The Burren region in western Ireland contains an almost continuous record of Viséan (Middle Mississippian) carbonate deposition extending from Chadian to Brigantian times, represented by three formations: the Chadian to Holkerian Tubber Formation, the Asbian Burren Formation and the Brigantian Slievenaglasha Formation. The upper Viséan (Holkerian-Brigantian) platform carbonate succession of the Burren can be subdivided into six distinct depositional units outlined below. A Cf5 Zone (Holkerian) assemblage of microfossils is recorded from the Tubber Formation at Black Head, but in the Ballard Bridge section the top of the formation has Cf6 Zone (Asbian) foraminiferans. A typical upper Asbian Rugose Coral Assemblage G near the top of the Burren Formation is replaced by a lower Brigantian Rugose Coral Assemblage H in the Slievenaglasha Formation. A similar change in the foraminiferans and calcareous algae at this Asbian-Brigantian formation boundary is recognized by the presence of upper Asbian Cf6 Subzone taxa in the Burren Formation including Cribrostomum lecomptei, Koskinobigenerina sp., Bradyina rotula and Howchinia bradyana, and in the Slievenaglasha Formation abundant Asteroarchaediscus spp., Neoarchaediscus spp. and Fasciella crustosa of the Brigantian Cf6 Subzone. The uppermost beds of the Slievenaglasha Formation contain a rare and unusual foraminiferal assemblage containing evolved archaediscids close to tenuis stage indicating a late Brigantian age.
Boreholes drilled in the Wexford Outlier have proved Permo-Trias conglomerate and red beds (Killag Formation), Westphalian D sandstone and mudrock, including at least one thin coal (Richfield Formation), and probable Namurian mudrock (Park Formation). The Killag Formation rests on the Westphalian, the Namurian, and on Dinantian (probably Asbian) limestone in different boreholes. The Westphalian contains horizons with bivalves, conchostracans, and plants and has yielded miospore assemblages which, in addition to indigenous taxa, contain reworked material of three different ages: Devonian or early Carboniferous; late VisCan or early Namurian; and Westphalian A . The western end of the Welsh massif of previous palaeogeographical reconstructions was of very low relief during the Silesian and probably was more often a site of deposition than of erosion.
The origin of the Geological Survey of Ireland's Palaeontological Collections dates back to the launch of a geological survey by the Ordnance Survey of Ireland in 1825. The history of geological mapping by the Ordnance Survey and later in the nineteenth century by the Geological Survey of Ireland has been covered in detail by Berries Davies (1983); only a brief appraisal of this history, based largely on Davies' work, is given here, as it relates to the formation and growth of the Palaeontological Collections.
The Wexford Basin (south‐eastern Ireland) is a NE–SW‐trending sedimentary basin containing carbonates and evaporites deposited during the Late Tournaisian and Viséan. Two separate depositional areas are defined on the basis of facies and facies associations. Sediments were deposited in inner ramp, lagoonal and peritidal environments near Rosslare, and in a more open‐marine, shallow‐ to moderately deep‐water, mid to outer ramp environment in the western area around Duncormick. Thick breccia deposits that occur in the Wexford Basin formed as a result of (i) fault movement that produced syn‐sedimentary debris flows in the Late? Chadian (Breccia type I); (ii) dissolution of anhydrite/gypsum and subsequent collapse of sedimentary strata (Breccia type II); and (iii) fracturing and brecciation of porous rock caused by the movement of high temperature, late diagenetic fluids along fault planes (Breccia type III). The NE–SW facies polarity displayed by both sedimentary successions was the result of NW–SE extension and the reactivation of the NE–SW‐trending Wexford Boundary Fault during the Chadian. Extension at the SE margin of the basin with downthrow to the NNW gave the basin a half‐graben character. Thickening of the debris flow deposits to the SW suggests that while the half‐graben was being tilted it also underwent a NE–SW block rotation due to an axial component of that normal fault.
Contemporaneous erosion and reworking of sediment is now known from a wide scattering of locations within the Dinantian rocks of the South Munster Basin. The phenomenon is most marked close to the northern margin of the basin, which lay within the Cloyne Syncline from Cork Harbour westwards to Ballygarvan. Exploration drilling further west in this syncline, near Inishannon, has found Dinantian/Namurian basinal sequences containing thicknesses of breccias with shelf carbonate clasts. The northern basin margin continues obliquely across strike westwards to cross the extension of the Cork Syncline near Crookstown, where recent drilling has located the basin margin. There is no evidence of reworking in the basin during the latest Devonian-early Tournaisian. A widespread sequence boundary is recognized in the middle Tournaisian (base of Courtmacsherry-Reenydonagan Formations). Within the Kinsale sub-basin, Member 2 Courtmacsherry Formation is a silt-sand unit within a mudstone-carbonate sequence; sourcing of the sand demands considerable intrabasinal or basin margin erosion. In the Bantry sub-basin, reworked conodonts occur at different levels within Member 3, Reenydonagan Formation (late Tournaisian to Arundian). There is indirect evidence for a carbonate shelf or intrabasinal high of Tournaisian to Asbian age in this western region.
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