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Discussion
Sedimentary environments of Lake Baikal
The three areas of Lake Baikal where deep boreholes
were drilled differ significantly by their sedimentary
environments. On the Academician Ridge, the drilling
site is isolated from the supply of the terrigenous mate-
rial by deep basins. On the Buguldeika Saddle, the
drilling site area is directly influenced by a fluvial sedi-
ment source. In Southern Basin, the drilling site is
representative of the deep central part of the rift
basin.
The different geomorphological settings at the
bottom of Lake Baikal are characterised by different
types of sedimentation processes (Fig. 8). On the
underwater highs, the hemipelagic sedimentation of
clay and fine silt takes place. The fine-grained sediment
settles from the water column. The dispersed coarse-
grained material is the contribution from ice rafting.
This type of hemipelagic sedimentation in Lake Baikal,
with low sedimentation rates on the topographic highs,
can be regarded as comparable to that occurring in the
central parts of the oceanic abyssal plains. At the
Buguldeika Saddle, which is another topographic high
in Lake Baikal, the sedimentary process has features of
hemipelagic sedimentation with a strong imprint of
sediment supply from tributaries, and turbidite deposi-
tion. The sedimentation in the deep Baikal basins is
similar to the oceanic sedimentation processes along a
continental slope or rise. This oceanic environment,
with slopes of 47 or less, is characterised by mass flows
and deposition of abundant turbidites reaching as far as
1000 km into the abyssal plain. In Lake Baikal, where
slopes reach 15–307, turbidites and mass flows become
the primary sedimentation mechanism on the steep
slope flanks of the Lake Baikal basins. These flows
carrying coarse material may reach across the lake
floor.
The age and rifting stages of Lake Baikal as recorded
on Academician Ridge
The sedimentary record of Lake Baikal enables us to
compare the interpretations of seismic data and the
reconstructions of the regional orogenic development
related to India/Eurasia collision (Molnar and
Tapponier 1975; Zonenshain and Savostin 1981) with
continuous sedimentary sections. The robust palaeo-
magnetic time scale established for the Lake Baikal
sedimentary record (BDP Members 1997b) is essential
for the age control of local and regional tectonic
models based on seismic and geological data
(Hutchinson et al. 1993; Kazmin et al. 1995; Moore et
al. 1997).
Numerous geological age models for the Lake
Baikal rifting stages are in general agreement. Most of
the models distinguish an initial phase of slow rifting, a
subsequent phase of fast rifting (beginning in mid-Plio-
cene) and also suggested another episode of fast subsi-
dence at the Pliocene–Pleistocene boundary
(Hutchinson et al. 1993). Kazmin et al. (1995) identified
four phases of rifting in Lake Baikal: early Miocene;
late Miocene; late Pliocene; and middle-late Pleisto-
cene. The upper 900 m of sedimentary strata at Acade-
mician Ridge are believed to have accumulated during
the past 2.5 Ma (Kazmin et al. 1995). This age estimate
implies a sharp intensification of uplift and subsidence
of different blocks in the late Pliocene. Fluvial supply
of terrigenous material by one of the Palaeo-Barguzin
channels is suggested as the main sediment source for
Academician Ridge from late Miocene till early Pleisto-
cene. According to the authors, the angular unconfor-
mity of middle-late Pleistocene age has marked the
beginning of another intense rifting phase (Kazmin et
al. 1995). Likewise, Moore et al. (1997) interpret the
upper boundary of seismic sequence B6 as a profound
depositional change at Academician Ridge, from a
shallow-water facies to the deep-water fine-grained
sediments associated with a sharp increase in the subsi-
dence rate in Lake Baikal. The distinct upper boundary
of sequence B10 was interpreted as an unconformity
caused pervasive widespread erosion in the lake asso-
ciated with the rejuvenation of rifting in the Northern
and Central Basins of Lake Baikal, and at Academician
Ridge. According to Moore et al. (1997), this erosional
event corresponds to the mid-Pliocene (3.5 Ma) initia-
tion of the Neobaikalian tectonic sub-stage (Mats
1993). However, the same unconformity on Academi-
cian Ridge was interpreted by Kazmin et al. (1995) as
the latest phase (middle-late Pleistocene) of intense
rifting.