Extreme geomagnetic reversal frequency during the Middle Cambrian as revealed by the magnetostratigraphy of the Khorbusuonka section (northeastern Siberia)

Magnetostratigraphic correlations of biostratigraphic stage boundaries have established calibration points for dating the polarity reversal sequence derived from marine magnetic anomalies. Interpolation between the best-estimate ages for these tie points gives a revised magnetic polarity timescale for the Cainozoic and Cretaceous. Recomputed sea-floor spreading rates for this time prove to be high during the Cretaceous quiet interval at several plate margins, but remained remarkably constant in the central Atlantic. The geomagnetic reversal frequency, when averaged over intervals of several megayears duration, has exhibited a steadily increasing trend since the late Cretaceous.

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Steady increase in geomagnetic reversal frequency after the Cretaceous Normal Superchron

10.21203/rs.3.rs-1186868/v1 ◽

2022 ◽

Author(s):

Yutaka Yoshimura ◽

Osamu Ishizuka ◽

Toshitsugu Yamazaki ◽

Yuhji Yamamoto ◽

Hyeon-Seon Ahn ◽

...

Keyword(s):

Heat Flux ◽

Mantle Convection ◽

Steady Increase ◽

Geomagnetic Reversal ◽

Core Mantle Boundary ◽

The Core ◽

Marine Magnetic Anomalies ◽

Reversal Frequency ◽

Geomagnetic Polarity ◽

Geomagnetic Polarity Time Scale

Abstract The Earth's core is constantly and efficiently cooled by mantle convection. The heat flux transferred from the core to the mantle through the core-mantle boundary (CMB) is critical for understanding the dynamics of solid Earth. Although it is difficult to estimate the CMB heat flux, its history could be reconstructed from geomagnetic reversal frequency. However, overlooked short geomagnetic reversals may exist in the geomagnetic polarity time scale (GPTS), which affects the estimation of the heat flux history. Here, we report four new high-precision 40Ar/39Ar ages of the Oligocene Ethiopian traps. The traps may contain undiscovered reversals in marine magnetic anomaly. Based on the ages, we identified new reversals in Chron C12n, which was not found in marine magnetic anomalies. Our non-parametric analysis of GPTS suggests four potential periods of missing geomagnetic reversals, which correspond to long polarity intervals in GPTS. We found that C12n correspond to one of the periods. This indicates that several undetected reversals may exist within or near the edge of long polarity intervals after the Cretaceous Normal Superchron (prolonged stable polarity period). Considering the undetected reversals, we conclude that the CMB heat flux increased more slowly and monotonically after the Superchron than that ever estimated.

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The SPICE carbon isotope excursion in Siberia: a combined study of the upper Middle Cambrian–lowermost Ordovician Kulyumbe River section, northwestern Siberian Platform

Geological Magazine ◽

10.1017/s0016756808004913 ◽

2008 ◽

Vol 145 (5) ◽

pp. 609-622 ◽

Cited By ~ 64

Author(s):

ARTEM KOUCHINSKY ◽

STEFAN BENGTSON ◽

YVES GALLET ◽

IGOR KOROVNIKOV ◽

VLADIMIR PAVLOV ◽

...

Keyword(s):

Carbon Isotope ◽

Siberian Platform ◽

Total Duration ◽

Local Maximum ◽

Magnetic Polarity ◽

Middle Cambrian ◽

Upper Cambrian ◽

Carbon Isotopic ◽

Reversal Frequency ◽

Northwestern Margin

AbstractAn integrated, high-resolution chemostratigraphic (C, O and Sr isotopes) and magnetostratigraphic study through the upper Middle Cambrian–lowermost Ordovician shallow-marine carbonates of the northwestern margin of the Siberian Platform is reported. The interval was analysed at the Kulyumbe section, which is exposed along the Kulyumbe River, an eastern tributary of the Enisej River. It comprises the upper Ust'-Brus, Labaz, Orakta, Kulyumbe, Ujgur and lower Iltyk formations and includes the Steptoean positive carbon isotopic excursion (SPICE) studied here in detail from upper Cambrian carbonates of the Siberian Platform for the first time. The peak of the excursion, showing δ13C positive values as high as +4.6‰ and least-altered87Sr/86Sr ratios of 0.70909, is reported herein from the Yurakhian Horizon of the Kulyumbe Formation. The stratigraphic position of the SPICE excursion does not support traditional correlation of the boundary between the Orakta and Labaz formations at the Kulyumbe River with its supposedly equivalent level in Australia, Laurentia, South China and Kazakhstan, where theGlyptagnostus stolidotusandG. reticulatusbiozones are known to immediately precede the SPICE excursion and span the Middle–Upper Cambrian boundary. The Cambrian–Ordovician boundary is probably situated in the middle Nyajan Horizon of the Iltyk Formation, in which carbon isotope values show a local maximum below a decrease in the upper part of the Nyajan Horizon, attributed herein to the Tremadocian Stage. A refined magnetic polarity sequence confirms that the geomagnetic reversal frequency was very high during Middle Cambrian times at 7–10 reversals per Ma, assuming a total duration of about 10 Ma and up to 100 magnetic intervals in the Middle Cambrian. By contrast, the sequence attributed herein to the Upper Cambrian on chemostratigraphic grounds contains only 10–11 magnetic intervals.

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