TY - JOUR

T1 - 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

AU - Zhang, Yang

AU - Ogg, J. G.

AU - Minguez, Daniel

AU - Hounslow, Mark W

AU - Olaussen, Snorre

AU - Gradstein, Felix M.

AU - Esmeray-Senlet, Selen

PY - 2021/6/1

Y1 - 2021/6/1

N2 - 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 polaritychron 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 Aptiancyclostratigraphy. The adjusted age model implies a commensurate faster average globaloceanic spreading rate of ∼12% during the Aptian–Santonian interval. Future radioisotopicdating and high-resolution cyclostratigraphy are needed to investigate where to expand themid-Jurassic to earliest Cretaceous interval by the required ∼4 m.y.

AB - 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 polaritychron 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 Aptiancyclostratigraphy. The adjusted age model implies a commensurate faster average globaloceanic spreading rate of ∼12% during the Aptian–Santonian interval. Future radioisotopicdating and high-resolution cyclostratigraphy are needed to investigate where to expand themid-Jurassic to earliest Cretaceous interval by the required ∼4 m.y.

U2 - 10.1130/G48591.1

DO - 10.1130/G48591.1

M3 - Journal article

VL - 49

SP - 733

EP - 737

JO - Geology

JF - Geology

SN - 0091-7613

IS - 6

ER -