Lithostratigraphy of the CESAR cores

Sixteen piston cores and twelve gravity cores were successfull_v recoveredfrom northern and southern crests of the eastern Alpha Ridge andfrom the Alpha Ridge graben. All but one core contain late Cenozoic muds with variable amounts o.fsandto pebble-sized elastic material that probably reflects transport by ice during the past 4-5 Ma. Sixteen CenozoicHolocene lithostratigraphic units have been delimited on the basis o.f sediment texture. structure, colour, detrital carbonate and authigenicferromanganese content. The composition of the upper J 3 units in the CESAR cores is similar to the Fletcher's Ice Island cores; hence most units can be broadly correlated over most of the Central Arctic Ocean. Three new lithostratigraphic units (Al-A3) occur at the base o.f CESAR cores.from the northern Alpha Ridge crest. Paleomagnetic and palynological data indicate a Late Miocene-Early Pliocene age for unit A3, which confirms previous reports of a slow sedimentation rafe during the Cenozoic. CESAR core 6 was obtained from an erosional surface on top o.f a.fi. 1ult block at the north edge o.f the Alpha Ridge graben. This core contains ea. 2m o.f laminated diatom ooze of Campanian-Maastrichtian age and two ? Paleogene volcanic ash units below a brown mud unit which probably corresponds to units A2 and A3. The biosiliceous ooze contains no foraminifera or silico_flagellates and only few dino_flagellates. There is little d! fference in biogenic or elastic sediment content between light and dark laminae and the rhythmites do not appear to be annual varves produced in an upwel/ing environment. The microstructure and fluctuating mineral composition of the laminae most closely resemble those o.f laminated chert beds in the Triassic forearc basins of Japan. Resume Seize carottes ont ere prelevees au moyen d' une carotteuse a piston et douze au moven d' une carotteuse a chute fibre dans Les cretes nord et sud de la partie est de la dorsale Alpha et du graben de la dorsale Alpha. Toutes Les carottes sauf une contiennent des boues du Cenozoique recent ainsi que di verses quantites de materiau clastique dont les dimensions varient de celles du sable a celles du galet et dont la presence re_flete vraisemblablement un transport par la glace au cours des quatre ou cinq derniers millions d' annees. Seize unites lithostratigraphiques d' age cenozoi"que-holocene sont delimitees en fonction de la texture sedimentaire, la structure, la couleur et le contenu en materiau carbonate detritique et en ferromanganese authigene. La composition des treize unites superieures clans les carottes CESAR s' apparente a celle des carottes qui proviennent de /'fie de glace Fletcher et ces unites peuvent etre correlees plus OU mains sur la plus grande partie de /'ocean Arctique central. On a decele la presence de trois nouvelles unites lithostratigraphiques (Al d A3) d la base des carottes CESAR prelevees dans la crete nord de la dorsale Alpha. Les donnees paleomagnetiques et palynologiques indiquent que /'unite A3 date du Miocene recentPliocene ancien, ce qui confirme que la sedimentation s'est.faite lentement au cours du Cenozoi"que, conclusion a laquelle avaient abouti d' autres travaux. 1Atlantic Geoscience Centre, Bedford Institute of Oceanography, Box 1006, Dartmouth, Nova Scotia, B2Y 4A2