V. Pavlov et Y. Gallet, UPPER CAMBRIAN TO MIDDLE ORDOVICIAN MAGNETOSTRATIGRAPHY FROM THE KULUMBE RIVER SECTION (NORTHWESTERN SIBERIA), Physics of the earth and planetary interiors, 108(1), 1998, pp. 49-59
We present the magnetostratigraphy of an Upper Cambrian to Middle Ordo
vician sedimentary section sampled along the Kulumbe river in northwes
tern Siberia. Thermal demagnetization yields the determination of two
magnetic components. A component of steep inclination is interpreted a
s a remagnetization acquired during the emplacement of the Siberian tr
aps at the Permian-Triassic boundary. Another component with a moderat
e inclination, essentially carried by hematite and sometimes by magnet
ite, likely represents a syndepositional or nearly syndepositional mag
netization of the studied deposits. A sequence of 17 magnetic interval
s is observed between the upper part of the Upper Cambrian and the Tre
madoc, three of them being poorly defined by single samples. We also f
ind that the Llanvirn magnetostratigraphic sequence contains only one
reversed polarity interval. Together with magnetostratigraphic results
previously obtained from the Moyero river section from Siberia, our d
ata suggest the occurrence of a 25-30 Myr-long period during the Lower
and the Middle Ordovician characterized by a very low magnetic revers
al frequency (possibly containing a superchron), and dominated by reve
rsed polarity. This geomagnetic feature would be compatible with a tim
e constant of about 150 Myr in the reversal process through the whole
Phanerozoic. (C) 1998 Elsevier Science B.V. All rights reserved.