Five boreholes in Shropshire and the relationships of shelly and graptolitic facies in the Lower Silurian

The shelly Lower Silurian in the classic area of Shropshire is correlated with the graptolite zones erected in Central Wales and the Southern Uplands of Scotland. Middle Llandovery rocks (previously unrecognized in the Welsh Borderland) are proved and the complete sequence of Upper Llandovery zones is probably present. In the Wenlock the two basal zones, centrifugus and murchisoni, are unproven in the boreholes and part at least of the succeeding riccartonensis Zone is also missing. The Middle Wenlock is complete. The shelly communities in the Llandovery show a complete sequence from a basal shallowest-water Lingula community to a deepest-water Clorinda community at the top. Above the latter, west of the Longmynd spur, is defined a ‘Marginal’ Clorinda community, with many usual elements absent. Other records of graptolites from the Shropshire Lower Silurian are re-assessed. The age of the lowest Wenlock Buildwas Beds (and hence the true position of the base of the Wenlock in the graptolite sequence) remains open, but the boundary is probably correctly placed at the bottom of the centrifugus Zone.