The Excursion to Devon 16-17th September 2023

We had two days of excursions, led by Malcolm Butler, to the coast near Torquay and to the Hay Tor
region of Dartmoor. While the weather was good on the first day, conditions on Dartmoor were such that
we abandoned the field visit on the second day, retiring to a nearby hotel for an extended coffee break
followed by lunch in Bovey Tracey.

 

Berry Head

The quarry is cut into the Berry Head Member of the Brixham Limestone, of Middle Devonian Eifelian to
Latest Givetian in age. The upper part of the quarry face consists of massive limestones, forming a
stromatoporoid reef‐complex, although details are difficult see because of recrystallisation. Some details
of the underlying bioclastic limestones can be seen in outcrops close to the sea edge and in fallen blocks.
This shows very well the amount of solution and fissure‐fill associated with the basal Permian
unconformity, which lies just above the top of the cliff. Open vertical fissures are lined by layers of calcite
crystals and often filled with purple muds and fine sands of Permian age. This type of fracture fill, solution
and cave formation is a common feature where Permian and Triassic rocks
laid down under desert condition unconformably overlie massive limestones in the UK, most
commonly where Carboniferous limestones subcrop, since Devonian limestones are only found in this area
of Devon. Studies are underway by the BGS and various university departments to investigate areas where
these rocks might have retained open cavernous porosity and be buried sufficiently deeply to form a host
for geothermal fluids. There was a debate about whether some of the caverns could have been formed
by hypogene fluids, rising from below.

Field Trip September 2023

A fissure infilled with Permian material.

Field Trip September 2023

Brecciated limestones with Permian infill.

 

Goodrington Sands

Folding in the Lower Devonian Meadfoot Group is well exposed in the cliffs at the southern side of
Goodrington Sands. The Meadfoot Group is again overlain unconformably by the Permian breccias.

Field Trip September 2023

An isoclinal fold in the Devonian.

Field Trip September 2023

En echelon tension gashes in the Devonian.

Field Trip September 2023

The unconformity with the Permian above the Devonian.

Field Trip September 2023

Permian conglomerates and sandstones.

 

Triangle Point

Daddyhole Limestone, of Eifelian age, which overlooks a disused quarry where the limestone was excavated down to sea
level. The beds dip down to the SW at 48 degrees and the relationship of the well‐developed axial planar cleavage to
bedding indicates that the beds are not inverted, although the interpretation has been subject to much discussion. In any
case, this is one of the few places where a well‐developed fossil assemblage including corals, crinoids and small
stromatoporoid colonies can readily be seen.

Field Trip September 2023

Field Trip September 2023

Corals, and possibly bryozoans.

Field Trip September 2023

Hay Tor – This is what we should have seen on the second day!

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