Landscape evolution

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Landscape evolution

• Steve Hill
• CRC LEME
• University of Adelaide

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Ancient landscapes are they relicts or are they
still evolving? How have they evolved in the
past?
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Landscapes change with time...

• Landscapes Evolve
• By looking at landscapes, including their
  components and environments, we see that they are
  not static
• Processes keep operating and environmental
  components go on interacting

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Erosion of an ancient landsurface near
Tibooburra, NSW
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Landscapes change with time...

• How do we perceive landscape change?
• What is the evidence of change?
• What are some fundamental changes and their
  implications?
• If we know how landscapes have changed, can we
  tell how they will change in the future?

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Landscape Change

• How did the landscape that we see today get to be
  the way it is?
• Has it always been this way?
• If we went back in time what may it have been
  like?

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Landscape Change

• Central Australian Deserts - arid today

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Landscape Change

• Central Australian Deserts - less arid
  yesterday?

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Identifying Landscape Change

• How can we tell landscapes have changed?
• Landscape Reconstruction
• Using clues to solve the mysteries of past
  environments

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Identifying Landscape Change

• Some tools for landscape reconstruction
• field preservation of ancient landscape facets
• HOWEVER, making reconstructions based on
  materials that are no longer preserved is
  negative evidence

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Ancient landscape overlain by basalt - Anthonys
Cutting near Bacchus Marsh, Vic
Miocene Sediments
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Landscape uncovered (exhumed) from beneath
Jurassic sediments at Tibooburra, NSW
Pre-Jurassic Landsurface
Tors of Devonian Granite
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Identifying Landscape Change

• Some tools for landscape reconstruction
• fossil remains in ancient landscapes

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Eocene rainforest remains in silcrete from
Fowlers Gap
Contemporary Landscape
Eocene Rainforest Fossils
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Botanical Refuges from Central Australia, Palm
Valley, NT
Finke River near Palm Valley
Palm Valley, Finke Gorge
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Riversleigh, Qld - landscape
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Fossils in Riversleigh tufa
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Riversleigh Landscape Reconstruction
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Identifying Landscape Change

• Some tools for landscape reconstruction
• dating techniques for landscape remnants
• Relative Age
• based on geological correlation and relationships
• Numerical Age
• generation of a number from a particular process
• Correlated Age
• relates features to an established time framework
• Calibrated Age
• relates variable rates of landscape processes to
  time

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Dating Methods

• Relative Age
• Field relationships and correlations derived from
  traditional geological field methods

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Palaeosol in dune sequence - Wilsons Promontory,
Vic
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Relative Dating

• The law of super-position is important in
  geological stratigraphic studies
• However it is not always as straight-forward for
  regolith and landscape studies
• Younger sediments overlie older sediments
• Younger depositional landsurfaces overlie younger
  depositional landsurfaces
• Younger erosional landsurfaces are incised into
  older erosional landsurfaces

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Regolith Stratigraphy within Landscape Evolution?

• Some challenges
• Lack of fossils etc.
• Patchy remnants poor preservation
• Discontinuous spatial extensions
• Multi-cyclic weathering overprints

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Dating Methods

• Numerical Age
• Relies on applying rates of radioactive decay to
  the age of materials
• e.g. Radiocarbon dating
• e.g. K/Ar, 40Ar/39Ar
• e.g. U-series
• e.g. Luminescence
• e.g. Cosmogenic (Be, Cl, Al)
• e.g. Fission Track
• e.g. Electron Spin Resonance

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Dating Methods

• Correlated Age
• Relates features to an established time framework
• e.g. Palaeomagnetism
• e.g. Oxygen Isotopes
• e.g. Pollen and Spores
• e.g. Fossils

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Dating Methods

• Calibrated Age
• Relates variable, but established, rates of
  landscape processes to time
• e.g. Amino acid racemization
• breakdown and alteration of amino acids in
  organic remains over time
• depends on local climate (esp. temperature)
• e.g. Weathering Rinds
• time it takes to form a weathering crust of a
  given thickness
• depends a lot on establishing weathering rates,
  which we all know are highly variable and complex

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HOW DO WE GO ABOUT DEVELOPING A REGIONAL MODEL
FOR LANDSCAPE EVOLUTION???

