Tectonic Evolution of the Southern ‐ Central Irish Sea Basin

Abstract

Interpretation of 2D seismic reflection data combined with correlation of five wells in the southern part of the Central Irish Sea Basin show a NE‐SW trending graben, whose bounding faults are considered to be reactivated lineaments of Precambrian age. The basin‐fill comprises mainly Carboniferous and Triassic successions, with localised and thin occurrences of Lower Jurassic and Tertiary rocks, all of which are unconformably overlain by Quaternary sediments. Due to poor data quality, the structural evolution of the area during the Late Palaeozoic is poorly understood. During the Triassic, the basin was subjected to thermal subsidence with a phase of minor uplift in the Anisian. The major phase of extension in the basin took place during the ?Middle ‐ Late Jurassic and had a NW‐SE orientation. Subsequent Late Jurassic sinistral shear along the NE‐SW trending basin bounding fault is suggested to have taken place, giving rise to a series of north‐south intra‐basinal faults. The present‐day structure of the basin is a broad anticline, inherited from a Cretaceous ‐ Early Tertiary compressional phase. During the Palaeocene the area was subjected to regional uplift, followed by minor extension along the NW boundary fault during the Eocene ‐ Oligocene. A Late Tertiary phase of transpression is postulated to have occurred, which inverted north‐south trending faults and folded the base‐Tertiary unconformity.

Hydrocarbon potential of the Kish Bank Basin: integration within a regional model for the Greater Irish Sea Basin

“…The absence of Namurian section in well 42/17-1 (Maingarm et al 1999) on the flank of the Caledonian Lleyn Ridge, may not be representative of the deeper parts of the basin.…”

Fault distribution and timing in the Central Irish Sea Basin

“…These north-south-trending extensional or transtensional faults are consistent with a period of sinistral fault movement along the main NE-SW-trending basin-bounding faults. The age of this transtension is uncertain but appears to pre-date a possible period of Late Cretaceous-Early Tertiary uplift along the central axis of the CISB (Maingarm et al 1999).…”

“…The structural and stratigraphic evolution of the CISB has been documented in a number of publications (Maddox et al 1995;Duncan et al 1998;Corcoran & Clayton 1999;Maingarm et al 1999;Floodpage et al 2001 marine carbonates, encountered in well IR42/17-1, which are unconformably overlain by interbedded coals, shales and sandstones of Westphalian C to Stephanian age (Maddox et al 1995). No Namurian sediments have been drilled in the basin to date but the presence of a Namurian A-B section cropping out on the southern coast of the Isle of Anglesey (Racey, pers.…”

“…Fault patterns within the CISB have been evaluated previously using maps generated from 2D seismic reflection data (Maingarm et al 1999). The fault trends described below have been identified following the interpretation of both 2D and 3D seismic data and the analysis of structure maps generated for the Top Dinantian and Top Lower Triassic Sherwood Sandstone Group horizons ( Fig.…”

“…Results and a synthesis of these wells have been provided in a number of recent studies, which have discussed the hydrocarbon prospectivity of the CISB (Maddox et al 1995 (Duncan et al 1998;Corcoran & Clayton 1999) and the structural evolution of the basin (Maingarm et al 1999). The aim of this paper is to provide an insight into the distribution and timing of faulting in the CISB, as recorded by the preserved Palaeozoic to Cenozoic sediments, and to discuss the implications of this tectonic activity for the hydrocarbon prospectivity of the basin.…”