Sampling of an industrial drill string from the northeastern Paris Basin
(Montcornet, France) provides early Jurassic magnetostratigraphic data
coupled with biochronological control. About 375 paleomagnetic samples
were obtained from a 145 m thick series of Pliensbachian rocks. A
composite demagnetization thermal up to 300 C and an alternating field
up to 80 mT were used to separate the magnetic components. A low
unblocking temperature component (<250degreesC) with an inclination of
about 64 is interpreted as a present-day field overprint. The
characteristic remanent component with both normal and reversed
antipodal directions was isolated between 5 and 50 mT. Twenty-nine
polarity intervals were recognized. Correlation of these new results
from the Paris Basin with data from the Breggia Gorge section (Ticino,
southern Alps, Switzerland), which is generally considered as the
reference section for Pliensbachian magnetostratigraphy, reveals almost
identical patterns of magnetic polarity reversals. However, the
correlation implies significant paleontological age discrepancies.
Revised age assignments of biostratigraphic data of Breggia as well as
an objective evaluation of the uncertainties on zonal boundaries in both
Breggia and Moncornet resolve the initial discrepancies between
magnetostratigraphic correlations and biostratigraphic ages. Hence, the
sequence of magnetic reversals is significantly strengthened and the age
calibration is notably improved for the Pliensbachian, a stage for which
sections combining adequate magnetic signal and biostratigraphic
constraints are still very few. (C) 2002 Elsevier Science B.V. All
rights reserved.