The origins and fill histories of buried palaeo valley systems and overdeepened bedrock troughs in the Midland Valley of Scotland

• Main Authors: Kearsey, Tim, Lee, Jon, Finlayson, Andrew, Lee, Kathryn, Lawley, Russell
• Format: Text
• Language: English
• Published: 2017
• Subjects: Glaciology; Midland; Ice Sheet
• Online Access: http://nora.nerc.ac.uk/id/eprint/518902/; https://nora.nerc.ac.uk/id/eprint/518902/1/bsrg-programme-book.pdf; https://conferences.ncl.ac.uk/bsrg2017/

‘Buried’ palaeo valley systems have been identified widely beneath lowland parts of the UK and the North Sea. Their concealed occurrence can have significant implications for groundwater, hydrocarbon and geothermal resources. Equally the links between geometry and the sediments that infill them are poorly understood but provide important clues to their genesis and applied properties. In the Midland Valley of Scotland ‘buried valleys’ of over 100 m depth have been recorded yet have typically only been studied in isolation. Utilising a digital dataset of over 100,000 boreholes which penetrates the full thickness of Quaternary deposits in the Midland Valley of Scotland, 18 buried palaeo valleys where identified, ranging from 5-36 km in length and 24-162 m in depth. Geometric analysis has revealed four distinct valley morphologies, some of which appear to cross cut each other with the deepest features aligning east-west. These east-west features align with the ice flow during the Late Devensian glaciation (c. 30-17 ka). The shallower features, appear more aligned to ice flow direction during ice sheet retreat, and were therefore probably incised under more restricted ice-sheet configurations. Analysis of the fills shows they also vary greatly. The shallower restricted ice sheet features are filled with between 52-82% diamicton. However, the large, east-west features have more heterogeneous fills, which are either dominated by clay (29-44%) or sand (6-22%). The presence of localised sand and gravels that pre-date the advance of the Main Late Devensian ice sheet confirms that the east-west features have been active over several glaciations, and that the fill may not be linked to the processes that cut the valley. All the features that sit below the Holocene marine incursion limits have more heterolithic fills than those above it suggesting that they existed as valleys after ice retreat with remaining accommodation space infilled during a final stage of marine inundation.