Limestone Bedrock Research Articles

Geophysical investigation for engineering construction assessment in Karst area

A geophysical survey involving electrical resistivity imaging was carried out in various parts of Perak state, Malaysia, to assess the risk of establishing engineering structures in a karst system. The area is underlain by the Palaeozoic Kinta limestone bedrock. A total of 9 survey lines were established on the proposed sites. The data collected from the survey areas was processed and subjected to computer iteration to simulates physical models of the most common karstic features in the area. The study results are remarkably vital in evaluating weathered zones and hard limestone bedrock, as well as in locating infiltrated water and cavities beneath them. This study emphasized the significance of geophysical surveys for foundation investigation because they can properly assess the competence of subsurface physical properties.

IRRIGATION AND LANDSCAPE COMMEMORATION IN NORTHERN ASSYRIA, THE ASSYRIAN CANAL AND ROCK RELIEFS IN FAIDA (KURDISTAN REGION OF IRAQ): PRELIMINARY REPORT ON THE 2019 FIELD SEASON

This article presents the preliminary results of the joint Kurdish-Italian Faida Archaeological Project (KIFAP) conducted by the Duhok Directorate of Antiquities and the University of Udine at the Assyrian Faida canal and rock art complex in the Kurdistan Region of Iraq. Investigation of this extraordinary and seriously endangered archaeological site was launched in 2019 and has led to the exploration of an 8.6 km-long irrigation canal cut into the limestone bedrock of the Chiya Daka hill range in the outskirts of the village of Faida, south of Duhok. Ten monumental sculpted rock panels carved along the canal's eastern bank were brought to light, representing an Assyrian ruler depicted at both ends of each panel, framing the cult statues of seven deities standing on pedestals shaped like striding animals. This article discusses the canal's role in the wider context of the Northern Assyrian Irrigation System and the function of the Assyrian hydraulic networks as economic infrastructures with transformative effects on the landscape and staple food production of the empire's core. The Faida bas-reliefs are examined from an archaeological and art historical perspective, and hypotheses are proposed about their religious and ideological meaning, as well as their dating and the identity of the king or kings who commissioned them.

The sediment at the end of the tunnel: Geophysical research to locate the Pleistocene entrance of Gruta da Companheira (Algarve, Southern Portugal)

AbstractUntil recently, evidence of Neanderthal cave use in the Algarve (Southern Portugal) came only from the site of Ibn Ammar. Over the last couple of years, archaeological excavations inside another cave, Gruta da Companheira, yielded Mousterian stone tools associated with possible human fossils. The discovery of this assemblage is groundbreaking because it may contribute to enlighten the Neanderthal/cave relationship and explain the dearth of similar sites in the Algarve. Gruta da Companheira, however, is a complex karst system, which was partly destroyed during its accidental discovery. As result, the original entrance of the cave remains unknown, and it is unclear how sediments, archaeological materials and Neanderthals accessed the site. To tackle these issues, we combined geomorphological observations with speleological, Electrical Resistivity Tomography (ERT) and Ground‐Penetrating Radar (GPR) prospections. Our data indicate that Gruta da Companheira was probably accessed from the hilltop through a sub‐vertical entrance. Additionally, our results suggest the existence of yet unexplored shallower cavities connected with the already known passages of Gruta da Companheira. These results will guide the opening of new excavation areas at the site. The limestone bedrock hosting Gruta da Companheira has been extensively dissolved by karst processes. Therefore, it is necessary to focus future research on the cave infillings to clarify whether Neanderthals exploited the cave's inner chambers or alternatively limited their occupations to the hilltop and geogenic processes reworked their materials into the endokarst system shortly after their stays. The deep karstification and partial collapse of the hill hosting Gruta da Companheira are common in limestone outcrops that occur throughout the Western Algarve. Poor visibility and poor accessibility of this karst area, densely covered with shrubby vegetation, are factors that need to be considered when addressing the scarcity of Middle Palaeolithic cave sites in this region.

