Late Quaternary turbidite systems in Lake Baikal, Russia C.H. Nelson1, E.B. Karabanov2 and S.M. Colman3

'l·s <~c·ologica\ Sur.-ey. Branch of l'acilk .~brint· Geology. ·' 4) Yliddlefield Road . \IS-999 .\lenlo Park . CA 9402'i. l'SA

!Limnological Institute. Academy of Scicnn:. lrku~:->k. Kussi~l. Pn:sem addre:-;s : lkpartnH:nt of Ccologicd SciL·nn:s. l 'n iH:Ts ity of South Carolina. Columhia. SC 2920H. t.:SA

.~LS Gl'ological Surn'Y. Woods Hok. :vtA. LSA

lntroduction Lake Baikai is the world's deepest (1637 m) and oldest (Late Oligocene- Early Miocene) Iake, with a length of 636 km and a width ranging from 30 to 87 km (Karabanov and Fialkov 1987; Mats 1992). It is located in south-eastern Siberia within the Baikai Rift System at the southern edge of the Siberian Platform (Hutchinson et al. 1992; Mats 1992). The borders of Lake Baikai are characterized by high topogra phic relief that reaches 2700 m in the intensely glaciated mountains on the eastern side of the North basin (Atlas of the Irkutsk Region, Lake Baikai 1:500000 map). Several small rivers drain the !arge glacial valleys into this north-eastern side of the Iake (Fig. 6.1). The !arge Selenga River flows into the south-eastern side of the Iake from north central Mongolia. The muddy delta of this dominant sediment source progrades far into the Iake and overlies the accommodation zone ridge between the Central and South basins (Fig. 6.1). Only local streams of less than 20 km length feed numerous coarse-grained fan deltas and alluvial fans along the western margin of the Iake (Atlas of the Irkutsk Region, Lake Baikai 1:500000 map; Mats 1992).

All of the Iake basins exhibit an asymmetric morphology with steep border fault margins on the western side and a more gradual ramp on the eastern side (Hutchinson et al. 1992; Mats 1992). Because there is only a 100-500m wide shelf on the western side of the Iake, sediment feeds directly on to the steep basin slopes (Fig. 6.1). The Iake shelf is 500-2000m wide on the eastern side, except where it is much wider (20 km) surroLmding the Selenga Delta (Fig. 6.1 ). The shelf araund the delta is cut by fault-controlled troughs

LAKE BAIKAL

EXPLANATION

- Setsmoc Renectoon Proflies

COre slauons

-- Sothymeuy (SOOmCon<ou- lnteNai)

- nA Prof\le Loca.uon ancl F"IQI.n!l Number

• 12 Cores Sho'Ml 1n Ftgu~:;.

Fig. 6.1. Bathymetric map of Lake Baikai showing the location of the 3.5 kHz and watergun seismic-reflection tracklines and core locations occupied in 1990-1991. Numbered cores and tracklines are keyed for Figs 6.2-6.5.

that funnel the river-derived sediment into the Central and Southern basins (Colman et al. 1992a, b; Mats 1992).

In this study seismic-reflection profiles and coincident piston-core transects were utilized to describe the main types of turbidite systems that are associated with the different sediment sources and morphologic setrings of the basins. The profHing equipment included a 3.5 kHz system that gave c. 0.5 m resolution with up to 30-50 m penetration, and a broad-band watergun system (100-1060 Hz) that gave about 1-2m resolution with up to 300 m penetration (Colman et al. 1992a). Navigation to a precision of about 50-100m was obtained by Global Positioning Satellites.

Cores with the greatest length were selected from this project, and from numerous previous Russian

0 50 IOO KM I I I I I I. I I I I

studies, to provide correlative sedimentary-facies information for the profile transects. Only general coarse-grained turbidite facies and grain sizes are shown for the transects. In more detail, the sediment stratigraphy and lithology typically consists of an upper diatomaceous, fine-grained hemipelagic mud that is inter-bedded with thin sand or coarse silt layers that grade to thick turbidite mud (Fig. 6.2). This upper unit with a high content of diatoms, biogenic silica and total organic carbon correlates approximately with Holocene (postglacial) time (Fig. 6.2) (Colman et al. 1992a, b; Karabanov et al. 1992; Qui et al. 1993). The Late Pleistocene glacial unit below consists mainly of unfossiliferous massive clay with occasional silt Iamina that is inter-bedded with graded sand or coarse silt beds that tend to be thicker and coarser-grained than Holocene turbidites. The lower unit also contains

Atlas of Deep Water Environments: Architectural s(yle in turhidite ~ystems. Edited by K.T. Pickering, R.N. Hiscott, N.H. Kenyon, F. Ricci Lucchi and R.D.A. Smith. Published in 1995 by Chapman & Hall, London. ISBN 0 412 56110 7.

diamicton beds of glacial lacustrine sediment (Karabanov et al. 1992). These lithologies and the base of the upper diatomaceous Stratigraphie unit have been used to establish the Holocene to Pleistocene boundary in cores at alllocations (Figs 6.3-6.5) .

