Pembrokeshire geology

Blustery conditions in Whitesands Bay / Porth Mawr, viewed from the coastal path leading to St David's Head, Pembrokeshire. The headland in the foreground is Trwynhwrddyn ('Ram's nose') - a narrow peninsula comprised of steeply dipping uppermost Cambrian and basal Ordovician shales and tuffs. The hills in the distance are on Ramsey Island.

Blustery conditions in Whitesands Bay / Porth Mawr, viewed from the coastal path leading to St David's Head, Pembrokeshire. The narrow peninsula is Trwynhwrddyn ('Ram's Nose'), comprised of steeply dipping uppermost Cambrian and basal Ordovician shales and tuffs.

Point St John is the westerly headland on the south side of Whitseands Bay / Porth Mawr, Pembrokeshire. I was intrigued by the steeply dipping bedding planes of Cambrian sediments, wet and glistening in the afternoon sun after a sharp shower had passed over.

A southwesterly view from close to the summit of Carn Llidi, a tor-like miniature mountain (181 m) comprised of gabbro, overlooking St David's, Pembrokeshire. Whitesands Bay / Porth Mawr and Ramsey Island are visible in the upper right.

This is a view of the Ordovician age pillow lavas on Strumble Head, Pembrokeshire. Pillow lavas are formed when molten basalt lava is erupted onto the sea floor. If the water is deep enough, the hydrostatic pressure stops the lava from exploding the sea water into steam. Instead, the liquid rock and liquid water co-exist together in an uneasy truce. The lava is extruded like toothpaste into successive oval globules, resembling pillows or sacks, hence the name. See the video clip here: oceanexplorer.noaa.gov/explorations/04fire/background/vol...

Originally uploaded for the Guesswhere UK group. Complex folding in Namurian rocks at Monkstone Point near Saundersfoot, Pembrokeshire, in the bottom left-hand corner of Wales. This is a complex anticlinal chevron fold. The main limbs of the fold are the straight parts, dipping at 40° to the south (L) and 30° to the north (R). One feature of tight folds like this is the SPACE problem. The rocks in the central part of the fold get compressed as the available volume they have to occupy reduces as the folding progresses. This leads to all sorts of seemingly chaotic deformation of the stuff in the middle. In this instance, the core of the fold is comprised of thin beds of sandstone interleaved with thin soft shale layers. The latter especially has deformed almost plasticly under the compressional stresses, and the thin sandstones also to a lesser extent. This results in the incompetent deformation structures seen in the photo, to accommodate the reduced space available in the core of the fold.

Originally uploaded for the Guesswhere UK group. Goskar Rock is a prominent feature of the North Beach at Tenby, Pembrokeshire. Comprised of Namurian age sandstones and siltstones, this is a great locality for teaching students to measure the dip (angle of slope) and strike (level course bearing) of the rocks.

This photo shows the cliffs in the small sandy bay known as The Settlands between Little Haven and Broad Haven in Pembrokeshire, west Wales. The rocks here are Upper Carboniferous Coal Measures and are part of the western extremity of the Pembrokeshire coalfield. The strata have been severely deformed by compressional tectonics during the Hercynian (Variscan) earth movements. In the centre of the photograph the rocks are folded into a recumbent fold, with the axis near horizontal - a sort of tilted " < " shape. A thrust fault separates this fold from the steeply dipping, inverted rocks on the LH side. These form the headland known as The Rain . Scanned from a Kodachrome 64 transparency.

Manorbier Bay, looking west. The wave-cut platform consists of vertically bedded Old Red Sandstone. Taken from the Pembrokeshire Coast Path at the height of the foot & mouth disease crisis, when only limited sections of the footpath were open.

Just south of Saundersfoot, Pembrokeshire. Scanned from a 35mm transparency, taken with a Zenit 'E' camera.

Originally posted for the Guesswhere UK group Thrust fault and related compressional structures in Coal Measures in the cliffs just west of Amroth, Pembrokeshire, west Wales. See where this picture was taken. [?]