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Geomorphology > British glacial land systems > Flashcards

British glacial land systems Flashcards

1
Q

lithostratigraphy

A
  • tills
  • interglacial deposits
  • fluvial deposits
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2
Q

biostratigraphy

A
  • pleistocene mammals

- pollen, beetles, chironomids

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3
Q

climatostratigraphy

A

record of warm & cold episodes

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4
Q

chronostratigraphy

A

construction of timing of events

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5
Q

23ka cycle in Britain characteristics

A
  • recessional cycles
  • high N. hemispheres insolation values
  • low amplitude climate fluctuations
  • glacial extent, minimal/no terrestrial evidence
  • maritime coastal processes/low energy fluvial
  • soil forming processes
  • chemical/biological weathering
  • high relative sea levels
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6
Q

evidence for 23ka controlled climate

A
  • East Anglia (shallow marine deposits)
  • Corraline Crag
  • Wroxham Crag
  • Red Crag
  • Crag - sandy, shell rich shallow marine deposit
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7
Q

41ka cycle in Britain

A
  • obliquity cycles (tilt)
  • more variable N. hemisphere insolation values
  • moderate amplitude climate fluctuations
  • covers period prior to 0.9Ma to 2.6Ma
  • upland glaciation
  • periglacial processes now influence
  • generation of coarser grained deposits
  • higher energy fluvial activity
  • maritime coastal processes
  • soil forming processes, less influential
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8
Q

Evidence for 41ka controlled climate

A

Major rive system active

  • Thames and Bytham, draining Wales and Midlands
  • evidence in Thames of volcanic gravels from wales
  • identified by detailed petrographic studies, glacial striations on clasts
  • acid igneous rock
  • found in terrace deposits MIS 68/1.78 Ma
  • suggestions of higher energy.more active geomorphic systems due to enhanced cold/glacier in mountain regions
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9
Q

100ka cycle in Britain

A
  • eccentricity cycles
  • highly variable N hemisphere isolation values
  • high amplitude extremes of climate fluctuations
  • covers period: present to 0.9Ma
  • continental scale, lowland glaciation
  • Periglacial processes highly influential (permafrost melting, gelifluction)
  • meltwater processse
  • rivers highly efficient, highly erosive
  • soil forming processes in warmer part of cycle
  • coastal processes active in warm part of cycle
  • considerable landscape changing processes
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10
Q

evidence for 100ka controlled climate

A
  • major glacial episodes in the UK
  • 3 main glacial episodes reflected in the stratigraphic record (East Anglia)
  • pre anglian
  • Anglian (450,000 years BP)
  • Devensian (115,000 - 15,000 years BP)
  • cold episode post Hoxnian
  • evidence wiped out by Devensian ice
    Key till units
  • pre Anglian, Happisburgh Till
  • Anglain, lowestoft Till
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11
Q

3 stage British glacial stratigraphy

A

1) Soils and shallow marine
2) Major rivers, upland glaciation
3) Glacial-interglacial cycles

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12
Q

complex offshore glacial history

A

Ice Rafted Debris (IRD)

  • particles greater than 150 microns deposited by ice bergs
  • source ID by chemistry (Crustal geology)
  • British sources, Canadian, Greenland, Icelandic sources
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13
Q

Last glacial: UK

A
  • ice development and expanion post 115ka BP (devesian ice)
  • Bowen et et. 2002
  • identified for the first time that the last British-Irish ice sheet was not static and had multiple advance and retreat phases
  • the LGM was one of theses
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14
Q

Last Glacial Maximum: UK

A
  • subsequent more detailed studies have added detail to this
  • problems of extent limited by lack of off shore data
  • clark et al. 2010 GSR (BRITICE large-scale mapping project)
  • maximum extent achieved after 27ka BP
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15
Q

off shore mapping

A
  • fishin boats
  • sonar and bathymetry
  • ability to identify offshore ice limits
  • moraine ridges and outwash fans
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16
Q

onshore mapping

A

identification of moraine ridges utilisation satellite data:

  • digital terrain models
  • ice maxima on land
  • ice recessional positions
  • Meltwater channels
  • directional indicators
17
Q

BRITICE

A
  • 1480 moraine ridges mapped
  • large moraines at continental shelf edge represent grounded ice
  • many still stands during retreat
  • bathymetric contours indicate regions which would have been regarded as terrestrial
18
Q

