East-central Ireland Research Articles

Characterising thermal water circulation in fractured bedrock using a multidisciplinary approach: a case study of St. Gorman\u2019s Well, Ireland

A hydrogeological conceptual model of the source, circulation pathways and temporal variation of a low-enthalpy thermal spring in a fractured limestone setting is derived from a multidisciplinary approach. St. Gorman’s Well is a thermal spring in east-central Ireland with a complex and variable temperature profile (maximum of 21.8 °C). Geophysical data from a three-dimensional(3D)audio-magnetotelluric(AMT) survey are combined with time-lapse hydrogeological data and information from a previously published hydrochemical analysis to investigate the operation of this intriguing hydrothermal system. Hydrochemical analysis and time-lapse measurements suggest that the thermal waters flow within the fractured limestones of the Carboniferous Dublin Basin at all times but display variability in discharge and temperature. The 3D electrical resistivity model of the subsurface revealed two prominent structures: (1) a NW-aligned faulted contact between two limestone lithologies; and (2) a dissolutionally enhanced, N-aligned, fault of probable Cenozoic age. The intersection of these two structures, which has allowed for karstification of the limestone bedrock, has created conduits facilitating the operation of relatively deep hydrothermal circulation (likely estimated depths between 240 and 1,000 m) within the limestone succession of the Dublin Basin. The results of this study support a hypothesis that the maximum temperature and simultaneous increased discharge observed at St. Gorman’s Well each winter is the result of rapid infiltration, heating and recirculation of meteoric waters within a structurally controlled hydrothermal circulation system.

Understanding hydrothermal circulation patterns at a low-enthalpy thermal spring using audio-magnetotelluric data: A case study from Ireland

Kilbrook spring is a thermal spring in east-central Ireland. The temperatures in the spring are the highest recorded for any thermal spring in Ireland (maximum of 25°C). The temperature is elevated with respect to average Irish groundwater temperatures (9.5–10.5°C), and represents a geothermal energy potential, which is currently under evaluation. A multi-disciplinary investigation based upon an audio-magnetotelluric (AMT) survey, and hydrochemical analysis including time-lapse temperature and chemistry measurements, has been undertaken with the aims of investigating the provenance of the thermal groundwater and characterising the geological structures facilitating groundwater circulation in the bedrock.The three-dimensional (3-D) electrical resistivity model of the subsurface at Kilbrook spring was obtained by the inversion of AMT impedances and vertical magnetic transfer functions. The model is interpreted alongside high resolution temperature and electrical conductivity measurements, and a previous hydrochemical analysis.The hydrochemical analysis and time-lapse measurements suggest that the thermal waters have a relatively stable temperature and major ion hydrochemistry, and flow within the limestones of the Carboniferous Dublin Basin at all times. The 3-D resistivity model of the subsurface reveals a prominent NNW aligned structure within a highly resistive limestone lithology that is interpreted as a dissolutionally enhanced strike-slip fault, of Cenozoic age. The karstification of this structure, which extends to depths of at least 500m directly beneath the spring, has provided conduits that facilitate the operation of a relatively deep hydrothermal circulation pattern (likely estimated depths between 560 and 1000m) within the limestone succession of the Dublin Basin. The results of this study support the hypothesis that the winter thermal maximum and simultaneous increased discharge at Kilbrook spring is the result of rapid infiltration, heating and re-circulation of meteoric waters within this structurally controlled hydrothermal circulation system.This paper illustrates how AMT may be useful in a multi-disciplinary investigation of an intermediate-depth (100–1000m), low-enthalpy, geothermal target, and shows how the different strands of inquiry from a multi-disciplinary investigation may be woven together to gain a deeper understanding of a complex hydrothermal system.

