The structure of the Culm Measures at Meldon, near Okehampton, North Devon

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Abstract
Summary: The Culm Measures along the northern margin of the Dartmoor Granite have been divided into two groups. The Lower Culm Measures, from 655 to 770 feet thick, and comprising shales, quartzites, tuffs, cherts and limestones, are overlain without apparent unconformity by a great thickness of Upper Culm shales and grits. A large overfolded anticlinal strip of Lower Culm Measures separates an outer band (the main outcrop) of Upper Culm Measures to the north from a major syncline of the same beds which lies next to the Dartmoor Granite. The granite contact appears to follow a constant horizon within this syncline. The tectonic pattern is set by zig-zag folding—with long straight limbs and sharply turned crests and troughs—which is overturned to the south, and which controlled the distribution and subsequent tectonic history of the local Culm Measures. The early flexural slip was continued in reverse and normal faulting along and parallel to the bedding-plane directions; these movements were followed by the intrusion of basic dykes, granite emplacement, jointing and mineralization. Each successive phase followed the deformation pattern initiated by the zig-zag folding. The structure is complicated by the presence of a faulted inlier of presumed Devonian slates in the core of the Lower Culm Measures anticline.

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