Detailed characterisation of thin-beds in Pennsylvanian slope and fan deposits, Co Clare, western Ireland

Sand-prone intervals within deep-water depositional systems tend to attract the bulk of academic and industry research attention as they typically form either the axial parts of terminal lobes or the axial fills of submarine channels. Finer grained and thinner bedded successions are often assigned to either overbank/levees or distal lobe-fringe settings but are less commonly investigated and hence are relatively poorly understood, particularly where they occur as subordinate components within otherwise relatively sandy successions. However, understanding how these thin-bedded units arise is important, particularly as they are often used to stratigraphically subdivide lobes and to recognise hierarchical stacking arrangements in basin-floor fan settings. The thin-bedded successions also act as important baffles and barriers within many hydrocarbon reservoirs, but may contribute to production elsewhere.

Recent work has demonstrated the occurrence of significant thin-bedded and fine-grained successions within the Ross Sandstone and Gull Island Formations of the Clare Basin; a Pennsylvanian-aged basin floor and slope succession respectively. Locally, these finer-grained facies subdivide lobes or lobe complexes forming either condensed sections or distinctive alternating stacks of thin-bedded hybrid event beds (HEBs) or low-density turbidites that persist laterally for several kilometres. High-frequency switching between HEB-prone and turbidite-prone packages has been identified in other systems (e.g. Forties Field, North Sea), however, the origin and depositional control of this distinctive partitioning of bed types is still poorly understood. The Clare outcrops have recently been the target of a behind-outcrop research drilling campaign by Statoil ASA and University College Dublin whereby twelve, fully cored and logged (wireline and borehole image) boreholes were acquired. This core and log dataset, in combination with the outcrop exposures on the west coast of County Clare, form a unique dataset with which to examine the thin-bedded component of this ancient deepwater system.