Gull Island Formation - Upper Carboniferous Deepwater Sediments
The Gull Island Formation reaches 550 m in the Loop Head region, but thins to c. 140 m in North Clare. Martinsen et al, 2003, record how the lower potion of the Gull Island is a mudstone-rich -bearing succession that onlaps the Clare Basin margin and the upper portion is a mudstone-dominated prograding slope succession.

The Lower Gull Island formation is represented by the following associations:

• Hemipelagic shales
• Mud-rich slumps
• Shallite channels
• Sheets formed by channel flanks and levee deposits

Most of of the Lower Gull Island Formation is formed by masses of intermixed deformed and slumped shales, silts and sandstone. The slumped materials are interpreted to have been derived from the northern and northwesin while the turbidite sands record an ENE transport to the along the axis of the Clare Basin. The turbidititic sandstones decrease upward and are replaced by commoner slumped sediments. The Lower Gull Island formation is thought to represent the fill of the deeper portions of the deep basin at the toe of slope while the overlying sediments record upslope instability that responded to high rates of sediment accumulation.

The Upper Gull Island Formation section is different lithologicaly from that of the Lower section and is made of a combination of deformed cycles of mudstones that locally pass upwards into siltstones. Locally 15 isolated channels are filled by turbidites, that were transported eastward. This upper portion is thought to represent the downdip equivalent to the updip overlying deltaic section if the Tullig Formation.

Further features of Gull Island Formation

The Gull Island deepwater section can be viewed in the attached galleries that can be reached by clicking on the thumbnail below.

Click on highlighted Deepwater Gallery for access to a complete index to images, maps, diagrams and photographs of deepwater geology including the geology of Co Clare.

Useful References

Chapin, M.A., Davies, P., Gibson, J.L. & Pettingill, H.S. (1994), Reservoir architecture of turbidite sheet sandstones in laterally extensive outcrops, Ross Formation, western Ireland. In Weimer, P., Bouma, A.H. & Perkins, R.F (eds), Submarine fans and turbidite systems, GCSSEPM Foundation 15th Annual Research Conference, 53-68.

Collinson, J.D., Martinsen, O. Bakken, B. and Kloster, A. (1991), Early fill of the western Irish Namurian Basin: a complex relationship between turbidites and deltas. Basin Research, 3, 223-242.

Davies, S.J. & Elliott, T. (1996), Spectral gamma ray characterisation of high resolution sequence stratigraphy: examples from Upper Carboniferous fluvio-deltaic systems, Co. Clare, Ireland. In Howell, J.A. & Aitken, J.F. (eds) High resolution sequence stratigraphy: innovations and applications. Special Publication of the Geological Society London, 104, 25-35.

Gill, W.D. (1979), Syndepositional sliding and slumping in the West Clare Namurian Basin, Ireland. Geological Survey of Ireland Special Paper 4, 31pp.

Hodson, F. (1954), The beds above the Carboniferous limestone in County Clare, Ireland. Quarterly Journal of the Geological Society of London, 113, 441-460.

Martinsen, O.J. (1989), Styles of soft sediment deformation on a Namurian (Carboniferous) delta slope, western Ireland Namurian Basin, Ireland. In Whatley, M.K.G. & Pickering, K.T. (eds) Deltas: sites and traps for fossil fuels, Geological Society Special Publication, 41, 167-177.

Martinsen, O.J. & Bakken, B. (1990), Extensional and compressional zones in slumps and slides in the Namurian of County Clare, Ireland. Journal of the Geological Society, 147, 153-164.

Pulham, A.J. (1987), Depositional and syn-sedimentary deformation processes in Namurian deltaic sequences of west County Clare, Ireland. Unpublished PhD thesis, University of Wales, Swansea.

Pulham, A.J. (1989), Controls on internal structure and architecture of sandstone bodies within Upper carboniferous fluvial-dominated deltas, County Clare, western Ireland. In Whatley, M.K.G. & Pickering, K.T. (eds) Deltas: sites and traps for fossil fuels, Geological Society Special Publication, 41, 179-203.

Rider, M.H. (1969), Sedimentological studies in the West Clare Namurian Basin, Ireland and the Mississippi Delta. Unpublished PhD thesis, Imperial College London.

Rider, M.H. (1974), The Namurian of West County Clare. Proceedings of the Royal Irish Academy, 74B, 125-142.

Rider, M.H. (1978), Growth faults in the Carboniferous of western Ireland. Bulletin of the American Association of Petroleum Geologists, 62, 2191-2213.

Sevastopulo, G.D. (1981), Upper Carboniferous. In Holland, C.H. (ed.) A geology of Ireland. Scottish Academic Press, 173-199.

Wignall, P.B. and Best, J.L. (2000), The Western Irish Namurian Basin reassessed. Basin Research 12, 59-78.

Wignall, P.B. and Best, J.L. (2002), The Western Irish Namurian Basin reassessed – a discussion. Basin Research 14, 523-542.