Moulin M., Fluteau F., Courtillot V., Marsh J., Delpech G., Quidelleur X., Gérard Martine, Jay A. E. (2011). An attempt to constrain the age, duration, and eruptive history of the Karoo flood basalt : Naude's Nek section (South Africa). Journal of Geophysical Research. Solid Earth, 116, B07403. ISSN 0148-0227.
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An attempt to constrain the age, duration, and eruptive history of the Karoo flood basalt : Naude's Nek section (South Africa)
We have carried out paleomagnetic sampling of a similar to 750 m sequence of the Karoo large igneous province (Naude's Nek Pass, South Africa). K-Ar dating (Cassignol-Gillot) has been performed on four samples from the 650 m upper unit (mean age 179.2 +/- 1.8 Ma) and a sample from the lower unit (184.8 +/- 2.6 Ma). A succession of two phases of volcanism is suggested. The lower 25 flows (115 m thick) have recorded a reversed polarity; the next 23 flows (135 m thick) are transitional and contribute a detailed record of the "Van Zijl" (1962) Jurassic reversal. The upper 38 flows (500 m thick) have normal polarity. Directional groups (DGs) of lava flows with quasi-identical remanence directions indicate eruption durations too short to have recorded geomagnetic secular variation and hence are interpreted as single eruptive events. Altogether, 19 DGs and 10 sheet lobes yield a sequence of 29 distinct directions. This could correspond to a total eruptive activity shorter than 3000 years, less than one per mil of the total duration over which the section was emplaced. We obtain a new paleomagnetic pole for South Africa at similar to 180 Ma (lambda = 75.2 degrees N, phi = 276.4 degrees E, A(95) = 5.8 degrees, N = 19), which is consistent with earlier reports.
