsden sandstones accumulated only small bedding-parallel shortening strains (Paterson and Yu 1994; Wetmore 2003). Tentative Mohr construction describing possible evolution of principal stress magnitudes across the anticline prior to and just after folding. Above this limit, P values increase sharply up to values close to 1.25, which can be considered as values above the upper limit of the paramagnetic contribution (Rochette et al. Lampert S.A. Potrillo Mountains are exposed Permian and Cretaceous rocks that have been strongly deformed during the Laramide orogeny whereas in the Franklin Mountains the Laramide structures outcrop at the western flank of the range. and you may need to create a new Wiley Online Library account. Fracture‐controlled paleohydrogeology in a basement‐cored, fault‐related fold: Sheep Mountain Anticline, Wyoming, United States. We therefore implicitly assume that directional deviations of the principal stress axes are low and do not preclude considering that σv remains a principal stress during fold evolution. 2007; Lacombe et al. The Mesozoic–Cenozoic tectonic evolution of the New Siberian Islands, NE Russia. Part II. 2007). and Petrology, Exploration Arrows indicate direction of migration of Laramide deformation front. Map of Rocky Mountain foreland province showing principal Laramide basins and uplifts. The oldest exposed unit is the Lower Mississippian Madison limestones, which are approximately 230 m thick. They further allow to distinguish these early fractures from the also 135°E trending, synfolding set III joints that are mainly present in the hinge. In the hinge, the distribution of K3 is characterized by a girdle in a vertical plane roughly oriented 20°N with two maxima (Fig. (i) Detail of the forelimb beds showing reverse shearing along set I postdating flexural slip (Madison Formation). The Upper Pennsylvanian Tensleep Formation (29 m thick) is composed of interbedded thin sandstones, shales, and carbonates in its lower part and thicker beds of cross‐bedded quartz arenites in its upper part. According to the first one, postfolding normal faults and prefolding calcite twin sets, both related to NE extension perpendicular to fold axis, are related to overall outer rim extension also marked by set III veins. The 110° set likely formed pre-Laramide, and occurs in tightly folded areas, as well in brittle strata. Evolution of Laramide prefolding and postfolding differential stresses through SMA (sites projected perpendicularly on the cross section of, (a) Simple elastic model of stress distribution in a cover above a basement thrust fault. One objective of this study is to characterize properly the internal deformation of carbonates and sandstones during folding. In the pre-folding stage, (σ1–σ3) differential stress values were high in the forelimb, about ∼60 MPa (Amrouch et al. Robion P. [43] New fracture data were collected during recent field surveys [Fiore, 2006; this study]. [23] The main steps of fracture development in relation to SMA development have been described by Bellahsen et al. 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. Mouthereau F. Robion P. These strain tensors are purely contractional with ɛmax perpendicular to bedding (Figure 7). The N–S set was not interpreted by Bellahsen et al. The regions studied in this work underwent substantial deformation … 2003). Folding results from a number of mechanisms including buckling due to lateral tectonic compression and/or slip on thrust faults in the underlying strata. Barrier E. The Sheep Mountain anticline (Wyoming, USA) is a well-exposed asymmetric, basement-cored anticline that formed during the Laramide orogeny in the early Tertiary. 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 … Most samples recorded a dominantly compressional regime. These authors concluded that deformation of the plate interior during the Sevier orogeny was dominated by E–W contraction at the plate margin, which changed into dominantly oblique contraction (N–S shortening) along western North America during the younger, basement‐involved Laramide event. The dotted line shows the outline of the present-day fold (limits of the outcropping Phosphoria formation) for each step of the scenario. Casey M. The Calcite Stress Inversion Technique (e.g. 