Evolution of the Carboniferous Lough Allen Basin, Northwest Ireland

Abstract

The Lough Allen Basin contains approximately 2.9 km of Dinantian (Courccyan) to Silesian (Arnsbergian) limestone, mudstone and sandstone, mostly of marine origin. The basin was initiated during the Courceyan Stage as a result of movement of the basin margin fault complex along the southeast side of the Ox Mountains inlier. The main rifting phase, during the late Courceyan, resulted in the deposition of a southeasterly thinning, initially non-marine, elastic wedge. The intrabasinal Dowra-Macncan High and Slisgarrow Trough developed during the Chadian Stage. Movement on the Curlew fault, which bounds the basin to the south, may have begun in the Courccyan but culminated in the Arundian. There is little direct evidence of fault-controlled sedimentation in the Holkerian and much of the Asbian, although the distribution of carbonate mudmounds of Asbian age in part coincides with earlier structural elements. During the late Asbian, there appears to have been renewed tectonic activity, which led to substantial regional differences of thickness of the lower formations of the Leitrim Group. Thcrc is little evidence of tectonic control on sedimentation from the Brigantian to the Arnsbcrgian.Vitrinite reflectance determinations show that the Carboniferous rocks in the basin arc supra-mature for the generation of oil but are mature with respect to the generation of gas. The maturation values for the youngest preserved rocks suggest that they have been buried under 3-5 km of Upper Palaeozoic cover.

Base Metal Sulfide Mineralization in Lower Carboniferous Strata, Northwest Ireland

“…Several earlier studies of the Sligo syncline region (Oswald, 1955;George et al, 1976;Philcox et al, 1992;MacDermot et al, 1996;Cózar et al, 2005Cózar et al, , 2006Somerville et al, 2009) focused on defining and correlating the Carboniferous strata that host sulfide mineral deposits in the Sligo area. The northwest was the last region of Ireland to be submerged by a northward-transgressing sea during the Late Devonian and Early Carboniferous.…”

“…The northwest was the last region of Ireland to be submerged by a northward-transgressing sea during the Late Devonian and Early Carboniferous. The basal Twigspark Formation was defined by Philcox et al (1992) from cores and quarries as a basal sandstone and sandy limestone (10-20 m thick), overlain by approximately 35 m of argillaceous micrites and capped by oolitic sandstones (Fig. 3).…”

Correlation of Mississippian (Upper Viséan) foraminiferan, conodont, miospore and ammonoid zonal schemes, and correlation with the Asbian–Brigantian boundary in northwest Ireland

“…In the eastern part of the Lough Allen Basin, tectonic activity associated with the Clogher Valley Fault (e.g. Philcox et al 1992; Figure 2), induced a five-fold increase in thickness of the Meenymore Formation on Slieve Rushen. Mitchell and Owens (1990) recognized the influence of dextral correlation of mississippian zonal schemes in northwest ireland 235 transtension, succeeded by periodic subsidence throughout the late Viséan in Northern Ireland (Figure 2).…”

“…The upper Viséan-Namurian succession of the Lough Allen Basin (Mitchell 1992;Philcox et al 1992) in northwest Ireland comprises the Tyrone and Leitrim groups (Brandon and Hodson 1984;Legg et al 1998). The upper part of the Tyrone Group consists mostly of limestone, whereas the Leitrim Group is mainly mudstone with accessory limestone and sandstone.…”

Early to mid‐Viséan shallow water platform buildups, north Co. Dublin, Ireland

“…Arundian buildups are recorded from the Lough Allen and Carrick-on-Shannon Basins of north-west Ireland (Philcox et al 1989;Kelly 1989;Kelly and Somerville, 1992). However, these buildups were located on the hanging walls of major normal faults (Kelly 1989;Kelly and Somerville, 1992) and developed in calmer and deeper water environments than the north Co. Dublin buildups.…”