Lower Wenlock Research Articles

New chitinozoan taxa from the lower Wenlock (Silurian) of the Welsh Borderlands, England

Abstract. One new chitinozoan genus, Salopochitina, and three new chitinozoan species Salopochitina bella, Eisenackitina varireticulata and Eisenackitina spongiosa, all of early Wenlock age, are described from two British Geological Survey boreholes at Lower Hill Farm, Shropshire, and Eastnor Park, Hereford and Worcester. The new taxa have short stratigraphical ranges, are relatively abundant, and may be useful for correlation in successions from Wales and the Welsh Borderlands.

Stratigraphy, palaeogeography and structure of the East Mendips Silurian inlier

Sedimentary way-up criteria in the ‘Wenlock shales’ of the East Mendips inlier show that these beds, previously believed to overlie Silurian andesitic lavas and tuffs unconformably, are inverted and underlie the volcanics, probably conformably. A regressive sequence of brachiopod communities occurs in the shale and overlying tuffs. This regression is dated as probable M. riccartonensis zone (lower Wenlock) by Eocoelia angelini , suggesting that the volcanics are also Wenlock. The regression is not contemporaneous with the widespread late Wenlock shallowing of Wales and the Welsh Borderland, and is probably related to the vulcanism. Remapping of the inlier shows that although the Silurian beds are situated in the core of the East Mendips anticline, they exhibit no anticlinal structure within themselves. This, taken together with the discrepant Old Red Sandstone thicknesses north and south of the inlier, demonstrates that the southern boundary of the Silurian rocks constitutes an overthrust and not an angular unconformity as hitherto believed. An exposed volcanic neck forms one possible source for the numerous Wenlock bentonites in Wales and the Welsh Borderland.

Silurian graptolites from Washington Land, western North Greenland

Fifty-six graptolite species and subspecies are described from the Silurian sediments of Washington Land and Hall Land, western North Greenland. The graptolite faunas indicate the following ages and zones: Middle Llandovery, the argenteus and convolutus Zones; Upper Llandovery, the turriculatus and spiralis Zones; probably the Llandovery to Wenlock transition; Lower Wenlock, the riccartonensis Zone; Uppermost Wenlock (?) and Lower Ludlow. The bulk of the graptolite species are well known, but some new minor morphological grades are recognised. Four new species and one new subspecies Pseudoclimacograptus (Clinoclimacograptus)? washingtoni, Plectograptus? intermedius, Monograptus kochi, Monograptus teicherti,– and Monograptus bjerringus schucherti – are erected. P. (C.)? washingtoni and P.? intermedius possess morphological characters which are referable to more than one previously described subgenus and genus. The retiolitid fills a gap in the known record of the retiolitids.

The stratigraphic distribution of conodonts in the British Silurian

Llandovery and early Wenlock conodont faunas show high diversity and rapid evolution, and conodonts provide a valuable biostratigraphic tool for this interval. Wenlock, Ludlow and Downtonian faunas are of lower diversity and variability, but, with the exception of the lower Ludlow, abundances are fairly high and several species are useful in local correlation. The local geographic distribution of conodonts is affected by facies variation, and this is particularly marked in the upper Llandovery and lower Wenlock. Geographic restrictions on distribution are also evident on an international scale, and of the ten conodont zones defined in the Silurian of Europe only four (the celloni, amorphognathoides, sagitta and eosteinhornensis Zones) have been identified in Britain. However, several species that are of value in Britain have been widely recognized, and with further work, the promise shown by eonodonts for international correlation should be fulfilled.

XVIII.—New Lamellibranchs from the Gutterford Burn Flagstones (Gala-Tarannon) of the Pentland Hills, near Edinburgh

SynopsisAlong with a note on Chonetes aff. edmundsi Williams and other associated fossils, nine new Lamellibranch species are described from what appear to be the Gutterford Burn Flagstones (Monoclimacis crenulata Zone), repeated by folding or thrusting, northwest of the North Esk reservoir and in the lower part of the Deerhope glacial-overflow valley, in the Pentland Hills. The localities occur respectively in the Midlothian and Peeblesshire parts of the Silurian sequence. The fauna represents an Upper Gala-Tarannon horizon, and is intermediate in age between Upper Llandovery and Lower Wenlock.