Bude geological structures

Nearly vertically bedded sandstones of the Bude Formation (upper Carboniferous) at Maer Down 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.

Nearly vertically bedded sandstones of the Bude Formation (upper Carboniferous) at Maer Down cliff between Northcott Mouth and Bude, north Cornwall.

This vertical slab of sandstone is at Northcott Mouth, near Bude, north Cornwall. See geotag for exact location. This is part of the Bude Formation (upper Carboniferous) - 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. This slab is the part of the vertical northern limb of an asymmetric anticline, and the view is of the underside of he bedding. There are sole structures - mostly trains of ripples/scours - on this surface, proving that it is the base of the bed. I would guess that the local rock climbing fraternity have given this slab a name, so if anyone knows it please let me know. Thanks!

An anticline in the Bude Formation (upper Carboniferous) at Crooklets, near Bude, Cornwall. The Bude Formation here consists of alternating thin beds of turbidite sandstones (pale grey/brown) and fine-grained shaly siltstones/mudstones (darker grey). Minor crumpling on the south (right-hand) limb of the fold has resulted in near vertical or slightly overturned bedding. The sandstones display sedimentary structures which can be used to determine the 'way up' of the bedding. Here, the sedimentary structures are mostly rippled upper surfaces and small-scale slump or load structures on the basal surfaces. The latter can be seen in detail in the next two photos: www.ipernity.com/doc/earthwatcher/39024212 www.ipernity.com/doc/earthwatcher/39024210

A broader view of the syncline shown in the previous photos. The Bude Formation here consists of alternating thin beds of turbidite sandstones (pale grey/brown) and fine-grained shaly siltstones/mudstones (darker grey).

Tight upright folds in the Bude Formation (upper Carboniferous) at Wrangle Point near Bude, Cornwall. The syncline shown in the next photo... www.ipernity.com/doc/earthwatcher/39024236 ...is on the left; I was standing on the axis of central anticline to take the photo and there is another syncline just right of centre. Detailed views of the right-hand syncline axis are shown in the following two photos.

A view of the axis of the right-hand syncline shown in the previous photo at beach level. The Bude Formation here consists of alternating thin beds of turbidite sandstones (pale grey/brown) and fine-grained shaly siltstones/mudstones (darker grey). These chevron folds are 'similar' in style, rather than concentric. This means that material (mostly the weaker shaly beds) has had to 'flow' into the hinge zones - notice how it is thicker in the hinge, compared with the limbs of the fold.

A closer view of the hinge zone of the fold in the previous photo. The 'space problem' of accommodating the beds in the hinge zone of the fold is well illustrated here. The thickened hinge zone contains several small-scale thrusts which have disrupted the thin sandstone bands. I should have included an object for scale in this view but forgot, sorry! The pale sandstone band in the central portion of the photo is about 4 cm thick.

More detailed view of the plunging chevron folds in the Bude Formation (Upper Carboniferous) at Wrangle Point, Crooklets, near Bude, Cornwall. For a more detailed explanation, please see this similar photo taken near Northcott Mouth about 1 km to the north: www.ipernity.com/doc/earthwatcher/39023798