GEOL 4010 QUATERNARY GEOLOGY Instructor: Dr' Hester Jiskoot

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GEOL 4010QUATERNARY GEOLOGYInstructor Dr.
Hester Jiskoot
LECTURE 12
Glacial sedimentology and tectonism
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GLACIAL DEPOSITSare complex

• Function of - Position relative to ice sheet
• Activity of ice sheet (advance/retreat/stagnation
  
• Time of year (meltwater)
• Proglacial environment
• Thermal regime of ice sheet

Genetic versus non-genetic terminology
Diamicton non-genetic Till, glaciotectonite,
ice rafted debris genetic Glacigenic,
Glaciofluvial, Glaciolacustrine, Glaciomarine,
Glaciodeltaic, Glacitectonic, Periglacial, Mass
movement
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You all know what tills are.but how to describe
glacial deposits in the quaternary record?

• Landform sediment association
• (describe geomorphologic setting)
• Describe units
• (colour, texture, clast lithology, matrix- or
  clast-supported, sedimentary structures, fabric,
  contacts, etc.)
• Measure height, lateral extension, orientation
• Record tectonic evidence
• (folds, faults, shearing, diapirs, clastic
  dykes/dikes)

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What will this look like in the sedimentary
record?
Landslide on Black rapids Glacier, Alaska, after
earthquake Nov 2002
Photo USGS
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SEDIMENTOLOGY VS TECTONICS

• Sedimentary processes (wind, water)
• lamination
• bedform morphology
• texture
• structure
• transitions relate to energy/input
  (abrupt/gradual) FU, CU

Tectonic processes (ice, orogenesis, gravity)
syn-, or post- sedimentary deformation or pre-,sy
n-,post-tectonic sedimentation
Glaciotectonic dislocations disrupt
stratigraphic units ? tills of one glaciation
can be discontinuous
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KINETO-STRATIGRAPHY(Berthelsen, 1973, 1978
Boulton, 1996)
Focus on the structural instead of the
sedimentary record
Kineto-stratigraphic zones of deposition and
erosion
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Ice divide slight erosion
Overdeepening Strong erosion
Inner margin advance/retreat tills with erosion
surfaces
Outer margin continuous till deposition
Extension
Compression
Ice flow
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TECTONIC STYLES
Subglacial shear zone Marginal compressive
belt fig 4.23
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Tectonic styles in NW EuropeVan der Wateren
(1996)
a dump moraine b push moraine (unknown
tect.) c overriden/overdeepened d tectonic
nappes e overridden nappes f subglacial
tills g stacked subglacial till sheets h tunnel
valleys
weichsel
saale
elster
weichsel
saale
elster
a
d
h
e
f
g
b
c
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PUSH MORAINES (1)
Annual push moraines minor advances subaqueous
or terrestrial no substantial glacitectonics
(gt75 sedimentary bedding preserved) Imbricated
thrust sheet single base décollement steep
dipping thusts maximal tectonic shortening Nappe
overthrusting subhorizontal thin sediment sheets
(10 m) bounded above and below by shear
zones displacement 100 m to few km. multiple
décollement surfaces restricted tectonic
shortening
GLACITECTONIZED MORAINE RIDGES
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Recessional dump moraines
Exitglacier, AK, USA
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PUSH MORAINES (2)
Imbricated vs. napped Fig 3.48 (Van der
Wateren, 1994)
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Location Dammer Berge
Semicircular 40 km series of ridges, 40-145 m
asl Around Quakenbrück glacial basin, -100 m
asl. Part of Saalian Rehburg Line
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REHBURG PHASE ICE ADVANCE AND PUSHING
low shear strength
high shear strength

• Fine to coarse-grained
• ?Surface profile
• ?Potential energy
• Push moraine

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WHAT IS A SHEAR ZONE?
Steady flow shear zone Fig 3.26 (Van der Wateren,
1994)
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DEFORMATION IN SHEAR ZONE

• Brittle deformation
• faults
• thrusts
• imbrication nappes

• Ductile deformation
• folds
• boudins
• anticlines

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CONTROLS ON PUSH MORAINE FORMATION
1) Build up stress 2) Reduce shear strength
Glaciological change in mb, surging, subglacial
drainage Geological conditions proglacial
outwash, groundwater, low K Structure basement
salt domes, folds/faults, slope Periglacial
conditions permafrost present/absent, thickness

• Positive mass balance (rapid advance, high Ppore)
• Weak layer fine grained décollement
• Permafrost not required

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INTERPRETATION REHBURG PUSH MORAINE
Not end moraine at margin of steady-state ice
sheet Drenthe (re)advance (overriding) Décolleme
nt at shallow depth Coupling glacier-bed Volume
push moraine lt volume overdeepening discharged
by meltwater
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Møns Klint, DK
Weichselian stacking thrusts of Cretacious
limestone and tills 1 Older Baltic (East) 2
Main Baltic (North) 3 Younger Baltic (East)
130 m
Erratics Shearing Folding
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PERVASIVE VS NON-PERVASIVE DEFORMATION
ice bed coupling---possible pervasive
deformation ice bed decoupling--- no pervasive
deformation

• PiotrowskyTulaczyk (1999)
• Decoupling depends on ice flotation index (
  If(H))
• Low K of substratum reduced discharge meltwater

Weichselian North Germany --gt no pervasive
deformation models 25 of basal meltwater
groundwater flow 75 through tunnel valleys
(outburst) Hence, ice-bed decoupling and
enhanced sliding Basal water film up to 5 mm.
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LLEYN PENINSULA
Confluence Irish Sea iceWelsh ice
North Clynnog fawr moraine South Stratified
drift Terraces Striae
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Glacigenic deposits at Aberdaron (McCarroll and
Harris, 1990)
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Unconformity Lower/Upper Till
(Hart, 1996)
Lower Till compressional strong
fabric Upper Till extensional From deforming to
rigid bed? Stratification parallels boundary ?
not erosive
Interpretations 1) In-situ decay of debris rich
ice meltout to flowtill, both immobile 2)
Retreating margin 3) Drainage of bed
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Unconformity Lower/Upper Till
(Hart, 1996)
Clay-rich
Sand-rich
Sand-rich
Clay-rich
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Inverted channels ?
(Hart, 1996)
a) canal b) channel c) inverted channel
(R-channel)
?
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Travers reservoir
Glaciotectonic structures
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What can we say about a sediment/tectonic
structure without the landscape setting?
VERY LITTLE
? NEED AN INTEGRATED APPROACH