• This problem has been faced by Earth scientists
  considering the Australian landscape for over 200
  years
• Lets have a look at some of the components of the
  study of landscape evolution in Australia and how
  the study of landscape evolution has evolved in
  Australia

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AUSTRALIAN LANDSCAPE EVOLUTION MODELS

• Several main themes
• 1. Lithological Controls
• 2. Climatic Controls
• 3. Tectonic Controls Highland Evolution
• 4. Eustacy
• 5. Landsurfaces
• 6. Anthropogenic Contributions

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REGOLITH AND LANDSCAPE EVOLUTION MODELS

• Lithological Controls

Hammersley Ra, WA
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Lithological Controls

• Lithological substrates to landscapes are
  variable and therefore they behave differently in
  the landscape
• Widely applicable landscape control but
  frequently overlooked
• This includes
• Variable resistance to weathering and erosion
• Different styles of weathering
• A simple rule Hard rocks tend to form relatively
  higher areas than soft rocks
• Structural controls are also important (e.g.
  joints and faults)

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Lithological Controls

• Mineral Weathering
• Goldich - increasing stability down the page
• Olivine Plagioclase Feldspar
• Augite
• Hornblende
• Biotite
• K feldspar
• Muscovite
• Quartz
• This is almost the opposite to the order that
  these minerals crystallise from a high
  temperature melt!

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Macdonnell Ranges, central Australia -
differential weathering and erosion
Resistant Quartzite
Less resistant Granite
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Devils Marbles, NT
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REGOLITH AND LANDSCAPE EVOLUTION MODELS

• Climatic Controls

Near Cobar, NSW
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CLIMATIC CONTROLS

• What attributes make up climate?
• Temperature
• Rainfall
• Wind
• Seasonality
• etc.
• How may some of these influence landscapes?

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CLIMATIC CONTROLS

• A very conveniently cited control on regolith and
  landscape evolution
• Chemical weathering reactions are enhanced in
  warmer climates, with physical weathering more
  enhanced in colder climates
• a 10o C increase in temperature will often double
  reaction rates
• Water controls chemical and physical weathering,
  erosion processes and vegetation colonisation
• Seasonal water controls are important
• Wind

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CLIMATIC CONTROLS

• Some implications of the emphasis on climatic
  controls
• Morphoclimatic maps / zones
• Interpret regolith based on palaeo-climate and
  vice versa

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Frost Weathering, Scotland
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Aeolian transport in action, NSW
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Soils in humid tropics / deserts
Iron-rich and leached regolith, Weipa, North
Queensland
Carbonate-rich regolith, Broken Hill, NSW
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Climatic modelling of Bauxite (Bardossy Aleva)
Modified after Bardossy G. Aleva G.J.J. 1990.
Lateritic Bauxites. Elsevier, Amsterdam, 624 pp.
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CLIMATIC CONTROLS

• Of course this may be all well and good for
  applications to contemporary landscape processes,
  but many regolith and landscape features in
  Australian landscapes are old
• Palaeoclimate is considered very important in
  many of Australias ancient landscapes that have
  evolved over the timeframe of major global
  climate changes

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Silcretes in inland Australia
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Long-term Climate Changes
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Australias Northward Migration
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CLIMATIC CONTROLS

• What impact may Australias northward drift have
  on its climate?
• Movement towards tropics
• Into arid belt leading to continental drying
• Drying leads to vegetation changes and more fires
  etc.

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CLIMATIC CONTROLS

• Climatic Controls - Extent of Glaciation
• One of the earliest landscape controversies was
  whether Australia had been glaciated during the
  Pleistocene
• Many of Australias early geologists had
  backgrounds in glacial studies in Britain or
  Europe
• Early discoveries of ice-worn boulders were
  assumed to be Pleistocene (e.g. Selwyn and David
  in the Mt Lofty Ranges Tate at Hallet Cove near
  Adelaide). These were later shown to be Permian

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Permian Tillites from near Bacchus Marsh, Vic
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CLIMATIC CONTROLS

• Climatic Controls - Extent of Glaciation
• Clarke (1852) found evidence of glaciation in the
  Australian Alps, however
• Glacial conditions during Quaternary ice ages
  were restricted in Australia (low latitude and
  altitude)
• Glacial ice accumulated in the Snowy Mountains
  and Tasmania
• This resulted in some glacial landforms
• e.g. cirques, U-shaped valleys, moraine deposits
• Periglacial conditions were perhaps more
  widespread

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Blue Lake,Snowy Mountains, NSW
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CLIMATIC CONTROLS

• The impact of glacial times in Australia was
  more profound than the minor presence of glacial
  ice

