Variscan sourcing of Westphalian (Pennsylvanian) sandstones in the Canonbie Coalfield, UK

Abstract

-The zircon age spectrum in a sample from the Canonbie Bridge Sandstone Formation (Asturian) of southern Scotland contains two main peaks. One is Early Carboniferous in age (348-318 Ma), and corresponds to the age of igneous activity during the Variscan Orogeny. The other is of late Neoproterozoic to early Cambrian age (693-523 Ma), corresponding to the Cadomian. Together, these two groups comprise 70 % of the zircon population. The presence of these two peaks shows unequivocally that a significant proportion of the sediment was derived from the Variscides of western or central Europe. The zircon population also contains a range of older Proterozoic zircons and a small Devonian component. These could have been derived from the Variscides, but it is possible that some were locally derived through recycling of northerly derived sandstones of Devonian-Carboniferous age. The zircon age data confirm previous suggestions of Variscide sourcing to the Canonbie area, made on the basis of petrographical, heavy mineral and palaeocurrent evidence, and extend the known northward distribution of Variscan-derived Westphalian sediment in the UK.

Warwickshire Group (Pennsylvanian) red-beds of the Canonbie Coalfield, England–Scotland border, and their regional palaeogeographical implications

“…The map falls within the National Grid 100 km square NY. (SHRIMP RG); the results of this work are reported elsewhere (Morton, Fanning & Jones, 2010).…”

The provenance of Western Irish Namurian Basin sedimentary strata inferred using detrital zircon U–Pb LA‐ICP‐MS geochronology

“…500–700 Ma grains are also a significant age component in slightly younger (Duckmantian to Westphalian D), southern‐sourced sedimentary strata within the nearby Pennine Basin, Northern England (Halesowen Formation, Westphalian D, and Dalton Rock, Bolsovian; Hallsworth et al , ), the Southern North Sea Basin (Westoe Formation, Duckmantian; Morton et al , ) and the Canonbie Coal field, southern Scotland (Canonbie Bridge Sandstone Formation, Westphalian D; Morton et al , ). The source direction for these sedimentary strata is less ambiguous than the WINB strata; U–Pb detrital zircon data contain grains of unequivocal Variscan age (320–360 Ma), which must have originated in the Variscan orogenic belt to the south.…”

Heavy-mineral, mineral-chemical and zircon-age constraints on the provenance of Triassic sandstones from the Devon coast, southern Britain

“…Variscan granites are widespread in the Armorican Massif of northern France and equivalent parts of the Variscan mountain belt in central Europe (Tischendorf et al, 1995;Brown & Dallmeyer, 1996;Ballèvre, 2009;Tyrrell et al, 2012). These granites are known to have been available as a sediment source as early as the Late Carboniferous, on the basis of the presence of detrital zircons in Westphalian sandstones of the UK (Hallsworth et al, 2000;Morton et al, 2010), and on the basis of evidence for rapid exhumation of such granites in the Variscan mountain belt (Schulmann et al, 2002). The scarcity of Late Carboniferous and Early Permian zircons in the Devon coast succession suggests that the catchment area did not extend into regions of Armorica that include widespread Variscan granites, and therefore implies that the source was more proximal, probably in the English Channel and possibly extending into the Channel Islands, the La Hague peninsula and the northern Brittany coast, where Variscan granites are comparatively minor (Brun et al, 2001;Sansom et al, 2005).…”