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Widemouth Bay, Cornwall | Macc Lad

The original, essentially unmoved, bedrock of central Devon north of the Meldon area, is dominated by the Crackington Formation, a thick sequence of interbedded sandstones and dark grey shales, of late Lower to Upper Carboniferous age. The Crackington Formation represents a classic ‘flysch’ sequence with the sandstones formed from sands which flowed into the deep Culm basin after being dislodged from its slopes by earthquakes associated with the rise of the ‘Variscan Mountains’ to the south, during the early stages of the orogeny. These ‘turbidity currents’ deposited their load as their velocity dropped on reaching the gentler slopes towards the bottom of the basin. The weight of these sands pressing down into the soft muds, which had settled quietly onto the sea-bed between flows, often created well developed lobe-shaped ‘lode casts’. These structures are crucial ‘way-up’ indicators in the subsequently tightly folded Crackington Formation sequence.