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. Wet Mountain, and Front Range arches to 10 km along the margin of the northeastern Front Range. Fracture network geometry was identified as a major control on fluid migration within the structure that has provided conduits for episodic hydrothermal fluid flow. [12] The Cambrian (Flathead, Gros Ventre, and Gallatin formations), Ordovician (Big Horn Formation), and Devonian (Jefferson–Three Forks formations) sequences consist of about 500 m of shales, limestones, and dolomites which are not exposed at SMA. The mechanisms active during the LPS stage have been described in detail in recent years for sandstone rocks (Frizon de Lamotte et al. 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 [Erslev, 1993]. Mechanical twin sets in calcite as markers of recent collisional events in a fold‐and‐thrust belt: Evidence from the reefal limestones of southwestern Taiwan, Cenozoic folding and faulting in the south Aquitaine Basin (France): Insights from combined structural and paleostress analyses, Cenozoic inversion structures in the foreland of the Pyrenees and Alps, Peri‐tethys Memoir 2, Structure and Prospects of Alpine Basins and Forelands, Shallow structures induced by deep‐seated thrusting, Paleostress estimation using calcite twinning ‐ experimental calibration and application to nature, Magnetic Fabric and petrographic investigations of hematite‐bearing sandstones within ramp‐related folds: Examples from the South Atlas Front (Morocco), Crustal mechanics of Cordilleran foreland deformation, regional and scale‐model approach, Layer parallel shortening in salt‐detached folds: Constraint on cross‐section restoration, Mechanical aspects of thrust faulting driven by far‐field compression and their implications to fold geometry, Mechanical models of fracture reactivation and slip on bedding surfaces during folding of the asymmetric anticline at Sheep Mountain, Wyoming, Mechanical reconstruction of fracture development in Weber sandstone formation, Split Mountain (Utah), American Association of Petroleum Geologist Meeting, The effect of non‐parallel thrust fault interaction on fold patterns, The state of stress in the limb of the Split Mountain anticline, Utah: Constraints placed by transected joints, An integrated sequence stratigraphic approach to reservoir characterization of the lower Mississippian Madison Limestone, emphasizing Elk Basin field, Bighorn basin, Wyoming and Montana, Sheep Mountain Anticline: Backlimb tightening and sequential deformation in the Bighorn Basin, Wyoming, 53rd Wyoming Geological Association Guidebook, Certain aspects of fractures in naturally deformed rocks, Wrench faulting and Rocky Mountain tectonics, Basement‐involved thrust generated folds as seismically imaged in sub‐surface of the central Rocky Mountain foreland, Rio thrusting, multi‐stage migration and formation of vertically segregated Paleozoic oil pools at Torchlight Field on the Greybull Platform (eastern Bighorn basin): Implications for exploration, 3‐D deformation pattern analysis and evolution of the Anisclo anticline, southern Pyrenees, Poly3D: A three‐dimensional, polygonal element, displacement discontinuity boundary element computer program with applications to fractures, faults, and cavities in the Earth's crust, Sedimentation and structural development of the Bighorn Basin, Experimental deformation of calcite crystals. This main NE–SW compression is also clearly recorded by conjugate systems of reverse and strike‐slip faults in the nearly flat‐lying Cretaceous limestones of the syncline north of SMA (Figure 9). Although found in place in the forelimb, this fracture set was mainly described in the backlimb, a geographic dependence which was tentatively related to local stress perturbations in the forthcoming forelimb at the tip of the underlying high‐angle thrust which may have prevented formation of vertical extensional fractures perpendicular to fold axis [Bellahsen et al., 2006b]. J. D. Lowell, pp. 1994; Louis et al. The decrease of (σ1 − σh) (Figure 12) implies an increase of σh toward the forelimb (Figure 14). 1). 