GSSP for Sheinwoodian Stage
Definition:
The base of the Wenlock Series and Sheinwoodian Stage is located at the base of the Buildwas Formation along the northern bank of Hughley Brook, 200m south-east of Leasows Farm.
Location:
The GSSP is located along the northern bank of Hughley Brook at SO 5688 9839, 200m south-east of Leasows Farm and 500m north-east of Hughley Church.
The GSSP lies at the base of Unit G of the Buildwas Formation. Unit G is comprised of grey-green mudstones at the base, becoming blue-grey upwards, with comminuted bryozoans, pelmatozoans, brachiopods, corals, etc.
Primary Markers:
The base of the Sheinwoodian Stage lies close to the base of the Cyrtograptus centrifugus Graptolite Biozone.
Secondary Markers:
Conodonts:
Basal beds of the Buildwas Formation contain diverse conodonts of the Pterospathodus amorphognathoides interval.
Correlation Events:
Imprecise. Between the base of acritarch biozone 5 and LAD of conodont Pterospathodus amorphognathoides. The current GSSP does not coincide with the base of the Cyrtograptus centrifugus Biozone, as was supposed when the GSSP was defined. Restudy recommends a slightly higher and correlatable level on condonts -- the Ireviken datum 2, which coincides approximately with the base of the murchisoni Graptolite Biozone
Other Locations around the World:
See:
Holland, C. H. and Bassett, M. G., 1989 (eds.). A global standard for the Silurian System. National Museum of Wales, Geological Series 9, Cardiff.
Notes on Derivation of Age:
References:
Lethaia 14
Holland, C. H., 1982. The state of Silurian Stratigraphy. Episodes 5/3, p. 21-23, 1982.
Bassett, M. G., 1989. The Wenlock Series in the Wenlock Area. In: Holland, C. H. and Bassett, M. G. (eds.). A global standard for the Silurian System. National Museum of Wales, Geological Series 9, p. 51-73, Cardiff.