New evidence for the relative age of the Ercall Granophyre and its bearing on the Precambrian-Cambrian boundary in southern Britain

✍ Scribed by John C. W. Cope; Wes Gibbons

• Book ID: 102845334
• Publisher: John Wiley and Sons
• Year: 1987
• Tongue: English
• Weight: 705 KB
• Volume: 22
• Category: Article
• ISSN: 0072-1050
• DOI: 10.1002/gj.3350220106

✦ Synopsis

Recent extension of the Ercall Quarry, Shropshire, has revealed an unconformable contact between the Ercall Granophyre and overlying Lower Cambrian sediments. Five metres of basal conglomerate with rare granophyre clasts overlie a weathered granophyre surface and precludes the possibility that the granophyre is intrusive into the quartzite. The age of the Cambrian quartzite is reviewed and is considered to be most probably late Tommotian. The granophyre is therefore pre-late Tommotian, but has been radiometrically dated as 533 ? 13 Ma (Rb-Sr WR, Patchett ef al. 1980) and 531 t 5 Ma (U-Pb zircon, Compston ef al. in Cowie and Johnson 1985). If these independent dating methods are recording the age of granophyre intrusion, then the absolute ages of both the Comley Series Lower Cambrian faunas, and therefore the Precambrian-Cambrian boundary, are younger than is generally recognized.