A review of joints (cleats) in British Carboniferous coals: indicators of palaeostress orientation

SUMMARY Joints in coals, arranged (sub) normal to bed boundaries, are commonly termed cleats. Cleat azimuths in Carboniferous coals are reviewed, and are interpreted as reflecting Variscan stress fields across different tectonic settings. Immediately proximal to the Variscan Front (South Wales, Kent), varied cleat azimuths provide evidence of stress deflection and block rotation, whereas north of the Wales-Brabant High (central and northern England), a consistent regional north-westerly maximum horizontal stress is indicated by regionally parallel cleat orientations in most coalfield areas. In the more distal Midland Valley of Scotland, varied cleat azimuths suggest that local structural developments had a significant effect on the stress field. Throughout Britain, major fault zones separate differing cleat sets, suggesting deep crustal compartmentalization during Carboniferous times. In all areas, most main fault movements post-dated the majority of cleats.

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