The Llandovery-Wenlock boundary and related stratigraphy in eastern mid Wales with special reference to the Banwy River section

The Banwy River section exposes a continuous section of Llandovery to mid-Wenlock strata, within which the following have been recognised for the first time in Britain: 1) the upper Telychian lapworthi and insectus biozones; 2) the Llandovery-Wenlock boundary, in a graptohtic section; and 3) the Sheinwoodian firmus Biozone. Correlation of the Banwy section with sections in Bohemia and Scandinavia is enabled by elements common to the graptolite faunas of the different regions. Palaeogeographically, the Banwy section lay close to the shelf edge; stratal disruption suggests periodic slope failure and, the Denbigh Grits of Wenlock age, present only a few kilometres to the west, are not represented. The Banwy Member nom. nov. is erected for the lower part of the Nantysgollon Shales Formation. The new member is a largely bioturbated, silty mudstone, and contrasts strongly with the overlying, dominantly anoxic hemipelagites. Two new graptolite species, Mediograptus flittoni and Me. morleyae, are described.