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  • 1
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    The Initiation, Propagation, and Arrest of Joints and Other Fractures (2004)
    London : The Geological Society
    Details
    Description / Table of Contents: This volume is a state of the art look at our understanding of joint development in the crust. Answers are provided for such questions as the mechanisms by which joints are initiated, the factors controlling the path they follow during the propagation process, and the processes responsible for the arrest of joints. Many of the answers to these questions can be inferred from the geometry of joint surface morphology and joint patterns. Joints are a record of the orientation of stress at the time of propagation and as such they are also useful records of ancient stress fields, regional and local. Because outcrop and subsurface views of joints are limited, statistical techniques are required to characterize joints and joint sets. Finally, joints are subject to post-propagation stresses that further localize deformation and are the focus for the development of new structures.
    Pages: Online-Ressource (VI, 330 Seiten)
    ISBN: 1862391653
    URL: http://sp.lyellcollection.org/content/231/1.toc
    Language: English
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    E-BOOK
  • 2
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    Magnetic and mineral fabric development in the Ordovician Martinsburg Formation in the Central Appalachian Fold and Thrust Belt, Pennsylvania (2007)
    In:  Geological Society Special Publication 238: 109-126.
    Details
    Publication Date: 2007-10-08
    Description: The Martinsburg Formation at Lehigh Gap, Pennsylvania, undergoes a transition from shales to slates, reflecting local progressive deformation on an outcrop scale. The anisotropy of magnetic susceptibility (AMS) was measured in low and high fields. The high-field measurements show that the magnetic susceptibility is controlled by the paramagnetic minerals. X-ray goniometry was used to define the mineral fabrics of chlorite and mica. The phyllosilicates are initially oriented preferentially in the bedding plane and are gradually reoriented into the cleavage plane through rotation, microfolding and recrystallization. The AMS fabric mirrors this change in mineral fabric. The magnetic fabric is originally oblate in the least deformed site, with the plane of flattening parallel to bedding, and becomes prolate with increasing deformation, reflecting the development of pencil structure in the shales. In the most deformed site, shortening results in a tectonic cleavage fabric, which controls the magnetic fabric. A similar pattern of fabric development can be observed on a regional scale at other sites across the central Appalachian fold and thrust belt. The AMS and mineral fabric from the Martinsburg Formation has undergone bedding compaction in the foreland near the Allegheny Front. The AMS and textural analysis both show that, as the deformation increases towards the hinterland, prolate fabrics develop and in the most deformed sites slaty cleavage controls both the mineral and magnetic fabrics.
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  • 3
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    The Initiation, Propagation, and Arrest of Joints and Other Fractures
    Geological Society of London
    In:  New York, Geological Society of London, vol. 231, no. 3, pp. 2-203, (ISBN 1-86239-165-3, vi + 330 pp.)
    Details
    Keywords: Rock mechanics ; Structural geology ; cracks and fractures (.NE. fracturing) ; Fracture ; Friction
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    Capillary tension and imbibition sequester frack fluid in Marcellus gas shale (2012)
    National Academy of Sciences
    Details
    Publication Date: 2012-12-10
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 5
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    Sequence stratigraphy and depositional environments of the Shamokin (Union Springs) Member, Marcellus Formation, and associated strata in the middle Appalachian Basin (2014)
    American Association of Petroleum Geologists (AAPG)
    Details
    Publication Date: 2014-03-04
    Description: Organic-carbon–rich shales of the lower Marcellus Formation were deposited at the toe and basinward of a prograding clinothem associated with a Mahantango Formation delta complex centered near Harrisburg, Pennsylvania. Distribution of these organic-carbon–rich shales was influenced by shifts in the delta complex driven by changes in rates of accommodation creation and by a topographically high carbonate bank that formed along the Findlay-Algonquin arch during deposition of the Onondaga Formation. Specifically, we interpret the Union Springs member (Shamokin Member of the Marcellus Formation) and the Onondaga Formation as comprising a single third-order depositional sequence. The Onondaga Formation was deposited in the lowstand to transgressive systems tract, and the Union Springs member was deposited in the transgressive, highstand, and falling-stage systems tract. The regional extent of parasequences, systems tracts, and the interpreted depositional sequence suggest that base-level fluctuations were primarily caused by allogenic forcing—eustasy, climate, or regional thermal uplift or subsidence—instead of basement fault reactivation as argued by previous workers. Paleowater depths in the region of Marcellus Formation black mudrock accumulation were at least 330 ft (100 m) as estimated by differences in strata thickness between the northwestern carbonate bank and basinal facies to the southeast. Geochemical analysis indicates anoxic to euxinic bottom-water conditions. These conditions were supported by a deep, stratified basin with a lack of circulation.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Published by American Association of Petroleum Geologists (AAPG)
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  • 6
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    Use of S-wave attenuation from perforation shots to map the growth of the stimulated reservoir volume in the Marcellus gas shale (2014)
    Society of Exploration Geophysicists (SEG)
    Details
    Publication Date: 2014-10-07
    Description: W ater-filled fractures stimulated by hydraulic fracturing will severely attenuate S-waves. By comparing the P- and S-wave amplitudes generated from perforation shots in the Marcellus gas shale, one can infer the existence and constrain the location of stimulated hydraulic fractures. The waveforms of the perforation shots in unstimulated gas shale are first analyzed to define the prestimulation radiation pattern. Then the change of perforation-shot S-wave waveform is examined for information about the development of hydraulic fractures. S-wave attenuation validates the existence of offstage hydraulic fractures and the invasion of treatment fluid from another neighbor stage. This method might have potential use in designing an active seismic survey to more effectively monitor hydraulic-fracture stimulation beyond the current microseismic mapping techniques.
