NW Ireland Research Articles

A thin-skinned thrust model for ice-marginal glacitectonic detachment and emplacement of Carboniferous bedrock rafts at Kilcummin Head, NW Ireland

This paper presents the results of a detailed macro- and microscale structural study of the glacitectonised sequence at Kilcummin Head on the western side of Killala Bay, County Mayo, northwest Ireland. The sequence comprises two laterally extensive, thrust-stacked rafts of Carboniferous limestone and mudstone emplaced upon the in situ bedrock of the Ballina Limestone Formation. Restored cross-sections reveal that the glacitectonised sequence has undergone extensive deformation and shortening of 61 %. This accompanied the formation of a prominent thrust-moraine associated with a northward ice advance across Killala Bay during the Midlandian (Devensian). A five-stage model is proposed to describe the deformation. Stage 1 comprises detachment of the rafts, and the majority of the sequence shortening. North-directed transport of the rafts occurred on a major décollement surface located at the base of the rafted sequence, marked by a mudstone-rich glacitectonite. Stage 2 accommodated further shortening via a series of imbricate thrusts leading to the stacking of the bedrock rafts (Stages 3 and 4). Stage 5 saw final stacking of rafts within a prominent thrust-block moraine, followed by the deposition of a sequence of coarse-grained, ice-marginal glacigenic deposits.

Arthropleura trackway ( Diplichnites cuithensis ) from the Carboniferous, Serpukhovian, Limestone Coal Formation, Clackmannan Group, Linn Park, Glasgow

The arthropleurid trackway Diplichnites cuithensis has previously been described from Scotland from the Upper Carboniferous Serpukhovian Limestone Coal Formation on the Isle of Arran and the Lower Carboniferous Visean Pittenweem and Anstruther Formations on the East Fife coast. Here we describe a new west coast single trackway from the Serpukhovian Limestone Coal Formation of Glasgow's Linn Park. The trackway occurs associated with simple horizontal burrows assignable to Planolites? , vertical openings of Arenicolites , examples of Taenidium barretti (formerly Beaconites barretti ), and irregular large-scale bioturbation or possibly rootlet casts. The trace fossils and sedimentary structures (including trough cross-bedding and flaser bedding) indicate a fluvial sandbar or plain environment, possibly of estuarine origin, locally colonized by plants. Diplichnites cuithensis (and other Diplichnites species) commonly occur associated with the burrow Taenidium barretti . The latter is known to have been widespread globally throughout the Carboniferous, and is a common component of fluviatile sequences within the Lower Carboniferous succession of NW Ireland. This suggests that previously undocumented older Scottish Carboniferous examples of both Diplichnites ichnospecies and Taenidium barretti may also be present, assuming that suitable environments persisted and are currently adequately exposed.

Tectonostratigraphic evolution of the Slyne Basin

Abstract. The Slyne Basin, located offshore NW Ireland, is a narrow and elongated basin composed of a series of interconnected grabens and half-grabens, separated by transfer zones coincident with deep crustal structures formed during the Silurian- to Devonian-aged Caledonian Orogeny. The basin is the product of a complex, polyphase structural evolution stretching from the Permian to the Miocene. Initially, relatively low-strain rifting occurred in the Late Permian and again in the latest Triassic to Middle Jurassic, followed by a third phase of high-strain rifting during the Late Jurassic. These extensional events were punctuated by periods of tectonic quiescence during the Early Triassic and Middle Jurassic. Late Jurassic strain was primarily accommodated by several kilometres of slip on the basin-bounding faults, which formed through the breaching of relay ramps between left-stepping fault segments developed during earlier Permian and Early–Middle Jurassic rift phases. Following the cessation of rifting at the end of the Jurassic, the area experienced kilometre-scale uplift and erosion during the Early Cretaceous and a second, less severe phase of denudation during the Palaeocene. These post-rift events formed distinct regional post-rift unconformities and resulted in a reduced post-rift sedimentary section. The structural evolution of the Slyne Basin was influenced by pre-existing Caledonian structures at a high angle to the basinal trend. The basin illustrates a rarely documented style of fault reactivation in which basin-bounding faults are oblique to the earlier structural trend, but the initial fault segments are parallel to this trend. The result is a reversal of the sense of stepping of the initial fault segments generally associated with basement control on basin-bounding faults.

