Identifying the characteristic signatures of fold-accommodation faults |
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| Institution: | 2. Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, United States;3. Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, United States;4. Universidad Nacional San Antonio Abad del Cusco, Cusco, Peru;1. China University of Petroleum-Beijing at Karamay, Karamay, Xinjiang 834000, China;2. Research Institute of Petroleum Exploration and Development, Tarim Oilfield Company, PetroChina, Xinjiang, Korla 841000, China;3. State Key Laboratory of Petroleum Resources and Prospecting, Beijing 102200, China;4. School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China |
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| Abstract: | Hand-specimen and outcrop scale examples of folds are analyzed here to identify the characteristic signatures of fold-accommodation faults. We describe and analyze the geometric and kinematic relationships between folds and their associated faults in detail including the structural position and spatial distribution of faults within a fold, the displacement distribution along the faults by applying separation–distance plots for the outcrop scale examples, and the change of cut-off angle when the fault cut across folded layers. A comparison between fold-accommodation faults and fault related folds based on their separation–distribution plots and the problem of time sequence between faulting and folding are discussed in order to distinguish fold-accommodation faults from the reverse faults geometrically and kinematically similar to them. The analysis results show that fold-accommodation faults originate and terminate within a fold and usually do not modify the geometry of the fold because of their limited displacement. The out-of-syncline thrust has a diagnostically negative slope (separation value decreasing away from the upper fault tip) in the separation–distance graph. The change of cut-off angle and the spatial distribution of faults display a close relationship with the axial surface of the fold. Our analyses show that fold-accommodation faults are kinematically consistent with the flexural slip of the fold. The interbedded strata with competence contrast facilitate formation of fold-accommodation faults. These characteristic signatures are concluded as a set of primary identification criteria for fold-accommodation faults. |
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| Keywords: | Fold-accommodation faults Hand-specimen Outcrop scale Separation–distance plot Characteristic signatures |
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