LGM subglacial bedforms

A
  • mapped remotely and in the field (drumlins, meltwater channels, eskers)
  • 39,000 landforms mapped
  • reveal complex patterns of ice flow (Cross cutting relationships switching ice flow patterns)
  • hughes et al. 2010 journal of maps
19
Q

confluent ice masses

A
  • individual ice lobes and flow patterns are traced clearly

- possible to identify where Scandinavian and British ice were confluent and unzipped during deglaciation

20
Q

timing of glacial maximum

A
  • based on 931 fates around the ice margin
  • variety of types of dates
  • organic/biological material (beetle and plant fragments along with pollen and lake mud)
  • sand (Luminescence)
  • Bedrock/boulders (Cosmogenic nuclide dates)
21
Q

retreat: 27-18ka BP

A

As ice shank back it:

  • reduced size
  • changed shape
  • broke into different centres of ice dispersal (multiple ice domes)
22
Q

glacial conditions

A
  • 41ka – enhanced geomorphic processes, fluvial transport of glaciated clasts
  • 100ka – direct glacial transport of material from remote regions plus enhanced cold-warm fluctuations
23
Q

Evidence of maximum extent

A
  • Limited/disturbed in terrestrial realm

* Marine sequences preserve more detail, recording numerous more extensive glaciations than terrestrial record

24
Q

section summary

A

• Complex Quaternary history driven by Milankovitch variation
• Limited to very intense geomorphic activity
- British isles have experienced multiple phases of glaciation throughout the Quaternary
- each subsequent phase has re-moulded previously glaciated terrain making it very difficult to unravel patterns

25
Q

sub-Milankovitch scale

A
  • higher frequency fluctuations
  • less than 23ka
  • operating over 100s-1000s year timescales
  • too rapid to be explained by orbital cyclicity
  • time period: lateglacial to holocene
26
Q

lateglacial period

A
  • 15-8Ka BP
  • characterised by many short-lived high magnitude climate shifts
  • variable duration
  • variable effects on the environment
27
Q

sub-Milankovitch events: UK

A
  • younger dryas (12000 years BP)
  • 8.2 event (8000 years BP)
  • little ice age (1550-1850 AD)
28
Q

sub-Milankovitch drivers

A
  • thermohaline circulation changes
  • volcanic aerosols
  • solar variations (Maunder minimum)
29
Q

re-initiation glaciation

A
  • year round snow cover and consequent build up of ice in Scottish mountains
  • requires mean annual temp decrease of 2.5-3.5
  • ELA currently 100m above summit of Ben Nevis
30
Q

Traditional view

A
  • glaciation decline through lateglacial interstadial warm period
  • no ice at low levels
  • younger dryas ice accumulated and expanded from an essentially zero point
31
Q

alternative view

A
  • large bodies of ice persisted to sea level

- ice then expanded from this position during the younger dryas

32
Q

rapid communication

A
  • ice caps existed throughout the lateglacial interstadial in northern Scotland
  • evidence for this is based on dates obtained on rock exposures ages from terrestrial and submarine moraines ridges
  • these yield ages of 13,000-14,000 years BP
33
Q

late surviving ice unlikely

A
  • glacier response to incursion of warmer oceanic waters
  • dating evidence poor
  • ages presented are not presented with full errors (i.e. 2 sigma uncertainties)
34
Q

Wester Ross readvance

A
  • related to cold event in Greenland
  • others suggest earlier event
  • chronological uncertainties
35
Q

little ice age

A
  • not thought to be forced by meltwater
  • no evidence in marine core records
  • variations in solar output rather than orbital parameters Effect on the UK?
  • permanent snow in Ben Nevis
  • lowering of snowline by 300-400m
  • increased strominess
  • no glaciers
36
Q

not a straightforward picture

A
  • ice marginal positions are becoming better defined

- many controversies exit, most are related to being unable to precisely date ice margins

37
Q

shaping of our landscape by multiple processes

related to glacial activity

A
  • Direct glacial erosion
  • Intensified geomorphic activity in the extraglacialregions (i.e. enhanced fluvial activity)
  • Periglacial and permafrost activity
38
Q

Investigation of the mechanisms that forced ice advance and retreat in the past

A
  • Provides us with better handle on how it may occur in the future
  • Allows us to mitigate or adapt

Geomorphology (9 decks)

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