SUPERIMPOSED ALLOGENIC AND BIOLOGICAL CONTROLS ON SILICICLASTIC ARCHITECTURE: AN EARLY MISSISSIPPIAN (VISEAN) EXAMPLE FROM TROPICAL LAURUSSIA

ABSTRACT The sedimentary-stratigraphic record is regularly considered only in the context of regional climate, tectonic configuration, and sea-level. In this study we provide examples of how biotically influenced autogenic processes may come to be overprinted on these extrinsic, allogenic controls. A sedimentological analysis is given for the Mississippian (Visean) siliciclastic strata which crop out in counties Donegal and Mayo in NW Ireland. Eleven sedimentary facies record deposition of dominantly clastic and humic organic sediments which accumulated in alluvial, fluvial, estuarine, and fully marine environments. The preserved architecture of the sedimentary deposits is shown to be dependent on local autogenic dynamics, processes that were in turn modified or entirely controlled by biota (“biosphere signatures”). Sedimentological criteria, specifically the type and distribution of preserved biosphere signatures, suggests deposition occurred in a dominantly wet, humid environment in keeping with Laurussia's proposed equatorial position but potentially at odds with previous suggestions of seasonal aridity. The humid climate and resultant perennially active water conduits facilitated the widespread preservation of inclined heterolithic stratification (IHS). Allogenic and autogenic processes are ultimately linked, with external factors such as sea-level, tectonics, and climate all impacting the spatial distribution, abundance and prevailing forms of biota. The flooding of the Laurussian continent is accompanied by a shift from plant-induced to animal-induced biosphere signatures basinwards of the estuary funnel. In this way, the interplay between allogenic and autogenic processes is recorded at sedimentary outcrop through the capacity of extrinsic forcings to influence the rates and locations of intrinsic life-sediment interactions.

A REVIEW OF UAV PHOTOGRAMMETRY APPLICATION IN ASSESSING SURFACE ELEVATION CHANGES

Assessing large scale topography and surface elevation changes usually requires temporal remote sensing and aerial photogrammetrically-based data. Usually, very high resolution (VHR) elevation data, for instance, digital surface models (DSM) from light detection and ranging (LiDAR) and unmanned aerial vehicles (UAV), are used to visualise the changes in surface elevation. Therefore, this study attempts to review different case studies of assessing topography and surface elevation changes, specifically on geomorphological change detection (GCD) based on UAV photogrammetry data. The case study areas at Five Finger Strand (NW Ireland), Rosolina Mare (Italy) and Elbow River, Alberta (Canada) were discussed. This paper reviews the theory of UAV, surface elevation changes, and the summary of a related case study of surface elevation changes. The finding can provide a deep understanding of UAV applications in assessing surface elevation changes using UAV photogrammetry data.

Kinematic interaction between stratigraphically discrete salt layers; the structural evolution of the Corrib gas field, offshore NW Ireland

The kinematic interaction of thin salt layers during basin evolution has received little attention to date, despite there being several basins which contain multiple thin salt layers across NW Europe. This study utilises high-quality 3D seismic reflection data coupled with borehole data to investigate the evolution of the structure containing the Corrib gas field which is composed of two distinct salt structures. Located in the Slyne Basin offshore NW Ireland, the structure consists of a NE-SW oriented Permian salt anticline which folds the overlying Mesozoic stratigraphy. Upper Triassic salt acts as a second mechanical detachment and forms an elongate salt roller parallel to the crest of the Permian salt anticline. The Upper Triassic salt roller forms the footwall of a listric fault which downthrows the anticlinal crest of the folded Jurassic section to the SE. The Permian salt anticline began rising during the Late Triassic and Early Jurassic driven by low-strain regional extension. During the main phase of rifting, a combination of basement tilting, gravity gliding, and salt welding resulted in a steep increase in the amplitude of the Permian salt anticline. The relief on the salt-cored fold resulted in gravity gliding on the Triassic salt, forming the parallel salt roller and listric fault. The throw distribution on the listric fault is driven by the combined mechanisms of gravity sliding on the Triassic salt and by inflation of Triassic salt in the footwall of the fault. The listric fault is reactivated post-rift, suggesting modification of the Permian and Triassic salt structures. This study improves the understanding of the kinematic interaction of thin salt layers during syn-rift and post-rift deformation, with implications for hydrocarbon exploration on the Irish Atlantic margin and further afield.

