Further Evidence for a Middle Würm Interstadial and a Main Würm Glaciation of South-west Wales

John, Brian

doi:10.1017/s0016756800050287

Cited by 12 publications

(4 citation statements)

References 11 publications

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“…(), Jensen & Vorren (), Jessen et al . (), John (, ), John & Ellis‐Gruffydd (), Johnsen et al . (, ), Jones & Keigwin (), Jones (, ), Jones & Gaunt (), Jones & Keen (), Jungner (), Jungner & Sonninen (, ), Junttila et al .…”

Section: References For Dated‐1 Databaseunclassified

The last Eurasian ice sheets – a chronological database and time‐slice reconstruction, DATED‐1

Hughes

Gyllencreutz

Lohne

et al. 2015

Boreas

859

888

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We present a new time-slice reconstruction of the Eurasian ice sheets (British-Irish, Svalbard-Barents-Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10 ka, and at four selected time periods back to 40 ka. The time-slice maps of ice-sheet extent are based on a new Geographical Information System (GIS) database, where we have collected published numerical dates constraining the timing of ice-sheet advance and retreat, and additionally geomorphological and geological evidence contained within the existing literature. We integrate all uncertainty estimates into three ice-margin lines for each time-slice; a most-credible line, derived from our assessment of all available evidence, with bounding maximum and minimum limits allowed by existing data. This approach was motivated by the demands of glaciological, isostatic and climate modelling and to clearly display limitations in knowledge. The timing of advance and retreat were both remarkably spatially variable across the ice-sheet area. According to our compilation the westernmost limit along the British-Irish and Norwegian continental shelf was reached up to 7000 years earlier (at c. 27-26 ka) than the eastern limit on the Russian Plain (at c. 20-19 ka). The Eurasian ice sheet complex as a whole attained its maximum extent (5.5 Mkm 2 ) and volume (~24 m Sea Level Equivalent) at c. 21 ka. Our continentalscale approach highlights instances of conflicting evidence and gaps in the ice-sheet chronology where uncertainties remain large and should be a focus for future research. Largest uncertainties coincide with locations presently below sea level and where contradicting evidence exists. This first version of the database and time-slices (DATED-1) has a census date of 1 January 2013 and both are available to download via the Bjerknes Climate Data Centre and PANGAEA (www.bcdc.no;

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Section: References For Dated‐1 Databaseunclassified

The last Eurasian ice sheets – a chronological database and time‐slice reconstruction, DATED‐1

Hughes

Gyllencreutz

Lohne

et al. 2015

Boreas

859

888

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“…12.1). The glaciations of Pembrokeshire have been described by John (1965;1967;1968;1970a;1970b;1984). The earliest glacial episode may be represented by erratics within early raised beach deposits or 'lower head' (PAnglian) (John 1970a;1970b;Bowen 1982).…”

Section: The Role Of Glaciation In the Transport Of Stonehenge Bluestmentioning

confidence: 99%

The Geological Sources and Transport of the Bluestones of Stonehenge, Wiltshire, UK

Thorpe

Williams-Thorpe

Jenkins

et al. 1991

Proc. Prehist. Soc.