Compositional multivariate statistical analysis of thermal groundwater provenance: A hydrogeochemical case study from Ireland

Thermal groundwater is currently being exploited for district-scale heating in many locations world-wide. The chemical compositions of these thermal waters reflect the provenance and circulation patterns of the groundwater, which are controlled by recharge, rock type and geological structure. Exploring the provenance of these waters using multivariate statistical analysis (MSA) techniques increases our understanding of the hydrothermal circulation systems, and provides a reliable tool for assessing these resources.Hydrochemical data from thermal springs situated in the Carboniferous Dublin Basin in east-central Ireland were explored using MSA, including hierarchical cluster analysis (HCA) and principal component analysis (PCA), to investigate the source aquifers of the thermal groundwaters. To take into account the compositional nature of the hydrochemical data, compositional data analysis (CoDa) techniques were used to process the data prior to the MSA.The results of the MSA were examined alongside detailed time-lapse temperature measurements from several of the springs, and indicate the influence of three important hydrogeological processes on the hydrochemistry of the thermal waters: 1) salinity and increased water-rock interaction; 2) dissolution of carbonates; and 3) dissolution of sulfides, sulfates and oxides associated with mineral deposits. The use of MSA within the CoDa framework identified subtle temporal variations in the hydrochemistry of the thermal springs, which could not be identified with more traditional graphing methods, or with a standard statistical approach. The MSA was successful in distinguishing different geological settings and different annual behaviours within the group of springs. This study demonstrates the usefulness of the application of MSA within the CoDa framework in order to better understand the underlying controlling processes governing the hydrochemistry of a group of thermal springs in a low-enthalpy setting.

A mineralogical and fluid inclusion study of the Harberton Bridge Fe–Zn–Pb deposit, County Kildare, Ireland

The Harberton Bridge deposit is located 2 km NW of the Lower Palaeozoic Kildare inlier in east central Ireland and represents one of a number of small, breccia-hosted Fe–Zn–Pb deposits that occur in the Kildare district. Widely regarded as an example of Mississippi Valley-type mineralization, the Harberton Bridge deposit provides important clues regarding the origin of the carbonate-hosted Zn–Pb deposits of the Irish orefield as a whole. Mineralization was studied in core using cathodoluminescence, transmitted and reflected light microscopy and fluid inclusion microthermometry. Fluid inclusions from calcite associated with sphalerite–galena–marcasite mineralization have homogenization temperatures in the range 45–69°C and salinities mainly between 12 and 17wt% NaCl equivalent. The data obtained suggest that the Harberton Bridge deposit formed from a single, low temperature (<80°C), moderate salinity fluid, considered to be a cooler version of the higher temperature fluids involved in mineralization at all of the economic Irish deposits. The inferred common fluid origin with the major deposits confirms the position of the Kildare district as representative of an end-member of mineralization styles in the Irish orefield. The differences in style are attributed to a late timing of mineralization, absence of abundant biogenic H 2 S and the involvement of a relatively shallowly basement-circulated, low temperature orefluid.

Landform modification by palaeo-ice streams in east-central Ireland

AbstractIn eastern Ireland, subglacial bedforms including drumlins and Rogen moraines were modified by headward erosion along two ice streams which had overlapping flow tracks. The ice streams, which had tidewater termini, are dated by geochronometric and morphostratigraphic methods to <15.014 C kyr BP (Castleblaney ice stream) and ~13.814C kyr BP (Armagh ice stream). Bedforms along ice-stream tracks show a morphological continuum which reflects a down-ice increase in the degree of modification by ice-stream activity (i.e. resulting in unmodified →remoulded/overprinted →crosscut →streamlined bedforms). The down-ice changes in bedform types are inferred to relate to changes in subglacial drainage and sediment-transport mechanisms. Bedform and sedimentary evidence suggest that discrete subglacial meltwater channels which developed up- ice changed in a down-ice direction to unchannelized flows which deepened towards the ice margin. Meltwater release from subglacial cavities, and produced by strain heating at sheared ice-stream margins, probably helped support ice-stream flow, which ended as the volume of subglacial meltwater discharge decreased. Dated millennial-scale cycles of ice activity may be related to instability at tidewater margins, followed by complex thermal and hydraulic responses within the ice mass.

The Public Forum and the Space Between: the Materiality of Social Strategy in the Irish Neolithic