The influence of multiple salt layers on rift‐basin development; The Slyne and Erris basins, offshore NW Ireland

AbstractIn contrast to much of the European Atlantic margin, the influence of salt on basin evolution has received little attention to date in the basins west of Ireland, despite salt being proven in several boreholes. Using an extensive seismic reflection database coupled with data from exploration wells and shallow boreholes, this study maps the distribution and composition of salt layers and investigates their role in the structural evolution of the Slyne and Erris basins offshore west of Ireland. Two salt‐prone intervals have been proven. The Upper Permian Zechstein Group is present throughout the Slyne and Erris basins, whereas the Upper Triassic Uilleann Halite Member is only developed in the Northern Slyne and Southern Erris sub‐basins. Both sedimentary units mechanically detach pre‐, post‐ and intra‐salt stratigraphy. Both salt layers underwent halokinesis during basin development, creating a variety of salt‐related structures. Salt pillows and salt rollers formed in the Zechstein Group, causing folding and rafting in the overlying Mesozoic section, driven by active faulting within the pre‐salt basement. Halokinesis in the Uilleann Halite Member caused thin‐skinned crestal collapse of the overlying Jurassic section above anticlines cored by Zechstein salt. Where both Triassic and Permian salt are present, unique structural geometries are formed when two stratigraphically discrete but kinematically linked halokinetic structures develop. The most common structural configuration consists of a Zechstein salt pillow and an Uilleann Halite salt wall separated by Lower Triassic sandstones. The fold axis of the salt pillow trends parallel to the strike of the salt wall. The results of this study provide a framework for the evolution of halokinetic structures in other basins on the Irish Atlantic margin, give a greater insight into the Permian and Triassic palaeogeography of the region and have more general implications for the evolution of salt‐related structures in rift basins with multiple stratigraphically discrete salt layers.

Coastal Impact From High-Energy Events and the Importance of Concurrent Forcing Parameters: The Cases of Storm Ophelia (2017) and Storm Hector (2018) in NW Ireland

Infrequent but high energy storm events can radically modify coastlines, at times displacing significant sediment volumes and changing the configuration of coastal shorelines. More frequent and more intense Atlantic storms over the last 40 years have heightened the potential risk to coastal environments, population and infrastructure. Understanding local environmental forcing conditions and associated variables involved in coastal impact and response, can better inform future coastal management planning. This study examines the coastal impacts of two separate storms that occurred at Five Finger Strand, on the northwest Irish coast, in late 2017 (Storm Ophelia) and mid-2018 (Storm Hector). Using forcing parameters (wind speed and direction, wave heights and wave run up) along with 3D topographic surveys, impacts that occurred along a sandy coastline site in NW Ireland are examined for both storm events. For Storm Ophelia, shore-oblique to shore-parallel waves (2 m height) coincident with low tide (~ 0.8m) were recorded at the study site. This resulted in minimal erosional impact which was revealed by a new proxy storm impact index, ‘Storm Dune Trimming’ (value of >0.03) as well as a sediment displacement volume of 8,300 m3, largely confined to the intertidal area with only limited foredune edge erosion. Storm Hector, on the other hand, a lower energy event than Storm Ophelia, resulted in much more pronounced sediment displacement (13,400 m3 in the intertidal area) and significantly more dune scarping taking place (Storm Dune Trimming >0.09) due to better synchronicity of forcing factors such as high tide level, high wave heights and onshore wind direction. We conclude that storm energy is not always a direct indicator of coastal impact where the synchronicity of local forcing factors and antecedent beach conditions appears to be the most important drivers of actual coastal response on sandy beaches. This study, therefore, shows the importance of particular environmental parameters and their simultaneous timing in forcing change and is a useful insight into which parameters may be more risk-relevant in producing erosion along many sandy, dune-fringed coasts of NW Europe.

