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Geological Society, London, Special Publications; 1995; v. 93; p. 79-80;
DOI: 10.1144/GSL.SP.1995.093.01.09
© 1995 Geological Society of London

Predictive model for the development and distribution of Triassic reservoir sands offshore southeast Ireland, based on seismic sequence geometries at the Variscan unconformity

P. S. Griffiths

Galliards, Hatch Hill, Churt, Farnham, Surrey, GU10 2NZ, UK

Although well data are sparse and seismic resolution of the pre-Jurassic section offshore southeast Ireland is poor, nevertheless several broad seismic sequences can be defined. The earliest such sequence recognized consists of steeply dipping seismic events believed to represent highly tectonized Lower Palaeozoic basement. This is onlapped by a seismic dead zone interpreted as comprising Devonian clastics. In the northern part of the study area, an interval that locally shows seismic evidence of ‘biostromal mounding’ is developed. This may be correlated with the development of Waulsortian ‘reefs’ in the Carboniferous Limestone in adjacent onshore areas. The next seismic sequence recognized consists of strong, parallel-bedded reflectors and is of variable thickness. It is interpreted as comprising marine shales of Namurian age. Based on onshore outcrop data, this interval may locally be as young as Westphalian ‘A’, where it may consist of finegrained clastics with thin coal beds. Evidence of block faulting at the base of the above sequence may be correlated with a late Viséan to early Namurian (Sudetic) episode of rifting. In the northern part of the study area, additional pre-Mesozoic sequences are recognized, comprising strong, parallel-bedded reflectors, interpreted as Westphalian ‘C’ and ‘D’ clastics with coals and organic-rich shales, succeeded by a seismic dead zone that may reflect the development of Stephanian red-beds.

Regionally, the Triassic rests on each of the aforementioned pre-Mesozoic seismic sequences with, in contrast to the East Irish Sea Basin, no record of intervening Permian sedimentation. The Triassic is divided into three sequences on the basis of

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