TRACE FOSSILS IN THE DELTAIC TULLIG CYCLOTHEM, CARBONIFEROUS, COUNTY CLARE, IRELAND

Trace fossils in the fluvial-dominated deltaic units of the Carboniferous (Namurian) Central Clare Group, County Clare, Ireland are not common, but are present as high-density, low-diversity assemblages on specific stratigraphic horizons or restricted within localized facies. This study focuses on the Tullig Cyclothem, which comprises three main coarsening upwards deltaic units and overlies deep water facies of the Shannon Group. The turbidite and slope deposits in the Clare Basin lack trace fossils, which suggests that infaunal life was restricted in some way (e.g., salinity, low oxygen levels). Nevertheless, the lowermost Tullig prodelta deposits preserve simple trails (e.g., Gordia) and very shallow-tier burrows (cf. Treptichnus), perhaps due to the introduction of fresh water, oxygen, and/or detrital food supply. The uppermost Tullig succession at Diamond Rocks near Kilkee preserves the most diverse trace fossil assemblage known, where the traces appear to be restricted by specific physico-chemical conditions. The succession comprises: (1) broad incised channels with wave-influenced lower mouth bar deposits and high-density Psammichnites (cf. Scolicia) on symmetrical rippled bedding planes; (2) upper mouth bar foresets of wave-reworked unidirectional rippled bedsets with cf. Cruziana on rare bedding planes; (3) unidirectional current-dominated ripples and dunes of the prograding fluvial system, with minor Skolithos and Arenicolites; (4) ravinement hollows with clayey deposits that lack trace fossils; and (5) a thin wave-dominated unit with abundant trace fossils, including Zoophycos, Rhizocorallium, Schaubcylindrichnus, ?Phycodes, and more. The bioturbated surface is sharply overlain by black shale and a goniatite bed (R. stubblefieldi). Although the trace fossil assemblage represents marine waters, the localized occurrences of traces associated with the deltaic packages may indicate otherwise stressed and/or restricted conditions in the Clare Basin.