Volume 8, numéro 2, june 1981

EN :

Sediments in cores collected from theScotian and Labrador shelves contain afaunal discontinuity where older benthicforaminiferal assemblages dominated byElphidium excavatum f. clavata change tomore diverse present day continentalshelf assemblages. A similar change isfound in Late Quaternary borings inDenmark (Jutland) and in the Oslofjordarea of Norway. The ,4C age of the faunalbreak varies from 10,000 years B.P. in theEuropean sediments to 13,000 years B.P.on the Scotian Shelf and 15,000 yearsB.P. on the Labrador Shelf.

The present day océanographie settingalong the coasts of Norway, Denmarkand eastern Canada was establshedwhen the glacial ice retreated inland. Thedominance of E. excavatum f. clavata inthe older sediments is related to dilutedand cold coastal waters during the timewhen continental ice was ablating on theinner shelf. The disappearance of E,excavatum f. clavata therefore can beused to estimate the Late Glacial-Postglacial boundary in the Canadianand Scandinavian North Atlantic contin-ental shelf sediments. This paper reviewsthe evidence of the faunal break to alertgeologists in its possible use.

EN :

Paleomagnetism is used in Pleistocenestratigraphie studies as a tool for correla-tion and relative age dating of equivalentstrata or for the absolute dating of depos-its. The method is based on the detectionof changes in the earth's magnetic fieldand especially changes of polarity thatare recorded by ferromagnetic sedimentsat the time of deposition.

The study of paleomagnetism as ageophysical dating method began in the1960s and has grown geometricallysince. Instrumentation has greatlyimproved and the statistical analysis ofdata, so essential to the proper interpre-tation of the magnetic record, would nothave been possible without computerfacilities.

Fine-grained sediments and lava flowsare the two media most frequently used.Because reversals have occurred repeat-edly in the past, their identification withinincomplete sedimentary records is onlypossible through comparison with otherstratigraphie or radiometric data col-lected for similar or related sedimentarysequences. Continuously depositedmarine or terrestrial sediments whichshow a high sedimentation rate provideisochrons which can be used for world-wide correlation. The recent flourish ofresearch activity into the secular variationof the earth's non-dipole field promises togreatly refine and embellish the geomag-netic time table for the Pleistocene.