Sequence and Structure in the Silurian Rocks of Kirkcudbrightshire

Abstract

The generally accepted interpretation of the structure of the Southern Uplands has been that of an anticlinorium to the north-west flanked by a synclinorium to the south-east. This structure, however, has always been illustrated as one large anticlinorium since the Hawick rocks in the core of the synclinorium have been considered to be older than the Riccarton (Wenlockian) Beds which lie to the south. In Kirkcudbrightshire, a reverse age relationship is demonstrated with the result that the beds could in fact form the southern limb of the synclinorium. When this is shown to be the case doubts are thrown on the validity of the fold and two alternative interpretations are given.

Deformation in Moffat Shale detachment zones in the western part of the Scottish Southern Uplands

“…The thrust sheets are older to the NW despite internally displaying dominant NW-younging directions. This paradox of Southern Uplands structure was resolved with the recognition of reverse faults (Craig & Walton, 1959) which have subsequently been shown to form the tract or thrust sheet bounding faults. The origin of the thrust sheets has been ascribed to the formation of an accretionary prism that developed along the northwestern margin of the Early Palaeozoic Iapetus ocean from Early Ordovician until Late Silurian times (Leggett, McKerrow & Eales, 1979;Leggett, McKerrow & Casey, 1982).…”

Structural history of the Silurian rocks of the coast west of Gatehouse, Kirkcudbrightshire

“…In this paper, correlation is effected between the Silurian sediments of the coast between Creetown and Gatehouse, Kirkcudbrightshire, and those of the areas between Gatehouse and Kirkcudbright (Craig and Walton 1959) and Whithorn, Wigtownshire (Rust 1965<J). Tectonic structures are also compared with the latter area.…”

The Southern Uplands Terrane in Scotland – a notional controversy revisited

“…Tellingly, Dewey identified the Southern Upland succession as a wedge of clastic sediment that initially built up in a continental margin trench, but then extended out across the subducting oceanic plate. Deformation was caused by shortening of the sedimentary succession accompanied by segmentation of the oceanic crust (Dewey 1971, see his figure 5), processes giving rise to a structural geometry similar to that proposed by Craig & Walton (1959). Dewey's interpretation foreshadowed the development of the full-blown accretionary prism model ( Figure 5) through a series of papers by McKerrow, Leggett and coworkers (Mitchell & McKerrow 1975;McKerrow et al 1977;Leggett et al 1979Leggett et al , 1982Leggett et al , 1983.…”

“…The new insight also forced a reconsideration of the regional structure and in a radical reinterpretation Craig & Walton (1959) proposed a series of large monoclines, each with steep limbs to the north and flat limbs cut on their south side by major strike-parallel reverse faults with substantial downthrow to the south. The steeply dipping, northern limbs contained uniformly north-younging strata; the flat limbs were corrugated by minor folds within a horizontal fold envelope that was faulted against the next steep limb southward.…”