Till Flashcards
What characterises a till?
Diamictic - all grain sizes
Little to no sorting
Cohesive
Massive (=no structure)
Mixed components (lithologies, mineralogy)
What differentiates tills from other glacial deposits?
That it is unsorted
What kinds of till is there, and what sequence would they come in? (Classification)
- Deformation till (land) - active
- Lodgement till (land) - active
- Melt-out till (land) - stagnant
- Flow till (land) - stagnant
Waterlain till (lakes/ocean)
What is deformation till?
Till that has deformed (often with the substratum) under the pressure and stresses of the ice, also leading it to mix with the substratum.
What characterises the deformation till?
- It has local material
- deformation structures (including mixing)
- abraded stones
- compact appearance
- elongated stones strongly aligned with ice movement
What is a lodgement till?
A till deposited right under the ice with debris from the basal.
What characterises a lodgement till?
- it has local and far travelled material
- massive structure
- elongated stones aligned to flow direction
- bullet-shaped and imbricated stones
- relatively fine grained
What is a melt-out till?
Deposition of material from gradual melting of the ice
What characterises a melt-out till?
- it has far travelled components
- unabraded stones
- stringers of sand
What is a flow till?
Material deposited after moving down from the surface of the glacier.
What characterises a flow till?
- folds
- heterogeneous
- loose structure
- far-travelled components
- some sorting by water
- relatively coarse grained
- strongly variable thickness
What is a waterlain till?
A till deposited in water
What environments is waterlain till deposited?
Proglacial - lakes or ocean (ice margin)
Subglacial - lakes or cavities
Will often find dropstones
What is a bedded till and how could it have been formed?
Bedded or stratified till.
Formed by:
- extremely weak folds
- redeposited frozen bed
- syn-depositional decoupling and washing