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
    Published by Society of Exploration Geophysicists (SEG)
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  • 7
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    The concept of joint saturation and its application (2014)
    American Association of Petroleum Geologists (AAPG)
    Details
    Publication Date: 2014-10-28
    Description: Two of the major joint-driving mechanisms are joint-normal stretching and poroelastic shrinkage, and these lead to joint sets commonly associated with structural bending and natural hydraulic fracturing, respectively. Regardless of joint-driving mechanism, joint infilling is a nonhomogeneous Poisson process in the presence of stress shadows. Through probability modeling, we show that in all cases joint spacing is best fit with gamma distributions. The shape parameter of the best-fit gamma distribution to joint-spacing data is a quantitative means to assess the extent of saturation, which is represented in a new parameter, the joint-saturation ratio (JSR). To test the utility of JSR, we call upon published structural bending joint data (Elk Basin, Lilstock, and Rives plate-bending experiment). The shape parameters for these well-developed structural bending joints are equal to around three, corresponding to a JSR of approximately 30%. Using the same analysis on the spacing of natural hydraulic fractures collected from outcrops in the gas-prone Devonian sections of the Appalachian Basin, we find that natural hydraulic fractures differ in two aspects from structural bending joints. First, the joint spacing is proportional to bed thickness in bedded rocks but not in gas shale sections. Second, the joint saturation of natural hydraulic fractures is generally lower than in well-developed structural bending joints. Thus, the JSR is a means to distinguish the joint-driving mechanism and to represent joint-saturation level independent of bed thickness effects. It can be used to distinguish natural fractures from drilling-induced fractures and to improve the fracture-network modeling.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Published by American Association of Petroleum Geologists (AAPG)
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  • 8
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    A model describing flowback chemistry changes with time after Marcellus Shale hydraulic fracturing (2014)
    American Association of Petroleum Geologists (AAPG)
    Details
    Publication Date: 2014-12-31
    Description: Between 2005 and 2014 in Pennsylvania, about 4000 Marcellus wells were drilled horizontally and hydraulically fractured for natural gas. During the flowback period after hydrofracturing, 2 to $$4\times {10}^{3}\hbox{ \hspace{0.17em} }\hbox{ \hspace{0.17em} }{\mathrm{m}}^{3}$$ (7 to $$14\times {10}^{4}\hbox{ \hspace{0.17em} }\hbox{ \hspace{0.17em} }{\mathrm{ft}}^{3}$$ ) of brine returned to the surface from each horizontal well. This Na-Ca-Cl brine also contains minor radioactive elements, organic compounds, and metals such as Ba and Sr, and cannot by law be discharged untreated into surface waters. The salts increase in concentration to $$\sim 270\hbox{ \hspace{0.17em} }\hbox{ \hspace{0.17em} }\mathrm{kg}/{\mathrm{m}}^{3}$$ ( $$\sim 16.9\hbox{ \hspace{0.17em} }\hbox{ \hspace{0.17em} }\mathrm{lb}/{\mathrm{ft}}^{3}$$ ) in later flowback. To develop economic methods of brine disposal, the provenance of brine salts must be understood. Flowback volume generally corresponds to ~10% to 20% of the injected water. Apparently, the remaining water imbibes into the shale. A mass balance calculation can explain all the salt in the flowback if 2% by volume of the shale initially contains water as capillary-bound or free Appalachian brine. In that case, only 0.1%–0.2% of the brine salt in the shale accessed by one well need be mobilized. Changing salt concentration in flowback can be explained using a model that describes diffusion of salt from brine into millimeter-wide hydrofractures spaced 1 per m (0.3 per ft) that are initially filled by dilute injection water. Although the production lifetimes of Marcellus wells remain unknown, the model predicts that brines will be produced and reach 80% of concentration of initial brines after ~1 yr. Better understanding of this diffusion could (1) provide better long-term planning for brine disposal; and (2) constrain how the hydrofractures interact with the low-permeability shale matrix.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Published by American Association of Petroleum Geologists (AAPG)
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  • 9