3D mapping efficacy of a drone and terrestrial laser scanner over a temperate beach-dune zone

Understanding dynamic earth surface processes requires various spatial and temporal information to help produce patterns of landform change. Recent developments in sensor technology such as Structure from Motion (SfM), camera-mounted airborne Unmanned Aerial Vehicles (UAVs) and Terrestrial Laser Scanning (TLS) have provided a means of acquiring high-resolution spatial data on land surface topography. Through repeat surveys, these techniques enable much better understanding of what is termed ‘geomorphometry’, where we can examine a geomorphic surface for change over space and time. In coastal environments, change can involve significant alteration and generation of landforms over relatively short periods and, therefore, we require a means of measuring surface morphology quickly and over large areas. Here, we examine a section of a beach-dune system in NW Ireland using SfM-UAV and TLS plus baseline dGPS data points to assess the value of these techniques and to understand their effectiveness (and limitations). Issues such as accuracy, resolution and differences of Digital Elevation Models (DEMs) are assessed for their efficiency, associated challenges and relative performance over variations in terrain types and analytical approaches. We also examine the implications for differences in areal and volume calculations of the coastal landforms using both approaches. We find that sensor performance is highly dependent on the terrain being measured, with undulations, slope, vegetation cover, acquisition resolution (point density) and interpolation issues all having pronounced impacts on effectiveness and data quality. In general, the TLS performed better over flatter, low-angled topography containing sparse/non-vegetated areas than in areas with complex landforms where survey shadows appear to compromise final DEMs. The SfM-UAV shows good performance over different terrains with the exception of relatively flat, featureless areas such as sandy beaches and densely-vegetated surfaces where differences between techniques are >1 m. Data acquisition however is much (×30) faster using a SfM-UAV with more extensive survey areas covered than using a TLS.

Catchment-scale heterogeneity of flow and storage properties in a weathered/fractured hard rock aquifer from resistivity and magnetic resonance surveys: implications for groundwater flow paths and the distribution of residence times

Abstract Groundwater pathways and residence times are controlled by aquifer flow and storage properties, which, in weathered/fractured hard rock aquifers, are characterized by high spatial heterogeneity. Building on earlier work in a metamorphic aquifer in NW Ireland, new clay mineralogy and analyses of geophysical data provided high spatial resolution constraints on the variations in aquifer properties. Groundwater storage values derived from magnetic resonance sounding and electrical resistivity tomography were found to largely vary laterally and with depth, by orders of magnitude. The subsequent implementation of hillslope, two-dimensional numerical groundwater models showed that incorporating heterogeneity from geophysical data in model parametrization led to the best fit to observations compared with a reference model based on borehole data alone. Model simulations further revealed that (1) strong spatial heterogeneity produces deeper, longer groundwater flow paths and higher age mixing, in agreement with the mixed sub-modern/modern ages (mostly <50 years) provided by independent tritium data, and (2) areas with extensive weathering/fracturing are correlated with seepage zones of older groundwater resulting from changes in the flow directions and are likely to act as drainage structures for younger groundwater on a catchment or regional scale. Implications for groundwater resilience to climate extremes and surface pollution are discussed together with recommendations for further research.

