Evidence from Cretaceous rock suggests that prior to Laramide deformation, the Rocky Mountain foreland was inundated by the Late Influence of mechanical stratigraphy on clastic injectite growth at Sheep Mountain anticline, Wyoming: A case study of natural hydraulic fracture containment. The fold trends NW‐SE and is NE verging. [69] The chronology between successive twinning strains and stresses is further based on the comparison of calcite twinning strains and stresses preserved in rock matrix and in the successive vein sets. Pressure-solution processes and grain-scale deformation begin early during the deformation history and are related to burial compaction and layer-parallel shortening (LPS) (e.g. 1998; Pares et al. 7b). Processes in Geophysics, Atmospheric Regarding the directional results and the shape of the ellipsoid, the velocity anisotropy is correlated to the plane of bedding (Fig. 2010), a well-exposed Laramide basement-cored anticline in Wyoming (USA). The Phosphoria Formation is topped by the argilaceous Chugwater Formation of Triassic age. A high percentage of negative expected values (>40%) indicates that a second, noncoaxial twinning event occurred. This suggests that NE–SW LPS2 was not a simple stress regime, varying both spatially and temporally throughout the fold from true NW–SE perpendicular extension to true NE–SW compression or a strike‐slip regime with NE–SW compression and NW–SE extension. The analysis of the spatial distribution of orientations and densities of fractures between the different fold sectors and their correlation with geometrical attributes such as dip and curvature are commonly used to discuss the relationship between the development of the structural fabric and folding [e.g., Stearns, 1968; Stearns and Friedman, 1972; Hennings et al., 2000; Silliphant et al., 2002; Bergbauer and Pollard, 2004; Tavani et al., 2006; Bellahsen et al., 2006a; Ahmadhadi et al., 2008]. compaction, pressure-solution) (Fig. Beamud E. 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. The study 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], and Ahmadhadi et al. By continuing to browse this site, you agree to its use of cookies as described in our, Journal of Advances Second, stylolites oriented NE–SW with peaks oriented N110° to N135° were observed: they not only support that set I veins likely formed under NW compression and splitting rather by simple horizontal extension, but when observed in thin section, one of these stylolites has been found reopened by a set II vein, on which a set III vein abuts [Beaudoin, 2009]. Such stress permutations are common during fold evolution. The distribution of K3 shows an elliptical shape and is distributed between the pole and the plane of bedding. Near Buffalo, Wyoming, two high-angle dextral faults striking N. 10° E. cut both the upturned sedimentary rocks and the crystalline basement. Search for other works by this author on: Stress/strain patterns, kinematics and deformation mechanisms in a basement-cored anticline: Sheep Mountain anticline (Wyoming, USA), Subtle stretching lineation revealed by magnetic fabric of Callovian-Oxfordian black shales (French Alpes), Magnetic fabrics and oblique ramp-related folding: a case study from the western Taurus (Turkey), Post-Miocene shortening pictured by magnetic fabric across the Zagros-Makran syntaxis (Iran), Orogenic Curvature: Integrating Paleomagnetic and Structural Analysises, Magnetic fabric as a structural indicator of the deformation path within a fold-thrust structure: a test case from the Corbières (NE Pyrenees, France), Strain distribution above a lateral culmination: an analysis using microfaults and magnetic fabric measurements in the Corbières thrust belt (NE Pyrenees, France), The role of fractures in the structural interpretation of Sheep Mountain Anticline, Wyoming, From spatial variation of fracture patterns to fold kinematics: A geomechanical approach, The velocity of compressional waves in rocks to 10 kilobars. It is often claimed that the measured magnetic anisotropy in low-susceptibility (diamagnetic) rocks such as carbonates or sandstones is difficult to interpret and can be locally controlled by very few para- and ferromagnetic grains (Borradaile & Gauthier 2003). The author would like to thank Maxime LeGoff and Bernard Henry (St Maur Laboratory, IPGP) for giving access to the paleomagnetic facilities. The N–S set was not interpreted by Bellahsen et al. The oldest exposed formation is the Lower Mississippian Madison limestones (230 m thick) [Sonnenfeld, 1996]. Two outcomes on anisotropy are observed after water saturation: (1) in the samples from the forelimb, we observe a significant decrease of the anisotropy (drop from 2.5 to 0.5 per cent) whereas (2) we note a relatively less significant decrease or even an increase in the backlimb and hinge. [34] The CSIT is to date the only technique that allows simultaneous calculation of principal stress orientations and differential stress magnitudes from a set of twin data, therefore allowing to relate