Critical Role of Groundwater Inflow in Sustaining Lake Water Balance on the Western Tibetan Plateau

AbstractIt is difficult to quantify the amount of groundwater inflow on the Tibetan Plateau (TP), yet it can be critically important for sustaining lake water balance. Here we show that most endorheic lakes on the western TP exhibited considerable water level increase during the ice‐covered period, which contrasts with lakes in other regions of the TP. An analysis of lake water balance attributes this water surplus to significant groundwater inflow, which is estimated to be about 59%–66% of total inflow into lakes. The groundwater inflow occurred after the 2000s, which is consistent with the rapid lake expansion and significant increase in precipitation. We suggest that the groundwater inflow is mainly related to large‐scale active faults in the limestone bedrock and sufficient meltwater from high elevations. Our results imply that groundwater may be deeply involved in the water cycle and modify the seasonal and inter‐annual lake variations on the western TP.

The threatened karst of the Great Western Lakes, Ireland

Limestone is a notoriously leaky rock. In many areas that are underlain by limestone, surface rivers are few and disjointed. They disappear into sinks only to reappear, sometimes many kilometres away, at springs. It is not an environment in which lakes are typically found. Some 40 percent of Ireland is underlain by limestone, yet the Irish lowlands are scattered with countless lakes, large and small. In many the limestone beneath is effectively sealed by a cover of glacial till; others have formed where hollows descend below a shallow water table. Around the shores of many, exposed limestone bedrock and boulders support a range of peculiar etched features that are virtually confined to this lakeshore environment.

Mapping the karstification potential of central Cebu, Philippines using GIS

Karstification is influenced by numerous factors, such as climate, geomorphology, and geology. Karstified areas are faced with numerous problems such as ground subsidence and groundwater vulnerability. In rapidly urbanizing areas like Cebu in the Philippines, it is imperative to know the karstification potential, especially if karst landforms are already present. We evaluated the karstification potential of central Cebu using Raster Overlay Analysis (ROA) in a geographic information system (GIS) platform. ROA uses multiple maps which represent different factors affecting karstification, such as precipitation, temperature, vegetation, elevation, slope, drainage, lineaments, and geology. These factors were then correlated with the karstification potential map using the Cell Statistics tool. ROA reveals that 17% of central Cebu has very low karstification potential, while < 65% has low to moderate karstification potential and 18% has high to very high karstification potential. High karstification potential is generally associated with high precipitation (> 2100 mm/yr), low temperature (< 24.5 °C), very dense vegetation, high elevation (> 787 masl), gentle slope (< 10°), very high lineament density (> 0.45), very low drainage density (0), and older limestone bedrock. Areas with moderate to very high karstification potential coincide with cave locations. Cell Statistics (Range) reveals that the karstification potential map is strongly correlated with precipitation and temperature, and weakly correlated with drainage density and geology. While assumed to greatly affect karstification, the weak correlation of local geology with the karstification potential is attributed to lithological heterogeneities in central Cebu. Information on an area’s karstification is beneficial to effective land use planning and reduction of karst-related hazards.

Three-dimensional Gauss–Newton constant-Q viscoelastic full-waveform inversion of near-surface seismic wavefields

SUMMARY Full-waveform inversion (FWI) methods rely on accurate numerical simulation of wave propagation in the analysed medium. Acoustic or elastic wave equations are often used to model seismic wave propagation. These types of simulations do not account for intrinsic attenuation effects due to material anelasticity, and thus correction techniques have been utilized in practice to partially compensate the anelasticity. These techniques often only consider the waveform amplitude correction based on averaging of overall amplitude response over the entire data set, and ignore the phase correction. Viscoelastic wave equations account for the anelastic response in both waveform amplitude and phase, and are therefore a more suitable alternative. In this study, we present a novel 3-D Gauss–Newton viscoelastic FWI (3-D GN-VFWI) method. To address the main challenge of the Gauss–Newton optimization, we develop formulas to compute the Jacobian efficiently by the convolution of virtual sources and backward wavefields. The virtual sources are obtained by directly differentiating the viscoelastic wave equations with respect to model parameters. In order to resolve complex 3-D structures with reasonable computational effort, a homogeneous attenuation (Q factor) is used throughout the analysis to model the anelastic effects. Synthetic and field experiments are performed to demonstrate the utility of the method. The synthetic results clearly demonstrate the ability of the method in characterizing a challenging velocity profile, including voids and reverse velocity layers. The field experimental results show that method successfully characterizes the complex substructure with two voids and undulating limestone bedrock, which are confirmed by invasive tests. Compared to 3-D elastic FWI results, the presented viscoelastic method produces more accurate results regarding depths of the voids and bedrock. This study suggests that the improvement of imaging accuracy would warrant the widespread use of viscoelastic wave equations in FWI problems. To our best knowledge, this is the first reported study on 3-D GN-VFWI at any scale. This study provides the new theory and formulation for the use of Gauss–Newton optimization on the 3-D viscoelastic problem.

