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Esri, DeLorm e, GEBCO , NO AA NGDC, and other contributors
Generalised ice sheet flow lines and m oraines indicating direction of ice flow. Flow lines are interpreted from the configuration ofsubglacial bedform s, e.g. drum lins, ribbed m oraines and eskers, and proglacial term inal m oraines. O ff shore flow lines towards the edge of the ice sheet are interpreted as reflecting the m ax im um ex tent of the last (W eichselian) ice sheet. Flow lines on shore probably relate to later stages of glaciation as the ice sheet shrank and divided into sm aller individual ice m asses.
Derived from Benetti et al. (2010), Cofaigh et al. (2012) and Finlayson et al. (2014).1:2,500,000 scale
Ex tent of the Irish Ice Sheet duringthe last Glacial m ax im um (c. 27 - 23 ka BP )
An tA
igéan
Atlanta
ch
Flow lines and m oraines are m apped from O SI and O SNI digital terrain models and INFO MAR bathym etry.
T he Q uaternary Geology of Ireland
ATLA
NTIC
OCE
AN
T he Q uaternary P eriod is the m ost recent period in the geologic tim e scale of the International Com m ission on Stratigraphy. T his period, coveringthe last 2.6 m illion years, is subdivided into two epochs: P leistocene (2.6 m illion to 10,000 years before present (BP )) and the H olocene (10,000 years BP to the present). lreland was affected by a num ber of glaciations during the P leistocene. T he m ost recent glaciation,stretching from 115,000 years ago to the H olocene, gave rise to m ost of the Q uaternary sedim ents we see today. T he erosive power of the last
Benetti, S., Dunlop, P. and Cofaigh, C.Ó., 2010. Glacial and glacially-related features on the continental m argin of northwest Ireland m apped
Digital m ap com piled in ArcGIS 10.3, designed by the Cartography U nit and published under authority of the Director, Koen V erbruggen, Geological Survey Ireland, 2017.
Scale: 1:500,000
Q uaternary Geological Map of Ireland
This publication contains m aterial that is based upon Crown Copyright and is reproduced with the perm ission of Land and P roperty Services under Delegated Authority from the Controller of her Majesty's Stationery O ffice, © Crown Copyright and database right 2017. Custom er ID 4104. P erm it num ber 100132.
Includes O rdnance Survey of Ireland data reproduced under O SI Licence num ber EN 0047210.Mapping © O rdnance Survey Ireland/Governm ent of Ireland.
Derived from the Geological Survey Ireland Q uaternary Sedim ents and Geomorpholgy Map, the Geological Survey of Northern Ireland 1:250,000 Q uaternary Map of Northern Ireland,
Coxon and McCarron (2009), Greenwood (2008), Greenwood and Clark (2009).
For data sources see Geological Survey Ireland Q uaternary Sedim ents and Geom orphology Mapand GSNI 1:250,000 Q uaternary Map of Northern Ireland.
Q uaternary Sedim ents
P eat
Marine and estuarine deposits
Slope deposits
Marine and estuarine deposits com prise sand and gravel beach sedim ents, raisedbeaches, tidal m arsh deposits and estuarine silt and clay. T hese have beendeposited as the ice sheet retreated from the continental shelf and sea levels rose.
Alluvium
W ind blown sand
Glaciofluvial and glaciolacustrine sand and gravel are indirect glacial depositstransported to their final position by m elt-water during the ice sheet m eltdown andsorted in this process. Glaciofluvial deposits are generally represented by stratified‘sands and gravels’, the clasts are usually (sub)rounded and loosely packed.Glaciolacustrine sedim ents often include bottom set facies com posed of fine sandand silts overlain by coarser sedim ents ascribable to foreset and topset facies.
Lacustrine sedim ents
Glaciom arine sedim ents
Glaciofluvial and glaciolacustrine sand and gravel
T ill derived fromlim estones
T ill derived from sandstones and shalesT ill derived from sandstones
T ill derived fromacidic volcanic rocks
T ill derived from basic igneous rocksT ill derived from granites
T ill derived from m etam orphic rocks
T ill derived from Devonian sandstones
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Dated Deposits
Sites recording sedim ents deposited during the P liocene (>2,600 ka BP ). Ages have been largely inferred from floral and faunal assem blages within these deposits.
Geomorphology
Com piled by S. Roberson and X.M. P ellicer.
An Roinn Cum arsáide, Gníom haithe ar son na hAeráide agus Com hshaoi.Departm ent of Com m unications, Clim ate Action and Environm ent,
© Ireland, 2017.
Glaciom arine sedim ents are indirect glacial sedim ents recorded in m arine depositional environm ents including glaciodeltaic sedim ents, subaqueous fans and subm arine
Drum lins
Eskers
Moraines
Eskers are elongate, sinuous ridges com posed of glaciofluvial sands and gravels. Eskers are form ed by the infilling of ice-walled channels and record deposition in subglacial, englacial or supraglacial drainage networks. T he planform of an esker network m ay illustrate the geom etry of a subglacial drainage network duringdeglaciation. Eskers are com m on across the central lowlands and are generally 10 – 20m high and 100 – 250m wide. Individual segm ents can be up to 10 km long.
