10 Be exposure age dating of Late Quaternary relative sea level changes and deglaciation of W Jura and NE Islay, Scottish Inner Hebrides

• Published in: Earth and Environmental Science Transactions of the Royal Society of Edinburgh
• Main Authors: DAWSON, Alastair G., BISHOP, Paul, HANSOM, James, FABEL, Derek
• Other Authors: Natural Environment Research Council
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2022
• Subjects: General Earth and Planetary Sciences; General Environmental Science; Islay; Jura; Long Beach; Ice Sheet
• Online Access: http://dx.doi.org/10.1017/s175569102200010x; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S175569102200010X

ABSTRACT New 10 Be exposure age dating and geomorphological mapping of emerged shoreline features in W Jura and NE Islay throw new light on the regional pattern of ice sheet deglaciation and late-glacial relative sea level change. We conclude that the oldest and highest emerged shorelines in this area were produced ~15.7–16.3 ka, shortly after ice sheet deglaciation ~16.5 ka. It is envisaged that the first incursion of marine waters into coastal areas took place close to a former ice sheet margin that oscillated in position across this part of the Scottish Inner Hebrides. The first evidence of late-glacial marine sedimentation following deglaciation consists of emerged marine terrace fragments and unvegetated gravel beach ridges, the former represented by a prominent glacio-isostatically tilted shoreline that declines in altitude NE to SW, from ~40 m above ordnance datum (OD) in NW Jura to ~19 m OD in central Islay. In W Jura, north of Loch Tarbert, spectacular staircases of up to 55 unvegetated gravel beach ridges were formed shortly after regional deglaciation, possibly within 1 ka. A preliminary estimate of the average rate of relative sea level lowering across W Jura between deglaciation and the Younger Dryas is in the order of ~7 mmyr −1 . Geomorphological evidence from Shian Bay, W Jura, indicates a truncation of the late-glacial beach ridge staircases by a large 480-m-long beach ridge (the Colonsay Ridge) at ~14.9 ka, when former relative sea level was at ~18 m OD. This ridge may represent the product of either a stillstand in the progressive lowering of relative sea level during the late-glacial or a reversal. This raises the intriguing possibility of an association between ridge formation and the timing of the well-established global meltwater pulse 1A between ~14.65 and ~14.8 ka.