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CLIMATIC CONTROLS

• Glacial Cycles / Ice Ages
• In the last 2 million years the Earths ice caps
  have undergone cycles of increasing and
  decreasing their volumes
• When an ice cap increases its volume it reduces
  the amount of water that enters the ocean and as
  a result global sea levels fall and continents
  increase their size
• Conditions are typically colder and drier during
  glacial times

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CLIMATIC CONTROLS

• Environmental and landscape response to ice ages
• Glacials
• colder
• lower sea-level / larger continents
• drier
• Interglacials
• wamer
• higher sea-levels / smaller continets
• moister

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Glacial Cycles Diagram
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Australian Sea level at last Glacial Maximum
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Lakes and Rivers During Glacials

• Lakes can be a very sensitive indicator of
  environmental (especially climate) change
• At the peak of glacial times lakes are at their
  driest
• Immediately prior to this though lake levels are
  highest (even higher than during interglacial
  times)
• reflect low evaporation and high runoff due to
  less vegetation cover (not just rain inputs)

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Dunes in Glaciations

• Dunes are more active during glacial conditions
• less vegetation
• drier landsurface
• generally windier

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Dunes in Glacials - things would have been more
like this!
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Linear Dunes near Innamincka, SA
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Dune Environmental Records lunettes(Hills,
1975)
Modified after Hills 1975. Physiography of
Victoria. Whitcombe and Tombs Pty Ltd., 373 pp.
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Lunette Sequences
Lake Mungo and lunette, NSW
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Dune Environmental Records - lunettes
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Lunette Sequences
5.
4.
3.
2.
1.
Lake Tyrell lunette, Victoria
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Climatic controls

• Weathering related to warm / wet episodes?
• Faster rates of chemical weathering
• Water integral to weathering reactions
• But are rocks near the surface weathering today?
• Maybe weathering is a continual processes with
  variable preservation potential of evidence
  (resembling episodes)

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Climatic controls

• Induration related to warm / wet conditions?
• Faster rates of chemical weathering
• Water integral to weathering reactions
• Enhanced production of iron oxides and silica
  derived from weathering solutions?
• Induration related to warm / arid conditions?
• Reduced leaching of easily dissolved materials
• Evaporative concentration
• e.g. NaCl, carbonates, sulphates

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Climatic controls

• Is that all there is to weathering and
  induration?
• Drainage
• Requires gradient (topography or groundwater)
• Chemical sources
• Labile lithologies
• Chemical inputs
• Preservation potential
• Rates of weathering greater than rates of erosion
• May have slow weathering rate as long as erosion
  rate is slower
• e.g. cool-climate bauxite
• e.g. high erosion rates in mountainous arid or
  alpine areas

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Climatic controls

• Some questions
• Watertable - Redox changes related to climate?
• Is that all there is???
• Relative movement associated with
• Tectonism
• Sedimentation
• Denudation (knickpoint incision/retreat)

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Climatic controls

• Some questions
• Palaeodrainage and sedimentation related to
  climate?
• Is that all there is?
• Alluvial response to climate is complex
• Knickpoint controls?

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AUSTRALIAN LANDSCAPE EVOLUTION MODELS

• Eustacy

Cumberland River, Vic
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EUSTATIC CONTROLS

• What effect may sea-level change have on
  landscapes?
• Climate changes
• Inundation
• Hydro-isostacy
• Base-level change

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EUSTATIC CONTROLS

• Base-level change
• As sea levels drop so too do stream base-levels
• Incision and knick-point retreat
• As sea levels rise so too do stream base-levels
• Sediment backfilling and reduced erosion

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Mesozoic Marine Incursions
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Eromanga Basin Marine Sediments
Cretaceous shoreline,Lagoon Hill, SA
Inter-tidal ripples in Cretaceous sandstone near
Tibooburra, NSW
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Murray Basin Marine Incursion
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Murray Basin Sediments
Miocene limestone, Murray River, SA
Pliocene Beach Deposits, near Kerang, Vic
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REGOLITH AND LANDSCAPE EVOLUTION MODELS

• Tectonism

Wahratta range-front, NSW
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TECTONISM

• Originally Plio-Pleistocene Kosciusko Uplift
  widely interpreted across the continent
• This was largely from analogy with Nth Hemisphere
  tectonically active landscapes
• Further mapping and better chronological controls
  (e.g. dating basalts and associated regolith and
  landscape materials) showed much of the tectonism
  to be older

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TECTONISM

• Australia is now typically thought of as mostly
  having tectonically stable landscapes

Redan, NSW
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TECTONISM

• Far removed from the turmoil from the depths of
  the Earth associated with other places...

