GCR block - Quaternary of Wales (QA-WL)

Quaternary of Wales

Block Description

UK map showing distribution of GCR sites of GCR block QA-WL
Distribution of GCR sites of GCR block Quaternary of Wales

The Quaternary Period is the most recent major subdivision of the geological record, spanning the late Cainozoic Era. Traditionally, it is divided into two intervals of epoch status – the Pleistocene and Holocene. The Holocene Epoch occupies only the last 10 000 years of geological time and is the warm interval or interglacial in which we now live. Consequently, it is often regarded as part of the Pleistocene rather than a separate epoch. In a strict geological sense, the base of the Pleistocene Epoch (and therefore that of the Quaternary Period) is defined in Italy at the type locality of Vrica, where it is dated to about 1.64 Ma (million years ago); it is now well established that the current warm period, the Holocene Epoch, is simply the latest interglacial in a long series of profound climatic fluctuations that have characterized the last 2.4 Ma.

The deep-sea sedimentary record shows that up to 50 ‘warm’ and ‘cold’ climatic oscillations have occurred within the last 2.4 Ma. Equally, the glacial and interglacial periods cannot be characterized simply as ‘cold’ or ‘warm’, respectively; the ice ages were not unbroken in their frigidity since the exceptionally cold phases (stadials) were punctuated by warmer periods (interstadials), in some cases lasting for several thousand years. The fundamental characteristic of the Quaternary Period is therefore one of change through time and space in geomorphological processes, floras, faunas and environmental conditions, all modulated by the changing climate. The record of such changes is preserved in a variety of landforms, sediment sequences and organic remains.

The abrupt onset of the late Cainozoic ice ages is, as yet, unexplained. However, the succession of ice ages (glacials) and interglacials has occurred at known frequencies, and changes in insolation (the receipt of solar radiation at the Earth’s surface and throughout its atmosphere) associated with the Earth’s orbital rhythms are now established as the principal external driving forces of the Earth’s climatic system.

Subdividing the Quaternary Period

The oxygen isotope chemistry of the deep-sea sediment pile now provides the main basis for subdividing the Quaternary swedimentary record, with a number of successive oxygen isotope stages recognized globally. These stages, running counter to normal geological practice, are numbered backwards in time and down through the geological column. Warm periods with correspondingly low volumes of ice are given odd numbers; the present interglacial, the Holocene, is numbered as Stage 1. Times of high ice volume (glacials) are given even numbers; the last main cold phase in Britain, the Late Devensian, being numbered as Stage 2. Stages are also divided into sub-stages, for example, Stage 5 into sub-stages 5a–5e, often reflecting stadial or interstadial events.

The position in the deep-sea sediment cores of a major reversal in the Earth’s magnetic field, the Matuyama–Brunhes Reversal at 780 ka, provides a yardstick with which to calibrate the oxygen isotope record. The boundaries of the different isotope stages have also been adjusted and refined with respect to known orbital patterns

British Quaternary environments

In Britain, the area covered by ice varied considerably during different glaciations. During the last (Late Devensian) glaciation, ice extended as far south as the north Midlands, impinging on the north coast of East Anglia and covering most of South Wales. During earlier glaciations ice sheets were more extensive, but probably never reached farther south in south-central and south-east England than the present Thames Valley. In the South-West, there is a longstanding debate over whether pre-Devensian ice masses reached the northern shores of Devon and Cornwall and even the Isles of Scilly.

The major shifts of climate that characterize the Quaternary Period were accompanied by equally profound changes in environmental conditions that left a strong imprint on the landforms, fossils and sediments of Britain. During the cold or glacial stages, substantial areas were subjected to the effects of glacial erosion and deposition and a wide range of landforms and deposits was produced.

As ice sheets melted, vast quantities of meltwater were liberated, giving rise to characteristic suites of landforms and deposits.

Repeated climate change also subjected the flora and fauna of Britain to stress: fundamental changes in the distribution of plants and animals took place. Beyond the margins of the ice sheets and during the cold climatic phases of the Quaternary Period, periglacial conditions prevailed. Such environments were characterized by frost-assisted processes and by a range of frost- and ground ice-generated landforms and deposits. Mass wasting (downslope movement of soil on both large and small scales) and increased wind action were prevalent, also producing a range of characteristic features. In the fossil record, the flora and fauna of these cold periods is, not surprisingly, restricted in diversity and dominated by cold-tolerant species; large areas were dominated by tundra vegetation.

