Fig. 1. Contrast between a) rigid and b) soft bed. After Hart and Boulton (1991)
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What is the processes are we talking about?
Place in the till depositional processes
Scale of occurrence
localized beds
major thrust slices
stress system allows subsequent fracturing
what is the significance
Source of heterogeneities
stress to make fractures (various scales)
Case Studies
Hart and Boulton
study objective processes at sediment-ice interface
proglacial/margin - thrusts, open folds
subglacial simple shear
how much undeformed till?
Provide a simple model of systems
Fig. 1. Contrast between a) rigid and b) soft bed. After Hart and Boulton (1991)
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Menzies
intact sand interclasts incorporated into diamictons
possible melt-our origin
looked at details around clasts
clasts may contain undistrubed bedding or fractures
scale: cm-m, irregular shapes
assoicated with moraine
fabrics used to demostrate the orgin
Aber and others
composite ridges, mostly outwash sand and gravels, repeated sequences
push moraines vs. deposition moraines
Brandon Hills
inclined stratified beds, till cap
inclined beds
scale: km’s long, 15 m high
Fig.4. Brandon Hills stratigraphy. (After, Aber and others, 1989.
Utrecht Ridge
fine sands, etc., from alluvium, coarser material from prior glaciation
thrust slices, basins upflow from ridges
scale: 10’s km long, 50 m high
Vatnajokull, Iceland
sands, tephras, not much diamicton
longitudinal differences in compression
scale: km’s long, 5-10 m high
Fig. 5. Eyjabakkajokull model stratigraphy. (After, Aber and others, 1989)
McKay and others
primary pathway for flow
3 orders of magnitude higher than unfractured in lab
porosity drops with depth, but the high values near the surface allow infiltration
high lateral migration (24 m/d)
Applications to OHiO
extensive moraine belts - what is their orgin
"tills" locally have deformed sediments
Advance and Retreat patterns
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