Riccarton Group, Silurian, Southern Uplands

From MediaWiki
Jump to navigation Jump to search
The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.
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.

Riccarton Group

Representative structural-stratigraphical profile for the Ross and Raeberry Castle formations in the Kirkcudbright area. P912334.

The Riccarton Group, the southernmost exposed part of the Silurian succession in the Southern Uplands, is in fault contact with the Hawick Group to the north but is unconformably overlain by lower Carboniferous strata to the south. It is composed of a range of turbidite lithofacies interbedded with finely laminated carbonaceous siltstone, most probably a hemipelagic deposit. Wenlock graptolite faunas are common in the latter, ranging in age from the riccartonensis Biozone to the lundgreni Biozone in the Kirkcudbright coastal outcrop (Raeberry Castle Formation), but ranging no higher than the rigidus Biozone farther north-east between Langholm and Hawick (Caddroun Burn Formation). The component turbidite sandstone, variably fine- to coarse-grained, is quartz-rich (up to 67 per cent of the grains) but can also contain abundant carbonate, largely as an alteration product but also as rock fragments and bioclastic debris. Minor grain contributions include 5–10 per cent feldspar (predominantly K-feldspar), mica (particularly in fine-grained sandstone) and lithic debris. The latter forms a significant component of coarser-grained sandstone and includes quartzite, chert, limestone and acid and basic (spilitic) igneous material along with sedimentary material likely to be of intrabasinal origin.

In Kirkcudbrightshire, the Raeberry Castle Formation (about 1500 m) is divided into three, partly coeval structural tracts that are accorded member status (P912334). In contrast to the adjacent Ross Formation tracts, the Raeberry Castle Formation members are internally coherent, with very little disruption of the bedding. The Gipsy Point Member is composed of thin- to medium-bedded turbidites overlain by channel-fill accumulations that include slump deposits, and which are interspersed with overbank or levee deposits of thinly interbedded sandstone and mudstone with well-developed dewatering structures. The Raeberry Member consists of variable but well-bedded turbidites with isolated thick sandstone and hemipelagite beds. The Mullock Bay Member features channelised sandstone, some very coarse, alternating with thinly interbedded, fine-grained sandstone and mudstone; this assemblage is overlain by upward thickening and coarsening units that pass from hemipelagite through thin- to medium-bedded to thick-bedded sandstone.

The equivalent strata in the Langholm to Riccarton area make up the Caddroun Burn Formation (about 1500 m). This comprises thin-bedded fine-grained sandstone and mudstone with intercalations, tens of metres in thickness, of more thickly bedded, coarser sandstone with thin mudstone interbeds. Laminated carbonaceous siltstone occurs throughout, generally as relatively thin beds but locally much thicker (8 m at one locality near Saughtreegrain (NY 568 998)). Palaeocurrent data indicate that most sediment transport was towards the southeast quadrant, with a subsidiary flow towards the south-west. Some thin, fine-grained beds are rich in plant and crustacean remains.


Clarkson, E N K, Harper, D A T, Owen, A W, and Taylor, C M. 1992. Ordovician faunas in mass-flow deposits, Southern Scotland. Terra Nova, Vol. 4, 245–253.

Duller, P R, and Floyd, J D. 1995. Turbidite geochemistry and provenance studies in the Southern Uplands of Scotland. Geological Magazine, Vol. 132, 557–569.

Elders, C F. 1987. The provenance of granite boulders in conglomerates of the Northern and Central Belts of the Southern Uplands of Scotland. Journal of the Geological Society of London, Vol. 144, 853–863.

Floyd, J D. 2001. The Southern Uplands Terrane: a stratigraphical review. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 91, 349–362.

Floyd, J D, and Kimbell, G S. 1995. Magnetic and tectonostratigraphic correlation at a terrane boundary: the Tappins Group of the Southern Uplands. Geological Magazine, Vol. 132, 515–521.

Floyd, J D, and Rushton, A W A. 1993. Ashgill greywackes in the Southern Uplands of Scotland: an extension of the Ordovician succession in the Northern Belt. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 84, 79–85.

Floyd, J D, and Trench, A. 1989. Magnetic susceptibility contrasts in Ordovician greywackes of the Southern Uplands of Scotland. Journal of the Geological Society of London, Vol. 146, 77–83.

Kemp, A E S. 1986. Tectonostratigraphy of the Southern Belt of the Southern Uplands. Scottish Journal of Geology, Vol. 22, 241–256.

Leggett, J K. 1987. The Southern Uplands as an accretionary prism: the importance of analogues in reconstructing palaeogeography. Journal of the Geological Society of London, Vol. 144, 737–752.

Merriman, R J, and Roberts, B. 1990. Metabentonites in the Moffat Shale Group, Southern Uplands of Scotland: Geochemical evidence of ensialic marginal basin volcanism. Geological Magazine, Vol. 127, 259–271.

Morris, J H. 1987. The Northern Belt of the Longford–Down Inlier, Ireland and Southern Uplands, Scotland: an Ordovician backarc basin. Journal of the Geological Society of London, Vol. 144, 773–786.

Phillips, E R, Smith, R A, and Floyd, J D. 1999. The Bail Hill Volcanic Group: alkaline withinplate volcanism during Ordovician sedimentation in the Southern Uplands, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 89, 233–247.

Phillips, E R, Evans, J A, Stone, P, Horstwood, M S A, Floyd, J D, Smith, R A, Akhurst, M C,and Barron, H F. 2003. Detrital Avalonian zircons in the Laurentian Southern Uplands terrane, Scotland. Geology, Vol. 31, 625–628.

Stone, P, and Evans, J A. 2001. Silurian provenance variation in the Southern Uplands terrane, Scotland, assessed using neodymium isotopes and linked with regional tectonic development. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 91, 447–455.

Stone, P, Breward, N, Merriman, R J, and Plant, J A. 2004. Regional geochemistry of cryptic geology: variations in trace element distribution across the Southern Uplands terrane, Scotland. Applied Earth Science (Transactions of the Institution of Mining and Metallurgy B), Vol. 113, B43–B57.

Stone, P, Breward, N, Merriman, R J, and Barnes, R P. 2006. The interpretation and application of regional geochemistry: lessons from the Paratectonic Caledonides. Scottish Journal of Geology, Vol. 42, 65–76.

Tucker, R D, Krogh, T E, Ross, R J, and Williams, S H. 1990. Time-scale calibration by high-precision U-Pb zircon dating of interstratified volcanic ashes in the Ordovician and Lower Silurian stratotypes of Britain. Earth and Planetary Science Letters, Vol. 100, 51–58.

Waldron, J W F, Floyd, J D, Simonetti, A, and Heaman, L M. 2008. Ancient Laurentian detrital zircon in the closing Iapetus Ocean, Southern Uplands Terrane, Scotland. Geology, Vol. 36, 527–530.

Warren, P T. 1964. The stratigraphy and structure of the Silurian rocks south-east of Hawick, Roxburghshire. Quarterly Journal of the Geological Society of London, Vol. 120, 193–218.