WENLOCK AND LUDLOW SEDIMENTATION IN THE AUSTWICK AND HORTON-IN-RIBBLESDALE INLIER, NORTH-WEST YORKSHIRE

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Abstract
Summary: The Wenlock and Ludlow rocks of the Austwick and Horton-in-Ribblesdale Inlier are the result of turbidite and pelagic sedimentation in the Silurian geosyncline. The Austwick Formation consists of units of several fine-grained greywacke turbidites alternating with units of mudstones. The turbidites exhibit typical Bouma sequences. However, whilst possessing many distal features they have a high proximality index based on Bouma divisions. Palaeo-current data indicate flow towards the north-west for the turbidity currents, whilst the turbidites actually thin north-eastwards. The mudstones show evidence of reworking by bottom currents. Bioturbation, although uncommon in this formation, is persistent throughout the area in one bed. The Arcow Formation consists of distal calcareous turbidites with a highly bioturbated pelitic division. Current ripple lamination indicates a palaeo-current from the north-west, and the beds thin and die out towards the west. Siltstones and mudstones deposited by normal pelagic processes, by bottom currents and by extremely weak turbidity currents make up the Horton Formation. The turbidites of the Studfold Formation were deposited by currents from the north-west. They are poorly exposed but are very similar to those of the Austwick Formation.

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