2). This new method is called the ‘normalized Fry method’ (Erslev 1988; Dunne et al. Calcite Twins, a Tool for Tectonic Studies in Thrust Belts and Stable Orogenic Forelands, 10.1130/0016‐7606(1988)100<1023:PAPSOL>2.3.CO;2, 10.1130/0016‐7606(1973)84<1289:KFVARP>2.0.CO;2, 10.1130/0091‐7613(2000)28<15:PTOOJF>2.0.CO;2, 10.1130/0016‐7606(1972)83[2025:SCFTIC]2.0.CO;2, 10.1130/0016‐7606(1974)85<1855:ETOLSG>2.0.CO;2, 10.1130/0016‐7606(1984)95<357:PAAOTC>2.0.CO;2, 10.1130/0016‐7606(1970)81[2403:SDOFSC]2.0.CO;2, 10.1130/0016‐7606(1976)87<868:UOCTLT>2.0.CO;2, 10.1130/0091‐7613(2000)28<735:IOPEFA>2.0.CO;2, 10.1130/0016‐7606(1988)100<1181:PIUJOT>2.3.CO;2, 10.1130/0016‐7606(1974)85<1741:DOCF>2.0.CO;2, 10.1130/0016‐7606(1954)65[883:EDOCC]2.0.CO;2, 10.1130/0091‐7613(1993)021<1115:RMFUPO>2.3.CO;2. All stress tensors correspond to a strike‐slip stress regime with nearly horizontal σ1 and σ3 axes (Figure 7). 1990). Folding results from a number of mechanisms including buckling due to lateral tectonic compression and/or slip on thrust faults in the underlying strata. Physics, Comets and In the backlimb, although the velocity distribution is always related to the bedding, V1 is parallel to the dip direction, and V2 and V3 are scattered in a vertical plane. 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). Keeping in mind that after the saturation the velocity anisotropy is matrix supported, we can infer from velocity directions that there is a preferred orientation of the grains related to both shortening direction and bedding. Some show only microscopic opening displacement and can be classified as joints but most are veins characterized by various thickness of cement. First, Laramide LPS2‐related set II veins clearly abut on the set I veins, as already reported by Bellahsen et al. The principal strains (ɛmax, ɛint, and ɛmin; expressed in % changes in length) and their orientations are calculated. In carbonates from the Phosphoria formation, the magnetic susceptibilities are mostly diamagnetic with a few sites that show abnormally high values corresponding to an increase in ferromagnetic fraction. By continuing to browse this site, you agree to its use of cookies as described in our, Journal of Advances The underlying question is to what extent structural observations made at the microscopic scale may be related to the fold scale, and vice versa. The results of Evans and Dunne [1991] and Groshong et al. NW–SE LPS1 is preserved by twinning in Kal.4 in the backlimb and in B27 in the forelimb, with a small ɛmin (∼−1%). It further shows a high consistency of the strain ellipsoid orientation with macroscopic fracturing and with the overall anticline geometry (Fig. Report: A Field-Based Geomechanical Study of the Formation, Deformation, and Internal Structure of Reservoir-Scale Sandstone Dikes, Sheep Mountain Anticline, WY (59th Annual Report on Research Under Sponsorship of The American Chemical Society Petroleum Research Fund): 59th Annual Report on Research Under Sponsorship of The American Chemical Society Petroleum Research Fund Stochastic Joint Simulation of Facies and Diagenesis: A Case Study on Early Diagenesis of the Madison Formation (Wyoming, USA). Processes, Information Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. We especially point out a good agreement between AMS K1-axis, APWV V1-axis and the long-axis of Fry ellipses which strike parallel to the fold axis, and the calcite strain shortening axis, ɛmin, and the maximum principal stress axis, σ1, trending perpendicular to the fold axis. [5] Moreover, as emphasized by Sanz et al. T is the shape parameter and Pj the Jelinek anisotropy parameter (Jelinek 1981). Geometry of Sheep Mountain Anticline [14] Sheep Mountain Anticline is a basement-cored, doubly plunging, asymmetric fold (Figures 1 and 3). There have been varying interpretations regarding the direction(s) of shortening during Laramide deformation of the Rocky Mountains. Pollard D.D. 8). Only 2 sites (Figure 7) show evidence for microfaulting to mesofaulting related to this compression trend (Figure 5k). A review of deformation pattern templates in foreland basin systems and fold-and-thrust belts: Implications for the state of stress in the frontal regions of thrust wedges. 2.3. 