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The last glaciation in Orkney, Scotland: glacial stratigraphy, event sequence and flow paths

Hall, Adrian M.; Riding, James B.; Brown, John F.. 2016 The last glaciation in Orkney, Scotland: glacial stratigraphy, event sequence and flow paths. Scottish Journal of Geology, 52 (2). 90-101. 10.1144/sjg2016-002

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Abstract/Summary

Three separate till units are recognized on Orkney deposited during the last ice sheet glaciation: the Digger, Scara Taing and Quendal Till members. The Digger Till records an ice advance from the south that extended on to the Atlantic shelf. The Scara Taing Till records a later period of full ice cover when ice moved from the SE out of the Moray Firth and reached Last Glacial Maximum (LGM) limits on the shelf edge. The Quendal Till records a late phase of ice sheet flow from the SE to limits c. 20 km west of Orkney. No till unit or flow set has been identified to confirm the presence of a local ice cap on southern Orkney during the last glaciation. Whilst the blocking presence of the Fennoscandian Ice Sheet (FIS) and the Shetland Ice Cap may have contributed to the deflection of ice flow over Orkney, similar flow patterns also occurred before and after the LGM. Scandinavian erratics on northern Orkney are probably reworked and provide no direct support for the passage of the FIS. Middle to Late Carboniferous palynomorphs found in tills in eastern Orkney may have been reworked from nearby Permian mudstones. Orkney carries the distinctive ‘shelly boulder clay’, a mud-rich till including far-travelled erratics and abraded Pleistocene marine shell fragments (Peach & Horne 1880). The shelly boulder clay has been long interpreted as a single stratigraphic unit deposited in the last glaciation (Peach & Horne 1880). Yet detailed lithological data exist for multiple till sequences (Rae 1976) and three separate till units have been identified on Rousay (Hall 1996b), implying a greater complexity in the lithostratigraphic record on Orkney that is comparable to that in Caithness (Hall & Riding 2016) and Buchan (Merritt et al. in press). This paper assembles a Late Pleistocene stratigraphic framework for Orkney and derives from it a new event stratigraphy. Till units are linked to indicator erratics derived from Scotland and Scandinavia and to palynomorph assemblages derived from erosion of mud rocks in the Moray Firth basin. These far-travelled components provide important evidence of changing ice flow patterns on Orkney through the last glaciation and point to switching ice sheet configurations in adjacent parts of the North Sea.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1144/sjg2016-002
ISSN: 0036-9276
Date made live: 23 Jan 2017 15:06 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/515994

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