Minggu-4 (Proxies in Quaternary).ppt

8/10/2019 Minggu-4 (Proxies in Quaternary).ppt

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MINGGU KE-4

Jurusan Teknik Geologi

Fakultas Teknologi Mineral

Institut Sains dan Teknologi AKPRIND Yogyakarta

Semester Genap Tahun Ajaran 2013 / 2014


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Except for the observations made over the

last 130 or so years at weather stations and onships, our knowledge of past climates is basedon records kept in sediment and ice. The taskof the palaeoclimatologist is to decipher theseproxies.

Wally Broecker, 1993


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Proxy: (the action of) a substitute, or deputy(OED)

In palaeoenvironmental research the properties ofnatural archives substitute for direct measurement.Reconstruction of palaeoenvironmental information

requires that these proxies be translated(qualitatively or quantitively) into environmentalparameters.


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Research question #1: How warm were the summersin Arctic Canada 6 000 years ago?Answer may be derived from various temperature-

sensitive properties of lake sediments, bogs, orglaciers.

Research question #2: How frequent were typhoons

in Japan in the period before records were kept?Answer may be derived from proxies recordingintense storms at sea and flooding on land.


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glaciologicalgeologicalhistorical

biological


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Ice cores:

a) oxygen isotopesb) ice fabric (size and shape of ice crystals)c) trace elements (gases), andd) microparticle (dust) concentration and

composition


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Terrestrial environmentsglacial deposits

periglacial featurespalaeo-shorelinesaeolian deposits (dunes, loess)lacustrine deposits

palaeosolsspeleothems


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Written records of paraclimatic phenomenae.g. Hudson Bay factors journals record freeze-upand breakup of Arctic rivers; ships logs recordtropical storm frequency (e.g. logs of Manila-

Mazatlan voyages of Spanish galleons); whalers catchrecords locate edge of sea ice in Antarctica; Norsesagas describe subpolar landscapes (e.g. Greenland);arrival of spring recorded in journals and diaries

(phenological records); size and date of crop harvestrecorded by merchants, etc..


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Oral traditionse.g. Haida stories of floodingof Hecate Strait

(but native traditions tendto float in time)Imagerye.g. Breughels Hunters in

the Snow records LIAwinters in N. Europe, caveart in SW France recordslocal game animals 20-30 ka.


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Phenology - study of the timing of natural events

e.g. Robert Marsham (1707-1797) kept

a journal on 27 indications of Spring onhis estate in Norfolk (England) from1736 until his death.

Indicators included flowering of springbulbs, leafing-out of shrubs and trees,appearance of migratory birds andbutterflies, etc.


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For example, from Marshams journals we read that

the first few months of 1740 were so cold that:

the gorse and heather died, the rabbits starvedin their warrens, the beer froze on the dinner table,

and the piss in his chamber pot froze to a cake.

In London the River Thames froze .


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biologicalcommunity

Physicalenvironment(esp. climate)

fossilcommunity

Reconstruction(palaeoecological methods)

taphonomicprocesses

ecologicalprocesses


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Species-related factors

1. Is the species abundant?

2. Is it (or are its parts) readily identifiable?

3. Is the abundance of the organism readilydeterminable from its fossil components?


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1 spruce trunk = 1 tree1 diatom frustule = 1 diatom

1 articulated shell = 1 clam1 skull = 1 mammoth1 articulated skeleton = 1 fish

2 spruce cones = ?20 fish vertebrae = ?

40 fish scales = ?200 spruce seeds = ?

2000 spruce pollen grains = ?

Estimatesof absolute

abundancepossible

Estimatesof relativeabundancepossible


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Environmental factors

1. Is the species abundance primarily controlledby environmental factors?

2. Is the relationship between abundance and

environment known or readily determined?


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Taphonomic factors

1. Does the organism (or ecological community)survive post-mortem diagenesis?

2. What changes take place pre-burial?

3. What changes take place post-burial?

*diagenesis: processes affecting sediments at temperatures

and pressures characteristic of the Earths surface.


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Preservation factors

Rapid

buria

l?

YES

NO

Hard parts?

YES NO

clams jellyfish

birds butterflies

ANATOMY


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1

10

100

1000

1 2 3 4 5 6 7 8 9 10

Live

Dead

1 2 3 4 5 6 7 8 9 10

R

elativeabundance

Live and dead assemblages of shelly invertebratesin the main tidal channel, Mugu Lagoon, California


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StageA B C

# phyla 9 7 7# species 80 45 18% preservation 100 56 23

A = original community;B = all hard parts preserved (e.g. late Quaternary subfossils).These are mainly molluscs and other species with hardskeletons ;

C = aragonitic, calcitic and siliceous skeletons lost(e.g. mid-Tertiary sediments)


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Aitken, A.E. 1990. Fossilization potential of Arctic fjord and continental shelf benthic macrofaunas.In: Dowdeswell, J.A. and Scourse, J.D. (eds.) Glacimarine Environments: Processes and Sediments.Geological Society Special Publication No. 53: pp. 155-176.

Fjords Nearshore Inner shelf Outer shelf

many fossils

few fossilsnofossils

112 217 197 126# genera


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Aitken, A.E. 1990. Fossilization potential of Arctic fjord and continental shelf benthic macrofaunas.In: Dowdeswell, J.A. and Scourse, J.D. (eds.) Glacimarine Environments: Processes and Sediments.Geological Society Special Publication No. 53: pp. 155-176.

Fjords Nearshore Inner shelf Outer shelf

Quaternary

fossilsnofossils


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1. Ambient temperature - fossils tend to bebetter preserved at low temperatures.

e.g. at water T>15C fish carcasses float -> scavenged-> bones scattered

2. Oxygenation - oxidation may destroy organicmaterials; anoxic water reduces scavenger activity

3. Water status - some organic material degrades whendry (see #2 above)4. pH - acidic porewaters may destroy some organic

materials.


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parts may suffer mild abrasion

Result = homogenization of fossil assemblages

needle/seedshadow

coneshadow

5m?40m?500 m?

Depositional shadows(90% of total production)

pollenshadow


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these parts may suffer severe abrasion

Result = homogenization of species?

sorting by body part?

Experiments with sheep and coyote bones in small streams

Not moved Moved gradually Moved immediately(traction) (saltation/suspension)

skulllower jaw

femurtibia

humerus

pelvis

ribsvertebraesternum

finger/toe bones


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bogs and lakeson floodplains

alpine lakes

valleysideslopes

Lake and bog sampling sites


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Terrestrial organismsplants (macrofossils, pollen, tree rings)

fauna (esp. insects, molluscs and mammals)

Aquatic organismsdiatoms, coccolithophores

foraminifers, ostracodes, coralschironimids, molluscs, fish


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HistoricPrehistoric

Past P.D.

instrumental record (e.g. summer T)proxy record (e.g. width of tree ring)

inferred summer T

calibrationperiod

warm

cold


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e.g. cold warm

Present-day environmental gradient

samples

e.g. single speciesmorphology


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e.g. cold warm

Present-day environmental gradient

samples

sp. Asp. B

sp. C

Relativeabun

dance

e.g. species distributions


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Replication: does the same proxy produceequivalent results at another site?

Validation: do several proxies produceequivalent results?

Complementary information: do alternativeproxies provide useful supplementary data?


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geochemical

proxy

Depth

sp. A B Cabundance


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Past P.D.

geochemical proxy recorddominant

species

reconstructed T


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DL in foreground;Hisnit Inlet (NootkaSd.) in background

Vibracoring


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Hutchinson et al., 2000. The Holocene10, 429-43


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Minggu-4 (Proxies in Quaternary).ppt

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