A monocline (or, rarely, a monoform) is a step-like fold in rock strata consisting of a zone of steeper dip within an otherwise horizontal or gently dipping sequence.
Formation
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Monoclines may be formed in several different ways (see diagram)
- By differential compaction over an underlying structure, particularly a large fault at the edge of a basin due to the greater compactibility of the basin fill, the amplitude of the fold will die out gradually upwards.[1]
- By mild reactivation of an earlier extensional fault during a phase of inversion causing folding in the overlying sequence.[2]
- As a form of fault propagation fold during upward propagation of an extensional fault in basement into an overlying cover sequence.[3]
- As a form of fault propagation fold during upward propagation of a reverse fault in basement into an overlying cover sequence.[4]
Examples
edit- Waterpocket Fold in Capitol Reef National Park, Utah[5]
- Comb Ridge in southern Utah[6]
- Grandview-Phantom Monocline in Grand Canyon, Arizona[7]
- Grand Hogback in Colorado[8]
- Lebombo Mountains in Southern Africa[9]
- Lapstone Monocline in the Blue Mountains (Australia)[10]
- Beaumaris Monocline in Victoria (Australia)[11]
- Purbeck Monocline on the Isle of Purbeck, Dorset, England[12]
- Fore-Sudetic Monocline, Poland[13]
- Sindh Monocline, Pakistan[14]
- Torres Flexure, southern Brazil[15]
See also
editReferences
edit- ^ Skuce, A.G. (1996). "Forward modelling of compaction above normal faults: an example from the Sirte Basin, Libya" (PDF). In Buchanan, P.G.; Nieuwland, D.A. (eds.). Modern Developments in Structural Interpretation, Validation and Modelling. Special Publications. Vol. 99. London: Geological Society. pp. 135–146. ISBN 978-1-897799-43-7. Archived from the original (PDF) on 2012-03-16.
- ^ Chadwick, R.A. (1993). "Aspects of basin inversion in southern Britain". Journal of the Geological Society. 150 (2): 311–322. Bibcode:1993JGSoc.150..311C. doi:10.1144/gsjgs.150.2.0311. S2CID 131396080.
- ^ Willsey, S.P.; Umhoefer, P.J.; Hilley, G.E. (2002). "Early evolution of an extensional monocline by a propagating normal fault: 3D analysis from combined field study and numerical modeling" (PDF). Journal of Structural Geology. 24 (4): 651–669. Bibcode:2002JSG....24..651W. doi:10.1016/S0191-8141(01)00120-1. Archived from the original (PDF) on 2011-07-20. Retrieved 2011-01-09.
- ^ Finch, E.; Hardy, S.; Gawthorpe, R. (2003). "Discrete element modelling of contractional fault-propagation folding above rigid basement fault blocks". Journal of Structural Geology. 25 (4): 515–528. Bibcode:2003JSG....25..515F. doi:10.1016/S0191-8141(02)00053-6.
- ^ "Geology". Capitol Reef National Park. National Park Service. 23 December 2017. Retrieved 1 March 2018.
- ^ "Comb Ridge, Utah". earthobservatory.nasa.gov. 2019-11-24. Retrieved 2021-10-22.
- ^ Abbott, Lon; Cook, Terri (2004). Hiking the Grand Canyon's Geology. Seattle: The Mountaineers Books. pp. 99–114. ISBN 978-0-89886-895-1.
- ^ Murray, Frederick N. (1967). "Jointing in Sedimentary Rocks along the Grand Hogback Monocline, Colorado". The Journal of Geology. 75 (3): 340–350. Bibcode:1967JG.....75..340M. doi:10.1086/627261. JSTOR 30071521. S2CID 128672429.
- ^ Klausen, M.B. (2009). "The Lebombo monocline and associated feeder dyke swarm: Diagnostic of a successful and highly volcanic rifted margin?". Tectonophysics. 468 (1–4): 42–62. Bibcode:2009Tectp.468...42K. doi:10.1016/j.tecto.2008.10.012.
- ^ "L001 : Lapstone Monocline". Heritage places and items. Office of Environment and Heritage, Government of New South Wales. Retrieved 1 March 2018.
- ^ "61. Beaumaris Cliffs 3 - Monocline". Sites of Geological and Geomorphological Significance. Agriculture Victoria. 8 June 2017. Retrieved 1 March 2018.
- ^ Nowell, D.A.G. (1997). "Structures affecting the coast around Lulworth Cove, Dorset and syn-sedimentary Wealden faulting". Proceedings of the Geologists' Association. 108 (4): 257–268. Bibcode:1997PrGA..108..257N. doi:10.1016/S0016-7878(97)80011-9.
- ^ Kluska, B.; Rospondek, M.J.; Marynowski, L.; Schaeffer, P. (2013). "The Werra cyclotheme (Upper Permian, Fore-Sudetic Monocline, Poland): Insights into fluctuations of the sedimentary environment from organic geochemical studies". Applied Geochemistry. 29: 73–91. Bibcode:2013ApGC...29...73K. doi:10.1016/j.apgeochem.2012.09.010.
- ^ Memon, A.D.; Siddiqui, I.; Memon, A. (1999). "Tectonics of the Sindh monocline, Pakistan and their effects on hydrocarbons". Mehran University Research Journal of Engineering and Technology. 18 (2): 87–96.
- ^ Seth, H. (2018). Tectonic Deformation of Flood Basalt Provinces. Springer. ISBN 978-3-319-67704-0.