The full programme book (PDF) - Royal Geographical Society

T8
Revolutions in micromorphology: new knowledge from real 3D fabric data and
applications to subglacial traction tills.
John Groves 1 *, Simon Carr 1
1 Centre for Micromorphology, School of Geography, Queen Mary, University of London, Mile End,
London, E1 4NS
Particle fabric data derived from subglacial tills is often used to constrain former ice flow
direction and reconstruct stresses associated with mechanisms of subglacial sediment
deposition and deformation. These processes are key indicators of ice-substrate coupling,
a significant component controlling glacier dynamics. However, till macro-fabric data has
come under significant criticism in recent years with operator bias, low sample populations
(typically ~50 grains per sample) and small-scale spatial variation compounding to
undermine traditional methods. The study of micro-fabric in till has revealed more subtle
indicators of stress direction and magnitude, and has suggested systematic variations in
particle size with particle fabric. However the 2D nature of thin-sections used for deriving
microfabric compromises their legitimacy as indicators of complex 3D stresses. As such,
there are several factors undermining the study of particle fabric, particularly the lack of
true 3D data, with significant implications for understanding particle motion and fabric
development during subglacial strain.
We present true 3D micro-fabric data from a subglacial traction till deposited at Falljökull,
Southeast Iceland. 10 samples of undisturbed till from three sites were scanned and
analysed using high-resolution 3D X-ray computed tomography (X-ray µCT). Over 6,000
particles are objectively identified using a machine-learning segmentation algorithm, and
fabric data is extracted and presented alongside a full logging and traditional
reconstructive investigation. Fabric is weighted by particle size and shape and
discrepancies are noted with macro-fabric data. µCT has shown to add new and impartial
data to the ongoing particle fabric debate.
Keywords: X-ray tomography; particle fabric; subglacial till; micromorphology