Permian and Triassic, Southern Uplands
|Stone, P, McMillan, A A, Floyd, J D, Barnes, R P, and Phillips, E R. 2012. British regional geology: South of Scotland. Fourth edition. Keyworth, Nottingham: British Geological Survey.|
Late in Carboniferous times, a major continental collision far to the south of southern Scotland produced the Pangaea supercontinent, and in the process drove the Variscan Orogeny. As a peripheral effect, the Carboniferous basins that had formed across southern Scotland and northern England were inverted, their strata uplifted, folded and faulted. The Permian Period commenced (at about 299 Ma) with the erosion of these strata, at a time when Britain lay, as a part of Pangaea, in tropical latitudes about 10 degrees north of the Equator (P912314e). Pangaea continued to drift slowly northward and by Triassic times (from about 251 Ma) the south of Scotland region had moved to about 30 degrees north. The palaeogeography is summarised in P912358. Desert conditions prevailed throughout this interval, creating depositional environments that included sandy dunefields, alluvial plains, ephemeral lakes and mudflats. There was localised volcanic activity early in the Permian, evidence for which is now best preserved in the Thornhill Basin.
Permian and Triassic continental clastic sedimentary rocks were formerly referred to the ‘New Red Sandstone’. Early descriptions of the ‘New Red Sandstone’ of the Dumfries Basin date back to the 1850s, with the desert red beds long known for their vertebrate trackway trace fossils. However the strata of southern Scotland lack biostratigraphically diagnostic fossils and so are difficult to date with any precision. Further, because the Permo-Triassic sedimentary basins in which they were deposited are tectonically and geographically isolated (P912359), a separate lithostratigraphical nomenclature has been established for each basin. For the exclusively Scottish basins these local schemes are now all included within the Stewartry Group. The large Carlisle Basin spans the border between southern Scotland and north-west England, and for this sequence the lithostratigraphy developed for the extensive English outcrop is extended across the border into the relatively small Scottish outcrop along the northern margin of the basin. Only general correlation is possible between the wholly Scottish and the trans-border successions (P912360).
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