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

• Published in: Geology
• Main Authors: Zhang, Yang, Ogg, James G, Minguez, Daniel, Hounslow, Mark W, Olaussen, Snorre, Gradstein, Felix M, Esmeray-Senlet, Selen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Geological Society of America 2021
• Subjects: Svalbard
• Online Access: https://livrepository.liverpool.ac.uk/3118015/; https://doi.org/10.1130/g48591.1; https://livrepository.liverpool.ac.uk/3118015/1/final-ms-plus%20si.zip

<jats:p>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.</jats:p>