The stratigraphy, sedimentary environments and palaeogeography of the Silurian strata of Clare Island, Co. Mayo, Ireland

Abstract

The Silurian succession of Clare Island, consisting of at least 1700 m of red siltstones, sandstones and conglomerates resting unconformably on Upper Dalradian and older basement, records a cycle of marine transgression and regression within marginal marine and fluviatile sedimentary environments along the northern margin of the Silurian basin of Ireland. Clastic and pyroclastic sediments of probable Wenlock age were derived from a northern land mass formed of high grade metamorphic rocks cut by acid volcanic centres. It is argued that the source area has been removed by large scale strike-slip fault movement along a fracture zone which previously controlled the margin of the Silurian basin

Palaeomagnetism of Silurian Sediments In W Ireland: Evidence For Block Rotation In the Caledonides

“…The petrography of the clastics indicates a northerly sediment source which can no longer be identified to the north of Clare Island (Phillips 1974). Similarly, volcanic rocks on Clare Island provide evidence of northerly provenance but no source area survives.…”

“…Dating of these rocks is established through well preserved faunas as Wenlock (Phillips 1974;McKerrow & Campbell 1960;Carruthers & Muff 1909). The sampled succession (Fig.…”

A strain section across part of the Caledonian orogen in W Ireland

“…6). Therefore the continuity of structure between the NW Mayo metamorphic inlier and the Ballytoohy Formation in the Clew Bay region suggested by Phillips (1974) may not exist. As the Ballytoohy Formation is everywhere separated from metamorphic Caledonides by large faults (Max & Riddihough 1975) and the strain is markedly lower, it is possible that the Ballytoohy Formation was being deposited and deformed as a wet sediment in a marginal trough while deformation and metamorphism had already begun in the underlying metamorphic Caledonides.…”

The distribution of trilete spores in Irish Silurian rocks

“…A few photographs are however reproduced in Plate 1 in order to illustrate the nature of the material under discussion. Phillips, Rickards & Dewey (1970) and revised by Phillips (1974). Evidence for the age of the Silurian strata of the Clew Bay area is scanty and largely indirect; a Wenlock age for the Knockmore Formation is probable, but not certain.…”

“…The postulated position of the Iapetus suture is from Phillips et al (1976) and is included as a reminder that substantial lateral displacements may have taken place during and after deposition of the strata under consideration. The Caledonian mountains were presumably uplifting at the time, but the only direct evidence for a shoreline is in the Clew Bay area, where shallow water red beds, cross-bedded sandstones, and conglomerates are seen in the vicinity of what is probably the Highland Border (Phillips et al 1970, Phillips 1974. In the Dingle peninsula ( Fig.…”