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) and contain less water (40%). However, unlike
the BDP-93 Buguldeika cores, the BDP-96 cores from
Academician Ridge reveal a rhythmic structure for the
entire length of the recovered section, whereas in BDP-
93 sediments the water content of the sediment was
steadily decreasing with depth.
A consistent trend of decreasing average diatom
abundance towards the top of the core is observed in
BDP-96 (Fig. 4). Below 110 m, diatom abundance is
high and does not drop below 15–20%. The interval at
110–100 m is characterised by low diatom abundance
and high clay content. This minimum is followed by
another diatom-rich interval at 100–65 m and yet
another deep minimum in diatom abundance at
65–60 m (Fig. 4). The top portion of the section is char-
acterised by high-amplitude fluctuations in diatom
abundance reflecting the regular alternation of layers
of diatomaceous ooze and silty clay (Fig. 4).
The lithological studies of the BDP-96 cores allow us
to make several important conclusions:
sediments suggests that the conditions of sedimenta-
tion, which presently correspond to the hemipelagic
lacustrine facies, were practically invariable for the
whole time interval of the sediment accumulation.
2. The rhythmic structure characteristic of the whole
length of the section is caused by global climatic
fluctuations in agreement with previous reconstruc-
tions (Bezrukova et al. 1991; BDP Members 1995,
1997a, 1997b, 1998; Colman et al. 1995; Grachev et
al. 1997).
3. The amplitude and frequency of variations in litho-
logy are much stronger in the upper 60 m of the
section than they are below (Fig. 4).
4. There is no evidence for erosional boundaries in the
lithology of the cores. This suggests that sedimenta-
tion at Academician Ridge was continuous for the
time period covered by BDP-96 cores. The magnetic
age model indicates that the section is continuous
and that the sedimentation rate remained remark-
ably stable for the last 5 Ma, with an approximate
average of 4 cm/ka (Kuzmin et al. 1997; Williams et
al. 1997; BDP Members 1997b, 1998).
Academician Ridge is a distinct topographic high
within the lake with a depth of 350–400 m. It borders
with a basin which is 500 m deeper in the northwest and
with a basin which is 1000–1200 m deeper in the south-
east. Such topography restricts sedimentation to the
accumulation of fine hemipelagic sediments settling
from the water column with contribution from ice-
rafted debris, and prevents the influence of turbidites
and mass-flow processes originating on the steep slopes
of the rift basin. Seismic profile 92-15 showing the posi-
tion of the BDP-96 drilling site (Fig. 5) demonstrates
mician Ridge. Three seismic stratigraphic complexes
are distinguished in the profile that are separated by
two major unconformities: B6 (lower) and B10 (upper;
Moore et al. 1997). The lower complex represents the
sediments of the delta of the Palaeo-Barguzin River
and shallow-water environments (Moore et al. 1997).
The middle complex represents the stratified sediments
with weaker and less continuous seismic signals. This
seismic pattern appears to reflect deposition in a grad-
ually deepening lake basin. The upper complex consists
of the undisturbed sub-parallel layers of fine sediments
that present the hemipelagic sedimentation of a deep
lake (Moore et al. 1997). The BDP-96 boreholes recov-
ered the uppermost complex (Fig. 5).
BDP-97, Southern Basin