Geometry of fold arrays in the Silesian-Cracovian region

Abstract: A zone of deformation characterized by en echelon folds extends along the northeast margin of the Upper Silesian Coal basin in southern Poland. The zone is well exposed by mining in numerous collieries where the deformation i volving Upper Carboni-ferous strata can be observed. Folds and associated faults form a structural pattern consistent with an origin in dextral convergent wrenching o both the principal deep-seated fractures and the subsidiary faults affecting crystalline basement beneath this part of the basin. The zone is cross-cut by sublatitudinal fold belts which, according to their geometrical par-ameters, seem to result from alternate transcurrent shearing along west east oriented fractures in the basement, sinistral in one case and dextral in the other. Among folds caused by the concentrated operation of a force couple whose vectors lie in th horizontal plane, there are examples of bending folds (forced folds) in each array resulting from vertical components of movement of deep-seated fault blocks. The dimensions of the folds change with depth, and the axial trend and the inclination of axial surfaces differ with distance from the basement fault trace. The length of fold segments trongly depends on axes orientation. Widely distributed evidence of interlayer slip demonstrates a variable spatial dis