Quaternary Lecture 3- Earth's Glaciation legacy

Question 1

When did the ice sheets in the NH peak during the last glacial?

Answer 1

Large areas of the mid- to high latitudes of
the Northern Hemisphere were covered by
continental ice sheets during the last glacial
that peaked at the Last Glacial Maximum

Question 2

When was the last glacial maxiumum?

Answer 2

26.5-19 ka

Question 3

What is palaeo-glaciology?

Answer 3

Constructions of former ice cover

Question 4

What are 4 types of palaeo-glaciology?

Answer 4

Former ice sheet ‘footprint’ of flow (subglacial landforms)
Former ice sheet margins (moraines, meltwater landforms)
Former ice sheet thickness (trimlines)
Dating (e.g. radiocarbon, surface expsoure dating)

Question 5

Discuss subglacial footprint.

Answer 5

Ice flow directional indicators (e.g. flutings, drumlins, mega-scale glacial lineations)
Form parallel to former ice flow direction
Record of glacier activity at cessation of glaciation

Question 6

How can we reconstruct former ice sheet flow?

Answer 6

By understanding subglacial processes, landform genesis and glacial landsystems.

Question 7

What are drumlins?

Answer 7

a low oval mound or small hill, typically one of a group, consisting of compacted boulder clay moulded by past glacial action.

Question 8

What are moraines?

Answer 8

a mass of rocks and sediment carried down and deposited by a glacier, typically as ridges at its edges or extremity.

Question 9

Discuss moraines and geomorphology of glaciation.

Answer 9

E.g. push moraines/hummocky moraines: indicative of glacial dynamics and glacier/climate coupling through time.

Question 10

What are examples of ice-contact glaciofluvial environments?

Answer 10

Fans
Deltas
Outwash systems

Question 11

What are trimlines?

Answer 11

• Erosional ‘tidemark’ that marks
  the upper limit of glacier
  occupancy
• Recognised by distribution of
  landforms.
• Ice-moulded bedrock (below)
  weathered, shattered bedrock
  (above).

Question 12

What are the 4 different options for dating glacial sediments?

Answer 12

1. Optically stimulated luminescence (radiation exposure dating)
2. Terrestrial cosmogenic radionuclides (radiometric dating)
3. Radiocarbon (radiometric dating)
4. varve dating (annually banded records)

Question 13

Discuss optically stimulated luminescence

Answer 13

Dates sediment burial

Question 14

Discuss cosmogenic surface exposure dating.

Answer 14

Dates ice retreat and expsure to cosmic rays
E.g. boulder on a moraine

Question 15

Discuss radiocarbon and varve couting.

Answer 15

Lake deglacial sequence
* Greenland ice sheet history – Jakobshavns Isbrae in west Greenland
* Holocene advance and retreat history from a seasonal lake core record
* Radiocarbon dating of organics (peats)
* Rapid ice margin advance c. 1800 AD and retreat (1850 AD)

Question 16

How can we tell multiple glaciations apart?

Answer 16

Dating
Intervening interglacial deposits
Superimposition of tills (poorly sorted sediments deposited beneath a glacier, oldest at the bottom and youngest on top)
Freshness of landforms (morphostratigraphy = subdivision of landforms based on surface form; fresher=younger)

Question 17

Discuss the UK glacial record.

Answer 17

• Multiple glaciations in UK but only fragmentary records for MIS 6, 8, 10, 12 glaciations.
• Most UK glacial evidence is from MIS 2
• Pre-MIS 2 glacial and interglacial deposits identified using a combination of approaches:
• Dating: e.g., OSL
• Biostratigraphy/Archaeology
• Sedimentology
• Morphostratigraphy

Question 18

What is an example of multiple glaciations within the UK?

Answer 18

Example of the cutting of the
Straits of Dover by glacial lake overspill in MIS 12 and MIS 6.

Question 19

When was the LGM (MIS)?

Answer 19

MIS 2

Question 20

What are problems with reconstructing multiple glaciations?

Answer 20

Older glaciations are more difficult to reconstruct than recent
(LGM and younger) & problems are particularly acute in terrestrial settings
a) Only a partial record due to erosion
b) Overprinting of events (palimpsest)

Question 21

Define periglacial.

Answer 21

Conditions, processes and landforms associated with cold, non-glacial environments regardless of their proximity to glaciers.
Freeze-thaw processes.

Question 22

Discuss permafrost.

Answer 22

Perennially frozen soil or bedrock. Develops where mean annual air
temps are <0C. 26% of earth’s surface
- continuous (MAAT = -6 to -8oC)
- discontinuous (MAAT = -1 to -8oC)

Question 23

What are 4 permafrost and periglacial landforms.

Answer 23

Patterned ground (sorted stripes and circles) = convection during freeze thaw process
Blockfield (felsenmeer) and tors= frost shattering (long periods of exposure)
Pingos (MAAT -2 to -8C) (growth of ice lens in former pond site)
Ice wedges (MAAT -3 to -6 C)(growth of vertical ice lenses in contraction cracks)

Question 24

Name two relict periglacial features. What do they imply?

Answer 24

Protalus ramparts
Ice-wedge casts
Imply presence of permafrost and severe winter ground cooling.

Question 25

What are protalus ramparts?

Answer 25

Fossil snowpatches that formed under conditions colder than today.

Question 26

What are ice-wedge casts?

Answer 26

Form by contraction and ice infill (subsequently infilled with sediment)

Question 27

What are pluvial lakes?

Answer 27

Saline and playa lakes Low latitude geomorphology Lakes related to wetter climate Can indicate changes in moisture balance during the late quaternary Old shorelines= periods of higher lake levels often at LGM due to lower temps and evaporation levels

Question 28

Discuss sand dunes and loess.

Answer 28

Low latitude geomorphology - Past periods of increased aridity. Extent of arid zones & palaeo-wind direction can change * Expansion of dunefields in glacials * Deposition of loess (wind-blown silt) with phases of aeolian activity (= cold stages) alternating with soil formation (= warm stages) * There are many loess records from around the planet that record warm/cold climate shifts beyond glaciated regions