106

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Stonehenge on Salisbury Plain is one of the most impressive British prehistoric(c.3000–1500 BC) monuments. It is dominated by large upright sarsen stones, some of which are joined by lintels. While these stones are of relatively local derivation, some of the stone settings, termed bluestones, are composed of igneous and minor sedimentary rocks which are foreign to the solid geology of Salisbury Plain and must have been transported to their present location. Following the proposal of an origin in south-west Wales, debate has focused on hypotheses of natural transport by glacial processes, or transport by human agency. This paper reports the results of a programme of sampling and chemical analysis of Stonehenge bluestones and proposed source outcrops in Wales.Analysis by X-ray-fluorescence of fifteen monolith samples and twenty-two excavated fragments from Stonehenge indicate that the dolerites originated at three sources in a small area in the eastern Preseli Hills, and that the rhyolite monoliths derive from four sources including northern Preseli and other (unidentified) locations in Pembrokeshire, perhaps on the north Pembrokeshire coast. Rhyolite fragments derive from four outcrops (including only one of the monolith sources) over a distance of at least 10 km within Preseli. The Altar Stone and a sandstone fragment (excavated at Stonehenge) are from two sources within the Palaeozoic of south-west Wales. This variety of source suggests that the monoliths were taken from a glacially-mixed deposit, not carefully selected from anin situsource. We then consider whether prehistoric man collected the bluestones from such a deposit in south Wales or whether glacial action could have transported bluestone boulders onto Salisbury Plain. Glacial erratics deposited in south Dyfed (dolerites chemically identical to Stonehenge dolerite monoliths), near Cardiff, on Flatholm and near Bristol indicate glacial action at least as far as the Avon area. There is an apparent absence of erratics east of here, with the possible exception of the Boles Barrow boulder, which may predate the Stonehenge bluestones by as much as 1000 years, and which derived from the same Preseli source as two of the Stonehenge monoliths. However, 18th-century geological accounts describe intensive agricultural clearance of glacial boulders, including igneous rocks, on Salisbury Plain, and contemporary practice was of burial of such boulders in pits. Such erratics could have been transported as ‘free boulders’ from ‘nunataks’ on the top of an extensive, perhaps Anglian or earlier, glacier some 400,000 years ago or more, leaving no trace of fine glacial material in present river gravels. Erratics may be deposited at the margins of ice-sheets in small groups at irregular intervals and with gaps of several kilometres between individual boulders.‘Bluestone’ fragments are frequently reported on and near Salisbury Plain in archaeological literature, and include a wide range of rock types from monuments of widely differing types and dates, and pieces not directly associated with archaeological structures. Examination of prehistoric stone monuments in south Wales shows no preference for bluestones in this area. The monoliths at Stonehenge include some structurally poor rock types, now completely eroded above ground. We conclude that the builders of the bluestone structures at Stonehenge utilized a heterogeneous deposit of glacial boulders readily available on Salisbury Plain. Remaining erratics are now seen as small fragments sometimes incorporated in a variety of archaeological sites, while others were destroyed and removed in the 18th century. The bluestones were transported to Salisbury Plain from varied sources in south Wales by a glacier rather than human activity.

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“…The youngest marine shell dates of 30000-29000 a b.p . from the younger Irish Sea till on the west coast of Wales (John 1967), and the presence of organic beds dated 30655 and 36340 a b .p . in fluvial sediments beneath the term inal zone of the same till sequence in Staffordshire (Shotton 1967), give a maximal date for the glacial advance.…”

Section: S E a Level During The Maximum Of The Last Glaciationmentioning

confidence: 99%

Records of sea levels during the Late Devensian

Synge

1977

Phil. Trans. R. Soc. Lond. B

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Shorelines of both eustatic and isostatic type record sea-level changes over the last hundred thousand years. Marine cut rock platforms at roughly 25-40 m, 6-13 m, and just below mean sea level, appear to represent successive interglacials. Since the culmination of the Last Glaciation, the steady rise of sea level from below — 100 m has been punctuated by rapid eustatic surges, notably at 16000-15000, 13000-12000, shortly after 10000, and round about 9000 a B.P. Retardation of crustal recovery due to ice-loading about 15000-14000 a B.P. in Scotland parallels that which occurred in Scandinavia about 11000-10000 a B.P. In each case a localized transgression of considerable magnitude took place. The ensuing deglaciation resulted in the very rapid phases of uplift that led to the low marine levels recorded at ca. 10500 in Scotland, and ca. 8000 a B.P. in Scandinavia.

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Further Evidence for a Middle Würm Interstadial and a Main Würm Glaciation of South-west Wales

Cited by 12 publications

References 11 publications

The last Eurasian ice sheets – a chronological database and time‐slice reconstruction, DATED‐1

The last Eurasian ice sheets – a chronological database and time‐slice reconstruction, DATED‐1

The Geological Sources and Transport of the Bluestones of Stonehenge, Wiltshire, UK

Records of sea levels during the Late Devensian

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