VISÉAN LOWER YOREDALE LIMESTONES ON THE ALSTON AND ASKRIGG BLOCKS, AND THE BASE OF THE D 2 ZONE IN NORTHERN ENGLAND

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Abstract
Summary: Re-examination of sections in the Viséan (Lower Carboniferous) lower Yoredale limestones and their equivalent in the Great Scar Limestone (the beds spanning the D 1 -D 2 zonal boundary) on the Alston Block, along the Dent Line and on the Askrigg Block, has shown that individual cyclothems can be traced throughout this area, and a detailed correlation is established. The strata thicken rapidly southwards from the Alston Block to the Stainmore Trough and then thin progressively on to the Askrigg Block. The absence of any obvious southern margin to the trough is interpreted as indicating that the Askrigg Block and Stainmore Trough are not distinct structural units and that the thicker sequence in the latter area is due to tilting of the Askrigg Block during sedimentation, with more rapid subsidence in the north than in the south. The base of the D 2 Zone is taken at the base of the Hawes/Peghorn Limestone, in preference to the previously accepted, somewhat higher, horizon at the base of the Girvanella Nodular Bed, and the correlation of this zone with the Bristol area is discussed.

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