The asbian to arnsbergian conodonts and sequence stratigraphy of the Northumberland trough

Abstract

Yoredale sequences are excellent exemplars of the sequence stratigraphy model; the spacial and temporal variation of these complex shallow marine/fluvio-deltaic/ coastal plain cycles, exhibit all the uiternal facies architecture that would be expected of a shelf succession. The detailed analysis of Yoredale successions has led to the designation of 15 sequences during the Namurian, which have true chronostratigraphic value. The stacking pattern of Yoredale sequences shows that deposition during the Asbian-Arnsbergian was influenced by three orders of eustatic sea-level change (high, medium and low frequency), which produced three orders of sequence stratigraphic unit (sequences, sequence sets and mega-sequences). Though all three orders of eustatic sea-level change had an influence on deposition, it was the interference of the cycles that produced the major sequence stratigraphic events. Almost two hundred conodont samples, contammg 1039 identifiable elements, representing eleven species, have been used m this study. The multielement species described in the systematic palaeontology and the extensive synonymy lists are a useful addition to British mid-Carboniferous conodont taxonomy. Five biozones have been erected based upon the first appearance of conodont species. The three Brigantian biozones can each be confidently related to a significant rise in sea level caused by the constructive interference of all three frequencies of sea-level cycle. Whatsmore, each successive biozone is related to a deeper water species which corresponds to the long-term rise in the low-frequency sea-level cycle during this period. The palaeoecology of the Great Lunestone was studied using constrained serration. This proved a clear shallo wing-up ward trend and was used to define four biofacies. A comparison between biofacies distribution and sequence stratigraphy proved an intimate relation between sea-level change and the resulting distribution of nekto- benthonic biofacies.