Images courtesy USGS
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TECTONISM

• How can we tell if Australia is more tectonically
  stable than other places???
• Low topographic relief
• Landscape antiquity
• Rare earthquakes
• Volcanic dormancy
• Plate tectonic setting
• Most of these features have a landscape
  expression
• How can we read this?

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TECTONISM

• Tectonic contributions to the landscape come from
  deep seated major crustal movements, such as
• Faulting
• Jointing and fractures
• Folding and warping
• Uplift and subsidence
• Extra-terrestrial impact

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TECTONISM

• ACTIVE FAULTING
• Active faulting causes a variety of landform
  features including
• fault scarps
• warped and tilted ground
• subsidence features
• offset features
• Most typically expressed by fluvial and coastal
  systems

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TECTONISM

• FLUVIAL EXPRESSIONS
• Longitudinal Stream Profiles
• Sensitive to vertical movements in baselevel,
  such as due to tectonism
• Baselevel change is often expressed as profile
  steepening -gt knickpoint (e.g. a waterfall)

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TECTONISM
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TECTONISM
Knick-point, Mundi Mundi range-front, NSW
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TECTONISM

• FLUVIAL EXPRESSIONS
• River Patterns
• maps showing river patterns may express tectonic
  influences
• e.g. Drainage network
• e.g. Meander morphology and evolution

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TECTONISM

• FLUVIAL EXPRESSIONS
• River Terraces
• Stream terraces represent time lines along
  valleys because they are formed during periods of
  equilibrium or threshold conditions in the
  fluvial system
• They may be faulted, tilted or folded
• They may initially form due to river down-cutting
  or valley filling in response to uplift or
  subsidence

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River Terraces
Campbells Ck near Broken Hill, NSW
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TECTONISM

• FLUVIAL EXPRESSIONS
• Alluvial Fans
• Sensitive indicators of tectonism
• Tectonically Active settings Fanhead deposition,
  large fans relative to catchment size

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Alluvial Fans - Death Valley, USA
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TECTONISM

• FLUVIAL EXPRESSIONS
• Fault scarp morphology
• Slope morphology widely used as an indicator of
  relative tectonic activity
• e.g. pattern of erosional degradation (typically
  by streams)

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Fault Scarp, Lake George, NSW
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Cadell Fault - Murray River, near Echuca
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Cadell Fault - Murray River, near Echuca
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TECTONISM

• COASTAL EXPRESSIONS
• Erosional Features
• Wave-cut platforms (uplifted marine terraces)
• wave-cut notch

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TECTONISM

• COASTAL EXPRESSIONS
• Depositional features
• Beach Strandlines (beach ridges, e.g. South
  Australia)

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TECTONISM

• COASTAL EXPRESSIONS
• Coral Coasts
• Organisms specific to particular water levels
• Mortality of intertidal organisms
• Uplifted coral terraces

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Uplifted Coral Terraces, Northwest Cape, WA
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TECTONISM
EARTHQUAKES Earthquakes result from sudden
slippage along fault zones in response to
stress Most earthquakes occur at plate
boundaries or along faults within
plates Earthquake hazards include ground
rupture and shaking liquefaction
landslides tsunamis coastal flooding
fires
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TECTONISM

• The crust of the Australian continent is
  experiencing compressive stress
• This is most likely to be released along
  pre-existing zones of crustal weakness, such as
  ancient fault zones
• Earthquakes do occur and are mostly associated
  with ongoing activity along ancient fault zones
• Dalton-Gunning area the most seismically active
  in Australia

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Earthquake Map of Australia
Image courtesy Geoscience Australia
102
TECTONISM

• Volcanic activity may be associated with tectonic
  evolution of passive margins
• Eastern Australia has experienced volcanism
  throughout the Cainozoic
• Youngest volcanic activity is in far north Qld
  and far western Vic - southeastern SA
• Some volcanics have been tectonically disrupted

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Australias Young Volcanoes
Mt Elephant, W Vic
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Australias Young Volcanoes
Mt Schank, SA
Tower Hill, W Vic
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TECTONISM