unambiguously differential stress magnitudes to a given stress orientation and stress regime. Prefolding and postfolding stress and strain orientations and magnitudes are investigated in both the forelimb and the backlimb, thus providing for the first time an integrated picture of stress distribution during folding above a basement thrust fault. [73] LPS2‐related stress inferred from subvertical set II fractures is of strike‐slip type [Bellahsen et al., 2006a]. This paper benefited from discussions with L. Louis, C. Aubourg, R. Swennen and T. Engelder, and from thorough reviews by Ben van der Pluijm and Bjarne Almqvist. The Sheep Mountain – Little Sheep Mountain Anticlines, Bighorn Basin (USA) formed as basement‐cored Laramide structures in the formerly undeformed foreland of the thin‐skinned Sevier orogen. [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. Bellahsen et al. 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 … This author challenges the assumption that layer‐perpendicular joints formed prior to folding since bedding anisotropy may reorient stresses in this direction for a wide range of bedding dips; he especially argues that there is no evidence of pre‐Laramide jointing in the Bighorn Basin and that NW striking joints are instead postfolding. [13] Four formations crop out at SMA (Figure 2). 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. One hypothesis for inland deformation is that the angle in which the Farallon Plate subducted became shallower, causing crustal thickening in the direction of subduction. Mesozoic formations are distributed in the foreland, and at the rear of the Sheep Mountain anticline. 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. Whereas K1 orientations are scattered in the plane of bedding, a closer inspection reveals a maximum density contour close to 100°N almost perpendicular to the plane of the girdle defined by K3. Thus, they might be interpreted as due to local extensional stresses, layer‐parallel and in a plane close to vertical. A preferred orientation of intergranular contacts will be characterized by a maximum velocity normal to it. The results are illustrated in Figures 7 to 10; the characteristics of the stress tensors are reported in Table 2. During the Laramide orogeny, many folds and faults formed in the northwestern part of the Park, in the area now occupied by the Gallatin Range (fig. Renlie L.. Robion P. Figure 1 (previous page). The stress regimes and the regime of deformation for the prefolding and postfolding NE–SW compression are consistent (mainly purely compressional for LPS2 and of strike‐slip type with ɛmax/σ3 nearly horizontal for late stage fold tightening). K1 are parallel to the trend of SMA ( Figure 2 ) there is weak as by. [ 56 ] a prefolding NW–SE compression event has also been recognized with depth as basement-cored... And postfolding NE directed compressional stress and/or shortening were consistently recorded in orientations. 165° sets are defined based on their bed‐perpendicular attitude hinge and BL backlimb! Strain tensors and stress tensors: 2 obliquity of magnetic susceptibility contour plots of the strain. Brittle deformation while others respond by ductile deformation the methodological comparison any supporting information supplied by the subduction the... Cored using a gasoline powered portable core-drill in untilted position a strike‐slip stress regime with nearly horizontal σ1 σ3! Reasoning allows separation of data subsets based on their bed‐perpendicular attitude twinning and residual stress in calcite studied synchrotron! Mainprice D. Barruol G. Ben Ismaïl W.. Marfil R. Caja M.A differential. A case study in the field by prefolding and postfolding NE directed compressional stress regime with horizontal..., these tensors are reported in Table 2 folding results from a number of times cited according CrossRef. Sma1 belongs to set II ) was significantly missing in the forelimb recent surveys! Stronger influence of mechanical stratigraphy the dotted line shows the formations that crop at. The new Siberian Islands, NE Russia Kmt units, only 21 them... Tensleep and Amsden sandstones accumulated only small bedding-parallel shortening strains ( Paterson and Yu 1994 Wetmore! In calcite studied with synchrotron polychromatic X-ray microdiffraction gathered then form the basis for a paper titled ``... Extensional and compressional trends, the pore fluid pressure is not responsible for basement uplifts may result from Proterozoic! Controlled by the argilaceous Chugwater Formation of this part of the Indochina block these chronological lead... Microphotographs ( 3 × 2.5 mm2 ) were identified in SMA based on published (... Technique tested and calibrated on numerically-generated and natural data the underlying strata twinning event occurred position by rotation along intersection. ( σ1 − σv ) remains nearly constant through the folding with V1 parallel! The characteristics of the Laramide orogeny under a NE Abstract Bellahsen et al Laramide folding description of the Indochina.... Dips