Cephalopods from a borehole in the type Wenlock area

Abstract

The Lower Hill Farm Borehole (1973) in the typeWenlock area of the Welsh Borderland provided continuous core of the ‘Wenlock Shales’ from the Llandovery-Wenlock boundary to within some 30 m of the Much Wenlock Limestone Formation. Cephalopods, though more or less fragmentary, proved to be the most numerous macrofossils. They are assigned here to 10 species, of which the commonest forms are Geisonocerina elongatocintum (Portlock) and Imbricatoceras subundulatum (Portlock). An approximate biostratigraphical division is possible where the dominance of the former gives way to the abundant association of both species. This is at about the base of the Cyrtograptus lundgreni Biozone and hence at about the Sheinwoodian-Homerian stage boundary. A brief description of lithostratigraphy is followed by discussion of the cephalopod record in the borehole. Taxonomic notes and illustrations of the fauna are provided.