Multi-scale variability of storm Ophelia 2017: The importance of synchronised environmental variables in coastal impact

Low frequency, high magnitude storm events can dramatically alter coastlines, helping to relocate large volumes of sediments and changing the configuration of landforms. Increases in the number of intense cyclones occurring in the Northern Hemisphere since the 1970s is evident with more northward tracking patterns developing. This brings added potential risk to coastal environments and infrastructure in northwest Europe and therefore understanding how these high-energy storms impact sandy coasts in particular is important for future management.This study highlights the evolution of Storm (formally Hurricane) Ophelia in October 2017 as it passed up and along the western seaboard of Ireland. The largest ever recorded Hurricane to form in the eastern Atlantic, we describe, using a range of environmental measurements and wave modelling, its track and intensity over its duration whilst over Ireland. The impact on a stretch of sandy coast in NW Ireland during Storm Ophelia, when the winds were at their peak, is examined using terrestrial laser scanning surveys pre- and post-storm to describe local changes of intertidal and dune edge dynamics. During maximum wind conditions (>35 knots) waves no >2m were recorded with an oblique to parallel orientation and coincident with medium to low tide (around 0.8m). Therefore, we demonstrate that anticipated widespread coastal erosion and damage may not always unfold as predicted. In fact, around 6000m3 of net erosion occurred along the 420m stretch of coastline with maximum differences in beach topographic changes of 0.8m. The majority of the sediment redistribution occurred within the intertidal and lower beach zone with some limited dune trimming in the southern section (10% of the total erosion). Asynchronous high water (tide levels), localised offshore winds as well as coastline orientation relative to the storm winds and waves plays a significant role in reducing coastal erosional impact.

First records of Jamaican walnuts Juglans jamaicensis (Juglandaceae) from Irish and UK waters, together with observations on other walnut species reported from NW Europe

On 30 December 2015, a single specimen of Juglans was found stranded on Tramore Beach (54° 48′ 25″N, 08° 30′ 01″W), Rosbeg, Co Donegal, NW Ireland. A second specimen was found on Black Rock Beach, Widemouth Bay, south of Bude, north Cornwall, UK (SS19760178) c.14 March 2016. Based on morphological features, both specimens were identified as J. jamaicensis C. DC., and represent the first records of this species from Irish, UK and NW European waters. It is hypothesised that these walnuts most likely originated in the Greater Antilles where J. jamaicensis is endemic to Cuba, Hispaniola (Dominican Republic & Haiti) and Puerto Rico. At least four other species of walnut have been recorded from NW European waters: J. regia, J. nigra, J. ailanthifolia, and J. californica.

Analysis of groundwater-level response to rainfall and estimation of annual recharge in fractured hard rock aquifers, NW Ireland

Summary Despite fractured hard rock aquifers underlying over 65% of Ireland, knowledge of key processes controlling groundwater recharge in these bedrock systems is inadequately constrained. In this study, we examined 19 groundwater-level hydrographs from two Irish hillslope sites underlain by hard rock aquifers. Water-level time-series in clustered monitoring wells completed at the subsoil, soil/bedrock interface, shallow and deep bedrocks were continuously monitored hourly over two hydrological years. Correlation methods were applied to investigate groundwater-level response to rainfall, as well as its seasonal variations. The results reveal that the direct groundwater recharge to the shallow and deep bedrocks on hillslope is very limited. Water-level variations within these geological units are likely dominated by slow flow rock matrix storage. The rapid responses to rainfall (⩽2 h) with little seasonal variations were observed to the monitoring wells installed at the subsoil and soil/bedrock interface, as well as those in the shallow or deep bedrocks at the base of the hillslope. This suggests that the direct recharge takes place within these units. An automated time-series procedure using the water-table fluctuation method was developed to estimate groundwater recharge from the water-level and rainfall data. Results show the annual recharge rates of 42–197 mm/yr in the subsoil and soil/bedrock interface, which represent 4–19% of the annual rainfall. Statistical analysis of the relationship between the rainfall intensity and water-table rise reveal that the low rainfall intensity group (⩽1 mm/h) has greater impact on the groundwater recharge rate than other groups (>1 mm/h). This study shows that the combination of the time-series analysis and the water-table fluctuation method could be an useful approach to investigate groundwater recharge in fractured hard rock aquifers in Ireland.

Population Structure of a Widespread Species under Balancing Selection: The Case of Arbutus unedo L.

