Fold-Related Faults Track Progressive Fold Development from Layer-Parallel Shortening to Subsequent Orthogonal Extension within an Appalachian Buckle Fold System: Bear Valley Mine, Shamokin, PA, USA
Outstanding three-dimensional exposures of adjacent folds in an abandoned coal mine within the Appalachian Valley-and-Ridge tectonic province permit a detailed analysis of macroscopic strain accommodation by minor faulting in the lead up to and during buckle folding. A kinematic analysis of more tha...
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GeoScienceWorld
2025-01-01
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| Series: | Lithosphere |
| Online Access: | https://pubs.geoscienceworld.org/gsw/lithosphere/article-pdf/doi/10.2113/2024/lithosphere_2024_186/7093139/lithosphere_2024_186.pdf |
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| author | Arlo Brandon Weil Mary Beth Gray Kylie G. Cush Mattathias D. Needle Juliet G. Crider |
| author_facet | Arlo Brandon Weil Mary Beth Gray Kylie G. Cush Mattathias D. Needle Juliet G. Crider |
| author_sort | Arlo Brandon Weil |
| collection | DOAJ |
| description | Outstanding three-dimensional exposures of adjacent folds in an abandoned coal mine within the Appalachian Valley-and-Ridge tectonic province permit a detailed analysis of macroscopic strain accommodation by minor faulting in the lead up to and during buckle folding. A kinematic analysis of more than 900 outcrop-scale faults coupled with clearly established relative age relationships allows delineation of distinctive fault sets and their roles in accommodating strain within a quartz-dominated sandstone and an overlying silty shale. Conjugate contractional faults are interpreted as evidence of layer-parallel shortening (LPS) prior to and during fold initiation, based on geometric relationships to primary bedding. A clearly overprinting population of younger conjugate faults accommodate layer-parallel extension (LPE) that is both parallel and perpendicular to the fold axes; they are interpreted to have developed during fold limb rotation and fold tightening. Curving and overprinting slip lineations on some strike-slip faults track the transition from LPS to LPE during fold growth. Although the fault-related extensional linear strain magnitudes are relatively small, LPE faults are present in all fold dip domains, in two contrasting lithologies, and on adjacent open and tight folds, highlighting the importance of minor faulting and LPE strains in the formation of contractional buckle folds in the shallow crust. Our findings do not strictly conform with those predicted by classical conceptual models of buckle folds, such as orthogonal flexure or flexural slip. The work further suggests that bed-parallel extension, both axis-parallel and perpendicular, is an underappreciated component of three-dimensional, buckle folding–induced strain and that models for minor fault sets that accommodate three-dimensional strain during fold formation are currently incomplete. |
| format | Article |
| id | doaj-art-fb0c387851594e93ab067277d7e46a34 |
| institution | Kabale University |
| issn | 1941-8264 1947-4253 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | GeoScienceWorld |
| record_format | Article |
| series | Lithosphere |
| spelling | doaj-art-fb0c387851594e93ab067277d7e46a342025-01-22T09:28:39ZengGeoScienceWorldLithosphere1941-82641947-42532025-01-012024Special 1510.2113/2024/lithosphere_2024_186Fold-Related Faults Track Progressive Fold Development from Layer-Parallel Shortening to Subsequent Orthogonal Extension within an Appalachian Buckle Fold System: Bear Valley Mine, Shamokin, PA, USAArlo Brandon Weil0https://orcid.org/0000-0003-2471-7455Mary Beth Gray1Kylie G. Cush2Mattathias D. Needle3Juliet G. Crider4Department of Geology, Bryn Mawr College, Bryn Mawr, Pennsylvania, USADepartment of Geology and Environmental Geosciences, Bucknell University, Lewisburg, Pennsylvania, USADepartment of Geology and Environmental Geosciences, Bucknell University, Lewisburg, Pennsylvania, USADepartment of Earth and Space Sciences, University of Washington, Seattle, Washington, USADepartment of Earth and Space Sciences, University of Washington, Seattle, Washington, USAOutstanding three-dimensional exposures of adjacent folds in an abandoned coal mine within the Appalachian Valley-and-Ridge tectonic province permit a detailed analysis of macroscopic strain accommodation by minor faulting in the lead up to and during buckle folding. A kinematic analysis of more than 900 outcrop-scale faults coupled with clearly established relative age relationships allows delineation of distinctive fault sets and their roles in accommodating strain within a quartz-dominated sandstone and an overlying silty shale. Conjugate contractional faults are interpreted as evidence of layer-parallel shortening (LPS) prior to and during fold initiation, based on geometric relationships to primary bedding. A clearly overprinting population of younger conjugate faults accommodate layer-parallel extension (LPE) that is both parallel and perpendicular to the fold axes; they are interpreted to have developed during fold limb rotation and fold tightening. Curving and overprinting slip lineations on some strike-slip faults track the transition from LPS to LPE during fold growth. Although the fault-related extensional linear strain magnitudes are relatively small, LPE faults are present in all fold dip domains, in two contrasting lithologies, and on adjacent open and tight folds, highlighting the importance of minor faulting and LPE strains in the formation of contractional buckle folds in the shallow crust. Our findings do not strictly conform with those predicted by classical conceptual models of buckle folds, such as orthogonal flexure or flexural slip. The work further suggests that bed-parallel extension, both axis-parallel and perpendicular, is an underappreciated component of three-dimensional, buckle folding–induced strain and that models for minor fault sets that accommodate three-dimensional strain during fold formation are currently incomplete.https://pubs.geoscienceworld.org/gsw/lithosphere/article-pdf/doi/10.2113/2024/lithosphere_2024_186/7093139/lithosphere_2024_186.pdf |
| spellingShingle | Arlo Brandon Weil Mary Beth Gray Kylie G. Cush Mattathias D. Needle Juliet G. Crider Fold-Related Faults Track Progressive Fold Development from Layer-Parallel Shortening to Subsequent Orthogonal Extension within an Appalachian Buckle Fold System: Bear Valley Mine, Shamokin, PA, USA Lithosphere |
| title | Fold-Related Faults Track Progressive Fold Development from Layer-Parallel Shortening to Subsequent Orthogonal Extension within an Appalachian Buckle Fold System: Bear Valley Mine, Shamokin, PA, USA |
| title_full | Fold-Related Faults Track Progressive Fold Development from Layer-Parallel Shortening to Subsequent Orthogonal Extension within an Appalachian Buckle Fold System: Bear Valley Mine, Shamokin, PA, USA |
| title_fullStr | Fold-Related Faults Track Progressive Fold Development from Layer-Parallel Shortening to Subsequent Orthogonal Extension within an Appalachian Buckle Fold System: Bear Valley Mine, Shamokin, PA, USA |
| title_full_unstemmed | Fold-Related Faults Track Progressive Fold Development from Layer-Parallel Shortening to Subsequent Orthogonal Extension within an Appalachian Buckle Fold System: Bear Valley Mine, Shamokin, PA, USA |
| title_short | Fold-Related Faults Track Progressive Fold Development from Layer-Parallel Shortening to Subsequent Orthogonal Extension within an Appalachian Buckle Fold System: Bear Valley Mine, Shamokin, PA, USA |
| title_sort | fold related faults track progressive fold development from layer parallel shortening to subsequent orthogonal extension within an appalachian buckle fold system bear valley mine shamokin pa usa |
| url | https://pubs.geoscienceworld.org/gsw/lithosphere/article-pdf/doi/10.2113/2024/lithosphere_2024_186/7093139/lithosphere_2024_186.pdf |
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