Page 216 - Carbonate Facies in Geologic History

Y oredale Cycles 203

Outcrop

Proved by
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boring
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Borehole

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Fig. VII -1. Distribution of Y oredale Series and equivalents in northern England and Scotland
from Moore (1959, Fig. 3)

y oredale Cycles

The first cycles described in the geologic literature are those of the Yoredale-
Wensleydale area in the Pennines of the English Midlands in beds of Visean age.
About eight cycles, each as much as 30 m thick, occur as widespread sheets across
the North Pennine block north of a basin in the Hercynian belt (Fig. VII-1). The
cyclic sediments of the platform are spread northward through Northumberland
in beds exposed along the east coast, north of Newcastie-On-Tyne and into the
Scottish Lowlands near Edinburgh. Along the southern edge of the North Pen-
nine block (Engleboro-Settie area) part of the Y oredale cyclic beds grade into
encrinite of the upper Great Scar Limestone (Fig. V -10).
The typical cycle consists of a basal limestone sheet overlain by an upward
shoaling and coarsening sequence of argillaceous and sandy sediments. The lime-
stone, described below, grades into a black shale or siltstone which is transition-
ally overlain by grey siltstone, in turn by cross-bedded sandstone capped by a
"seat earth" with rootlets and an overlying coal.