Arbutus unedo L. is an evergreen shrub with a circum-Mediterranean distribution that also reaches the Eurosiberian region in northern Iberia, Atlantic France, and a disjunct population in southern Ireland. Due to the variety of climatic conditions across its distribution range, the populations of A. unedo were expected to display local adaptation. Conversely, common garden experiments revealed that diverse genotypes from a range of provenances produce similar phenotypes through adaptive plasticity, suggesting the action of stabilizing selection across its climatically heterogeneous range. Nonetheless, since a uniform response might also result from extensive gene flow, we have inferred the population structure of A. unedo and assessed whether its extended and largely one-dimensional range influences gene flow with the help of AFLP genotypes for 491 individuals from 19 populations covering the whole range of the species. As we had anticipated, gene flow is restricted in A. unedo, providing further support to the hypothesis that stabilizing selection is the most likely explanation for the homogeneous phenotypes along the range. The Euro-Siberian populations were not particularly isolated from the Mediterranean. Instead, there was a distinct genetic divide between the populations around the Mediterranean Sea and those sampled along Atlantic coasts from northern Africa up to Ireland. This genetic structure suggests the action of historic rather than biogeographic factors as it seems consistent with a scenario of independent glacial refugia in the Atlantic and Mediterranean portions of the range of A. unedo. Genetic exchange was likewise restricted within each set of populations. Nevertheless, isolation-by-distance (IBD) was stronger, and FST increased faster with distance, along the Atlantic, suggesting that gene flow might be larger among Mediterranean populations. Genetic diversity was significantly lower in NW Iberia and Ireland than in other populations whereas Ireland was more closely related to populations in NW Iberia than to a population in Atlantic France, suggesting a postglacial stepping-stone colonization of the Atlantic coast. Altogether, our results show that stabilizing selection is able to homogenize the phenotypic response even when population structure is strong, gene flow is constrained, and the phylogeographic past is complex.

Arcuate moraines on the continental shelf NW of Ireland

The geomorphological record of ice sheets on continental shelves includes a range of flow-transverse ridges that indicate the former position of the ice-sheet margin or grounding zone in time and space. On the continental shelf offshore of NW Ireland, well-developed arcuate sediment ridges are moraines that record the lobate retreat of a grounded Irish Ice Sheet from the shelf edge during the last deglaciation (Fig. 1). Retreat across the shelf was episodic and punctuated by occasional minor readvances or oscillations of the ice-sheet margin. Fig. 1. Moraines on the continental shelf off NW Ireland. ( a ) Multibeam image showing the NE–SW-aligned arcuate moraines. Acquisition system Kongsberg Simrad EM1002 and EM3002. Frequency 95 and 300 kHz. Grid-cell size 20 m. ( b ) Enlarged image of the NE–SW-aligned arcuate moraines on the mid-shelf and the prominent moraine at the mouth of Donegal Bay. ( c ) Oblique view of the large moraine looking northwards (about 12 km across the bottom). VE×15. Grid-cell size 20 m. ( d ) Sub-bottom profile (x′–x) across the large moraine. Note asymmetrical eastern slope. ( e ) Cross-section (y′–y) of the nested moraines. VE×6. ( f ) Location of study area (red box; map from IBCAO v. 3.0). The continental …

Submarine drumlins on the continental shelf offshore of NW Ireland

Drumlins are streamlined subglacial landforms, usually formed of sediment, that record the former direction of ice-sheet flow across a landscape (Clark et al. 2009). They have been widely observed in a range of glacial environments, both terrestrial and marine. On the continental shelf offshore of NW Ireland multibeam-bathymetric data show elongate landforms with a morphology consistent with published observations of drumlins (Fig. 1). These landforms record the former flow of a terrestrially sourced, grounded Irish Ice Sheet across the continental shelf during the last glaciation (O Cofaigh et al. 2012). Fig. 1. Drumlins on the continental shelf offshore of NW Ireland. Acquisition systems Simrad EM1002S and EM3002 on the Celtic Voyager and EM1002 on the Celtic Explorer . Grid-cell size 20 m. ( a ) Oblique view of the seabed 5 km NW of Tory Island showing a swarm of closely spaced drumlins indicating NW ice-flow. VE×5. ( b ) Close-up of drumlins showing …

