Palaeoecology of the Chaetetes-Band : a marine biostrome in the Carboniferous, basal Namurian (basal Serpukhovian) Great Limestone of northern England

The Chaetetes-Band commonly occurs near the base of the basal Namurian (basal Serpukhovian) Great Limestone in northern England and classically comprises compact ‘bands’ of the sclerosponge Chaetetes depressus and the colonial coral Diphyphyllum lateseptatum. Samples have been collected from seven sections in the Alston area and the macrofossils and conodont elements from each limestone facies of the Chaetetes-Band (as it exists at those localities) have been identified. Based largely on the palaeoecological interpretations of Carboniferous macrofossils by Wilson (1989) and conodonts as synthesised by Dean (1987) a fuller understanding has been gained of the environmental setting and community structure of each fossil assemblage from each limestone facies of the Chaetetes-Band. Work on the amalgamated assemblages (palaeocommunities) suggests the following: ‘Planar-bedded’ limestone has a dominant macrofauna of crinoids and brachiopods, and a dominant conodont fauna of genera Lochriea and Gnathodus with Synclydagnathus. The environmental setting appears to have been one of firmer substrates and clearer, current affected waters on the marine shelf. ‘Bioclastic’ limestone has a dominant macrofauna of crinoids with productoid brachiopods and corals, and a dominant conodont fauna of genera Gnathodus and Lochriea with Synclydagnathus and Vogelgnathus. The environmental setting appears to have been one of relatively firm to sporadically relatively soft substrates and clearer, calm to current-affected waters on the marine shelf. It was probably shallower than the ‘Planar-bedded’ limestone environment. ‘Wavy-bedded’ limestone has a dominant macrofauna of Diphyphyllum with Chaetetes and the brachiopod Eomarginifera, and a conodont fauna comprised solely of genus Cavusgnathus. The environmental setting appears to have been one of relatively soft substrates beneath generally clearer, possibly wave-agitated waters on the marine shelf. ‘Chaetetes-band’ limestone has a dominant macrofauna of Chaetetes with brachiopods, crinoids and corals, and a dominant conodont fauna of genera Gnathodus with Cavusgnathus and Synclydagnathus. A biohermal palaeoenvironment is suggested with firm substrates and clearer, apparently calm to current affected, perhaps sub-tidal and sporadically wave-agitated, waters on the marine shelf. ‘Chaetetes-bioclastic transitional’ limestone has a dominant macrofauna of Chaetetes with crinoids and productoid brachiopods, and a dominant conodont fauna of genera Gnathodus with Synclydagnathus and Lochriea. An environmental setting transitional to those of the ‘Chaetetesband’ and ‘Bioclastic’ limestones is suggested. ‘Coral-band’ limestone has a dominant macrofauna of Diphyphyllum with other corals, Chaetetes, and brachiopods, and a dominant conodont fauna of genera Kladognathus with Gnathodus and Vogelgnathus. A biohermal, lower reef slope or shelf setting is suggested, with relatively firm or soft substrates beneath clear, shallow, low energy marine waters. ‘Coral-band and bioclastic’ limestone has a dominant macrofauna of Diphyphyllum and crinoids, and a dominant conodont fauna of genera Gnathodus and Lochriea with Cavusgnathus, Synclydagnathus and Vogelgnathus. An environmental setting transitional to those of the ‘Coralband’ and ‘Bioclastic’ limestones is suggested. ‘Planar-wavy transitional’ limestone has a dominant macrofauna of crinoids with productoid brachiopods, and a dominant conodont fauna of genera Gnathodus with Synclydagnathus, Lochriea and Vogelgnathus. An environmental setting transitional to those of the ‘Planarbedded’ and ‘Wavy-bedded’ limestones is suggested. ‘Planar-bedded limestone/sandstone’ has a dominant macrofauna of crinoids with productoid brachiopods, the rhynchonellid brachiopod Pleuropugnoides and burrow traces, and a dominant conodont fauna of genera Gnathodus with Synclydagnathus and Cavusgnathus. The environmental setting appears to have been varied, including firm to soft substrates and clear to muddy, low to high-energy waters, off to near shore on the marine shelf. A minor biohermal presence is also suggested. ‘Sandstone’ has a flora of plant debris and roots and may represent an environment of a possibly emergent, prograding, lobate delta.