Bude’s Geology

I walk the coast path and sit on the beach several times a month, but rarely did I take any real notice of Bude’s Geology.  I often looked at the formations in amazement, but A Level Geography was years ago and I could only just remember the difference between a syncline and an anticline!

This all changed a few weeks ago, when I joined Dr Roger Higgs (Geoclastica Ltd) and a couple of other visitors who had booked onto one of his guided two-hour Geology walks.

Roger is Bude’s very own, very friendly geologist.  He conducts his public walks every Monday afternoon (or private walks at any time).  If you have the remotest interest in geology and would like to learn about Bude’s amazing rocks, I can’t recommend his guided walk enough.

Basically, the so called “Bude Formation” of North Cornwall is such a fine example that is has been studied by generations of geologists.  During the walk, Roger showed us where the sand and mud layers were deposited in a giant tropical “Lake Bude” 300 million years ago.  These layers were eventually folded when Britain and France collided.  This was so long ago, that the Dinosaurs were yet to evolve!

Roger is particularly proud of Bude’s very unique fossilised fish which is found nowhere else in the world.  Fossils are hard to find in Bude, but this toothy, goldfish-sized fish called Cornuboniscus budensis is on display for all to see at the Bude Castle Heritage Centre.  The fish is evidence of a life form from an era when Bude’s climate was similar to modern day Africa.

You can book a place on one of Roger’s public geology walks on Thursday afternoon (click here to see the VisitBude events calendar), or arrange for a private walk (great for groups and families) on a different day.  All bookings are made at the Bude Tourist Info Centre (01288 354240).

Image-20-Bude-coast,-lookin

Bude coast, looking north from Compass Tower. Note Bude Sea Pool in upper centre, beyond the yellow boat. Alternating beds of sandstone and mudstone (aka shale) totalling 1.3 km in thickness, known as the Bude Formation, are superbly exposed for many kilometres along the cliffs and in the wave-cut platform, attracting geology students and professionals alike. About 300 million years old (Carboniferous Period of the Palaeozoic Era), these beds were deposited as soft sand and mud in a tropical ‘Lake Bude’, home to a globally unique fish, Cornuboniscus budensis, an exquisite fossilised specimen of which is displayed in Bude Castle museum. Accumulation of such a great thickness of strata (1.3 km) was accomplished by subsidence.  The beds were then deformed into spectacular zigzag folds (‘chevron folds’) by collision of England and France, which uplifted the whole of Cornwall to form a mountain belt, in latest Palaeozoic time, before dinosaurs existed.

Image-62 Southward view over Maer Low Cliff Beach from Maer High Cliff top

Southward view over Maer Low Cliff Beach from Maer High Cliff top. The V-patterns made by resistant upstanding Bude Formation sandstone beds in the wave-cut platform (partly covered by beach sand) indicate that the beds are folded into a seaward plunging syncline (downfold) and adjacent anticline (upfold).  Note Bude cricket ground at top left and Bude Sea Pool to the right of it.

Image-31-Bude-geologist-Dr-

Bude geologist Dr Roger Higgs, who wrote the captions for this series of photographs. The background cliffs are of Bude Formation folded sandstone and shale beds at Efford Ditch (see next two photos). Between his professional consulting commitments overseas, Roger guides ‘Bude Geo-Walks’ for the public and for schools, universities and other interested groups.

Image-29-Strongly-folded-saStrongly folded sandstone and shale beds of the Bude Formation at Efford Ditch, looking northeast. People on cliff top for scale. The strata on the right dip to the right, and those on the left to the left, defining an anticline (flanked by a syncline in the far right; close-up in next photo).

Image-26-Close-Up-of-StrongClose-up of previous photo’s right half.  Bude Formation sandstone beds appear rusty brown due to a coating of iron oxide on fracture surfaces. Darker shale beds are more recessive, i.e. softer (more easily eroded).

Image-17-Bude-Formation-exhBude Formation exhumed anticline known as ‘Whales Back’ (1963 Ordnance Survey map, 6 inches to 1 mile scale), immediately west of Bude breakwater, looking west. The near end, truncated by erosion (bombarded by shingle carried in storm waves), exposes alternating beds of sandstone and dark shale.

Image-42-Bude-Formation-sanBude Formation sandstone and shale beds folded into a syncline and adjoining anticline. Maer High Cliff, looking northeast. Man for scale at far right, near cliff base.

Image-44-Steeply-dipping-foSteeply dipping folded Bude Formation sandstone and shale beds. Maer High Cliff, looking east. People on cliff top for scale.