Framed within an interpretive, humanistic ‘archaeology of inhabitance’, the study explores the means by which a social, intellectual order particular to time and place is embedded within the material universe. Through the mediation of the human body, natural and architectural space is considered to be a medium for the production and reproduction of social relations. The specific materiality of places inhabited in the past is explored in detail, focusing on possibilities for and constraints upon the body and the senses.The phenomenon of monumentality at the Loughcrew passage tomb cemetery in east-central Ireland is considered in the context of changing narratives of place and biographies of person and landscape. In contrast to many previous studies, the focus is upon engagement with the exterior spaces of the complex: the more frequent and larger-scale involvement of the communal body in these ‘public’ spaces will have played a critical role in the validation of knowledges and claims to authority which a more restricted group will have articulated within the confines of tomb chambers and passages.The earlier tombs draw out qualities latent within the landscape, placing particular emphasis on prior, natural boundaries. Through time, the regionalisation of the Loughcrew hills acquires increasing architectural definition, by means of which a series of interconnecting spaces emerge at a much more human scale. The latest architectural and spatial developments may well form part of material strategies through which were engendered particular structures of authority carrying the potential for substantially heightened individual prominence within increasingly exclusive kinship solidarities. Ultimately, mediation between the physical and metaphysical elements of existence may be controlled with reference to distinct lines of descent rather than to a more generalised ancestral community. At the same time, the range of hills is gradually transformed from a meaningful locus which conceals within it the human efforts of monumental construction, to a landscape that derives its significance from massive summit cairns visible from considerable distances. This appropriative transformation may be seen as a material strategy which moves communities' conceptions of existence from an integrated, cultural whole in which people and landscape are embedded in each other, towards a vision of individuals and places as increasingly separate and self-contained.

Biofacies and sediments in an emergent Late Pleistocene glaciomarine sequence, Skerries, east central Ireland

Late Devensian sedimentation (ca. 18 ka B.P.) on the coastal margins of the Irish Sea Basin occurred in shallow-water glaciomarine environments around retreating tidewater ice margins. High relative sea levels were the result of glacioisostatic crustal depression around the periphery of the last British ice sheet. At Skerries, in east central Ireland, ice-proximal glaciomarine diamict, mud, sand and gravel facies are selectively preserved in a bedrock depression. The coastal exposure, about 500 m long, can be divided into three lithofacies associations. (1) A diamict/gravel association resting on bedrock was emplaced by sediment gravity flows and records the downslope reworking of glacial debris released from a retreating ice margin. (2) An overlying mud association was deposited from suspended sediment plumes, with minor ice-rafting, and records ice retreat and increasing distality of the site. Muds contain a mixed foraminiferal microfaunal assemblage typical of open-water shallow-marine shelves. Species can be grouped into reworked temperate, cosmopolitan and well-preserved boreo-arctic elements and indicate mixing of derived and retransported temperate species with an in-situ glaciomarine fauna. (3) At the top of the section a gravel association, derived from a nearshore fan delta, rests on planated muds and is attributed to wave reworking and slumping of the fan delta front in shallow water during rapid basin rebound. This and other sequences elsewhere in the Irish Sea Basin is a record of rapid evacuation of the basin by calving tidewater glaciers and the uplift and erosion of glaciomarine sedimentary sequences in response to rapid late glacial crustal rebound.

The Late Devensian (

The Late Devensian (<20 ka BP) glacial geology of the Irish Sea Basin (4000 km 2) is an event stratigraphy recording the entry of marine waters into a glacio-isostatically-depressed basin, and the rapid retreat of the Irish Sea Glacier as a tidewater ice margin. Marine limits occur up to 140 m O.D. Across much of the central basin, the ice margin was uncoupled from its bed exposing a subglacially-scoured topography to glaciomarine processes. The Irish Sea Glacier was a major drainage conduit of the last British Ice Sheet; calving of the marine ice margin resulted in fast flow (surging) of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys. Rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones (e.g. Cheshire/Shropshire Lowlands) and initiated the collapse of the ice sheet. Thick wedges of ice-contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the Irish Sea coast. Where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins, the development of fast flowing ice streams, drumlinization and the pumping of subglacial sediment to tidewater. Raised delta complexes are locally associated with marine limits along the high relief coastal margins of Wales, east central Ireland, and the Lake District. Associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat. Co-eval offshore deposits are represented by well-stratified glaciomarine complexes that infill a subglacially-scoured topography that shows networks of tunnel valleys. Glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin (e.g. North Devon, Scilly Islands, Southern Ireland). The age of these distal sediments, previously mapped as pre-Devensian tills, is constrained by amino acid ratios. Basin rebound following deglaciation was rapid, with over 100 m recovery in 3 ka, and was followed by a low marine still stand. Peat, accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level. The glacio-sedimentary model identified in this paper, involving rapid ice retreat and related sedimentation triggered by rising relative sea level, suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves.

