Hydrogeology of Wales: Permo-Triassic and Jurassic aquifers

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This page is part of a category of pages that provides an updated review of the occurrence of groundwater throughout Wales.
Author(s): N S Robins and J Davies, British Geological Survey
Contributor(s): D A Jones, Natural Resources Wales and G Farr, British Geological Survey

Geological setting

Jurassic Lias limestone cliffs at Nash Point, South Glamorgan. P802430.

In North Wales Permo-Triassic age strata are limited to part of the Vale of Clwyd on the edge of the East Irish Sea Basin and the western margin of the Cheshire Basin. Much of the Triassic sequence comprises red beds, deposited in an arid desert-like environment, which are uniform, cross-bedded, generally well cemented, fine to medium grained with occasional mudstone horizons but no pebble beds. Halite, gypsum and anhydrite lenses are common and there are occasional wadi-type channel deposits.

The Jurassic Lower Lias is present in a limited area between Cardiff and Porthcawl. Here the Blue Lias Formation comprises up to 90 m of thinly bedded argillaceous marls and calcareous mudstones, increasing in subcrop towards Bridgend to a thickness of 150 m where marginal oolitic limestones are present (Plate P802430).

Hydrogeology of Wales - contents