Conversely, the warmer or interglacial periods of the Quaternary are characterized by the absence of glacial, periglacial and glaciofluvial features, and there were times when chemical weathering, soil formation and the accumulation of organic sediments took place. Variations in the quantity and type of pollen grains preserved in organic deposits, such as peats and lake muds, have been used to define systems of pollen zones or pollen biozones. These zones are characterized by particular vegetational assemblages which can be used to chart sequences of vegetational, climatic and environmental change. Traditionally, these have been used as the principal basis for distinguishing between various interglacial phases in the land-based Quaternary record and for the definition of chronostratigraphic stages. Unfortunately, although several distinctive interglacial episodes in the British Pleistocene can be distinguished, very little evolution of the flora actually occurred, thus hindering biostratigraphic correlation. However, interglacial periods can be differentiated broadly on the basis of pollen assemblage zone biostratigraphy, with individual parts of interglacial cycles (sub-stages) being recognized; for example, pre-temperate, early temperate, late temperate and post-temperate sub-stages. Interglacial environments in the British Isles were generally characterized by a climax vegetation of mixed deciduous oak forest. The last time Britain experienced conditions similar to today was about 125 ka, when the interglacial (part of the Ipswichian Stage) lasted about 10 ka.

Unlike the flora, some elements of the Quaternary fauna have evolved. Therefore, certain glacial and interglacial periods can be characterized broadly by distinctive fossil assemblages, particularly those of large mammals. During the last interglacial, for example, creatures such as the hippopotamus, lion and elephant were indigenous to Britain. Likewise, fossils of both terrestrial and marine molluscs and Coleoptera (beetles) can be sensitive indicators of changing climatic conditions by analogy with their present-day environmental tolerances and geographical ranges.

The succession of glacials and interglacials and the growth and decay of ice sheets have been accompanied by equally profound changes in the coastal zone. World sea level has varied in time with the amount of water locked up in the ice sheets, and during glacial stages, world or eustatic sea levels have been lowered. The converse is true during warmer interglacial phases. The level of the land has also varied, sinking under the weight of advancing ice sheets and rising up or rebounding when they melted (isostasy). This complex interplay of changing land and sea levels has left a widespread legacy in Britain, manifested by the many beaches, shore platforms and marine sediments which now lie above the present sea level. Equally, a range of submerged shoreline features, drowned forests and valleys provide important evidence for sea levels which were relatively lower in the past.

Significant changes in the courses of rivers and their channel patterns have also occurred in the Quaternary Period. These are related to changes in discharge, sediment supply and sea level. Some rivers have reworked and built up large quantities of glacially derived sediments along their floodplains. Subsequent down-cutting has sometimes resulted in ‘staircases’ of terraces both in rock and superficial materials. In some valleys, terraces have been traced for considerable distances and been assigned specific names and ages with respect to their contained fossils and stratigraphical position; in many cases they can be ascribed with some certainty to particular interglacial or glacial phases or, more recently, to the oxygen isotope timescale.

Wales in the Quaternary Period

Because of its maritime position adjacent to the warm North Atlantic, it is probable that ice in Wales grew rapidly in response to orbital changes that cooled the land. A conventional text-book view would be that, initially, ice thickened in upland hollows enlarging them into cirques. The ice flowed out from these into valleys, overdeepening and oversteepening their slopes as it moved. Converging valley glaciers coalesced on lowlands where they formed piedmont lobes which eventually grew in size to form an ice-sheet. An alternative theory proposed that ice developed, more or less everywhere, across the landscape (instantaneous glacierisation), especially on upland plateaux that were partially surrounded by higher ground. For example, it is clear that the thickest ice mass in Wales lay on plateau areas the Rhinog and the Arenig Mountains, and that it far exceeded ice thicknesses farther north in Snowdonia. Another theory proposed that marine based ice-sheets grew on shallow water continental shelf areas, such as the Irish Sea.

Glacial erosion

Glacial erosion was not uniform. The distribution of (i) cirques (corries) (ii) troughs (U-shaped valleys) and rock basins, and (iii) streamlines forms such as ridge tops or roches moutonees shows that glacial erosion was most intense in north-west Wales.

Glacial deposition

The products of glacial erosion were transported, then deposited by a variety of means. Till (boulder clay) was deposited beneath ice as lodgement til, from within the ice as englacial till (melt-out till), and from the surface ofthe ice as it melted as supra-glacial and flow till.

