Colman Gallagher

The age of the Pleistocene raised beach near Fethard, County Wexford, using infra red stimulated luminescence (IRSL)

Stratified sediments, interpreted to be part of the Courtmacsherry Formation Pleistocene raised beach that overlies a marine rock platform near Fethard. south Wexford, were sampled and dated using the technique of Infra Red Stimulated Luminescence (IRSL). The technique yielded ages for the formation of most of the raised beach of between c. 162 ka BP and c. 129 ka BP. These arc the first age determinations for the Courtmacsherry Formation itself and. as such, represent an important advance in the development of a chronostratigraphy of the Pleistocene in Ireland. These dates are consistent with results obtained by others using UTD dating of sediments overlying the Courtmacsherry Formation in County Kerry and, therefore, suggest that IRSL holds great promise for the dating of hitherto updateable sediments.

Morphological evidence for geologically young thaw of ice on Mars: A review of recent studies using high-resolution imaging data

Liquid water is generally only meta-stable on Mars today; it quickly freezes, evaporates or boils in the cold, dry, thin atmosphere (surface pressure is about 200 times lower than on Earth). Nevertheless, there is morphological evidence that surface water was extensive in more ancient times, including the Noachian Epoch (∼4.1 Ga to ∼3.7 Ga bp), when large lakes existed and river-like channel networks were incised, and early in the Hesperian Epoch (∼3.7 Ga to ∼2.9 Ga bp), when megafloods carved enormous channels and smaller fluvial networks developed in association with crater-lakes. However, by the Amazonian Epoch (∼3.0 Ga to present), most surface morphogenesis associated with liquid water had ceased, with long periods of water sequestration as ice in the near-surface and polar regions. However, inferences from observations using imaging data with sub-metre pixel sizes indicate that periglacial landscapes, involving morphogenesis associated with ground-ice and/or surface-ice thaw and liquid flows, has been active within the last few million years. In this paper, three such landform assemblages are described: a high-latitude assemblage comprising features interpreted to be sorted clastic stripes, circles and polygons, non-sorted polygonally patterned ground, fluvial gullies, and solifluction lobes; a mid-latitude assemblage comprising gullies, patterned ground, debris-covered glaciers and hillslope stripes; and an equatorial assemblage of linked basins, patterned ground, possible pingos, and channel-and-scarp features interpreted to be retrogressive thaw-slumps. Hypotheses to explain these observations are explored, including recent climate change, and hydrated minerals in the regolith ‘thawing’ to form liquid brines at very low temperatures. The use of terrestrial analogue field sites is also discussed.

The sedimentology of a Late Pleistocene drumlin near Kingscourt, Ireland

Abstract An exposure in a Late Pleistocene drumlin near Kingscourt, Ireland, provides a good insight into some of the processes that give rise to such subglacial bedforms. The drumlin is located on a ridge, cored by red sandstone of Carboniferous (Namurian) age, which rises to 150 m above m.s.l. The drumlin itself is about 380 m long by 170 m wide and is 20 m in height. It is orientated VVNW-ESE. Ice flow direction in the area, as inferred from general drumlin orientation, striae, and erratic dispersal, was NW-SE. The drumlin is composed of diamicton (with four constituent facies), containing large-scale (up to 20 m long and 1.5 m high) slabs of the sandstone bedrock, which have been displaced tens of metres by ice dragging. The thin diamicton matrix is sand-rich with few clasts greater than pebble size. It contains green sandstone erratics from west and northwest of the study site along with clasts of weathered Namurian sandstone which have been sheared from local bedrock. The diamicton attains a maximum thickness of 5.4 m. The slabs are confined to the basal 2.5 m of the diamicton. Thus the drumlin is essentially rock cored. Parts of the matrix: are interpreted as injection sediments that have been squeezed into fractures and voids in the bedrock, and between rock slabs, under high porewater pressures, when the ice began to displace fractured substrate. Deformation structures, at a variety of scales are seen in the matrix. Deformation, erosion and deposition were all important in the formation of the drumlin. Much of the upper part of the diamicton has been sheared, subsequent to initial deposition, by ice action. The sheared units are uppermost in the stratigraphic sequence. The shearing is the last glacial process apparent in the drumlin sediment and may have been contemporaneous with drumlinisation. Both the squeezing process, which deposited the injections within the matrix, and the deflection in flow of ice were influenced by the obstructing bedrock ridge which, in this case, is also responsible for the anomalous orientation of the feature.

Glacier Dynamics around Slieve Bloom, Central Ireland

Analyses of both till and glacioaqueous sedimentary fabrics and their lithological characteristics have been carried out on sediments sampled at eight sites located around the northern margin and piedmont of Slieve Bloom. Results indicate that Slieve Bloom was overtopped by ice (lowing locally from between the south-south-west and west. The pattern of ice (low indicated by the sedimentary fabrics, the presence in the glacigenic sediments of a distinctive variety of Galway granite and the spatial variability of limestone in these sediments indicate that this local flow direction resulted from the deflection to the north-north-east of ice (lowing from the west. As the most widely accepted ice flow model for this region during the last glaciation requires ice (low to have been from between north-north-west and north-north-east, the results presented in this paper have important implications for the modelling of regional ice (low in the Irish midlands during the last glaciation.