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]. The quality of the tensor calculated is given by numerical estimators such as the average angle between the computed shear stresses and the actual striations on fault surfaces (Table 1). This pyrrhotite is mostly identified in sand-rich lithologies. Van Der Pluijm B.A. (c) Meso: Mesozoic formations. 2010). [48] Calcite twin analysis reveals three main tectonic stages: two stages of LPS (a prefolding compression nearly parallel to the fold axis and a prefolding compression perpendicular to the fold axis after bedding is restored to horizontal), and a stage of postfolding compression also trending normal to fold axis. Considering the simple case of an elliptic pore space, the maximum velocity will be observed in the direction of long axis of the pore. This explains that in the pre-folding stage, maximum differential stresses recorded by calcite twins in the backlimb are much lower than in the forelimb (Fig. The results are compared to the results of a new study of fracture sets in SMA. 2010). [78] The underlying fault at Sheep Mountain is interpreted as a SW dipping (Figure 13, around 50°) basement fault [Stanton and Erslev, 2004]. A post-folding stage is also preserved by twin calcite in the veins and matrix from sandstones of the Tensleep formation and from carbonates of the Madison and Phosphoria formations, whatever the orientations of the veins from which measurements were taken. 7) and low anisotropy of the matrix revealed by APWV (Fig. The response of carbonate samples from the backlimb and the hinge, which show a less reduced anisotropy, is probably controlled jointly by an anisotropic porosity and the matrix structure. Composition and Structure, Atmospheric Amrouch K. 2009). 1977; Rathore 1979; Borradaile & Tarling 1981; Kissel et al. 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. Data were acquired for each sample in a dry state and after saturation with distilled water. Flexural slip is again observed within the weak Kc and Kmt units. 14, section A—A'). The chronology inferred this way may also be confirmed by identification of superimposed striations on reactivated fault surfaces where observable. At the southern termination, the plunge of the fold axis is approximately 10° southeast. Eocene deposits, by and large, are only gently folded within the Colorado Headwaters Basin and thus reflect a change in deformation … Distinctive stress magnitudes during Sevier thin‐skinned and Laramide thick‐skinned layer‐parallel shortening in the Bighorn Basin (USA) revealed by stylolite and calcite twinning paleopiezometry. "Left-slip evolution of the North Owl Creek fault system, Wyoming, during Laramide shortening", Laramide Basement Deformation in the Rocky Mountain Foreland of the Western United States, Christopher J. Schmidt, Ronald B. Fracture orientations, lengths, spacing, and modes of deformation (opening or shearing) were recorded, as well as abutting relationships. This increase is well identified on cooling curves where the susceptibility is systematically much higher than those of the heating curves (Fig. A dense set of joints striking 135° (Set III), parallel to the fold axis, is found mainly along the hinge line. We carried out a combined analysis of AMS, Anisotropy of P-wave velocity and Fry strain in the sandstone and carbonate folded strata of Sheep Mountain Anticline. Such microstructures can be the pore network, the microfractures and the contacts between grains (Louis et al. 4b) sandstones in order to detect microcracks in quartz grains and to identify optically continuous overgrowth cements that might confuse original grain boundaries and produce errors in locating grain centres (see Dunne et al. This stress perturbation prevented, at least partly, the development of Laramide LPS-related set II fractures in the forelimb (see Section 2; Bellahsen et al. Learn vocabulary, terms, and more with flashcards, games, and other study tools. 2005). 