Bude geological structures

A closer view of the chevron fold anticline in mainly sandstones of the Bude Formation (upper Carboniferous), just south of Northcott Mouth, near Bude, north Cornwall. The 'space' problem along the fold axis has been partly accommodated by bedding plane slippage along the more shaly bands (darker), which have 'flowed', being squeezed out along the fold limbs and and accumulating as thicker cusps in the fold crests. The Bude Formation consists mainly of deltaic and some turbidite sandstones interbedded with shales. The sandstones are relatively thick, compared with those in the underlying Crackington Formation, and as a result, more competent. The response to the Variscan earth movements at the end of the Carboniferous was to form more open, mostly upright or slightly asymmetric angular folds, compared with the cascades of tight recumbent folds which characterise the Crackington Formation a few kilometres to the south.

A chevron fold anticline in mainly sandstones of the Bude Formation (upper Carboniferous), just south of Northcott Mouth, near Bude, north Cornwall. A smaller crumple fold is visible in the higher part of the cliff, to the left of the main fold crest; this fractures and becomes a thrust as it is traced downwards towards lower left quadrant. The Bude Formation consists mainly of deltaic and some turbidite sandstones interbedded with shales. The sandstones are relatively thick, compared with those in the underlying Crackington Formation, and as a result, more competent. The response to the Variscan earth movements at the end of the Carboniferous was to form more open, mostly upright or slightly asymmetric angular folds, compared with the cascades of tight recumbent folds which characterise the Crackington Formation a few kilometres to the south.

Chaotically deformed and disrupted thin sandstone bands within a horizon of highly sheared dark grey shale - behind the person - in the Bude Formation (upper Carboniferous) at Maer Cliff between Northcott Mouth and Bude, north Cornwall. As a result of compression as part of the Variscan earth movements at the end of the Carboniferous, the weak (incompetent) shale has been strongly deformed, compared with the strong (competent) sandstone beds above and below the shale. Thin sandstone beds have been caught up in the deformed shale and have undergone severe folding and fracturing. The brown sandstone beds in the upper part of the cliff have moved to the left (north) relative to the lower sandstone beds, with the planes of thrusting and shearing being concentrated in the dark shale. This deformation probably represents substantial slippage along the bedding planes of the weak shales to accommodate the 'space' problem in the series of chevron folds which characterise this area.

Chaotically deformed and disrupted thin sandstone bands within a horizon of highly sheared dark grey shale - behind the person - in the Bude Formation (upper Carboniferous) at Maer Cliff between Northcott Mouth and Bude, north Cornwall. As a result of compression as part of the Variscan earth movements at the end of the Carboniferous, the weak (incompetent) shale has been strongly deformed, compared with the strong (competent) sandstone beds above and below the shale. Thin sandstone beds have been caught up in the deformed shale and have undergone severe folding and fracturing. The brown sandstone beds in the upper part of the cliff have moved to the left (north) relative to the lower sandstone beds, with the planes of thrusting and shearing being concentrated in the dark shale. This deformation probably represents substantial slippage along the bedding planes of the weak shales to accommodate the 'space' problem in the series of chevron folds which characterise this area.

Chevron fold syncline in sandstones of the Bude Formation (upper Carboniferous) at Maer Cliff between Northcott Mouth and Bude, north Cornwall. The Bude Formation consists mainly of deltaic and some turbidite sandstones interbedded with shales. The sandstones are relatively thick, compared with those in the underlying Crackington Formation, and as a result, more competent. The response to the Variscan earth movements at the end of the Carboniferous was to form more open, mostly upright or slightly asymmetric angular folds, compared with the cascades of tight recumbent folds which characterise the Crackington Formation a few kilometres to the south.

Chevron fold syncline in sandstones of the Bude Formation (upper Carboniferous) at Maer Cliff between Northcott Mouth and Bude, north Cornwall. The Bude Formation consists mainly of deltaic and some turbidite sandstones interbedded with shales. The sandstones are relatively thick, compared with those in the underlying Crackington Formation, and as a result, more competent. The response to the Variscan earth movements at the end of the Carboniferous was to form more open, mostly upright or slightly asymmetric angular folds, compared with the cascades of tight recumbent folds which characterise the Crackington Formation a few kilometres to the south.

Bedding traces of plunging chevron folds in the Bude Formation (upper Carboniferous) sandstones in the beach at Northcott Mouth, near Bude, north Cornwall. Two faults cut the bedding traces in the lower right quadrant. Synclines 'V' towards the camera; anticlines 'V' towards the sea. The plunge is seawards. What does this mean? Here's a simple model - fold a sheet of thin card into a few zig-zag folds so it becomes angularly corrugated like a fan. Open the card out a little and hold it horizontally. Look along the length of the folds. That's the situation with no plunge. Now, tilt the card slightly downwards at the far end, still continuing to look down the length of the folds. The tilt you have applied is the 'plunge' of the fold set. Now, keeping that same gentle angle of tilt, partially immerse the folded, tilted card into a bowl of water. Quickly, before it gets too soggy and distorts, notice the pattern of the water-line where the card intersects the water surface: a series of elongated zig-zags just like these on the flat surface of the beach. The steeper the angle of plunge, the shorter the elongation and vice versa .

Chevron fold syncline in sandstones of the Bude Formation (upper Carboniferous) at Maer Cliff between Northcott Mouth and Bude, north Cornwall. 'Smooth Rock' is the name given to the steeply dipping slab on the right - a favourite with rock climbers. The Bude Formation consists mainly of deltaic and some turbidite sandstones interbedded with shales. The sandstones are relatively thick, compared with the underlying Crackington Formation, and as a result, more competent. The response to the Variscan earth movements at the end of the Carboniferous was to form more open, mostly upright or slightly asymmetric angular folds, compared with the cascades of tight recumbent folds which characterise the Crackington Formation a few kilometres to the south.

Chevron fold syncline in sandstones of the Bude Formation (upper Carboniferous) at Maer Cliff between Northcott Mouth and Bude, north Cornwall. 'Smooth Rock' is the name given to the steeply dipping slab on the right - a favourite with rock climbers.