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    Fracture patterns associated with the evolution of the Teton anticline, Sawtooth Range, Montana, USA (2019)
    Geological Society of London
    Details
    Publication Date: 2019
    Description: 〈p〉The Teton anticline and adjacent structures, in the Sawtooth Range, Montana, USA, are fractured in such a way that may be taken as a model for fractures propagating during buckle folding. However, advances in understanding both the process of folding in forelands and the evolution of fracture patterns found within these folds suggest that it is time to reinterpret the nexus between fracturing and folding within these classic structures. With the benefit of seismic lines, the Teton anticline is best described as a fault-propagation fold. Joint propagation initiated with the formation of two major sets whose orientation is controlled by pre-folding, regional stresses. Two more joint sets propagated in local stress fields, developed in response to anticline growth. Some early joints were reactivated as wrench faults during amplification and tightening of the anticlines. The fracture sets identified are consistent with: (a) propagation in a regional stress field, which may be related to stretching in the Sawtooth Range orocline; and (b) tangential longitudinal strain of the backlimb and forcing or trishear of the forelimb during anticline development. Thus, we suggest that fracture networks across folded structures should be interpreted and characterized in the light of the geological history of the entire system.〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society of London
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  • 10
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    Paleomagnetism of the Oatka Creek Member of the Marcellus Formation: A Devonian paleopole for North America (2016)
    Geological Society of America (GSA)
    Details
    Publication Date: 2016-04-29
    Description: This study presents paleomagnetic results from the Oatka Creek Member of the Marcellus Formation. Paleomagnetic specimens were subsampled from a 50.8-mm-diameter subsurface drill core obtained from the Valley and Ridge physiographic province of Pennsylvania. Alternating field (AF) demagnetization techniques demonstrate that the Oatka Creek specimens retain multiple components of magnetization. The lowest-coercivity component, component A, was isolated by peak fields up to 20 mT and has characteristics of a drilling-induced remanence. Component B was isolated over a range of peak AF fields between 20 and 50 mT in the upper 100 m of the core, and points south with intermediate downward inclinations in geographic coordinates. Scanning electron microscopy, energy dispersive spectroscopy, and rock magnetic experiments yield evidence that suggests component B is a detrital remanent magnetization in magnetite. We corrected these directions for bedding tilt and inclination shallowing and calculated a paleopole at lat. 29.4°, long. 116.9°, A 95 = 1.3°, with an age of 388–389 Ma constrained by biostratigraphy and radiometric dating. This paleomagnetic pole could help fill a data gap in the paleomagnetic record for North America that spans the Middle Devonian to Early Mississippian Periods. Component C was isolated throughout the core using AF fields between 50 and 100 mT and points south with shallow downward inclinations in geographic coordinates. Component C directions agree with a chemical remanence in pyrrhotite from a previous paleomagnetic study of the Marcellus Formation. Component C is likely also a chemical remanent magnetization in pyrrhotite acquired during maximum burial temperatures achieved in the Permian, which may have catalyzed pyrrhotite formation. Component D was isolated in specimens from the lower 20 m of the core, using peak AF fields between 20 and 100 mT, and it points north with shallow downward inclinations in geographic coordinates. The lower 20 m of the core shows evidence of significant hydrothermal alteration. The component D directions yield a paleopole in good agreement with the Jurassic reference pole, and a pulse of hydrothermal alteration in the lower portion of the Oatka Creek Member is consistent with other thermal events in the region ca. 180 Ma. Our results indicate that subsurface cores from the Appalachian foreland may provide an opportunity to greatly improve the Paleozoic paleomagnetic record for North America.
    Print ISSN: 0016-7606
    Electronic ISSN: 1943-2674
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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