Image-45Bude Formation sandstone and shale beds folded into a syncline and (at far right) an anticline. Pearce’s Cove, looking northeast. For scale, note climber at upper right-hand side and man’s head protruding above cliff top.

Imge-48-Bude-Formation-sandBude Formation sandstone and shale beds folded into a syncline. Pearce’s Cove, looking east. For scale, note two men seated on beach boulder.

Image-58-View-from-Maer-HigView from Maer High Cliff top, looking west. People on beach for scale. The wave-cut platform exposes upstanding ribs of Bude Formation sandstone (harder to erode); thicker sandstones locally form sea stacks. In the right half of the photo, the ribs are folded into V-shapes pointing seaward. This pattern, and the outward dip on either side of each V, indicate that the fold is an anticline (upfold) plunging seaward. Such 2D horizontal cross sections through Bude Formation folds complement the vertical cliff sections, allowing the folds’ 3D geometry to be discerned.

Image-52-View-from-Maer-CliView from Maer Cliff top, looking west. People on beach for scale. On the wave-cut platform (partly covered by beach sand), Bude Formation sandstone ribs dip left and right on either side of the centre line (top to bottom), defining an anticline. The ribs meet in a V-shape at the centre, indicating that the anticline plunges seaward. Note sandstone sea stack in foreground.

Image-51-View-from-Maer-CliView from Maer Cliff top, looking southwest. People for scale, near water’s edge. On the wave-cut platform, the V-patterns and opposed dips of Bude Formation sandstone ribs reveal two seaward-plunging folds, namely an anticline (right-hand side; close-up in previous photo) and adjoining syncline (upper left).

Geo-Walks-36-Bude-Sea-Pool,Bude Sea Pool, looking east. In the foreground and background are Bude Formation sandstone and shale beds dipping north, in the north limb of an anticline and south limb of a syncline.

Image-38-Bude-geologist-Dr-Bude geologist Dr Roger Higgs at First Cove. Bude Formation sandstone and dark shale beds dip inward toward the centre of the view, defining a syncline. The next few photos show some of the ‘sedimentological’ details of Bude beds, helping us to interpret the ancient ‘environment of deposition’. The scarcity of fossils and burrows, and the presence of a unique fossil (a fish), suggest a lake (called ‘Lake Bude’ in geological publications by Roger) rather than a sea. Palaeomagnetic studies show that the latitude was equatorial, consistent with tropical plant fossils in the Coal Measures (same Carboniferous age) of South Wales.

image-67-Bude-Formation-sanBude Formation sandstone and dark shale beds in the low cliff at Summerleaze Beach (north side). Sandstone beds have sharp bases and many of them have rippled tops, e.g. the bed under the hammerhead (which is the lowest bed in the next photo). The ripples are nearly symmetrical, suggesting that waves contributed to forming them, in turn suggesting deposition in water less than 200 m deep.

Image-69-Bude-Formation-strBude Formation strata at Summerleaze Beach (north side; enlargement of previous view). Three sandstone beds alternate with dark shales. Each sandstone has a sharp base and a less-sharp top showing near-symmetrical ripples. To the right of the £1 coin (for scale, 22 mm across), the second sandstone bed is cut by a vertical, mud-filled, cylindrical burrow (dark grey), made about 300 million years ago by a probable worm or shrimp digging into the soft sandy floor of ancient ‘Lake Bude’ (see enlargement, next photo).

Image-70-zoom-Bude-FormatioBude Formation strata at Summerleaze Beach (north side; enlargement of previous photo). Close-up of a burrow (right hand side) excavated in a soft sand bed by a Palaeozoic lake-floor animal and filled by dark grey mud after abandonment.

Upper portion of Maer High Cliff, looking north from cliff top. Quad bike for scale at upper left. The top surfaces (facing south) of several Bude Formation near-vertical sandstone beds, exhumed by erosion of intervening shales, show ripples in plan view. The ripples were made in soft sand on the flat floor of ‘Lake Bude’ about 300 million years ago.

Image-74-Millook-Haven,-7-kMillook Haven, 7 km south of Bude. Note South West Coast Path (cliff top, upper right) and people on beach for scale. Sandstone and shale beds of the Crackington Formation have been spectacularly deformed into a vertical cascade of zigzag folds (anticlines and synclines), lying on their sides. See enlargement, next photo. The Crackington Formation is similar to the Bude Formation (which was deposited immediately above it, before the folding took place), but lacks the very thick (3-10 m) sandstone units typical of the Bude. The photo of ‘chevron folds’ in Wikipedia is from here.

image-75-zoomed-Zigzag-foldZigzag folds in Crackington Formation at Millook Haven (enlargement of previous view). For scale, note lady on beach at lower left.

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