The Winery in Context: The Workshop Complex at Ambarçay, Diyarbakır (SE Turkey)

Abstract The paper examines the physical and contextual situation of a series of nine rock hewn pressing installations forming a complex of a winery workshop (ca. 5 decares) which was unearthed during excavations executed at the Roman site of Ambar village. Matching the Upper Mesopotamia and fed by a fair distance permanent water source – the Ambarçay Stream in close proximity, the site lies over limestone bedrock convenient for processing in a hard ground, right nearby a moderate size quarry besides two spring spouts. The site’s scale and function is cross-questioned through the instrumentality of original data and interrelatedness of a couple of archaeo-environmental features as well as through a selection of comparative evidence and proxy figures addressed in the ancient and historical accounts. Appearingly; topography, surrounding agricultural land and hydrology were three driving agents of the positioning and planning of the complex which looks spacious for household usage but rather demonstrates itself as an atelier of inhabitants (belike run at the institutional level) that expanded into post 3rd century. When also confined to the economic convergence of the value of wine recorded in the ancient and pre-modern sources, total relative capacity of one-time pressing operation generates an idea over figures that could suffice to more than a latifundium or a resident population.

Reinterpreting a “Roman villa” site: First results of nondestructive archaeological research in Dračevica (Donji Radišići, Bosnia and Herzegovina)

AbstractThe article presents the results of archaeological prospection of site Dračevica (Donji Radišići, Ljubuški municipality, West Herzegovina Canton, Bosnia and Herzegovina) which was partly excavated in the late 19th century and so far has been interpreted as a Roman villa, possibly with a special function (road station) and a name attested in ancient sources (Bigeste). Through the use of various nondestructive prospecting methods (aerial photogrammetry, fieldwalking survey, magnetic susceptibility, magnetometry, earth resistance), precise location with RTK GNSS and integration of the data in GIS, the site was restudied and reinterpreted. It was established that the structures are not isolated, as was assumed in the earlier research but rather were a part of a much larger Roman settlement. The research proves that the internal spatial division of the site is more complicated than previously thought, consisting of several building complexes located along a road, as well as land division systems. Such settlement pattern suggests similar, average‐sized land plots and farms. The importance of the research lies also in the methodological approach and the outcome of the geophysical research. Our research was the first application of nondestructive methods of archaeological prospection on Roman sites in the karst landscapes of West Herzegovina, proving the usefulness of the applied methodology in these specific and difficult conditions. We have found dependencies in between the geological background (thin layer of low resistive, colluvial soil on shallow limestone bedrock and the occurrence of highly magnetic terra rossa, formed on weathered limestone) and the geophysical responses registered by various instruments, that is, moderate to good magnetic and electric contrasts between the features and their surroundings, with relatively strong anomalies from geological features. The most important was finding relationships between particular magnetic and electrical anomalies and the presence of very shallow bedrock or faint archaeological remains (e.g. limestone walls). Our methodology, as well as some of our interpretations, will be helpful as a reference for further surveys in the region.

Late Quaternary Evolution of a Submerged Karst Basin Influenced by Active Tectonics (Koločep Bay, Croatia)

Koločep bay is a 30 km elongated karst basin located between the Elafiti Islands and the mainland with a NW–SE general direction. The bay lies within the seismically active southern Dalmatia zone. Irregular grid sub-bottom profiles and two legacy reflection seismic profiles have been used to determine the overall morphology of the bay and to establish the seismic stratigraphy of its sedimentary infill. Three major seismic–stratigraphic units have been identified in the upper ~50 m of the ~120-meter-thick sedimentary sequence that lies above the karstified limestone bedrock. The karst polje basin was flooded due to sea-level rise before 12.1 kyr BP. The morphology of the bay implies complex influences of Late Glacial meltwater discharges, aeolian sand deposition, the existence of paleo–ponor/karst spring zones and buried Pleistocene river channels. The Pleistocene seismotectonic units are deformed in the NW and SE parts of the basin. The central part of the basin has no signatures of intensive tectonic activity during the Holocene. A major erosion event was identified that led to the formation of a basin within the older sedimentary infill. In the southern part of the basin, we have evidence of Holocene tectonic activity with the formation of erosional scarps on the seafloor of the bay.

