Conodont faunas from the lower carboniferous Waulsortian mudbank complex of Southern Ireland

Hill, Peter Julian (1977) Conodont faunas from the lower carboniferous Waulsortian mudbank complex of Southern Ireland. University of Southampton, Doctoral Thesis.

Abstract

The study is based on 198 rock samples, weighing in total 620.65 kg that were treated with 10% acetic acid for conodont extraction. The samples were collected mainly from lower Carboniferous outcrops in NY Co. Limerick Eire, with additional samples from Co. Clare, Co. Galway, Co. Laoighis in Eire, from the Avon Gorge in England, from Borke-Wehr in the Rhenish Schiefergebirge Germany and from the New Providence Shale of Indiana, North America.The samples yielded over 11,000 specimens referable to 16 genera,38 species and 6 subspecies. Three chronological subspecies Gnathodus typicus simplicatus subsp. nov, Gnathodus typicus nodosus subsp. nov. and Gnathodus typicus multinodosus subsp. nov. are new.Well documented phylogenetic species in a continually evolving lineage offers a sound basis for time correlation. Gnathodus typicus Cooper has' been objectively defined by comparing successive, biometrically characterised sample populations. The total variation displayed by five measured biocharacters is a composite of ontogeny and phylogeny. Consequently evaluation of the growth of G. typicus was determined before any interpretation was made about phylogenetic development. This was achieved statistically by the product moment correlation coefficient. The ontogenetic development of G. typicusis shown to involve an increase in element length, platform length, carina width and in part an increase in platform node number.Platform node number is however demonstrated to be statistically discriminate from the other biocharacters and supplies a method by which the phylogeny of G. typicus can be determined. A plot of the node means of successive gnathodid populations has been used to define three chronological subspecies of G. typicus that biostratigraphica]ly zone the Waulsortian Mudbank Complex. In addition as each sample locality of the collected gnathodid populations in N W Co. Limerick defines a precise stratigraphic position, this enables-the area to be geologically mapped. The map shows the area to have undergone a relatively simple tectonic history with only gentle, open folding.The three chronological subspecies of G. typicus have been identified in, and correlated with, the erected conodont Assemblage Zones in the Avon Gorge England, in the Mississippi Valley in N. America, in the Rhenish Schiefergebirge Germany and in Belgium. The recovery of S. anchoralis Branson and Mehl greatly assists in inter and intra continental correlation. The Waulsortian Mudbank Complex in Co. Limerick is considered to be Tn 3c in age which equates to a late Z2 - C1 or Cu II B/Y age.

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