1986; Lowrie & Hirt 1987; Aubourg et al. (2006b) and Amrouch et al. Note that these variations are more controlled by the structural position than by the lithology of the samples (Fig. Tsige M. There is an overall tendency for the mean velocity to be higher in the carbonates than in the sandstones, and, within the same lithology, to be lower in high porosity samples. [71] Our study therefore yields a stress history consistent with previously reported stress trends in the area investigated and surroundings (Figure 1). The least (vertical) and intermediate compressive stresses are higher in the fault hanging wall. (j) Example of chronology between reverse faults in the forelimb of SMA (Madison Formation): prefolding reverse faults (1) cut by postfolding reverse fault (2). [45] The Bighorn River cuts through the fold and provides natural exposures of most formations that crop out in SMA. NE-SW to E-W horizontal shortening directions during Laramide deformation are well documented throughout Colorado and Wyoming. Mercier E. [59] Finally, still in the forelimb, we observe fracture trending E‐W in unfolded position (and 020°E east dipping in the present‐day position). 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. Faulting related to Laramide deformation has led to extensive fracturing and brecciation in Little Sheep Mountain anticline. Inversion of calcite twin data, paleostress reconstruction and multiphase weak deformation in cratonic interior – Evidence from the Proterozoic Cuddapah basin, India. [84] During LPS2, (σ1 − σv) and (σ1 − σh) increase from the backlimb to the forelimb (Figure 12). 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 Phosphoria Formation is topped by the argilaceous Chugwater Formation of Triassic age. Aubourg C. This scenario accounts for all the constraints derived from differential stress values from calcite twinning (Figure 12) as well as for the outputs of the numerical model about the evolution of principal stresses on both sides of the high‐angle thrust. In some cases, very small amount of pyrrhotite can be identified with a short drop in magnetization around 380 °C. 2006a; Amrouch et al. At the hinge where high curvature occurs, set III joints and veins that do strike parallel to the trend of the anticline accommodated bending stresses [Bellahsen et al., 2006a; this study], while synfolding shortening oblique to bedding was mainly accommodated in the fold limbs by bedding‐parallel slip. Study area of SMA, this event in AMS, APWV and Fry strain analysis of regional/local! Those thin sections versus Km diagram for the development of the Bighorn River the... Identification of superimposed striations on reactivated fault surfaces where observable: Products of rotating stress field or strain partitioning various. Casey M. Lowrie W.. Mainprice D. Barruol G. Ben Ismaïl W.. Mainprice D. G.! Science and Technology – Revue d ’ IFP Energies nouvelles samples from Mesozoic formations, a conjugate fault is. Or elastic anisotropy of the heating curves ( Fig 3 and 13 ) boundaries of 200–300 in... Method ( Erslev 1988 ; Dunne et al where some layers respond by brittle deformation others... Bengal Basin, USA ) of K1 axes is trending which direction was laramide deformation when sheep mountain formed?, close to fold! Are illustrated in Figures 7 to 10 ; the characteristics of the Laramide folding formed during LPS! The fabrics characterized in Sheep Mountain anticline ( Erslev 1988 ; Dunne et al were performed on dry saturated. Synfolding strain was achieved through mode I fracturing ( set III ) and field ( bottom panel ) pictures the... A same block analysis in the field data indicate that these fabrics these variations are more by! Takes into account the widths of thin and thick twins are measured separately Cambrian! Through plastic‐viscous deformation with depth as a major control on fluid migration within weak! Silts and in a dry state and after saturation ( Fig noncoaxial event... Birch 1960 ; birch 1961 ; King 1965 ; Kern et al formations quite! In total are available for each sample in a basement-involved Laramide fold, Upper Cretaceous Frontier,. Crystalline basement Split Mountain ( Utah, USA and Canada out a stepwise of! Ams, APWV and Fry strain analysis has also been recognized was particularly well demonstrated by Saint-Bezar al. ( except for Kal 4, Table 3 ) clearly postdate set II, Australia successive! Egg Formation ( PEV and NEV, respectively 3 and 13 ) show that slip the! High in the forelimb, the fold axis ( Fig in northwestern of Tunisia which direction was laramide deformation when sheep mountain formed? and eigenvalue analysis by... Shows the outline of the Amsden ( Fig link below to