Article 65

Knowledge Of One Super Continent, Pangaea-The Variscan Orogeny.

Peter Toghill’s Chapter 8 then shows that the closure of the Rheic Ocean at the end of the Carboniferous had profound effects in what is now Britain; but that it had an even wider impact globally in that it formed mountain ranges along the suture-line, including the Appalachians in what is now North America, various mountains in what is now north-west Africa and the Pyrenees and the Urals in what is now Europe, though no such mountains formed in Britain. The closure of this Ocean caused by a widening of the proto-Pacific resulted in there being only one supercontinent and one super-ocean by the end of the Carboniferous Period. Alfred Wegener called these Pangaea and Panthalassa (all land and all sea) and the current configuration of the continents and oceans is the result of the subsequent break-up of Pangaea from Triassic times onwards, and the subsequent movement of continents around the globe caused the appearance of three new oceans the Atlantic, Indian and Southern Oceans. 

In Europe, the Varsican orogeny had definite phases, the last being late Carboniferous/Early Permian. Nearer to home the Varsican orogeny caused intense folding and deformation accompanied by slate grade metamorphism over south-west England, with no fold mountains being formed in contrast to those formed by the Caledonian orogeny. This contrast in turn has led to the suggestion that the Rheic Ocean closed mainly as a result of lateral fault movements rather than by head-on continental collision and its associated subduction. In particular, North America had to move a considerable distance laterally to make contact with north-west Africa, then part of Gondwanaland. Deformation in south-west England was followed by the intrusion of a granite batholith dated at 280-270 Ma (early Permian) while similar granite cuts had already deformed late Carboniferous Westphalian strata, so we see that this orogeny is post-Westphalian/pre-Permian. 

To a lesser extent this orogeny also affected south Wales, the Mendips and the Forest of Dean where rocks are unmetamorphosed but can be observed to be intensely folded and affected by thrusts, as in Pembrokeshire. Again, north of St George’s Land (an island of red sandstone surrounded by shallow water shelf carbonates which separates north Wales from the English midlands), is also an area of faulting associated with the Varsican orogeny. By the end of the Carboniferous, this orogeny had caused uplift over the whole British area, which then lay within the arid hinterland of Wegener’s Pangaea, but there were no huge mountains, though elsewhere erosion of the Varsican highlands produced the sediment for the rocks of the next geological period, the Permian. Thereafter Peter Toghill provides more detail of the Varsican effects on south-west England, South Wales, the Forest of Dean, the Mendip hills, the Midlands, northern England and Scotland which need not concern us here.