The UK’s wet and stormy winter of 2013/2014

The <scp>UK</scp>’s wet and stormy winter of 2013/2014

Integrating petrography, mineralogy and hydrochemistry to constrain the influence and distribution of groundwater contributions to baseflow in poorly productive aquifers: Insights from Gortinlieve catchment, Co. Donegal, NW Ireland

Identifying groundwater contributions to baseflow forms an essential part of surface water body characterisation. The Gortinlieve catchment (5km2) comprises a headwater stream network of the Carrigans River, itself a tributary of the River Foyle, NW Ireland. The bedrock comprises poorly productive metasediments that are characterised by fracture porosity. We present the findings of a multi-disciplinary study that integrates new hydrochemical and mineralogical investigations with existing hydraulic, geophysical and structural data to identify the scales of groundwater flow and the nature of groundwater/bedrock interaction (chemical denudation). At the catchment scale, the development of deep weathering profiles is controlled by NE-SW regional scale fracture zones associated with mountain building during the Grampian orogeny. In-situ chemical denudation of mineral phases is controlled by micro- to meso-scale fractures related to Alpine compression during Palaeocene to Oligocene times. The alteration of primary muscovite, chlorite (clinochlore) and albite along the surfaces of these small-scale fractures has resulted in the precipitation of illite, montmorillonite and illite-montmorillonite clay admixtures. The interconnected but discontinuous nature of these small-scale structures highlights the role of larger scale faults and fissures in the supply and transportation of weathering solutions to/from the sites of mineral weathering. The dissolution of primarily mineral phases releases the major ions Mg, Ca and HCO3 that are shown to subsequently form the chemical makeup of groundwaters. Borehole groundwater and stream baseflow hydrochemical data are used to constrain the depths of groundwater flow pathways influencing the chemistry of surface waters throughout the stream profile. The results show that it is predominantly the lower part of the catchment, which receives inputs from catchment/regional scale groundwater flow, that is found to contribute to the maintenance of annual baseflow levels. This study identifies the importance of deep groundwater in maintaining annual baseflow levels in poorly productive bedrock systems.

A paraglacial coastal gravel structure: Connell's Bank, NW Ireland

ABSTRACT Knight, J., Burningham, H., 2014. A paraglacial coastal gravel structure: Connell's Bank, NW Ireland. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 121–126, ISSN 0749-0208. Coastal gravel structures have been well documented worldwide and are formed dominantly by onshore wave transport of gravel, mainly during storm events. They are commonly observed along paraglacial coastlines where their origins are more ambiguous because of the effects of antecedent patterns of sediment supply, glacioisostatic sea-level change, and contemporary coastal processes. This paper describes the properties and polygenic origin of Connell's Bank, a small paraglacial gravel structure on the Atlantic-facing coast of NW Ireland. This feature has been shown on historical maps, air photos and satellite imagery since ca. 1850 but its outline has varied depending on seasonal migration, expansion and co...

Constraints on a shallow offshore gas environment determined by a multidisciplinary geophysical approach: The Malin Sea, NW Ireland

During the Irish National Seabed Survey (INSS) in 2003, a gas related pockmark field was discovered and extensively mapped in the Malin Shelf region (NW Ireland). In summer 2006, additional complementary data involving core sample analysis, multibeam and single-beam backscatter classification, and a marine controlled-source electromagnetic survey were obtained in specific locations.This multidisciplinary approach allowed us to map the upper 20 m of the seabed in an unprecedented way and to correlate the main geophysical parameters with the geological properties of the seabed. The EM data provide us with information about sediment conductivity, which can be used as a proxy for porosity and also to identify the presence of fluid and fluid migration pathways. We conclude that, as a whole, the central part of the Malin basin is characterized by higher conductivities, which we interpret as a lithological change. Within the basin several areas are characterized by conductive anomalies associated with fluid flow processes and potentially the presence of microbial activity, as suggested by previous work. Pockmark structures show a characteristic electrical signature, with high-conductivity anomalies on the edges and less conductive, homogeneous interiors with several high-conductivity anomalies, potentially associated with gas-driven microbial activity.