1Magnetostratigraphy Wout Krijgsman & Cor Langereis Paleomagnetic LaboratoryFort HoofddijkDepartment of Earth SciencesUtrecht University
2Magnetostratigraphy Possibilities, pitfalls and applications Cor Langereis, Wout KrijgsmanPaleomagnetic Laboratory Fort HoofddijkDept. of Earth Sciences, Utrecht UniversityGiovanni MuttoniDept. of Earth Sciences, University of MilanManfred MenningGeoforschungs Zentrum Potsdam, Germany
3Magnetostratigraphy a dipole reversing at irregular times
4Origin of reversals Mantle Liquid outer core Solid inner core Convection time scale ~100 MyrReversal frequency, superchronsSolid inner coreDiffusion time scale 3-5 kyrStabilises geodynamo processKuang & Bloxham, 1997Liquid outer coreConvection time scale yrGeodynamo action: Secular variation, excursions, reversals
5GPTS: Geomagnetic Polarity Time Scale Lavas & K/Ar dating?Sediments (DSDP) & biostratigraphyBarcode: may give unique solutions- but of an essentially BINARY nature- and can be distorted in the rock recordMarine magnetic anomalies
6Magnetostratigraphy part of integrated stratigraphy Biostratigraphy: first-order chronology- taxonomy, reworking, diachrony, agesMagnetostratigraphy: globally synchonous barcode- depends on good paleomagnetic signal & recordingCyclostratigraphy: astronomical dating, fine-tuning- astronomical solutions (> 20 Ma)- interpretation of phase relations
20Geomagnetic Polarity Time Scale (GPTS) or … Polarity zones (subchrons) or excursions (cryptochrons) ?Geomagnetic Polarity Time Scale (GPTS) or …Geomagnetic Instability Time Scale (GITS) ‘reversal excursions’
21Magnetostratigraphic 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.
22Magnetostratigraphic resolution Nomenclature OK …but for practical (integrated) stratigraphy andconstraints on chronostratigraphy ?
26The times they are a-changin’ (Bob Dylan, 1964)Wout Krijgsman
27Time: dates and rates Tools: Biostratigraphy Magnetostratigraphy AstrochronologyIsotopic datingAims:Marine-continentalParatethys-MediterraneanSynchrony-diachronyEvent stratigraphy
28Geological Time Scale Gradstein et al. (2004) GTS2004 Neogene:based on astronomical agesWhy is it so important that both methods are identical? The new GTS as published last year is based on astronomical ages for the Neogene part of the time scale and on radio-isotopic ages for e.g. the Paleogene part. The geological time scale is the framework for deciphering the history of the Earth and therefore it is crucial that astronomical and radio-isotopic dating methods produce identical results.The base of the Neogene is defined in the Lemme-Carrosio section in northern Italy. This section correlated to ODP site 926 based on detailed calcareous nannofossil correlations. ODP site 926 is astronomically tuned to La2004 and yields an age of Ma. Wilson et al. (2002), Naish et al. (2001) published Ma n=19 and Ma n=52 relative to FCT 27.84, single crystal anorthoclase for two tuffs bracketing Oligocene-Miocene boundary….Still to be explained….Paleogene:based on radio-isotopic ages
45Sand-marls cycles, Mio-Pliocene, Romania PONTIAN Acc. rate in C3r = 137cm/kyrPeriodicity cycles = 22.7kyrPutna river section, eastern CarpathiansAnother aspect is the Cyclic pattern of the sedimentary rocks .Vertically bedded sandstones units, alternating with finer sediments on Putna Valley. The calculated duration of each cycle is very close to 21.7 which is very close to the average duration of the Precession Cycle.
56Radio-Isotopic dating Problems:Technique (K/Ar vs. Ar/Ar)Error determinationMineral dating standards
57Error determinationAr/Ar ratio: mass spectrometer precision depends on e.g. measurement protocol, mass discriminationDecay constantJ is an irradiation parameter and its accuracy depends onan accurately known age of a mineral standard.
64Intercalibration Isotopic ages and astronomical ages Morocco / Spain Kuiper et al., 2008
65Intercalibration Inter-laboratory calibration Kuiper et al., 2008 (Science)
66Intercalibration Isotopic ages and astronomical ages K/T Boundary Zumaia (Spain): new age of Ma
67Mediterranean vs Paratethys Late Miocene -Early PlioceneSince the end of Oligocene, Paratethys area evolved as the northern branch of the Neo- Tethys Ocean while its southern branch is the actual Mediterranean region. It is very important to know the connections between water masses. When they were open or closed we do not know. We do not know even all of them were there or not. Taking into account that we that for Mediterranean already exists a very good time frame we want to do the same for the eastern Paratethys. EVOLVED
68‘Evolution’ of the Time Scales from Eastern Paratethys ~3Ma~0.3Ma10 TIMES longer
69Carpathians foredeepPontianDacianStoica et al., submittted
70Carpathians foredeepECSCVasiliev et al., 2004; 2005
71Putna Valley PONTIAN Acc. rate in C3r = 137cm/kyr Periodicity cycles = 22.7kyrAnother aspect is the Cyclic pattern of the sedimentary rocks .Vertically bedded sandstones units, alternating with finer sediments on Putna Valley. The calculated duration of each cycle is very close to 21.7 which is very close to the average duration of the Precession Cycle.
72Eastern Southern Carpathians Carpathians Schematic time scale for Mediterranean. The local stage boundaries show no direct connection with the changing from Mediterranean. The desiccation and the Pliocene flooding from Mediterranean seems to not be reflected at all in the western most part of the eastern Paratethys. Anyway the presumed influx of Paratethyan water into Mediterranean did not left any sign in Paratethys. no clue. The Meotian/Pontian boundary which was associated previously with the Tortonian/Messinian boundary can be maybe connected now with the onset of the Messinian Salinity crisis. The change in the magnetic components from oxic to anoxic conditions reveal a huge change in the basin configuration occurring at the Me/Po boundary, in the C3r chron. It may be related to the MsC or not.EasternCarpathiansSouthernCarpathians
73The evolution of Paratethys: the lost sea of Central Eurasia Vici project 20113 PhD / 2 Postdoc positions