Fluvioglacial deposition and erosion

During deglaciation (ice wastage) the ice margins ‘retreat’, stages in this retreat are marked by the end-moraines of the South Wales valleys, the Wye Valley, at Tregaron in the Teifi Vallet and in the upper Clwyd. Glacier thinning led to the detachment of masses of stagnant ice: for example, in the Alun and Wheeler Valleys of Clwyd, where eskers and kettle holes developed.

An impressive number of glacial meltwater channels occur in Wales. The majority appear to have been fashioned by subglacial stream erosion (that is erosion below the ice). The pattern of some, such as the Fishguard Channels, allows the course of deglaciation to be reconstructed: initially, glacial drainage in Preseli was directed southwards and south-westwards, but with ice-retreat in Cardigan Bay, the drainage was able to flow to the north.

GCR site selection

This GCR Block encompasses sites that merit conservation because of their significance to the geomorphological evolution and Quaternary history of Wales. Sites important for coastal and fluvial geomorphology, in the sense of modern landforms and processes, and large-scale mass-movement features are encompassed by other GCR Blocks.

The landscape of Britain displays a rich diversity of Quaternary features and evidence of environmental change, often with distinct regional associations, related for example to a combination of geology, evolution of river systems, mountain glaciation or patterns of sea-level change.

A prime aim of site selection was to reflect this diversity and to select networks of sites representing the major regional variations in landscape evolution and the history of environmental change during the Quaternary Period in Britain; hence the regional approach adopted for site selection.

Within the general regional framework, the approach adopted was to identify networks of sites that represent the main landscape features, distinctive aspects of Quaternary history and the principal research themes. Such features and themes were recognized at two levels: (a) those relating to the specific characteristics of the area in question; and (b) those relating to national interests or distributions (e.g. pollen biostratigraphy and sea-level changes during the Holocene) for which regional representative sites were required. It should be noted that this categorization relates to the occurrence of the interests and does not imply differences in the importance of sites in the different categories. Thus sites selected for a regionally occurring interest are nevertheless of national importance.

GCR site selection encapsulates the Pleistocene evolution of Wales. They include some unique evidence for the timing of glacier advances and retreats, major changes in sea-level, and movements of the Earth’s crust. These sites are important in a wider context, because Wales lies on the margin of the North Atlantic Ocean, where climatic change is translated, through the dynamic coupling of atmosphere, oceans and biosphere, into rapid environmental changes. These changes have been exceptionally rapid by comparison with the geological timescale, and their implications are potentially relevant to society. Thus, the Quaternary history of Wales assumes a disproportionate importance in the wider context of research in our hemisphere into why and how environments change through time.

For Wales, the site networks considered are those representing:

• Quaternary litho and biostratigraphy: Gower

• Quaternary litho- and biostratigraphy: west and south-west Wales

• Quaternary litho- and biostratigraphy: north-west Wales

• Quaternary of South Wales: erosion, deposition and fluvioglacial features

• Quaternary of Mid Wales: erosion, deposition and fluvioglacial features

• Quaternary of North Wales: erosion, deposition and fluvioglacial features.

