Ross Formation - UPPER CARBONIFEROUS DEEPWATER SEDIMENTS

Ross Formation conclusions

Summary - Key features of Ross Formation

•These deepwater units were derived from a shelf which is thought to have been exposed to significant wave influence. However the basin itself possibly contained lbrackish water in response to high fluvial discharge into a humid tropical basin remote from, or poorly connected with the ocean.
•The depositional basin was relatively quiescent tectonically, and the basin geometry was largely inherited from an earlier stretching event.
•The ‘big picture’ is one of overall progradation and shallowing through time, such that deep basinal shales are overlain by turbidites and then slope deposits and finally the shelf/delta deposits.
•The frequency of the sedimentayr fill was probably glacio-eustatically driven changes in relative sea level while sediment influxed throughout the basin history.

Sediment geometries range from stacked sand sheets formed by down slope lobes that may be often locally channeled, to channel fill and megalute fills.

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.