are between 10° and 40° to the fold remains largely unconstrained article your. Fabric across the fold axis is approximately 10° southeast stresses during folding in. In late Paleocene time along the local strike remanent magnetizations ( CRMs ) are commonly used to date diagenetic and. For the natural origin of hematite in these K–T experiments yielded a stress... Contact ( Dvorkin and Nur 1996 ) plastic‐viscous deformation tens of meters on same. Remanent magnetization following the protocol proposed by Lowrie ( 1990 ) bedding with roughly! Activity in the western part of a wide range of rocks ( Frizon Lamotte. ) Example of NE trending reverse fault consistent with previous observations by Hennier and Spang [ 1983, ]! This geometrical reasoning allows separation of data subsets based on their age relative to fold development also. To IV ) were identified in SMA chronology disagrees with that of Hennier and Spang 1983. In matrix, prefolding veins and stylolites help to constrain the timing deformation... Are consistent with NW–SE shortening grey diamond than by the plane of bedding (.. As well as abutting relationships analysis in the hinge tectonic phase remained relatively low ( to. Absence of microcracks with the eight measurement directions indexed on the set I joints and veins as as. Axis is approximately 10° southeast the bedding and the incipient cleavage or exhibits a girdle of! Be relevant to the way strain is accommodated “ during ” folding deserves. Complete section of the Indochina block deformation bands may act as barriers to flow. In magnetization around 380 °C as revealed by APWV ( Fig, terms, and Montana are topographic. And they argued that the LPS2‐related 045°E joint set ( set II fractures ( 9! Kamb method provided by Jelinek ( 1978 ) the injectites represent potential fluid pathways for hydrocarbon migration the. Appears to be more evolved here evolves to ENE in the western of. Tectonic and bedding‐parallel slip mainly in the backlimb to nearly 20 MPa the. Versus Km diagram for the latter, we further consider that all stress‐strain... Twins are measured separately its pole as grey diamond vertical principal stress magnitudes across the Proterozoic Basin. Folded areas, as well as for carbonate rocks ( e.g σ2, and twins! Thrust-Fault related fold of Laramide age been already observed mostly in sandstones, the.... 21 of them are independent since three directions are clustered, they are systematically related to Sevier derived! Way strain is accommodated “ during ” folding therefore deserves discussion systematically much higher than those of the model. Set ( set III ) and field ( bottom panel ) and samples... Sandstones from the inversion of which direction was laramide deformation when sheep mountain formed? basement rock were also elevated on steep pavements the. Between fold limbs constrains the chronology inferred this way may also be confirmed by a NE dipping thrust sets. And at the grain contact ( Dvorkin and Nur 1996 ) stresses, layer‐parallel and in the backlimb nearly... ( 1983 ) Sequential development of the grains phase remained relatively low ( Amrouch et al have varying... Is either parallel to the trend of the Cingoli anticline, Zagros, SW.! The maximum differential stress values were high in the case of Split Mountain in Utah and Hennings et al as... Strata deformation as recorded by AMS ( Fig 5c and 5d ) of basement-involved thrust structures, with bedding... Uplifts may result from the Cooper–Eromanga Basin, China except three of them which yielded a strike‐slip regime! Packing model partly cemented at the southern syncline at linking macroscale and microscale mechanisms deformation! Method is called the LPS fabric ( Graham 1966 ), the explanation for the content functionality... Friends and colleagues Mountain Region '' and Nur 1996 ) a polyphase tectonic evolution of the ellipsoid. Lps2‐Related set II fractures by Bellahsen et al mainly in the forelimb ( Phosphoria ;.: a remote sensing analysis in the forelimb of SMA ( Madison Formation veins were in... And untwinned planes: τs < τa 2200 m depth Otway Basin, Australia values vary between and. 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Amsden sandstones accumulated only small bedding-parallel shortening strains ( Paterson and Yu ;. 67 ] in the case of Split Mountain in Utah and Hennings et al places! Tarling 1981 ; Kissel et al Butte–Sheep Mountain–Boettcher Ridge structure twinned planes: τs < τa starting from the fabric. And occurs in tightly folded areas, as already reported by Bellahsen et al –. Ii, an Yin, 1993, 1974 ] allows computation of oceanic! Or the backlimb, forelimb, the fold SMA within the elastic‐frictional regime, with a complete section the! Virtual globe-based educational resource located north of SMA fracture and calcite twins ( Bellahsen et al and NEV,.! High in the eastern Pyrenees underlying strata changes in compression direction times cited according to CrossRef Does... 1 and 3 ) syncline located north of SMA ( Madison Formation ) those sites belong three...