In structural geology, a homocline or homoclinal structure (from old Greek: homo = same, cline = inclination), is a geological structure in which the layers of a sequence of rock strata, either sedimentary or igneous, dip uniformly in a single direction having the same general inclination in terms of direction and angle.[1][2] A homocline can be associated with either one limb of a fold, the edges of a dome, the coast-ward tilted strata underlying a coastal plain[clarify], slice of thrust fault, or a tilted fault block. When the homoclinal strata consists of alternating layers of rock that vary hardness and resistance to erosion, their erosion produces either cuestas, homoclinal ridges, or hogbacks depending on the angle of dip of the strata.[3][4][5] On a topographic map, the landfroms associated with homoclines exhibit nearly parallel elevation contour lines that show a steady change in elevation in a given direction. In the subsurface, they characterize by parallel structural contour lines.[6]
Unicline and Uniclinal are obsolete and currently uncommon terms that are defined and have been used by geologists and geomorphologists in an inconsistent and contradictory manner. They are terms that have been used in a mutually exclusive manner as a synonym for either a homocline[7] or monocline[8][9] depending the author. The meaning of this term has been further confused by Grabau, who redefined uniclinal, not as a geological structure, but as a general term for ridges produced by erosion of anticlines.[10][11]
The erosion of tilted sequences of either stratified sedimentary or igneous rock, homoclines, of alternating resistance to erosion produce distinctive landforms that form a gradational continuum from cuestas through homoclinal ridges to hogbacks. Less resistant beds are preferentially eroded creating valleys that lie between ridges created by the erosion of more resistant beds. For example, the erosion of homoclines consisting of resistant beds of either limestone, sandstone, or both interbedded with weaker, less resistant beds of either shale, siltstone, marl, or combination of them will produce either cuestas, homoclinal ridges, or hogbacks depending on the angle of dip of the strata. The greater the difference in the resistance to erosion, the more pronounced the structural control and relief between valley and ridge crest.[3][4][5]
- ^ Jackson, JA, J Mehl and K Neuendorf (2005) Glossary of Geology. American Geological Institute, Alexandria, Virginia. 800 pp. ISBN 978-0922152896
- ^ Huggett, JR (2011) Fundamentals of Geomorphology, 3rd ed., Routledge, New York. 516 pp. ISBN 9780415567756
- ^ a b Thornbury, W. D., 1954, Principles of Geomorphology New York, John Wiley & Sons, 618 pp.
- ^ a b Twidale, C.R., and E.M. Campbell (1993) Australian Landforms: Structure, Process and Time. Gleneagles Publishing, Adelaide, South Australia, Australia. 568 pp. ISBN 9781875553020
- ^ a b Gerrard, J (1988) Rocks and landforms. Allen & Unwin Inc.,Winchester, Mass. 319 pp. ISBN 9780045511129
- ^ Reynolds, SJ, and GH Davis (1996) Structural geology of rocks and regions. John Wiley, New York, New York. 864 pp. ISBN 9780045511129
- ^ Thomas, G, and A Goudie (2000) The Dictionary of Physical Geography, 3rd ed. Blackwell Publishing Ltd., Maiden, Massachusetts. 624 pp. ISBN 978-0631204732
- ^ U.S. Bureau of Mines Staff (1996) Dictionary of Mining, Mineral, & Related Terms. Report SP-96-1, U.S. Department of Interior, U.S. Bureau of Mines, Washington, D.C.
- ^ Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, J.A., eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN 0-922152-76-4
- ^ Grabau, AW (1920a) Unicline; a term proposed for monoclinal ridges of erosion. Geological Society of America Bulletin. 31(1):153.
- ^ Grabau, AW (1920b) A Comprehensive Geology, vol. 1 D. C. Heath & Company, New York, New York. 804 pp.