Examining the geometry, age and genesis of buried Quaternary valley systems in the Midland Valley of Scotland, UK

Abstract

Buried palaeo‐valley systems have been identified widely beneath lowland parts of the UK including eastern England, central England, south Wales and the North Sea. In the Midland Valley of Scotland palaeo‐valleys have been identified yet the age and genesis of these enigmatic features remain poorly understood. This study utilizes a digital data set of over 100 000 boreholes that penetrate the full thickness of deposits in the Midland Valley of Scotland. It identified 18 buried palaeo‐valleys, which range from 4 to 36 km in length and 24 to 162 m in depth. Geometric analysis has revealed four distinct valley morphologies, which were formed by different subglacial and subaerial processes. Some palaeo‐valleys cross‐cut each other with the deepest features aligning east–west. These east–west features align with the reconstructed ice‐flow direction under maximum conditions of the Main Late Devensian glaciation. 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. The bedrock lithology influences and enhances the position and depth of palaeo‐valleys in this lowland glacial terrain. Faults have juxtaposed Palaeozoic sedimentary and igneous rocks and the deepest palaeo‐valleys occur immediately down‐ice of knick‐points in the more resistant igneous bedrock. The features are regularly reused and the fills are dominated by glacial fluvial and glacial marine deposits. This suggests that the majority of infilling of the features happened during deglaciation and may be unrelated to the processes that cut them.

Late Pleistocene sediments, landforms and events in Scotland: a review of the terrestrial stratigraphic record

“…These palaeo-valleys all have undulating longitudinal profiles and are interpreted as tunnel valleys (cf. Kehew et al 2012) formed during the LGM (Kearsey et al 2018). The shallower features are generally aligned with ice flow during ice sheet retreat.…”

“…The Broomhill Clay, Cadder Sand and Ballieston Till are mainly located within concealed bedrock depressions, particularly a 108 m deep, 1500 m wide and 26 km long elongate depression, probably a tunnel valley (cf. Kehew et al 2012), that trends WSW-ENE beneath the floodplain of the River Kelvin (Kearsey et al 2018) (Fig. 29F).…”

“…28). The history of glaciation has been disputed (Price 1975;Menzies 1976Menzies , 1981Sutherland & Gordon 1993e;Rose & Smith 2008), but recent geomorphological, lithostratigraphical and three-dimensional mapping investigations have substantially resolved the glacial history this area (Finlayson 2012;Finlayson et al 2010Finlayson et al , 2014Kearsey et al 2018). ).…”

“…At Wilderness Pit the Sand is sheared, folded and includes seams of diamicton, possibly glacitectonite, and the overlying Wilderness Till includes tectonic slices and rafts of sand and laminated clay from underlying units (A.M. Hall unpublished). In eastern Glasgow the Wilderness Till is overlain by the Broomhouse Sand and Gravel Formation, which forms ice-contact topography including eskers, mounds, flat-topped kames and kettleholes (Browne & McMillan 1989;Rose & Smith 2008;Finlayson 2012;Kearsey et al 2018). The formation may be subdivided locally into the Ross Sand Member (deltaic sand and gravel) and the Bellshill Clay Member (glaciolacustrine laminated clay) (Browne & McMillan 1989).…”

Glacial erosion: status and outlook

“…At a larger scale, fluvial action creates tunnel valleys (tunnel channels) in both sediment and bedrock (e.g. Booth and Hallet, 1993; Kehew and others, 2012; Atkinson and others, 2013; Kearsey and others, 2018). Recent work on occurrence and causes of narrow canyons incised into the floors of glacial troughs (‘inner gorges’) in the Swiss Alps and Scandinavia also argues for vigorous and relatively extensive subglacial fluvial erosion (Dürst-Stucki and others, 2012; Jansen and others, 2014; Beaud and others, 2018).…”