Transcript Radiocarbon age-modelling I – introduction to age

Radiocarbon age-modelling
I – introduction to age-models
Dr. Maarten Blaauw
School of Geography, Archaeology and Palaeoecology
Queen’s University Belfast
Northern Ireland
My background
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Born 1974 in Hardenberg (nl)
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‘92-’98 Msc Biology, Groningen (nl)
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‘98-‘03 PhD Palaeoecology, Amsterdam (nl)
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‘03-’04 Postdoc Trinity College Dublin (ie)
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‘04-’06 Postdoc CIMAT (mx)
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‘07-... Postdoc Queen’s Univ Belfast (uk)
Today
Lectures
Introduction to age-depth modelling
Bayesian age-depth modelling
Practicals
 Calibrating
 Basic age-depth modelling
 Bayesian age-depth modelling
Pollen-diagram
4
Blaauw et al. in press, The Holocene
Poisson random walk
5
Blaauw et al. in press, The Holocene
6
Blaauw et al. in press, The Holocene
7
Blaauw et al. in press, The Holocene
Types of chronologies
No uncertainties
Yearly resolution
Decadal / centennial – (multi-) millennial resolution
Annually layered ice cores
History peat dating
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Pre 14C dating (relative dating)
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Peat stratigraphy (Sernander 1866-1944) & pollen
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Link pollen with archaeology (bronze age etc.)
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Link with Swedish varve chronology (de Geer)
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(Sub) millennial precision
Von Post 1946
History peat dating
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Carbon dating → 'absolute', independent dates
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Smith & Pilcher 1973: 14C dating vs. pollen zones
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'Wishful thinking obscures reality' (von Post 1946)
14C
date depths along peat core
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At levels with major proxy changes
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At regular intervals
Assume linear accumulation between dated levels
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e.g.: Aaby 1976, van Geel 1978
History peat dating
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High-resolution 14C dating
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wiggle-match dating (van Geel&Mook 1989)
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Bayesian (e.g., Blaauw&Christen 2005)
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post-bomb dating (e.g., van der Linden et al. 2008)
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Tephra (e.g., Pilcher et al. 1995, Davies et al. 2003)
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210Pb
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All form age estimates for age-depth models
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dating (e.g., Turetsky et al. 2004)
The estimates and models are uncertain
Carbon dating
14C
dating
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14C
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Ratio 14C/C gives age fossil
unstable, half-life 5568 yr
Tree-ring coverage for IntCal04: until 12.4 kcal BP
Irish Oak
Waikato
German Oak
Groningen
German Oak
Pretoria
German Oak
German Pine
Heidelberg
German Oak
Irish Oak
Belfast
PNW/CA
German Oak
Seattle
German Pine
Swiss Pine
Tree-ring coverage for IntCal04
Tree-ring coverage for IntCal04
http:///www.chrono.qub.ac.uk/blaauw/
Age-depth modelling
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So now we have dates... what's next?
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Estimate ages of non-dated levels
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Use available information
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all dates together
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environmental settings site
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other comparable archives
Age-depth modelling
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14C
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Basic age-modelling techniques
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interpolation, regression, spline, ...
Bayesian approaches
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and other dates
chron. ordering, wiggle-match dating
Compare multiple archives
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tuning, eye-balling, Bayesian
Age-depth modelling
Age-depth modelling
Uncertainty accumulation
Many date$
Few dates
Which age-depth model?
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800 cm core
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9 14C dates
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surface = recent
Which age-depth model?
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800 cm core
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9 14C dates
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surface = recent
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Linear interpol.
Too much weight on
individual dates?
Which age-depth model?
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800 cm core
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9 14C dates
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surface = recent
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Linear interpol.
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date 6 = outlier
Which age-depth model?
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800 cm core
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9 14C dates
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surface = recent
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Linear interpol.
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470 cm = hiatus
Which age-depth model?
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800 cm core
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9 14C dates
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surface = recent
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Linear interpol.
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Linear regression
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470 cm = hiatus
Too narrow error ranges?
Which age-depth model?
wide uncertainties when extrapolating!
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800 cm core
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9 14C dates
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surface = recent
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Linear interpol.
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Linear regression
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Polyn. regression
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470 cm = hiatus
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second degree
Which age-depth model?
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800 cm core
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9 14C dates
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surface = recent
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Linear interpol.
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Linear regression
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Polyn. regression
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Smooth spline
Which age-depth model?
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800 cm core
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9 14C dates
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surface = recent
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Linear interpol.
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Linear regression
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Polyn. regression
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Smooth spline
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date 6 = outlier
Which age-depth model?
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800 cm core
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9 14C dates
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surface = recent
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Linear interpol.
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Linear regression
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Polyn. regression
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Smooth spline
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470 cm = hiatus
Age-depth modelling
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How did our sediment accumulate over time?
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Constant? Varying? Pulses? Hiatuses? Site settings
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Should we try to fit a curve through all dates?
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Balance belief in dates and belief in model
Use stratigraphic information
How many dates do I need?
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The more, the better? The more problems?
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Depends on your questions
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“is my sediment of glacial age?” “early 8.2 k event?”
Dating uncertainties
14C
dating
14C
dating
Uncertainties dates
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5 calibrated dates
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surface = recent
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simulate yr every date
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draw age-model
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linear interpolation
repeat
Uncertainties dates
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5 calibrated dates
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surface = recent
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simulate yr every date
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draw age-model
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polynomial regression
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does not cross all dots
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weighted by error sizes
repeat
Uncertainties dates
Basic age-modelling
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Choose which one looks nicest...
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How treat point estimates? (mid/max, multimodal)
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Not much literature
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Why just one line?
Bennett 1994, Bennett and Fuller 2002, The Holocene,
Telford et al. 2004, QSR
Software
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Calib + Excel
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clam, Blaauw in press (Quaternary Geochronology)
Today
Lectures
Introduction to age-depth modelling
Bayesian age-depth modelling
Practicals
 Calibrating
 Basic age-depth modelling
 Bayesian age-depth modelling