Magnetostratigraphy Wout Krijgsman & Cor Langereis Paleomagnetic Laboratory Fort Hoofddijk Department of Earth Sciences Utrecht University
Mar 30, 2015
Magnetostratigraphy
Wout Krijgsman & Cor Langereis
Paleomagnetic Laboratory
Fort Hoofddijk
Department of Earth Sciences
Utrecht University
MagnetostratigraphyPossibilities, pitfalls and applications
Cor Langereis, Wout KrijgsmanPaleomagnetic Laboratory Fort Hoofddijk
Dept. of Earth Sciences, Utrecht
University
Giovanni MuttoniDept. of Earth Sciences, University of
Milan
Manfred MenningGeoforschungs Zentrum Potsdam,
Germany
Magnetostratigraphya dipole reversing at irregular times
Origin of reversals
MantleConvection time scale ~100 MyrReversal frequency, superchrons
Solid inner coreDiffusion time scale 3-5 kyrStabilises geodynamo process
Kuang & Bloxham, 1997
Liquid outer coreConvection time scale 300-500 yrGeodynamo action: Secular variation, excursions, reversals
Barcode: may give unique solutions- but of an essentially BINARY nature- and can be distorted in the rock record
Sediments (DSDP) & biostratigraphy
Marine magnetic anomalies
Lavas & K/Ar dating
?
GPTS: Geomagnetic Polarity Time Scale
Magnetostratigraphy part of integrated stratigraphy
Biostratigraphy: first-order chronology
- taxonomy, reworking, diachrony, ages
Magnetostratigraphy: globally synchonous
barcode
- depends on good paleomagnetic signal &
recording
Cyclostratigraphy: astronomical dating, fine-
tuning
- astronomical solutions (> 20 Ma)
- interpretation of phase relations
Integrated stratigraphy
Biostratigraphy
- first-order chronology
Magnetostratigraphy
- globally synchonous barcode
Cyclostratigraphy
- fine-tuning & astronomical dating
Geomagnetic time scales
K/Ar dating of lavas Cox et al., 1964
Magneto-bio-stratigraphy
Opdyke et al., 1966
- Advent of deep-sea cores: inclination only- Biostratigraphy (faunal zones) for dating
Marine magnetic anomalies
Marine magnetic anomalies
Marine magnetic anomalies
Pit
man a
nd H
eir
tzle
r,
19
66
MarineMagneticAnomalies
DeepSeaCores
vs.
Continental drift
Developing the GPTS
Paleomagnetism
DRM vs. CRM:
- inclination error
- delayed NRM acquisition
Accuracy of recording reversals
Watkins, 1968
Geomagnetic Polarity Time Scale(GPTS)
or …
Geomagnetic Instability Time Scale(GITS)
‘reversal excursions’
Polarity zones (subchrons) or excursions (cryptochrons) ?
Magnetostratigraphic resolution
Laj & Channell (2007) proposed:
Resolution depends on:- sampling resolution (easy … just take more samples)- sediments: sedimentation rate & suitable recording medium- diagenesis, lock-in depth, overprints, etc., etc.
Magnetostratigraphic resolution
Nomenclature OK …but for practical (integrated) stratigraphy and constraints on chronostratigraphy ?
World crustal age
Marine magnetic anomalies
Triassic magnetostratigraph… beyond the sea floor record
Even older:
magneto-stratigraphy ?
