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Geological Society, London, Special Publications; 1987; v. 29; p. 181-196;
DOI: 10.1144/GSL.SP.1987.029.01.15
© 1987 Geological Society of London

Part II Processes

Slump strain in the Tertiary of Cyprus and the Spanish Pyrenees. Definition of palaeoslopes and models of soft-sediment deformation

S. G. Farrell* & S. Eaton

BP Petroleum Development Ltd, Farburn Industrial Estate, Dyce, Aberdeen, Scotland
Grant Institute of Geology, The University of Edinburgh, Edinburgh EH9 3JW, Scotland

Slumps exposed in Tertiary sediments in Cyprus and the Spanish Pyrenees vary in inferred translation distance from metres to hundreds and possibly thousands of metres. Contractional strain initiates open to tight upright to inclined folds with hinges that are sub-parallel to the strike of the palaeoslope. This strain is produced mainly by pure shear layer parallel shortening as the slump detachment propagates, but may involve a component of simple shear strain. Downslope translation of the failed unit commonly imparts a simple shear strain which tends to tighten folds and rotate fold hinges and fold axial surfaces. Fold hinges rotate towards the downslope direction, and fold axial surfaces rotate towards parallelism with the upper and lower surfaces of the slump. Coaxially refolded folds and sheath folds may also develop. Steeply plunging folds may initiate in slumps, due to the development of steeply dipping shear zones with margins sub-parallel to the downslope direction which accommodate differential downslope movements of segments of the slump. Fold axial surface attitude and fold profile may be used as a rough estimate of the degree of fold rotation.


* Steven Farrell died on 30 January 1987 after a brave two-year fight against cancer.