Abstract

Contorted structures can be formed in mud or sand as a result of differential loading. Fifteen sets of experiments were conducted in water tanks to test various factors of possible significance in the contortion of mud by loading. Of six factors tested, the most significant was distribution of load, but others affecting the type of structure under certain conditions were (1) the manner of depositing the mud, (2) the form of the underlying surface, (3) the direction of loading, and (4) the movement or lack of movement of water during loading. Organic material was shown to be unneccessary in forming conical structure or convolute bedding. Strength of base had little or no influence on convolute-structure development.

Contortions ranged from the simple anticlinal type with vertical axial plane, commonly referred to as convolute, to structures with gently dipping axial planes, to others with lateral extensions or “flames” from the apexes, and, finally, to those with complex overturned folds. Causes of these variations were determined in terms of the factors listed above. Some additional forms of contorted bedding result from other types of penecontemporaneous deformation such as slumping from undermining or from oversteepening, differential lateral movement, and surface drag; these forms differ from those structures formed by loading.

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