High concentrations of caesium occur in the New Red Sandstone of Devon, England. Values are most abundant in breccias at the base of the Permian and decrease upwards through the sandstones and marls. Caesium resides in the clay fraction (<2 μm) where it reaches 468 ppm in Watcombe breccia, 146 ppm in Exmouth mudstone and 35 ppm in Triassic Otter sandstone. Credition Trough values attain 108 ppm in the Cadbury breccia.

Extensive volcanic activity on the south eastern edge of the Cornubian Massif provided a supply of Cs. Due to its low ionic potential, this alkali was concentrated at source under extreme weathering in the hydrolysate fraction of red bed sediments. The source area was largely exhausted by late Permian, reflected by a reduction in Cs content of New Red Sandstone detritus.

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