Monocline

block diagram of a monocline The Grandview-Phantom Monocline in the Grand Canyon, Arizona Monocline at Colorado National Monument Monocline formed at tip of small thrust fault, Brims Ness, Caithness, Scotland

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

Possible modes of formation of monoclines

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

• Waterpocket Fold in Capitol Reef National Park, Utah
• Grandview-Phantom Monocline in the Grand Canyon, Arizona
• Lapstone monocline in the Blue Mountains (Australia)
• Purbeck Monocline on the Isle of Purbeck, Dorset, England

See also

• Anticline
• Syncline
• Homocline

References

1. ^ Skuce, A.G. (1996). "Forward modelling of compaction above normal faults: an example from the Sirte Basin, Libya". In Buchanan,P.G. and Nieuwland,D.A.. Modern Developments in Structural Interpretation, Validation and Modelling. Special Publications. 99. London: Geological Society. pp. 135–146. ISBN 9781897799437. http://s-s-consulting.com/pdf_articles/geol%20soc%201996.pdf. 
2. ^ Chadwick, R.A. (1993). "Aspects of basin inversion in southern Britain". Journal of the Geological Society 150: 311-322. doi:10.1144/gsjgs.150.2.0311. http://jgs.lyellcollection.org/cgi/content/abstract/150/2/311?ijkey=075ea7d0d92cd14125f610d8bc8feed0be8fb091&keytype2=tf_ipsecsha. 
3. ^ Willsey, S.P.; Umhoefer,P.J. and Hilley,G.E. (2002). "Early evolution of an extensional monocline by a propagating normal fault: 3D analysis from combined field study and numerical modeling". Journal of Structural Geology 24: 651-669. doi:10.1016/S0191-8141(01)00120-1. http://earthsciences.stanford.edu/research/geomech/Software/publications/Willsey_JSG_2002.pdf. 
4. ^ Finch, E.; Hardy,S. and Gawthorpe,R. (2003). "Discrete element modelling of contractional fault-propagation folding above rigid basement fault blocks". Journal of Structural Geology 25: 515-528.. doi:10.1016/S0191-8141(02)00053-6. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V9D-45XR8BC-4&_user=10&_coverDate=04%2F30%2F2003&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1601106920&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=bdbd1bcb3c66f603cb8a41c0771bd602&searchtype=a. 

External links

http://bio-geo-terms.blogspot.com/2006_12_01_bio-geo-terms_archive.html