Drum lins are sm ooth, oval-shaped hills com posed of glacial sedim ents, typically with a long ax is aligned with ice flow direction. Drum lins are very well preserved in the northern sector of Ireland. Ice directions associated with drum lin orientation are indicative of a num ber of ice sheets interacting in the region during the last glacial period. For cartographic reasons this m ap displays only c.10% of the60,000 m apped drum lins in Ireland.
Last Glacial
Last Interglacial
Middle P leistocene
P re - P leistocene
Moraine ridges dem arcate the m ax im um ex tent of form er ice sheets. H ere a com plex interaction of glacigenic and paraglacial processes have com bined to form a ridge of sedim ent. Moraines are particularly well ex pressed and well researched in mountain regions in Ireland, e.g. W icklow and Kerry.
P re-Q uaternary bedrock
Slope deposits consist of an assem blage of rock fragm ents, blocks and sedim ent atthe base of steep slopes and cliffs in the form of sheets or cones. T hese are createdby large scale slope m ovem ents, continuous rock fall, peat slides, debris flows orperiglacial processes. V ery large slope failures took place im m ediately following theretreat of the last ice sheet, as the Earth's crust rebounded. Sm aller scale slopedeposits are still being form ed today.
Alluvium is a post-glacial deposit along river valleys consisting of generally bedded gravel, sand, silt or clay in a variety of com binations, often with a high percentage of organic carbon (10 – 30%). Alluvium is m apped on modern day river floodplains orH olocene river terraces.
Sites dated recording sedim ents deposited during the last glacial period: between the Kilfenora Interstadial at Marine Isotope Stage (MIS) 5d/c (120 – 115 ka BP ) and the Nahanagan Stadial at isotope stage 2 (c.12.9 - 11.7 ka BP ). Sites recording sedim ents deposited during MIS 5e (132 – 120 ka BP ) are rare in Ireland because of subsequent ice sheet coverage. T wo key sites are Knocknacran in Co. Monaghan and the Screen H ills in Co. W ex ford. H owever, the Knocknacran datescould be interpreted as m uch later MIS 4. Sim ilarly, the age of deposits at the Screen H ills are contentious, because they are based on pollen assem blages, rather than anabsolute dating m ethod.Middle P leistocene sites record sedim ents deposited between MIS 11 (c. 424 – 374 ka BP ) and MIS 6 (c. 198 – 132 ka BP ). Most sites have been assigned to the Gortian interstadial (equivalent to the H olsteinian) on the basis of pollen assem blages, but it rem ains unclear whether this stage is equivalent to MIS 9 or MIS 11.
W ind-blown sand is deposited following ice sheet retreat. T hese deposits are com posed of well sorted m edium to fine sands and are found along coastal areas in the form of sanddunes or sand sheets.
Lacustrine sedim ents were deposited during deglaciation or post-glacially in depressions left behind by the ice during retreat. T hese sedim ents are generally com posed of sand, siltand clay and are com monly overlain by peat bogs infilling form er lakes.
P eat is a post-glacial deposit, consisting m ostly of partially decom posed vegetation.T he peat m ay be deposited as blanket bog accum ulating in elevated areas withex cessive rainfall or as raised bogs or fens on lower ground. Much of Ireland’s peat has been cut away for burning as solid fuel or has been ox idized as the resultof agricultural drainage schem es.
Ireland has a very rich legacy of glacial deposits and landform s. Glacial landform s, associated with the direct action or m elting of ice, include ice-sculpted bedrock from glacial erosion and ice-moulded glacial deposits ex pressed as drum lins, moraines and eskers. Mapping the shape and the spatial distribution of these landform s aided the reconstruction of the glacial history of Ireland. More than 85% of the Irish land surface is covered by sedim ents of Q uaternary age. P ostglacial sedim ents, covering a fifth of the land surface, were mostly deposited during the H olocene and include lacustrine and alluvial plains, peat bogs and coastal landform s.
ice sheet rem oved m uch of the evidence for earlier glaciations. T he H olocene, in Ireland, is the post-glacial period.
Marine Isotope stages of the last 500,000 years
O x ygen isotope data are derived from deep sea core sam ples and help estim ating the clim ate of the past. Marine ox ygen isotope stages show alternating warm (odd num bers) and cool (even num bers) periods in Earth's paleo-clim ate.
table for the last 2.7 m illion.
