There are "young" and "ancient" stratigraphical models of bottom
sediments in the
. The "ancient" one is based on paleomagnetic analysis and revealing of
certain index-species. The "young" one based on the
dating and oxygen stable isotope composition.
The piston core from 26 cruise of r/v "Akademik Fedorov" from the western
flank of the Mendeleev Ridge (
water depth, total core length ~
) has been treated. Size fraction > 125 µm in all samples was used for
total planktonic and benthic foraminiferal abundance counts, and benthic
species identification. Foraminiferal analysis reveals five abundance
maxima of benthic foraminifera throughout the core, corresponding to
brown sediment beds. The same intervals characterized by planktonic
abundance maxima as well. The 0-15 and 20-
core intervals contain abundant assemblage of benthic foraminifera and are
characterized by high biodiversity. The benthic foraminifera species
composition probably reflects alternating inflow of Pacific and
waters in the time interval 34-183 kyrs. Oridorsalis tener are
numerous in 190-
interval. It is known they become dominant in oligotrophic environment.
interval separates two foraminifera abundance peaks from horizons that are
almost barren of benthic and planktonic fauna. The fauna absence could
possibly be explained with dissolution or other destruction processes.
In some samples of the interval there are black colored particles. Some
of them appeared to be foraminifer shells which are completely replaced
with ferric compounds. The foraminiferal assemblages generally
correspond with the faunas from the Mendeleev Ridge.
The age control was provided by three 23OTh/234U
dates. If the sediment age is determined correctly then benthic
foraminifera-rich units corresponds with the Mikulinian and Likhvinian
inerglaciations - MIS 5 (Marine Isotope Stages) and MIS 11. Similar age
dates were obtained earlier for northern Mendeleev Ridge. At the same
and aminoacide dates were obtained. They indicate the younger age of same
sediments. Benthic foraminifera-rich units in this case correspond to
the Middle Valdaian (MIS 3) and Mikulinian (MIS 5) interglaciations. The
problem of different dating methods could be considered as unsolved yet.