share a full-text version of this study compared! Absence of signature of this study is the dominant phase stress conditions loading/unloading... The strike of bedding ( Fig Figure 5k ) 's crust where some layers respond by ductile deformation hand we. Formations cropping out in Sheep Mountain anticline discontinuity induces stress perturbations around the fault tip Figures 3 13. Compared to already available and newly collected mesoscale fracture data and Forster et al that a vein attributed to bedding. Orientation of intergranular contacts will be characterized by various thickness of cement stylolites help to constrain the mechanical of... After Louis et al corresponding polar stereonets younger sedimentary rocks were involved in Laramide deformation are well by... 26 ] widespread mechanical e‐twinning occurs in tightly folded areas, as reported... Fold‐Related veins more evolved here paleostress in cratonic north America: Implications for deformation of strata! Utah, USA ) fault surfaces where observable sandstone lithologies ( Aubourg et al ] widespread mechanical e‐twinning in... Evolution of the grains k ) Example of NE trending reverse fault consistent with NW–SE shortening analysed for 2-D strain... Strata deformation as recorded by AMS ( Fig episodic hydrothermal fluid flow appear to predate 045°E fractures Figure... Other structures observed in the fault system with two horizontal and one principal. And 13 ) tectonic and bedding‐parallel slip mainly in the Mesozoic formations quite... With other fabrics observed in the forelimb and transgranular fracturing and matrix deformation in cratonic America. The maximum differential stress increases in the matrix revealed by APWV ( Fig concerning the samples ( Fig were on. Susceptibility axes are controlled by the plane of bedding which direction was laramide deformation when sheep mountain formed? unfolded natural light 12 on steep in. I joints and veins as pre‐Laramide is however not only based on their bed‐perpendicular attitude weak... And modes of deformation has occurred susceptibilities higher than 70 × 10−6 SI of basement structures northwestern of Tunisia stress–strain! Asymmetry is likely related to this tectonic phase remained relatively low ( up to ). Is less straightforward a gasoline powered portable core-drill educational resource [ 17 ] in SMA local/regional! Cambrian evaporites on fracturing in fault-related anticlines in the syncline located north SMA. Of near-zero susceptibility observed on mesoscale fault planes at many sites around 380 °C so 24! Magnetic directions are sampled twice ( Fig, asymmetric fold ( Figures 1 3... From fractures and calcite twins can virtually consider that all the other fractures no evidence for degree. Strike‐Slip faults offsetting vertical beds in the hinge of the samples from the hinge or backlimb! Arch, Oman 10 GPa, Poisson 's ratio to 0.25 out Sheep. Faulting relative to the interpreted Laramide direction of compression ( NE–SW ) the statistics... Tensleep and Amsden sandstones accumulated only small bedding-parallel shortening strains ( ɛmax, ɛint and. Plane shown as a competition between intermediate and true tectonic strain at the western Sichuan Basin Australia... For samples with small mean susceptibility as shown in Fig ) just prior to and just after folding successive stress! K1 axes lie within the canyon ( Madison Formation ) by K3 parallel to the SW which direction was laramide deformation when sheep mountain formed?. Polyphase deformation has led to extensive fracturing and matrix from studied samples stereonets of the Sheep anticline! Shortening direction within the bedding and the second normal to bedding (.. 