Persistence of arable Chernozems and Chernic Rendzic Phaeozems in the eroded undulating loess plateau in Central Europe

Chernozems are considered to degrade under the temperate humid climate of Central Europe, particularly in the arable and undulating areas and, thus, exposed to erosion. The present study was carried out in the loess-covered Proszowice Plateau (southern Poland), which was found to have a continuous cover of chernozemic soils in the past. Ten soil profiles located in two neighbouring slope catenas have documented the sequence of chernozemic and non-chernozemic soils (Chernozems, Phaeozems, and Calcisols), impacted by water erosion under intense arable land use and spatially dependent on the relief intensity. Soils in elevated, strongly inclined (and, thus, intensely eroded) slope positions lost their mollic horizons and gained the features of Calcisols. However, soils in elevated, slightly inclined positions preserved the morphological and physicochemical features of Chernozems, even if their chernic horizons were thinned to a ploughing depth. Also the colluvial soils located on the short slopes, in close proximity to eroded hilltops, are saturated with secondary carbonates throughout the profile and retain their chernozemic features (Calcic Chernozems). Whereas, the colluvial soils located on the long, slightly inclined slopes, at a large distance to eroded hilltops, are deeply leached from carbonates and meet the criteria of Haplic Phaeozems (in well drained sites) or Gleyic Phaeozems (in poorly drained foothills and depressions). Moreover, the Chernic Rendzic Phaeozems with thick mollic/chernic horizons are present in elevated (thus expectedly eroded) parts of hills with thin loess overlying the limestone bedrock. The presence of chernic horizons in soils threatened by erosion indicates that the persistence of Chernozems and Chernic Rendzic Phaeozems is possible in undulating arable lands threatened by erosion in temperate humid climate of Central Europe if supported by sustainable agriculture, preventing soil erosion and organic matter loss from humus horizons.

Geoglomeris subterranea (Diplopoda, Glomerida, Glomeridae), the first morphologically non‐specialized semiaquatic glomerid millipede?

<i>Geoglomeris subterranea</i> (Diplopoda, Glomerida, Glomeridae), the first morphologically non‐specialized semiaquatic glomerid millipede?

Use of cenotes and the cave environment by mammals on the Yucatán Peninsula, Mexico

AbstractMammals are important sources of nutrients to cave ecosystems, and in some circumstances, caves may be an essential resource for mammals. Few studies, however, have focused on the use of caves by terrestrial mammals. The Yucatán Peninsula encompasses an extensive carbonate karst region that includes the world's largest underwater cave system. Forest in the region overlies fractured limestone bedrock, so flooded caves known regionally as cenotes represent the only reliable source of free‐standing water for much of the Peninsula's wildlife. We used camera traps at 17 cenotes on the Yucatán Peninsula to determine patterns of use by mammals. Eighteen non‐volant mammal taxa were identified using cenotes, the most commonly occurring being lowland paca (Agouti paca), opossums (Didelphis spp.), white‐nosed coati (Nasua narica), gray fox (Urocyon cinereoargenteus), tayra (Eira barbara), and gray four‐eyed opossum (Philander opossum); collectively these taxa accounted for 76% of all mammal records. We also recorded several felids using cenotes, including jaguar (Panthera onca) and puma (Puma concolor). Activity patterns at cenotes usually matched normal activity schedules, but some species were nocturnal in the forest but diurnal at cenotes. Mammals mostly accessed cenotes to drink, but a range of activities were recorded including foraging, nesting, mating, resting, and bathing. The Yucatán region has experienced continued population growth and economic development over many decades which directly threatens cenotes. Because our work has revealed that cenotes are important to the Yucatán's mammals, we believe protection of cenotes should be a central issue for regional wildlife conservation.Abstract in Spanish is available with online material.