Dating recent alluvial sediments in the Wicklow Mountains

Modern floodplain sediments in the Wicklow Mountains display a stratigraphy and sedimentology that contrasts them with earlier Holocene alluvium. During previous research 14 C dates of lightly constrained stratigraphies in one valley indicated a commencement date between 190+/-60 yr BP and 580+/-50 yr BP and mining generated enhanced lead metal values in another valley implied a commencement date there of AD 1780–1800. The paper presents the results of a 14 C dating programme the objects of which were to date (a) more definitively their commencement throughout the Wicklow Mountains and (b) their internal stratigraphies with a view to establishing a Hood chronology. AMS and radiometric 14 C dating techniques were applied to organic fractions and paniculate organic matter extracted from thin organic-rich layers within sampled sedimentary sequences. The dates spanned 780+/-60 BP to 3396+/-46 BP and provided neither a Coherent commencement period nor an accurate chronostratigraphy and the modern sediments appear to be dominated by old carbon derived from the catchment blanket peats. Although these results show that the immediate research aims cannot be achieved using 14 C dating they have led to a clearer understanding of the sourcing and dynamics of the modern style of sedimentation.

The morphology and palaeohydrology of a submerged glaciofluvial channel emerging from Waterford Harbour onto the nearshore continental shelf of the Celtic Sea

Abstract The results of an acoustic geophysical survey of the seabed off Waterford Harbour are presented. The survey revealed a probable submerged palaeochannel extending from the mouth of Waterford Harbour to the south‐west for 22 km and to a depth of 56 m below present sea level. Palaeomeander geometry and inferred sedimentology indicate that the palaeochannel was adjusted to discharges up to several orders of magnitude greater than those of the present. Together, these characteristics imply that the palaeochannel was probably formed by proglacial discharges of meltwater during a period of low sea level.

Alluvial Heavy Minerals as Indicators of Late Pleistocene Ice Flow in the Irish Midlands

The alluvial heavy minerals of Slieve Bloom consist of an allochthonous group, glacially imported from the Carboniferous limestone piedmont, and an autochthonous group derived from the Lower Palaeozoic rocks of Slieve Bloom. The spatial distribution of each group is distinct from the other along the river valleys; the allochthonous minerals are found only where till is being fluvialiy eroded; the autochthonous dominate in valley reaches devoid of till. Given this spatial arrangement, it is proposed that the distribution of allochthonous minerals now hosted by alluvial sediments reflects the pattern of glacial depositional processes within the mountains, in particular a directionally specific distance decay in the carryover of minerals from the limestone piedmont into Slieve Bloom.

Submerged ice marginal forms in the Celtic sea off Waterford Harbour, Ireland

Abstract This paper presents the results of acoustic surveys and video imaging of the seabed off Waterford Harbour, beyond a previously identified submerged palaeochannel. This system extends south‐west into waters at c. ‐56 m OD and terminates in an area of possible glacigenic sediments. The aim of the new surveys was to obtain multibeam sonar imagery and to correlate it with seismic profiles in order to understand the genetic relationships between the morpho‐sedimentological elements of the seabed in this area. The multibeam sonar imagery revealed four arcuate, morphologically complex features that on‐lap the regional bedrock and confine the previously identified palaeochannel. Both the morphology of these forms and their sedimentology, as revealed by video imaging, imply formation in an ice‐marginal environment. These forms are hypothesised to reflect several stages of sedimentation at the margins of ice progressively retreating from the nearshore shelf of the Celtic Sea during the Last Glacial Maximum.

The Fluvial Concentration of Heavy Minerals in the Slieve Bloom Mountains, Central Ireland

The detrital mineralogies of both alluvial sediments and their glacigenic and bedrock sedimentary sources undergoing fluvial entrainment in the mountains are outlined. Relationships between patterns of heavy mineral concentration in the alluvial sediments and the controlling factors of source material distribution and provenance, the hydrodynamics of heavy minerals, the spatial variability in process environments of concentration and the interaction of these factors are deduced and the spatial distributions of correlated heavy mineral assemblages and concentrations are explained. Thus, a better understanding is gained of the processes and process interactions responsible for alluvial heavy mineral concentration in paraglacial environments.

A background to Mars exploration and research

Abstract Mars is the fourth planet in our Solar System and orbits roughly 230×106 km from the Sun. It has an orbital period of 687 Earth days and a solar day that is approximately 40 min longer than an Earth day. Mars is less dense and has half the radius of the Earth, and so has about one-tenth the mass; hence, the surface gravity of Mars is about four-tenths that of the Earth. Mars has no oceans and its surface area is therefore almost as large as that of Earths continents. In this chapter, we present a summary of the Martian environment, global geography and geology, and provide some background on the missions and instruments that have played a role in developing our current understanding. Our aim is to provide a broad overview for those unfamiliar with Mars, rather than providing an exhaustive summary of every aspect of the planets evolution.