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NahanaganStadial
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GortianInterstadial
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W eichselianGlaciation
SaalianGlaciation
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Adm inistration (NO AA), and National Geographic, DeLorm e, H ERE, Geonam es.org, and Esri, and various other contributors.General Bathym etric Chart of the O ceans GEBCO _08 Grid, National O ceanic and Atmospheric Adm inistrationAcknowledgement :
Modified from the International Com m ission of Stratigraphy Global chronostratigraphical
Scale 1:500,000
Geological Survey Ireland, © 2017.30 0 30 60 90
Kilom eters
Making the m ap: T his All-Ireland Q uaternary geology m ap at 1:500,000 scale is an am algam ation of Q uaternary m aps from Ireland and Northern Ireland. Soil geochem istry and radiom etrics data from the T ellus and T ellus Border projects were used to subdivide undifferentiated till deposits in Northern Ireland to m atch the till types m apped in Ireland. Soil A-horizon geochem istry data from the two surveys were levelled and m erged using population distribution pairing. T hese data were divided into spatial clusters using principal com ponent analysis of log-ratio values and k-m eans cluster analysis of the resultant principal com ponent scores. T he radiom etric data were viewed as a ternary m ap of the ratio of radionuclides potassium , thorium and uranium , from which, areas of different till lithology could be readily identified. Data from the Geological Survey of Ireland (Geological Survey Ireland, 2016), the Geological Survey of Northern Ireland and the relevant literature (Greenwood, 2008; Cox on and McCarron, 2009; Greenwood and Clark, 2009; Benetti et al., 2010; Cofaigh et al., 2012; Finlayson et al., 2014) were com piled, hom ogenized and sim plified to produce a seam less data set com prising six teen sedim ent types, four geom orphological features and the location of key sites with Q uaternary and pre-Q uaternary dated sedim ents.
avalanche deposits.
O ffshore m orainesIce sheet flow lines
T ills are tightly packed, unsorted, unbedded, glacial deposits possessing m any different particle sizes with com monly sharp, angular to sub-angular clasts. T ill form s beneath a glacier as it erodes the bedrock or pre-ex isting sedim ent that it is flowing over. Glacial ice is the principal depositional agent, but gravity and, in som e cases, water, also plays a part. In Ireland, till lithology can often be related to the type of bedrock directly beneathit (e.g. Dem pster et al., 2013). T ills presented in this m ap are categorised according to their dom inant lithology. T ill lithology is im portant, as it greatly influences the physical properties of the till, e.g. shear strength, porosity and cohesion. T he transport and deposition of tills by the movem ent of an ice sheet m eans that in som e cases, tills of a specific lithology becom es ‘sm eared’ across a lithological boundary. T hese ‘sm ears’ of till m ay be up to 10 km in length and can be recognized using field observations, m aps of soil geochem istry and radiom etric data. T he action of ice sheets deposits till in a range of landform s that can be characterised and grouped as landform associations. T hese landform associations can be used as predictive tools to reconstruct the nature and ex tent of past glacial events. T he most com mon till dom inated landform associations encountered in Ireland are: (i) ice-m arginal moraines consisting of irregular ridges indicative of the form er position of the edge of an ice sheet; (ii) drum lin and ribbed moraine topography consisting of rolling landscape com posed of high-frequency, low altitude elongated hills (drum lins) and flat-topped ridges (ribbed m oraines) - both indicators of direction of movem ent of form er ice sheets in the Northern sector of Ireland; (iii) rolling landscapes com prising rounded or elongated low altitude and low frequency hills with generally gentle slopes and; (iv) flat to gently undulating topography or till plains - com monly occurring in low lying areas of the Irish Midlands.
References:
Greenwood, S.L. and Clark, C.D., 2009. Reconstructing the last Irish Ice Sheet 1: changing flow geom etries and ice flow dynam ics deciphered from the glacial landform record. Q uaternary Science Reviews, 28, 3085-3100.
Finlayson, A., Fabel, D., Bradwell, T. and Sugden, D. , 2014. Growth and decay of a m arine term inating sector of the last British–Irish Ice Sheet: a geomorphological reconstruction. Q uaternary Science Reviews, 83, 28-45.
Greenwood, S.L., 2008. A palaeo-glaciological reconstruction of the last Irish Ice Sheet. U npublished P hD T hesis, Departm ent of Geography, U niversity of Sheffield. pp. 360.
Coxon, P. and McCarron, S.G., 2009. Cenozoic: T ertiary and Q uaternary (until 11,700 years before 2000). In Geology of Ireland, H olland, C.H . and Sanders, I.S. (Eds Dunedin Academ ic P ress, Edinburgh, pp.356-396).
Geological Survey Ireland (2016). Q uaternary Sedim ents and Geom orphology digital m ap of Ireland. Dublin. https://www.gsi.ie/Mapping.htm.
Northern Ireland. Journal of Maps, 9, 373-389.Dem pster, M., Dunlop, P., Scheib, A., and Cooper, M., 2013. P rincipal com ponent analysis of the geochem istry of soil developed on till in
Q uaternary Science Reviews, 44, 160-179. Cofaigh, C.Ó., T elfer, M.W ., Bailey, R.M. and Evans, D.J., 2012. Late P leistocene chronostratigraphy and ice sheet lim its, southern Ireland. from geophysical data. Journal of Maps, 6, 14-29.
