| Popis: |
Mesofault systems in the Upper Cretaceous rocks of the steep zone in the Purbeck monocline are reinterpreted by analysing their geometry with reference to the orientations of sedimentary layers. As a consequence of using layering as a datum rather than the horizontal, the five original groups of mesofaults, previously recognised by Arkell and Phillips, have been condensed into two sets of conjugate extension faults. These faults are symmetrically arranged about the layering, the dip of which varies from vertical to steeply inclined. Mesofaults previously considered to have been generated during a complicated history of thrusting, related to the tightening of the synformal bend of the monocline and horizontal compression, are reinterpreted as being a result of layer-parallel extension during flexuring. Thus they are accommodation structures formed during the development of the monocline, itself related to drape over reactivated Jurassic growth-faults during N-S shortening. South-dipping reverse macrofaults are reinterpreted as being the continuation to the surface of the reactivated Jurassic growth-faults, whilst north-dipping reverse macrofaults are interpreted as being antithetic to these reactivated faults. A tectonic implication arising from the proposed kinematic classification of the mesofaults is that they can be perceived as being the products of stretching of a steep fold limb during flexuring, rather than being related to several phases of horizontal compression. |