The times they are a-changin’
(Bob Dylan, 1964)
Wout Krijgsman
Time: dates and rates
Tools:BiostratigraphyMagnetostratigraphyAstrochronologyIsotopic dating
Aims:Marine-continentalParatethys-MediterraneanSynchrony-diachronyEvent stratigraphy
Geological Time Scale
Gradstein et al. (2004)
GTS2004
Neogene:based on astronomical ages
Paleogene:based on radio-isotopic ages
Hilgen et al., 2004
Magnetostratigraphy & Cyclostratigraphy
Astronomical Tuning
Climate cycles
Astronomical solutions
Astronomical Polarity Time Scale (APTS) Astronomical Polarity Time Scale (APTS) for the Mediterranean Neogenefor the Mediterranean Neogene
Sicily, 2 weeks ago
Sicily, 2 weeks ago
Sampling, 15 years ago
Lourens et al., 2004
Cyclostratigraphy & astronomical tuning ... ATNTS in GTS2004
Accurate definition of GSSP (Oued Akrech, Hilgen et al., 2000)
Biostratigraphy vs. Magnetostratigraphy
Problems:• Taxonomy• Diachrony• Reworking• Ages
Problems:• Correlation• Primary signal
vs. overprint• Ages
Correlation
Requires
unique pattern fit
Garces et al., 2001
K/Ar age6.16 ± 0.30
Magneto age7.6 ± 0.1
Ages
GPTS not independent of other dating techniques
The times they are a-changing’
Ages change with time …
Astrochronology
Problems:• Cycle recognition• Phase relation• Correlation• Astronomical solution
Astrochronology: correlation of cyclic variations in the geological record to computed astronomical (age) curves
Eccentricity from -1200 kyr to -0 kyr (La90)
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0 200 400 600 800 1000 1200
Age (in kyr)
ecce
ntric
ity
Obliquity from -1200 kyr to -0 kyr (La90)
21.5
22
22.5
23
23.5
24
24.5
25
0 200 400 600 800 1000 1200
Age (in kyr)
ob
liqu
ity
Precession - Eccentricity -1200 to 0 kyr (La90)
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0 200 400 600 800 1000 1200
Age (in kyr)
prec
essi
on /
ecc
entr
icity
Milankovitch cycles
Sapropel-marl cycles, upper Miocene, Sicily
Precessionminimum
Eccentricityminimum
Gibliscemi, Sicily, Italy
Partial Unit-Stratotype of the Zanclean stage (Lower Pliocene)
Punta di Maiata, Sicily, Italy
Precessionminimum
Lignite-marls cycles, Mio-Pliocene, Greece
Ptolemais quarry, Greece
PONTIANAcc. rate in C3r = 137cm/kyrPeriodicity cycles = 22.7kyr
Sand-marls cycles, Mio-Pliocene, Romania
Putna river section,eastern Carpathians
Clay-carbonate cycles, Miocene, Spain
Orera section, Spain
Clay-carbonate cycles, Triassic, USA
Painted desert/Petrified forrest, Arizona
MioceneAPTS
• Astrochronology for
the Late Miocene
• Sections on Crete
correlated bed-to-
bed to Sicily
Hilgen et al. (1995)
Messinian evaporitesNorthern Apennines (Italy)
Messinian Chronology
Messinian Salinity Crisis
Krijgsman et al. 1999
Evaporites synchronousall over Mediterraneanat ~5.96 Ma
La93 <> La2004
Radio-Isotopic dating
Problems:• Technique (K/Ar vs. Ar/Ar) • Error determination• Mineral dating standards
]Ar[
]Ar[J1ln
λ
1t
39
*40
K
Ar/Ar ratio: mass spectrometer precision depends on e.g. measurement protocol, mass discrimination
J is an irradiation parameter and its accuracy depends on
an accurately known age of a mineral standard.
Decay constant
Error determination
Mineral dating standards:
Fish Canyon Tuff
Betic Corridor problem
Magnetostratigraphy Tortonian Salinity Crisis: Fortuna Basin
(Garces et al. 1998; 2001)
K/Ar age of6.16 ± 0.30
Ar/Ar age of7.71 ± 0.11
Method
Garces et al. (2001) Magnetic age: 7.6 ± 0.1 Ma
Bellon et al. (1983) K/Ar age: 6.16 ± 0.30 Ma
Kuiper et al. (2002) Ar/Ar age: 7.71 ± 0.11 Ma
40Ar/39Ar vs. astronomical ages
Fan-a1, CreteMiocene, marine
2: 0.01 Ma; N = 443 different irradiations
6.65 6.75 6.85 6.95 7.05 7.15
Age (Ma)
6.94 Ma
Kuiper et al., 2003
Intercalibration
Isotopic ages and astronomical ages
Morocco / Spain
Kuiper et al., 2008
Intercalibration
Inter-laboratory calibration
Kuiper et al., 2008 (Science)
Intercalibration
Isotopic ages and astronomical ages
K/T Boundary Zumaia (Spain): new age of 65.96 Ma
Mediterranean vs ParatethysLate Miocene -Early Pliocene
‘Evolution’ of the Time Scales from Eastern Paratethys
10 TIMES longer~3Ma
~0.3Ma
Carpathians foredeep
Stoica et al., submittted
Pontian Dacian
Carpathians foredeep
SC
EC
Vasiliev et al., 2004; 2005
Putna Valley PONTIANAcc. rate in C3r = 137cm/kyrPeriodicity cycles = 22.7kyr
EasternCarpathians
SouthernCarpathians
The evolution of Paratethys: The evolution of Paratethys:
the lost sea of Central Eurasiathe lost sea of Central Eurasia
Vici project 2011Vici project 2011
3 PhD / 2 Postdoc positions3 PhD / 2 Postdoc positions