Separation of multiple stress events by fault striation analysis: an example from Variscan and younger structures at Ogmore, South Wales

Abstract

The study of minor structures in Carboniferous and Triassic sedimentary rocks at Ogmore- by-Sea, Bridgend. reveals that the observed microstructures are the consequence of successive brittle deformation events. Age relationships can be deduced from sets of structures consisting of conjugate faults, oblique slip faults, tension gashes and stylolites. from which deductions can be made about the orientations of principal stresses corresponding to pre-and post-Triassic events. The demonstrable polyphase tectonic history at Ogmore and the occurrence of large numbers of striated faults at four sites allow the opportunity of testing a newly proposed strategy for palaeostress analysis from striated faults with complex stress histories. The new technique, based on the statistical procedure of cluster analysis, involves the sorting of fault-slip data into coherent dynamic setsasa preliminary stage of formal stress inversion. The fault sets separated using this technique yield stresses which are similar to those deduced from field observations. Four stress configurations are distinguished, of which two are pre-Triassic in age. Correlations with previously derived stresses are discussed.