Ice dynamics and sediment movement: last glacial cycle, Clyde basin, Scotland

Abstract

ABSTRACT. The nature and behaviour of sediment beneath glaciers influences how they flow and respond to changing environmental conditions. The difficulty of accessing the bed of current glaciers is a key constraint to studying the processes involved. This paper explores an alternative approach in which accessible sediments under the beds of former mid-latitude ice sheets are examined and related to changing ice behaviour during a glacial cycle. The paper focuses on the partly marine-based Pleistocene British Ice Sheet in the Clyde basin. A three-dimensional computation of subsurface glacial sediment distribution is derived from 1260 borehole logs. Sediment distribution is linked to an empirically-based reconstruction of ice sheet evolution, permitting identification of distinctive phases of sedimentation. Maximum sediment mobilisation and till deposition (<0.04 m a -1 ) occurred during ice advance into the basin from adjacent uplands. Subglacial processes were influenced locally by the relative stiffness of pre-existing sediments, the permeability of the sub-till lithology, and topography; the resulting mean till thickness is 7.7 m with a high standard deviation of 7.0 m. In places, focused till deposition sealed pre-existing permeable substrates, promoting lower effective pressures. Sediment remobilisation by meltwater was a key process as ice margins retreated back through the basin, upon deglaciation.

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

“…: feature 2) and Ochils palaeo‐valley (Fig. : feature 3) have been identified previously (Parthasarathy & Blyth ; Soons ; Browne & Gregory ; Browne & McMillan ; Finlayson ). The form of the Kelvin palaeo‐valley is constrained by 214 boreholes; it has a maximum depth of 107.90 m, an average width of 1500 m and a length of 26 km (Table ).…”

“…). The till is typically overlain by glacifluvial sand and gravel deposits of the Broomhouse and Ross formations (Browne & McMillan ; Finlayson ) and in turn by lateglacial marine clays of the Paisley Formation that were deposited prior to the Loch Lomond Stadial re‐advance (Browne & McMillan ). The Paisley Formation is overlain by Holocene‐age fluvial sand and gravels of the Gourock Formation (Browne & McMillan ).…”

“…One area of the UK where sufficient sub‐surfaceborehole data exist to reconstruct the geometry and cross‐cutting relationships of the network of buried palaeo‐valleys is the Midland Valley of Scotland. Here, boreholes (>100 m depth) with thick sequences of Quaternary sediments have been used to suggest the presence of buried palaeo‐valley systems beneath Alva in Clackmannan (Parthasarathy & Blyth ), under the modern River Kelvin to the northwest of Glasgow (Browne & McMillan ; Rose & Smith ; Finlayson ) and under Grangemouth (Cameron ). Additionally, several shallower ‘drift‐filled buried channels’ have been recorded in the vicinity of Irvine, Ayrshire (Monro ).…”

Integrating deterministic lithostratigraphic models in stochastic realizations of subsurface heterogeneity. Impact on predictions of lithology, hydraulic heads and groundwater fluxes

“…Comprehensive descriptions of the geological and hydrogeological settings can be found in previous publications (e.g., Campbell et al, 2010;Finlayson et al, 2010;Finlayson, 2012;Turner et al, 2014;Kearsey et al, 2015) and reports published by the British Geological Survey (e.g., Browne and McMillan, 1989;Hall et al, 1998;McMillan et al, 2005;Merrit et al, 2007;Merrit et al, 2012). Here, we present a synthetic description of main stratigraphic and hydrogeological features that are relevant for this study.…”

Testing the application and limitation of stochastic simulations to predict the lithology of glacial and fluvial deposits in Central Glasgow, UK

“…It is recognised that future sustainable development in Glasgow requires an understanding of the nature and distribution of subsurface events during and following the last glacial cycle in Glasgow, and associated lithostratigraphic variations is described elsewhere (Browne and McMillan, 1989;Finlayson et al, 2010;Finlayson, 2012).…”