• PUTTING IT TOGETHER...
• For the most part tectonic activity in the
  Australian landscape has been explained by some
  vaguely defined active tectonic process.
• More recent explanations include
• pushing of plate from ocean spreading ridge and
  stress transmission
• pulling of plate from northern collisional
  boundary and stress transmission
• friction on the base of the crustal plate from
  the underlying mantle
• departures from isostasy, arriving from ancient
  mountain belts or marine transgressions
• heterogeneous lithosphere density, especially due
  to injection of magma into the crust related to
  volcanic activity

106
TECTONISM

• Conclusions
• Australia may not have the most tectonically
  active landscape on Earth, however ongoing
  tectonism occurs
• Even relatively small tectonic disruptions can
  have a major impact on a low relief landscape
• By reading the landscape record we can help to
  assess the potential for continued tectonic
  activity

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REGOLITH AND LANDSCAPE EVOLUTION MODELS

• Palaeo-surfaces

108
AUSTRALIAN LANDSURFACES

• Australian landscapes are famous for their
  ancient landsurfaces

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Ancient landsurfaces, Hammersley Range, WA
Ancient landsurfaces, Innamincka, SA
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Ages of Australian Landsurfaces
Modified after Beckman G.G. 1983. Development of
old landscapes and soils. In Soils and
Australian viewpoint. CSIRO, Melbourne.
111
AUSTRALIAN LANDSURFACES

• How do these ancient landsurfaces form?
• Several interpretive models.

112
Davisian Cycles

• A widely adopted model
• Structure - lithology and tectonics
• Process - Slope decline mainly by water
• Stage - length of time giving particular forms
• Youth (steep V-shaped valleys with broad flat
  interfluves)
• Maturity (landscape of all slopes as streams cut
  down towards baselevel)
• Old Age (gently undulating surface peneplain)
• Uplift results in repetition of the cycle

113
Davisian Cycles

• This model was very popular in Australia
• Incorporated with duricrust studies and extended
  to interpret a single duricrusted peneplain of
  Miocene age extending across Australia (e.g.
  Woolnough, 1927)

114
King

• King (Pediplanation)
• King later maintained that slopes tend to replace
  themselves by parallel retreat forming a
  pediplain (coalescence of pediments)
• Pediplains may also be cyclic (as with
  peneplains)
• Popular in arid Australia where duricrusts
  restrict downwasting and duricrusts occupy
  different low relief landsurface levels

115
AUSTRALIAN LANDSURFACES

• How do they form?
• a) Peneplains or,
• b) Pediplains???

116
AUSTRALIAN LANDSURFACES

• Some things to consider
• How well is the reconstruction based on both its
  age and correlation across the landscape
• Are some upland surfaces that appear concordant
  really just optical illusions?
• How do we know all low relief landsurfaces are a
  single ancient landscape facet?
• What triggered the formation and destruction of
  the landsurface?
• Careful! The older landscape research in
  Australia was very caught up on hidden models!!!!

117
AUSTRALIAN LANDSURFACES

• Dynamic Equilibrium (Gilbert, Hack)
• Removed from cyclic concepts
• Slopes tend to be constant in form after an
  initial period of adjustment
• Weathering, erosion and deposition are in balance
• Difficult to account for ancient landscape
  remnants
• Not widely adopted in Australia

118
AUSTRALIAN LANDSURFACES

• Basin sedimentation and hinterland landsurface
  evolution
• The erosion of ancient landscape materials
  typically means that they are not present to be
  used as evidence for landscape reconstruction
• However adjacent areas of deposition can be used.

119
AUSTRALIAN LANDSURFACES

• Basin sedimentation and hinterland landsurface
  evolution
• Some things that basin sediments can tell us
  about hinterland landscapes
• Stratigraphic framework enables chronological
  framework
• Clastic sediment volumes can be related to eroded
  source areas (calculate denudation amounts and
  possibly even rates)
• Composition can be related to eroded source
  areas(e.g. weathered landscape tend to shed
  resistant and secondary minerals)

120
Some Fundamental Features of Australian Landscape
Change

• Human Inputs To Landscape Change

Canola fieldnear Boorowa, NSW
121
HUMAN INPUTS TO LANDSCAPE CHANGE

• Humans are part of the landscape but they also
  potentially have a major impact on it

122
Aboriginals and Landscape
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Colonial Australia
124
Colonial Australia

• Ranger Uranium Mine, NT

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Urban Australia.
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Urban Australia.
Uluru, NT
127
CAN WE TAKE THIS FURTHER?

• If we can demonstrate that landscapes have
  changed in the past, can we predict how they
  might change in the future???