Detailed S-wave structure in the Dublin Basin and its northern margin

Summary. The seismic structure has been measured to a depth of about 3 km along a 30 km seismic profile in east central Ireland. This profile is unusual in that it is the S-wave velocity—depth structure that has been measured to a degree of precision more normally associated with P-wave results. One reason for this is that the sources used were quarry blasts which generated strong S-waves and short-period surface waves but rather weak P-waves. The results show a layer of Carboniferous limestone with shear velocity 2.65 km−1 s overlying a layer with a velocity of 3.06 km s−1. This second layer was interpreted as Lower Palaeozoic strata (Silurian/Ordovician) since this velocity was evident in an inlier seen at the surface at the northern end of the line. A third refraction horizon, shear velocity 3.45 km s−1 and displaying a basinal structure, was also recognized. This may be Cambrian or Precambrian basement.

The Late Quaternary history of east-central Ireland

SummaryThe drift succession in east-central Ireland is the result of a series of ice movements spreading from major centres of dispersion within theIrish Sea Basin and over the north-central Irish plain, and from local mountain sources. These glaciations have produced laterally and vertically complex sequences of deposits. The large-scale events influenced almost the entire area; problems of correlation emerge when considering episodes of relatively restricted extent such as those associated with upland ice-caps in the S and the hitherto unreported readvances which interrupted the withdrawalof ice-sheets across the northern part of the region under examination. Thetask of assigning the older units to particular Quaternary cold stages is frustrated by the absence of interstratified organic horizons. Two possible models of glaciation are considered: one may be regarded as ‘traditional’; the other requires a much shorter period of time by assuming that the stratigraphy records differences in the relative strengths of essentially contemporaneous ice-masses.

Paleomagnetic results from the Lower Paleozoic of Ireland

Paleomagnetic data are presented for a variety of Ordovician rocks from two regions in Ireland: the South Mayo Trough and some Ordovician inliers of east-central Ireland. Some of these data update previous preliminary results, while others provide new information. In some instances the original remanence direction has been obscured by subsequent remagnetization.Although magnetic inclinations of the Ordovician results are mostly shallower than contemporaneous British results, poor precision precludes any reliable estimate of closure across this sector of the Proto-Atlantic ocean. Declination differences between the South Mayo Trough and British data indicate a 30° clockwise rotation of this tectonic block during the Middle to Upper Devonian.

The Regional Variation in Emigration from Ireland between 1821 and 1841

THE HISTORY of population change in Ireland is usually held to fall into two main periods: that before and that after the Great Famine of 1846-51. The rigid division of the demographic history of Ireland into these two chief periods has credited the famine with more influence than it in fact exerted. Population still increased more in the West than elsewhere after the famine;1 whilst an examination of conditions in the generation before the crisis, reveals that even then emigration was on such a scale, and natural increase was restricted through increased celibacy and postponed marriage to such an extent, that the emphatic loss of population after the famine was clearly foreshadowed. It is intended in this paper to isolate the effect of emigration on the regional variations in population change during the generation preceding the famine. The early censuses of Ireland (I812, 1821, 183I and I841) varied much in their content and accuracy. Of the four, the last was by far the fullest, and was probably the most accurate. The first failed because of insufficient direction. The enumerators chosen in Ireland not only lacked suitable qualifications, but were working under the direction of the Grand Juries, which met for two short periods only during the year. Consequently, after two years returns had been made for only a quarter of the country.2 The 183I census was unsatisfactory because enumerators considered they would be paid, and in many cases were paid, according to the numbers recorded, so that the population was exaggerated. The 1821 census was more satisfactory in this respect, and, moreover, contained valuable information on the ages of the people, which the I83I census lacked. Thus, of the censuses of the pre-famine period, those of 1821 and 1841 were most reliable. During the twenty years 1821-41 the regional variation in population change was emphatic, ranging from 7 per cent in Longford to 37 per cent in Clare. The mapping of changes by baronies shows that increases of more than 30 per cent were almost confined to the west, apart from some linen manufacturing areas of the north-east (Fig. I). Some remoter western areas recorded an increase of over 50 per cent, whilst in east-central Ireland gains of less than io per cent were common. Most eastern counties had at least one barony recording an increase of less than 5 per cent, and there were sporadic occurrences of losses: population there had indeed become almost static.