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Magnetostratigraphy of U-Pb–dated boreholes in Svalbard, Norway, implies that magnetochron M0r (a proposed Barremian-Aptian boundary marker) begins at 121.2 ± 0.4 Ma

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  • Yang Zhang
  • J. G. Ogg
  • Daniel Minguez
  • Mark W Hounslow
  • Snorre Olaussen
  • Felix M. Gradstein
  • Selen Esmeray-Senlet
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<mark>Journal publication date</mark>1/06/2021
<mark>Journal</mark>Geology
Issue number6
Volume49
Number of pages5
Pages (from-to)733-737
Publication StatusPublished
Early online date4/03/21
<mark>Original language</mark>English

Abstract

The age of the beginning of magnetic polarity Chron M0r, a proposed marker for the base of the Aptian Stage, is disputed due to a divergence of published radioisotopic dates and ambiguities in stratigraphic correlation of sections. Our magnetostratigraphy of core DH1 from Svalbard, Norway, calibrates a bentonite bed, dated by U-Pb methods to 123.1 ± 0.3 Ma, to the uppermost part of magnetozone M1r, which is ∼1.9 m.y. before the beginning of Chron M0r. This is the first direct calibration of any high-precision radioisotopic date to a polarity
chron of the M sequence. The interpolated age of 121.2 ± 0.4 Ma for the beginning of Chron M0r is younger by ∼5 m.y. than its estimated age used in the Geologic Time Scale 2012, which had been extrapolated from radioisotopic dates on oceanic basalts and from Aptian
cyclostratigraphy. The adjusted age model implies a commensurate faster average global
oceanic spreading rate of ∼12% during the Aptian–Santonian interval. Future radioisotopic
dating and high-resolution cyclostratigraphy are needed to investigate where to expand the
mid-Jurassic to earliest Cretaceous interval by the required ∼4 m.y.