Turonian-Senonian organic-rich sedimentary strata and coal facies in Parnassos-Ghiona Unit, Central Greece: An assessment of palaeoenvironmental setting and hydrocarbon generation potential

In the past few years, scientific research related to the hydrocarbon potential in Greece has been focused on the formations of the Ionian Unit in the western areas of the country, where oil-seepages are well known. In contrast, Parnassos-Ghiona geotectonic Unit (PGU), Central Mainland Greece, has mainly been studied for the presence of bauxite ores. However, Upper-Cretaceous organic-rich strata, including local coal lenses, are occurring on top of the b3 bauxite horizon across PGU. In the present study, two underground mine sites, at Vagoneto and Gouves, where coal lenses occur, as well as an outcrop of the b3 bauxite horizon and the overlying gray limestone (PBF section) have been studied by means of organic petrology, mineralogy and inorganic geochemistry, as well as Rock-Eval analysis. The aim of the study is to evaluate the palaeoenvironmental conditions that favoured the organic matter accumulation subsequently to the bauxite formation, as well as the assessment of the hydrocarbon potential of the Upper Cretaceous strata within PGU. The study of the sections of interest revealed the establishment of three different modes of organic matter depositional settings, including paralic mires on the top of the lateritic mud deposition, paralic mires developed upon the Lower Cretaceous limestone bedrock, as well as shallow-marine basins with limited water circulation, followed by a deepening trend upwards. The low/very low grade humic coal lenses at the Vagoneto and Gouves sites formed by accumulation of mostly herbaceous plants, being characterized by elevated amounts of detrovitrinite and inertinite, and variable amounts of liptinites usually in the form of sporinite and alginite. Accordingly, the Rock-Eval data indicate the occurrence of all kerogen types, with the Types III and IV generally prevailing. The overall coal-petrographic data indicate intense oxidation in the palaeo-mires, possibly related to the dry warm Turonian climate and/or the influence of brackish waters. Additionally, the thermal maturity derived from both vitrinite reflectance and Rock-Eval analysis, point to Medium Rank Bituminous coals or, in terms of hydrocarbon generation, to the early oil window stage. The data suggest a good-to-excellent gas potential for Parnassos-Ghiona Unit, whereas the oil-potential seems to be limited.

A case study on the application and workability of the crosshole seismic survey in a karstic area

Crosshole seismic tomography is currently one of the reliable methods used in identifying the seismic velocity patterns for the development in areas challenged by presence of karstic features due to dissolution of the underlying limestone bedrock formation. The crosshole seismic tomography which provides a persistent image of the borehole and its surroundings in the form of P-wave velocity, picks up in-depth information compared to other surface geophysical methods. A crosshole seismic survey which consists of 99 lines connecting a total of 48 boreholes were conducted at Jalan Cochrane for a proposed residential development to determine the subsurface geology of the area. The site was divided into four main towers, namely Tower A and B (East) and Tower A and B (West). Jalan Cochrane is underlain by the Kuala Lumpur Limestone formation. This survey was mainly conducted to identify the possible cavities and incompetent rocks which are fractured and infilled in the proposed area. The crosshole seismic survey tomography correlated well with the borehole information obtained. Several drop in velocity observed were concluded to be possible cavities in the bedrock. Data obtained in Tower A and B (West) are more uniform and have a uniform bedrock level compared to the data in Tower A and B (East) which has an undulating bedrock level as well as fractured rocks and infilled cavities. This paper presents the findings obtained from the crosshole seismic survey conducted at Jalan Cochrane which successfully mapped out the cavities and bedrock level.

Topographic amplification and debris remobilization as a cause for increasing rockfall hazard in seismic areas: A case study in Central Italy

The long-lasting earthquake sequence of Central Italy in 2016 triggered around 1370 landslides, most of which were observed close to ridge areas. The area of San Pellegrino di Norcia (PG) was badly affected by the 6.5 Mw Norcia earthquake that triggered 95 rock falls and slides with volumes ranging from 0.5 m3 to 380 m3 over an area of 0.6 km2. The presence of such a large number of coseismic landslides in a small area provided a suitable case study for investigating triggering mechanisms related to slope morphology and the subsequent propagation dynamics of rockfalls. To this aim, detailed field data collection and up-to-date terrain modelling based on Unmanned Aerial Vehicle (UAV) imagery were carried out. They permitted to perform morphometric analyses oriented at defining: (a) the frequency of occurrence of rockfall with reference to the energy relief, (b) the relationships between extensions of source and propagation areas and (c) the change in the shape of the propagation area as a function of the different terrains crossed by rockfalls. The results of the morphometric study were compared with dynamic analyses of rock-slides onset and simulations of rockfall propagation. They highlighted that, disregarding the presence of steep rock faces, the failures were located close to ridge and slope edges, thus pointing out the role of topography on triggering of landslides.Moreover, it was possible to observe that even small-sized rockfalls had a widening effect in the foothill characterized by longer runouts compared to rockfall simulations. This issue was due to the mobilization of the talus debris covering the limestone bedrock. This study investigates an area where a significant increase in rockfall hazard can be expected due to the coupled effect of topographic amplification and debris remobilization.