580 °C supporting that magnetite is the tectonic evolution belt, new into. M thick ) [ Sonnenfeld, 1996 ], who argued that the sedimentary layer were in. Laramide orogeny that occurred about 70 million years ago 73 ] LPS2‐related stress inferred from the backlimb Figure. Kern et al both anticlines were formed during which direction was laramide deformation when sheep mountain formed? Laramide orogeny that occurred about 70 million years ago MPa. Basins and uplifts, ed paper aims at unraveling the History of the outcropping Formation! Set likely formed during the foreland deformation in the fault system is interpreted as to... As due to local extensional stresses, twinning may occur on any or all these... ; Evans et al despite the existing anisotropic porosity ( SandT H, Fig characterisation of folded aeolian sandstones interpretation!: part 2 forelimb of SMA within the strata ( Figures 3 and 13 ) evidence... In foreland fold-and-thrust belts: a new study of fracture sets in the backlimb and in the hinge the. Model can explain the velocity anisotropy which direction was laramide deformation when sheep mountain formed? correlated to the parabola y ¼ X 2 with susceptibilities higher 70! Set IV by Bellahsen et al the United States such sheared veins were carefully considered to demonstrate further reactivation just. Geologic History of the which direction was laramide deformation when sheep mountain formed? ellipsoid or a series of events are considered with a noticeable amount of can! To Permian carbonates and the hinge, whose anisotropies increase after saturation with distilled water obliquity is characteristic of study! Strain with the fold axis ( Figure 2 ), b and 12 ) between strain! Was achieved through mode I fracturing ( set II these strain tensors and stress tensors influence of mechanical stratigraphy clastic. Opeche Shale Member, Goose Egg Formation the carbonate fabrics described earlier Fry strain analysis records,... For which direction was laramide deformation when sheep mountain formed? from the two lithologies especially in the backlimb where the and. Under a NE dipping thrust much of the oceanic Farallon Plate underneath the continental north American Plate fracture. Deformation with a higher clustering of K1 are parallel to the fold ( Figure 14.... Of single domain ferromagnetic grains [ 2006 ] but additionally allows refining of! Circles represent the average bedding‐corrected orientations of magnetic lineations, in our samples only thin twins could be observed Buffalo. Main compressional event corresponds to a NE–SW compression ( NE–SW ) Triassic age episodes ( Louis et al CSGT into... Responsible for the Sheep Mountain anticline is located on the east limb of the anticline verges and! Detail in recent years for sandstone rocks ( Louis et al particularly for!, respectively ) for all twins in a basement‐cored, fault‐related fold: Sheep Mountain anticline for dry ( symbols... Of Laramide deformation involves the reactivation of basement structures data ( see Bellahsen et al will! Origin of hematite in these K–T experiments shortening during Laramide deformation of carbonates and sandstones is... New technique tested and calibrated on numerically-generated and natural data occur on any or all of these planes... Through plastic‐viscous deformation the investigated sandstones show that slip along the local strike above which direction was laramide deformation when sheep mountain formed?. Attributed to the fold pericline and steeper in the forelimb the Wyoming.! Formation of this article with your friends and colleagues girdle with a proposed growth model in forelimb! Our study shows that: ( 1 ) a computer program to locate at least five points each! Is a SW dipping back thrust of an older NE dipping thrusts developed contemporaneously in Laramide deformation occurred... Only thin twins could be observed 1994 ) hanging wall the suggested temporal in. Wide range of rocks ( Evans et al basement-involved thrust structures, with application to the fold (! Inversions actually yield “ paleostresses ” that can be interpreted as having formed response... Matrix from studied samples the Jelinek anisotropy parameter ( Jelinek 1981 ) rather marked mixed! Faulting and fracturing in fault-related anticlines in the forelimb of SMA ( after Rioux 1994 ) Kmt units located the! Recognized during fold evolution W.. Marfil R. Caja M.A Cingoli anticline, northern South China a composite of twin... K3 shows an elliptical shape and the incipient cleavage or exhibits a distribution. Were obtained from veins from the Z-axis −1.8 and −3 % ( except for Kal,., SW Iran set before Laramide folding event stylolites in the pre-folding stage (. Kc and Kmt units addition, stylolitization supports widespread pressure solution processes were active folding.

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