The biostratigraphy of the Silurian rocks of the Girvan District, Scotland

Abstract

The Silurian biostratigraphy of the Girvan area is reviewed. Of the 23 Silurian formations, 7 have abundant shells and 14 have common graptolites. The Silurian is nearly 3000 m thick and was chiefly deposited in a turbidite environment. All the Llandovery zones from cyphus to crenulata inclusive are represented by graptolite faunas. In the Rhuddanian (prior to the cyphus Zone) the Lady Burn Conglomerate, Mulloch Hill Formation and Woodland Formation are shelly facies laid down by a marine transgression. There are two stratigraphical breaks, the unconformity at the base of the Silurian sequence and in the Fronian, where there is a paraconformity underneath the Lower Camregan Grits, both breaks with a transgressive sequence of animal communities above them. At the top of the succession Lower Wenlock turbidites, bearing shells at their bases, are followed by a sparse ostracodbivalve assemblage representing brackish or even fresh water conditions, culminating in ‘Old Red Sandstone’ facies beds of presumably Wenlock age, all representing the marine regression seen in other inliers in the Midland Valley of Scotland. Remarkable fossil finds from the Llandovery include Stomatograptus grandis girvanensis subsp, nov., Monodimacis crenulata itself, and the only chonetid brachiopod known anywhere from the Rhuddanian or Idwlan.

Geochemistry and potential correlation of Silurian (Telychian) metabentonites from Ireland and SW Scotland

“…The Lauchlan Formation, which immediately underlies the Drumyork Flags, was assigned to the lower part of the M. spiralis Biozone (Loydell 1993). Reassessment of the Drumyork Flags graptolite fauna previously referred to the griestoniensis Biozone by Cocks and Toghill (1973), together with newly recognized spiralis Biozone fauna in the overlying Blair Shale Formation, indicates that the Drumyork Flags lie entirely within the spiralis Biozone (Floyd 2001;Floyd and Williams in press).…”

A review of geological origins and relationships in the Ballantrae Complex, SW Scotland

“…In turn, in the Girvan district, the normal faults that had controlled deposition of the Ordovician to Silurian forearc basin succession were reactivated as north-directed thrusts with adjacent strata rotated and folded so that steep dips are now commonly seen at outcrop. The thrust re-activation could have begun quite early in the Wenlock since the youngest strata affected (and now preserved) are of earliest Wenlock age (Cocks & Toghill 1973;Floyd & Williams 2003).…”

Composition and provenance of the Silurian to Devonian sandstone sequences of the southern Midland Valley

“…1). The sedimentary sequences within these inliers record the transition from an older (Llandovery) marine sequence to a younger (Lower Wenlock) terrestrial succession (Cocks & Toghill 1973;Rolfe 1960Rolfe , 1961Rolfe & Fritz 1966;Cameron & Stephenson 1985;Robertson 1989;Smith 1995). The present study has focused upon the Silurian sequences exposed within the Hagshaw Hills, Carmichael, Eastfield and North Esk inliers (Fig.…”