Earthwatcher's photos with the keyword: Variscan

A nice example of a tight, nearly isoclinal, upright syncline in the Bude Formation (Upper Carboniferous) at Wrangle Point, Crooklets near Bude in Cornwall.

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.

These plunging chevron folds are in the Bude Formation (Upper Carboniferous). 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

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

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.

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.

On the limb of an anticline, near-vertically bedded turbidite sandstones in the Bude Formation (upper Carboniferous) display sedimentary structures which can be used to determine the 'way up' of the bedding. Here, the sandstones display small-scale slump or load structures on the basal surfaces, and some beds show 'fining up' on the grain size (indicated by gradual darkening of the bed). These structures demonstrate that the vertical beds here get younger to the right. Here's structure in its proper setting and orientation: www.ipernity.com/doc/earthwatcher/39024212 and here: www.ipernity.com/doc/earthwatcher/39024214

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).

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

Turbidite sandstones in the Bude Formation (upper Carboniferous) display sedimentary structures which can be used to determine the 'way up' of the bedding. Here, the sandstones display small-scale slump or load structures on the basal surfaces, and some beds show 'fining up' on the grain size (indicated by gradual darkening of the bed). These structures demonstrate that the beds here are the right way up, i.e. have not been completely inverted by the strong folding this area has undergone. The sequence shown here gets younger upwards and to the right.

Disharmonic recumbent fold at Broad Haven - view along the fold crest . On the north headland of Broad Haven, Pembrokeshire, is this spectacular fold structure in Coal Measures strata. The fold is essentially an anticline strongly overturned northwards (to the left) so that its fold axis is near to horizontal. The relatively strong sandstone beds (orange-brown) have deformed into an angular chevron-shaped fold, while the softer seatearth below the coal has deformed into a rounded fold, seen in the lower part of the structure, almost from the camera viewpoint. This has been achieved by considerable slip along individual bedding planes and softer, incompetent, material has been squeezed into the hinge zones from the fold limbs. This has occurred particularly along the horizon of a thin coal seam and the immediately overlying dark shales, which have 'flowed' into the angular apex of the fold to the left of centre. The seatearth is also cut by a coarsely-developed axial planar cleavage, which is partly responsible for the 'nubbly' texture on the rounded part of the fold. The cleavage fans out almost radially, best seen in section on the rounded bed in the middle distance.

Disharmonic recumbent fold at Broad Haven - view of the hinge zone On the north headland of Broad Haven, Pembrokeshire, is this spectacular fold structure in Coal Measures strata. The fold is essentially an anticline strongly overturned northwards (to the left) so that its fold axis is near to horizontal. This photo shows a closer view of the hinge zone along the horizon of a thin coal seam and the immediately overlying dark shales, which have 'flowed' into the angular apex of the fold just to the left of centre. The relatively strong sandstone beds (orange-brown) have deformed into an angular chevron-shaped fold, while the softer grey seatearth below the coal has deformed into a rounded fold, seen in the lower part of the structure, to the right of centre. The seatearth is also cut by a coarsely-developed axial planar cleavage (better seen in the previous photo), which is partly responsible for the 'nubbly' texture on the rounded part of the fold.

Disharmonic recumbent fold at Broad Haven - general view . On the north headland of Broad Haven, Pembrokeshire, is this spectacular fold structure in Coal Measures strata. The fold is essentially an anticline strongly overturned northwards (to the left) so that its fold axis is near to horizontal. The fold is disharmonic - individual beds in the fold have become detached and are no longer concentric with each other, as can be seen above and to left of centre. This has been achieved by considerable slip along individual bedding planes and softer, incompetent, material has been squeezed into the hinge zones from the fold limbs.

This is a view of the plunging syncline in the small islet in Middle Cove, just north of Stackpole Quay, Pembrokeshire. The fold is developed in Carboniferous Limestone, with a plunging axis trending approximately ESE-WNW, dipping easterly. The fold style is mostly concentric, but the 'space problem' in the centre of the fold has been accommodated by small-scale thrusting and crumpling, and additional movement taking place along bedding planes.

Another view of the Middle Cove islet at Stackpole Quay, Pembrokeshire, formed of Carboniferous Limestone folded into a plunging syncline. In this photo, the axis of the syncline crosses the islet from L-R with a gentle plunge easterly (R). Cliffs of Devonian age Old Red Sandstone are visible in the background.

The Stackpole Fault exposed in a small cove at Stackpole Quay, Pembrokeshire. The camera location of the previous photo in the photostream was in the notch at the top of the photo. Jan is standing just to the left of the fault plane, which consists of a jumbled smash-zone of fragmented limestone recemented with calcite. To the left of the fault plane, the rocks are dipping northwards at about 45°. There is a well-developed, nearly vertical set of fractures (parallel to Jan). These are axial planar cleavage developed around the Stackpole Quay anticline, but have probably been amplified as pinnate cleavage by the proximity and movement of the Stackpole Fault. (A bit like trying to plane a piece of wood against the grain - the plane 'chatters' and you get a rough surface, not a smooth one)

As well as being a very picturesque spot, Stackpole Quay is really interesting in terms of structural geology. The rocks are Carboniferous Limestone which have been folded and faulted. Of particular interest is the Stackpole Fault, which is a tear fault or strike-slip fault. This means that rocks on either side of the fault are shifted mainly horizontally relative to each other, rather than vertically. Here, the off-set across the fault is about 100 metres to the right (dextral). In some ways the Stackpole Fault is like a miniature version of California's San Andreas Fault, although the mechanism driving the fracture is different. In this southwards view, the Stackpole Fault can be seen in the quarry face in the distance. It runs towards the camera, causing the outcrop of rocks in the harbour just to the right of the boat to be truncated suddenly. The camera location (i.e. me) is directly on the fault. The main Stackpole Quay anticline axis is located in the slipway in the foreground on the RH side of the fault, but is truncated by the fault and off-set 100 m southwards to reappear at the far end of the harbour wall on the LH side of the fault. Hmm... it takes a lot of words to explain. It's much easier to understand when you go there and see it for yourself :-)

Another view of the rocks - Carboniferous Limestone - at Stackpole Quay, Pembrokeshire. In the left foreground, the crest of the Stackpole Quay anticline is just visible. In the left background, the northerly dip of the rocks does not match with the foreground. This is because the Stackpole Fault runs across the photo from L to R with different structures visible on either side. On the far side of the fault, the axis of the Stackpole Quay anticline is offset by 100 metres to the right (south).