JOINT DENSITIES AND THEIR RELATION TO LITHOLOGY IN THE GREAT SCAR LIMESTONE

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Abstract
Summary: Joint systems in the Great Scar Limestone of the Settle area have been re-examined and three varieties found: conjugate joints, tension joints and low angle joints, the first being by far the commonest. Plumose structures found on conjugate joint faces suggest cleavage fracture as the method of origin. Conjugate joint spacings are fairly regular except where joints extend across bedding planes. A method for assessing conjugate joint densities in beds from scars is described and its application throughout the area shows consistent results; the limestones of the S zone present little variation whereas those of the D 1 zone form a sequence of nine rhythms where the succession is complete. Modal analyses of limestone suites collected from the rhythms of the D 1 zone demonstrate a correlation of high joint density with coarse-grained limestones and low joint density with carbonate mudstones. Differences in joint density do not appear to influence the orientation of conjugate joints, and bed thickness does not control densities.