Volume Introduction

Quaternary of Wales

Site List

Your selection found 73 GCR sites. Sites are sorted alphabetically by country, local authority and then by site name -
CodeNameCountryLocal AuthorityGrid RefGCR Site Account
1860Cwm NashWalesCARDIFF AND VALE OF GLAMORGANSS905701Not available
2292Cwm NashWalesCARDIFF AND VALE OF GLAMORGANSS905701Not available
1826Cadair IdrisWalesCONWY AND DENBIGHSHIRESH730620Not available
1369Cefn and Galltfaenan CavesWalesCONWY AND DENBIGHSHIRESJ021705Not available
1926Cors GeualltWalesCONWY AND DENBIGHSHIRESH734584Not available
1371Pontnewydd CaveWalesCONWY AND DENBIGHSHIRESJ015710Not available
1372Tremeirchion Caves (Cae Gwyn, Ffynnon Beuno)WalesCONWY AND DENBIGHSHIRESJ085724Not available
1825Y GlyderauWalesCONWY AND DENBIGHSHIRESH650600Not available
2285CaerwysWalesFLINTSHIRE AND WREXHAMSJ129719Not available
2262Ddol UchafWalesFLINTSHIRE AND WREXHAMSJ142714Not available
2293Singret QuarryWalesFLINTSHIRE AND WREXHAMSJ354561Not available
1473Vicarage MossWalesFLINTSHIRE AND WREXHAMSJ360540Not available
1924ClogwynygarregWalesGWYNEDDSH560538Not available
1361Cwm DwythwchWalesGWYNEDDSH570580Not available
1470Dinas DinlleWalesGWYNEDDSH437562Not available
1362GlanllynnauWalesGWYNEDDSH459373Not available
1354Gwydir BayWalesGWYNEDDSH389479Not available
1356Llyn GwernanWalesGWYNEDDSH702158Not available
1360Llyn PerisWalesGWYNEDDSH593593Not available
1359Moel TryfanWalesGWYNEDDSH518561Not available
1358Moelwyn MawrWalesGWYNEDDSH660450Not available
1467MoranneddWalesGWYNEDDSH507381Not available
1472Porth CeiriadWalesGWYNEDDSH315249Not available
1468Porth NeigwlWalesGWYNEDDSH287258Not available
1469Porth OerWalesGWYNEDDSH167300Not available
1466Rhinog FawrWalesGWYNEDDSH645285Not available
1827Snowdon (Yr Wyddfa)WalesGWYNEDDSH630550Not available
2099Y CarneddauWalesGWYNEDDSH680650Not available
1355Y LlethrWalesGWYNEDDSH659261Not available
1476Hen BorthWalesISLE OF ANGLESEYSH321931Not available
1357LleiniogWalesISLE OF ANGLESEYSH619787Not available
1474Red Wharf BayWalesISLE OF ANGLESEYSH532820Not available
1828Llanfihangel–CrucorneyWalesMONMOUTHSHIRE AND NEWPORTSO315203Not available
1920Cors y LlynWalesPOWYSSO016553Not available
1363Craig Cerrig-gleisiadWalesPOWYSSN964223Not available
1364Cwm LlwchWalesPOWYSSO005220Not available
1925Elan Valley BogWalesPOWYSSN857756Not available
1471Traeth MawrWalesPOWYSSN968257Not available
1460AbermawrWalesSOUTH WEST WALESSM883346Not available
1927Banc-y-WarrenWalesSOUTH WEST WALESSN204475Not available
1922ClarachWalesSOUTH WEST WALESSN588838Not available
1462Cledlyn ValleyWalesSOUTH WEST WALESSN473482Not available
1918Cwm yr Eglwys (Dinas) and Esgyrn BottomWalesSOUTH WEST WALESSN010399Not available
1465Cwm Ystwyth (Cwm-du and Cwm Tinwen)WalesSOUTH WEST WALESSN811742Not available
1477Druidston HavenWalesSOUTH WEST WALESSM862172Not available
2027Hoyle's Mouth and Little Hoyle CavesWalesSOUTH WEST WALESSS112999Not available
1353Llan-nonWalesSOUTH WEST WALESSN509673Not available
3274LlanpumsaintWalesSOUTH WEST WALESSN420276Not available
1861MaesypriorWalesSOUTH WEST WALESSN374203Not available
1451Marros SandsWalesSOUTH WEST WALESSN201076Not available
1464Morfa-bychanWalesSOUTH WEST WALESSN561763Not available
1862Mwnt (Traeth-y-Mwnt)WalesSOUTH WEST WALESSN194519Not available
2576Mynydd Du (Black Mountain)WalesSOUTH WEST WALESSN797218Not available
1919Mynydd PreseliWalesSOUTH WEST WALESSN140330Not available
1461Poppit SandsWalesSOUTH WEST WALESSN146489Not available
1459Porth ClaisWalesSOUTH WEST WALESSM741237Not available
1917TrefgarnWalesSOUTH WEST WALESSM954248Not available
1463Tregaron Bog (Cors Tregaron)WalesSOUTH WEST WALESSN690640Not available
1458West Angle BayWalesSOUTH WEST WALESSM853031Not available
1352Ynyslas and Borth BogWalesSOUTH WEST WALESSN630912Not available
1366Bacon Hole CaveWalesSWANSEASS561868Not available
1367Bosco's DenWalesSWANSEASS559868Not available
1455Broughton BayWalesSWANSEASS419930Not available
1368Cat Hole CaveWalesSWANSEASS538900Not available
1730Eastern Slade and Western SladeWalesSWANSEASS487855Not available
1829Glais MoraineWalesSWANSEASN696005Not available
1454HortonWalesSWANSEASS481855Not available
1452Hunts BayWalesSWANSEASS563869Not available
1453Langland Bay (Rotherslade)WalesSWANSEASS613871Not available
1757Long Hole CaveWalesSWANSEASS452851Not available
1365Minchin Hole CaveWalesSWANSEASS555869Not available
1457Rhosili BayWalesSWANSEASS416892Not available
1456Worm's HeadWalesSWANSEASS394874Not available
Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access. Search Again