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Using the seismic profiles VERE-92-2 Line 7
(Fig. 3A) and VERE-92-2 Line 12 (Fig. 3B), it is
possible to estimate the age of the widespread uncon-
formity across the Selenga and Buguldeika area asso-
ciated with the initiation of the uplift in Primorsky
Range (DB3 surface according to Scholz and
Hutchinson, this volume). The BDP-93 drill site lies
1.3 km from profile 12 and 0.5 km from profile 7.
Around the BDP-93 site the unconformity D3B lies at
approximately 0.7-s two-way travel time on profile 12
(Fig. 3B) and on profile 7 it plunges towards the shore
to the northwest and lies approximately at 0.75 s two-
way travel time (Fig. 3A). Using the seismic velocity
value at 100 m sediment depth measured at Academi-
cian Ridge, and accounting for differences in water
depth between the BDP-93 and BDP-96 sites, we find
that D3B lies at approximately 162 m sediment depth
on profile 12 and at approximately 199 m sediment
depth on profile 7. By extrapolating the average sedi-
mentation rate of BDP-93 (15 cm/ka) down the section,
the age of the bottom of the sequence overlaying the
boundary D3B can be estimated as 1.07 Ma (profile 12)
to 1.31 Ma (profile 7). This age range constrains the
timing of the uplift of Primorsky range marked by
erosional boundary D3B. The new age estimate for the
base of the overlying sequence according to BDP-93
data exceeds the previous age estimate for initiation of
Primorsky Range uplift placed at 0.8–0.7 Ma by Mats
(1993).
range of different sedimentary environments are distin-
guished in Lake Baikal. The BDP-97 borehole demon-
strates that turbidite deposition is the dominant sedi-
mentation process in the deep basins of Lake Baikal.
The thickness of individual coarse sand and gravel
turbidites reaches 1.5 m, which is a unique feature for
lacustrine systems.
Lake Baikal is the only freshwater basin in the world
whose sediments contain gas hydrates. This unique
feature allows studying the thermodynamics of gas-
hydrate formation in fresh waters as compared with
those in salt waters on the continental slopes and in
marginal seas. These studies will become an important
contribution to understanding the process of oil and gas
formation.
The BDP-96 section drilled at Academician Ridge
yields important implications for the history of the rift
basin development. The following features interpreted
from seismic stratigraphic models are not supported by
the actual lithology and magnetic age model of the
BDP-96 boreholes and might have to be re-evaluated:
1. It is unlikely that a channel of the Barguzin River
was the sediment source for Academician Ridge
throughout late Cenozoic.
2. There is no evidence for a pervasive basin-wide
unconformity of Pliocene or Pleistocene age in the
BDP-96 cores, but instead this boundary corre-
sponds to a dramatic lithological change from diato-
maceous ooze to diatom-barren silty clay over
approximately 10 m interval of core depth.
3. The lithology reveals no evidence for a depositional
change from shallow-water to deep-water facies at
the boundary of the seismic stratigraphic complexes
and for intense lake-level fluctuations and transgres-
sions during the Pliocene at Academician Ridge,
because the complete 5 Ma section was formed by
continuous hemipelagic sedimentation.
4. Correlation of the lithology of BDP-96 with seismic
profiles allows us to constrain the age of the B10
seismic boundary, which marks a phase of intense
rifting and drastic changes in sedimentation
throughout the Lake Baikal basin. Previously, this
boundary was estimated as late Pliocene (3.5 Ma;
Moore et al. 1997) or as middle-late Pleistocene
(Kazmin et al. 1995). The BDP-96 record yields a
new age of 2.5 Ma for the B10 seismic boundary.
This estimate suggests that the upper sequence of
the Northern Basin (1.5–1.7 km thick) formed
during the last 2.5 Ma with average sedimentation
rates of 60–70 cm/ka.
The Buguldeika borehole BDP-93 suggests that the
uplift in the Primorsky Range took place prior to 1.07
and 1.31 Ma, which exceeds the age of the geological
model of Mats (1993) based on on-shore sections.
National Science Foundation (grants EAR-93-17204 and EAR-
94-13957 to D.F. Williams), and by the Science and Technology
Agency, Japan. The authors thank the crew of the R/V Ulan-Ude
for the successful transportation of the drilling complex through
the ice, the members of the Nedra drilling team for the successful
implementation of the technical program of drilling, and the
research groups of the Institute of Geochemistry and the Limno-
logical Institute who took part in core description and sampling.
We thank the reviewers D. Hutchinson and S. Back for their
constructive comments.