GP2: Deposition and Glacial Sediments Flashcards
What are the 3 ways of categorising sediments based on deposition process?
Glacigenic - generated directly by ice
Glacifluvial - eroded then carried by meltwater channels
Gravitational mass movement - downflow movement of material through effect of gravity
What are the two divisions of glacigenic deposits?
Primary (till)
Secondary (reworked till)
Where are primary glacigenic deposits deposited?
ice-interface or subglacial traction zone
Describe the style of primary glacigenic
unsorted mixture of clast sizes known as a diamict
What is the other name for primary deposits?
Till
What can support the till deposits?
a matrix of well sorted fine material or a matrix of clasts.
What can we infer about the clasts within a clast matrix that is supporting a till based on their shape?
Whether they are subglacial or supraglacial in origin
What are secondary glacigenic deposits comprised of?
reworked primary till as a result of gravity stream flows
What might be responsible for reworking primary glacigenic deposits?
meltwater floods or land collapses
What aids distinction of secondary from primary glacigenic deposits and how?
Because secondary deposits have been reworked they are usually sorted more than primary ones.
What is the overriding factor that affects sediment transport potential for glacifluvial deposits?
the amount of glacial water - greater amount of water the greater sediment transport potential
What is a key feature of temperate regions that affects sediment transport potential?
Seasonal variations - warmer seasons means greater ablation which means more sediment transport in summer
What makes glacifluvial deposits easy to identify?
Well sorted
What are the two types of glacifluvial deposit?
Plane-bed
Cross-laminated facies
What produces plane-bed deposits?
fine sized sediment deposited on to flat sandy stream beds under a calm marine environment
What produces cross-laminated facies?
migration and vertical accretion of channel current ripples.
What are the two types of glacifluvial transport?
Suspension (within an R-channel)
Bedload (along the bed)
What affects the rate of sediment transport for glacifluvial transport?
Sediment availability and characteristics of water flow
What are the two aspects of water flow that affect the rate of sediment transport for glacifluvial transport?
Flow competence (largest particle flow can carry) Flow capacity (total quantity of available sediment that can be transported)
What is the overriding influence upon flow competence and flow capacity for water flow characteristics that affect glacifluvial sediment transport?
Velocity and discharge
What are the two drainage types of a glacier that affect method of sediment transport?
Distributed drainage systems (can access large expanses of the bed but have limited flow velocities)
Channelised drainage systems (reverse of drainage)
What are the two types of mass movement that are most common for glaciers?
rockfalls and flows
What are the 3 types of fall deposits?
talus/scree
solifluction
debris flows
What are talus/scree slopes?
generated by frost-wedging causing material to fall down the steep slope. The material then forms a diamict at the base that also forms a fan shape. The talus diamict differentiates from a glacial diamict because of the levle of sorting that occures.
