Tectonic and stratigraphic aspects of the East Irish Sea Basin and adjacent areas: contrasts in their post-Carboniferous structural styles

Abstract

A revised geological map and lithostratigraphic correlation chart are presented for Carboniferous–Lower Jurassic strata in the East Irish Sea Basin (EISB) and contiguous basins of the NW–SE- to NNW–SSE-trending Clyde Belt. The significance of the exceptionally thick Triassic succession (4375 m) is documented in relation to other Triassic rifts of NW Europe. Basin margin faults within the Clyde Belt are basement-controlled and located either along the margins of exposed and concealed Ordovician–early Devonian buoyant granites, or orthogonal to earlier Paleozoic structures.Four basic and markedly different structural styles have been identified from seismic interpretation. The styles comprise: solitary Caledonoid-trending folds (typically elongate centroclines) with minimal NW–SE faulting (style 1); synthetic and antithetic fault systems in single NW–SE half-graben on the fringes of the Clyde Belt (style 2); linked half-graben with large tilted fault blocks and stacked Permo-Triassic halite detachments in the centre and north of the EISB (style 3); and small step-faulted tilt blocks without thick Permo-Triassic halites, but again forming linked half-graben, in the south and on the fringes of the EISB (style 4). The styles are largely independent of the age of the basin-fill, except style 3 which is restricted to Permian–Lower Jurassic successions.

The correlation and sequence architecture of the Ormskirk Sandstone Formation in the Triassic Sherwood Sandstone Group of the East Irish Sea Basin, NW England

“…Basinward extrapolation of these sequences implies that they are likely to be the lateral equivalents of intervals in the base of the Mercia Mudstone Group. These are probably the dolomite-and halite-dominated intervals that, as noted by Jackson and Mulholland (1993), pinch out progressively southwards with stratigraphically higher halites overstepping those below such that only the youngest of the Anisian halites (the Preesall Halite) in the East Irish Sea Basin (Figure 1) has an equivalent in the Cheshire Basin (the Northwich Halite). Well and borehole data in the area, as described by Jackson and Mulholland (1993), make it clear that the halites have not been post-depositionally eroded but rather were non-depositional beyond their mapped limits.…”

“…These are probably the dolomite-and halite-dominated intervals that, as noted by Jackson and Mulholland (1993), pinch out progressively southwards with stratigraphically higher halites overstepping those below such that only the youngest of the Anisian halites (the Preesall Halite) in the East Irish Sea Basin (Figure 1) has an equivalent in the Cheshire Basin (the Northwich Halite). Well and borehole data in the area, as described by Jackson and Mulholland (1993), make it clear that the halites have not been post-depositionally eroded but rather were non-depositional beyond their mapped limits. As the halites have marine isotopic affinities (Naylor et al 1989) it therefore seems reasonable to infer that the halites mark the limits of successive marine transgressions, each reaching progressively further south and east through the southern parts of the East Irish Sea Basin and ultimately the Cheshire Basin.…”

“…That such intervals are preserved as integral parts of compound channel fills, commonly 96 n. s. meadows Figure 2. Generalized present-day structure of the East Irish Sea and Cheshire Basins (after Jackson and Mulholland 1993;Jackson et al 1995;Chadwick et al 1999) with the location of oil and gas fields, wells referred to in this paper and major faults.…”

Signature of cryptic sedimentary basin inversion revealed by shale compaction data in the Irish Sea, western British Isles

“…This kind of analysis is only applicable to remnant stratigraphy however, and cannot yield any information on rifting beyond the age of the youngest preserved stratigraphy [Rowley and White, 1998]. Jackson and Mulholland's [1993] fault displacement analyses of major synsedimentary normal faults in the EISB suggested that 64-76% of extension was concentrated within the Late Permian-Triassic period, and displacement rates were highest during Lower-Middle Triassic SSG deposition. Ruffell and Shelton [1999] argued, on the basis of seismic stratigraphic analyses of growth faulting, that a larger proportion of faultcontrolled, synsedimentary movement occurred during the Middle-Late Triassic deposition of the MMG, rather than the Early Triassic.…”

Evidence for kilometre-scale Neogene exhumation driven by compressional deformation in the Irish Sea basin system

“…Subsequent work in this basin however, aided by both a substantially enlarged dataset and methodological advances, has demonstrated the importance of advective fluid-related heating and periods of elevated basal heat flow, implying that the elevated palaeotemperatures recorded by AFTA cannot be interpreted in terms of heating due solely to deeper burial (Green et al 1997;Green 2002;Holford et al 2005a). Since the youngest pre-Quaternary sediments in the EISB are Lower Jurassic in age (Jackson & Mulholland 1993) minimal stratigraphic constraints can be placed upon the timing and magnitude of late Mesozoic-Cenozoic exhumation; the top Mesozoic unconformity in this basin is in all likelihood a composite feature which records at least three separate pulses of uplift and erosion (Holford 2006).…”