Assessment of Sinkholes Investigations in Jangseong-Gun Area, South Korea, and Recommendations for Similar Studies.

This paper reviews the site investigation field data and access work performed between 2016 and 2019 in the study area located close to Gun-dong mine. The research was aimed at defining the cause of sinkholes and their relationship with the underlying karstic limestone bedrock and nearby mining activities. Only a limited number of small sinkholes appeared in 2014, 2016, and 2018 in the agricultural land close to the limestone mine. The previously open pit mine started its underground operations in 2007. Since then, the mine has developed, and is now comprised of, large underground excavations at several levels below the surface. The studies carried out concluded that the appearance of sinkholes may be related to a general lowering of the groundwater table because of nearby agricultural and mining activities and also due to over-extraction of water due to increased urban use. Whilst these are the best determinations, this paper identifies missing elements of the previous investigations mentioned above, some issues with the interpretation of poorly prepared borehole logs and the improper preservation of borehole cores. The authors make recommendations for a systematic approach for implementation of an investigation strategy. This paper concludes that the appearance of sinkholes is a natural phenomenon, developing over geological time. However, human intervention contributes to sinkhole formation, which in urban areas may result in human, property, and economic losses. A better understanding, based on a methodical approach and suitable technologies, can determine the causes of sinkholes and can lead to the formulation of solutions and the implementation of economically and socially acceptable mitigation measures.

Släktskap och neolitiska kulturer

Kinship and Neolithic cultures. As a result of their alkaline soil, due to limestone bedrock, the two Swedish islands of Öland and Gotland, are locations where bone is well preserved. Stable isotope investigations have shown that there were two contemporary populations during Middle Neolithic on the islands. One population was buried in megalithic graves, and shows evidence of a subsistence lifestyle with high proportion of terrestrial food, most probable from agriculture. The other population has had a lifestyle based on marine subsistence, and buried their dead in earth graves at shore sites. Ancient DNA investigations now show that the two populations may also have different origins. The hunter-gathers of the ”Pitted Ware Culture” might descend from a Mesolithic population, while the supposed farmers buried in the megaliths and affiliated with the ”Funnel Beaker Culture”, are more likely to descend from immigrants that arrived in the Ewarly Neolithic and brought agriculture to the islands.

Quantitative analysis of Cenozoic faults and fractures and their impact on groundwater flow in the bedrock aquifers of Ireland

Faults and fractures are a critical store and pathway for groundwater in Ireland’s limestone bedrock aquifers either directly as conductive structures or indirectly as the locus for the development of karst conduits. From the quantitative analysis of post-Devonian faults and fractures in a range of lithological sequences, this report describes the principal characteristics of Cenozoic strike-slip faults and joints, the youngest and the most intrinsically conductive fractures within Irish bedrock. Analysis of these structures in more than 120 outcrop, quarry, mine and cave locations in a range of bedrock types, provides a basis for: (1) definition of quantitative models for their depth dependency, lithological control, scaling systematics and links to preexisting structure, (2) conceptualisation of their impact on groundwater behaviour, and (3) estimation of groundwater flow parameters. The quantitative models provide constraints on fracture-controlled flow connectivity. Commonly observed decreases in sustainable flows and water strike interceptions with depth are attributed to increasing confinement and decreasing fracture connectivity and dissolution. Faults and joints have quite different end member geometries, with faults having strongly heterogeneous scale-independent properties and joints more often showing scale-dependent stratabound properties. The highest and most sustainable groundwater flows are usually associated with the complexity of structure of Cenozoic faults and of preexisting Carboniferous structures (on which conductive fracturing localises), enhanced by karstification and strongly jointed limestone bedrock particularly in the near-surface. Increased groundwater flow is promoted within bedded, rather than massive (i.e. unbedded), limestone sequences, characterised by bedding-parallel fractures and karst connecting otherwise subvertical fractures and subvertical wells.

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.