The Longmyndian Rocks of the Old Radnor Inlier, Welsh Borderland
✍ Scribed by N. H. Woodcock; J. C. Pauley
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- English
- Weight
- 484 KB
- Volume
- 24
- Category
- Article
- ISSN
- 0072-1050
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✦ Synopsis
Two formations are named in the presumed Precambrian sedimentary rocks of the Old Radnor Inlier. The Strinds Formation comprises fine-to medium-grained sandstones and pebbly sandstones. Grain-size, texture, clast types, and lithological invariance support correlation with the homogeneous and cross-bedded sandstone facies of the Bayston-Oakswood Formation of the Longmyndian, assigned to a braided alluvial plain environment. The Yat Wood Formation comprises fine-grained sandstones, siltstones, and laminated mudstones. It may be equivalent to some part of the Burway. Synalds, or Lightspout Formation. The Strinds and Yat Wood Formations are petrographically similar to each other and to the type.Lonmyndian, and were soured either directly or indirectly from a magmatic arc.
The Strinds and Yat Wood Formations are seen only in faulted contact, and the inlier itself is partly or wholly bounded by strands of the Church Stretton fault zone. Similar faulted relationships are seen further northeast along the system at Pedwardine and in the Church Stretton area. A fault explanation for the juxtaposition of contrasting facies is favoured over that of an original unconformity of Strinds on Yat Wood Formation. KEY WORDS Longrnyndian Stratigraphy Wales Precambrian Church Stretton Fault 1. GEOLOGICAL SETTING The Old Radnor area exposes one of the string of inliers of pre-Silurian rocks close to the Church Stretton fault zone (Figure l), one element of the Welsh Borderland Fault System (Woodcock and Gibbons 1988).
This system has a long history, most notably as the boundary between the Early Paleozoic Welsh Basin to the northwest and the Midland Platform to the southeast. Callaway (1900) first recognized the similarity between the Old Radnor rocks and part of the Longmyndian sequence in its type area on the Long Mynd. This amended the previous correlation by Murchison (1867) with early Silurian sandstones. Garwood and Goodyear (1918) later proposed a more precise match with parts of the 'Bayston Group' of the Lond Mynd.
Restudy of the type Longmyndian (Pauley 1986, in press) and the Old Radnor area (Woodcock 1988) has prompted a new look at this correlation, aided by the extensive new exposure in the inlier created by quarrying.
Within the inlier the supposed Precambrian rocks are unconformably overlain by the lower Wenlock Dolyhir Limestone (Figure 2a). The inlier is surrounded by Wenlock shales, in probable faulted contact on the southeast and north sides but in possible sedimentary contact along the west side.
STRINDS FORMATION
2a. Location andjield description
The Strinds Formation forms the major part of the inlier. It is extensively exposed in the northern part of Gore Quarry (SO 257 593, Figure 2b), in the SW comer of Dolyhir Quarry (around SH 245 583, Figure 2d)