Excursion to the South Devon coast led by Prof John CW Cope (National Museum Wales)

Mervyn Jones (UK) GA field meeting on 6 and 7 April 2019 This field meeting was the second following the publication of Prof Cope’s GA Guide No 73, Geology of the South Devon Coast (reviewed in Issue 51 of Deposits), the companion to GA Guide No 22, Geology of the Dorset Coast (reviewed in Issue 50). Our mission for the weekend was to complete our examination of the complex Devonian succession from Torbay to the western limit of Lyme Bay at Start Point and then beyond; farther into South Devon. Of great interest was the marine Devonian, first described by Adam Sedgwick, assisted by Roderick Impey Murchison, who finally realised that these facies were contemporaneous with the familiar Old Red Sandstone found north of the Bristol Channel. The area has much to offer enthusiasts of structural geology because the Devonian strata have been tectonised by the closure of the Rheic Ocean during the Variscan orogeny. The story has only been unravelled in the last 50 years as follows. First, sediments filled a series of basins caused by crustal extension; the basement beneath the Devonian rocks may well be a massif of Precambrian mica-schist, inferred from the copious amounts of mica and the occasional xenolith in the rocks above. Then, from the Early Carboniferous, continental collision caused a series of major thrust structures and metamorphic zones that progressively moved northward. As a consequence, any Carboniferous rocks that were deposited in the Torbay area were rapidly stripped off. The marine Devonian was … Read More