Base-of-slope sand-rich aprons Small base-of-slope sand-rich aprons generally are present at the base of the border fault on the north­western side of the Lake Baikai basins (Fig. 6.3). Similar to other sand-rich aprons (Nelson et al. 1991), they are characterized on seismic reflection profiles by high amplitude, discontinuous and wedging reflections that extend a few kilometres out from the base-of­slope. No channels areevident in the apron profiles and reflections gradually become flatter lying and more continuous downslope as the aprons grade into basin plain deposits (Fig. 6.3) .

At the basin edge, proximal sand-rich aprons typically are dominared by thick sand and gravel beds (Nelson et al. 1986, 1991), which also appears to be the case in Lake Baikal. Several sampling attempts 2-3 km upslope from core 1 (Fig. 6.1) could not penetrate beyond Holocene mud. In the distal apron and continuing downslope into the basin plain, numerous turbidite sand beds occur in the Late Pleistocene deposits (Fig. 6.3). The lithology of the proximal to distal sand layers and the seismic stratigraphy show the longitudinal continuity of these numerous apron systems that feed sediment laterally into the north to south elongate basin plains of Lake Baikai (Fig. 6.1).

The high net sand content and thicker individual sand beds exhibited by Late Pleistocene deposits suggests that turbidite systems carried more coarse­grained sediment more frequently at that time compared to Holocene time (Fig. 6.3). The turbidite systems are active during the Holocene; however, turbidite muds predominate (Fig. 6.2). The importance of these Holocene turbidites is shown by the thick Holocene basin plain deposits which have ponded to the east of the fault that cuts the eastern edge of the apron (Fig. 6.3).

•

LITHOLOGY OF CORE 323

DIATOM AV. AMOUNT 0 5 10 15 20 25%

0-

400 =

450-=

~ DIATOM MUD + 8 (:;:.-:;:~ TURBIDIT M UD

... TURBIDITE SAND ~ GRAY LAY W/

S AMJNAE + 8 PJ-U M AN DIAMET E R

Sand-rich fans The north-eastern and south-eastern sides of the basin floors bordering the most extensively glaciated regions of the Iake margin are characterized by small sand-rich fans (Nelson et al. 1991). Data from one of the Iargest of these fans, forming off the Tompuda River, shows proximal inner fan gradients of 1:20 and distal outer fan gradients of 1:150 over a total fan length of c.

15 km (Fig. 6.4A). Near 775 m water depth the slightly concave upward inner fan with steep gradients changes to a middle fan area with reduced slope

SEDIMENT AGE 0 5 10 15 20 2Ska BP

I I I I I I I

~ \ \ \ \ Fig. 6.2. Lithology, median

grain size (mm) of mainly mud interbeds, diatarn abundance estimated from smear slides and radiocarbon age for USGS core 323-PCl. Phi mean diameter data are modified from Takemura et al. 0992), average diatom amounts are calculated from smear slide counts of Felton (Bureau of Mineral Resources, Canberra, Australia, personal communication, 1991) and corrected radiocarbon ages are modified from Ogura (1992). Original radiocarbon dates derived from total bulk

\ \ \

.~ ' ' I I I I I I I I I

' I I I I I I I I I

* I I I I I I I I I \ I I I I I I I I I I I I I I I I I I

' I I I I I I I I

CORRECTED I SAMPLE AGE- 1

organic carbon are shown along with the best estimate of corrected age of the sediment based on lass of 16 cm of sediment from 323-PCl correlated with its trigger core. See Fig. 6.1 for core location.

I 0 10 20 30 40 50cmlka SEDIMENTATION RATE

gradients and a slightly convex upward profile. The echo character of the entire longitudinal 3.5 kHz profile exhibits high reflectivity and no penetratior1, suggesting thick near-surface sand layers (Damuth 1980). A 3.5 kHz transverse profile across the middle fan shows the same character, i.e. high reflectivity and no penetration with a highly convex upward shape and numerous channels over a central depositional lobe area (Fig. 6.4B). Multiple channels c. 100m wide and 10m deep characterize these convex lobe deposits.

The high-resolution transverse profile grades

laterally on either side of the lobe area to lower reflectivity, deeper penetration and development of flat lying reflectors with continuity (Fig. 6.4B). The lateral characteristics are typical of the basin plain and fan fringe deposits that enclose channelized middle fan depositionallobes. In the watergun transverse profile, these lateral basin plain deposits are observed to onlap the channelized and lenticular stacked depositional Iobes of the middle fan (Fig. 6.4C).

The near-surface sediment facies observed in cores generally confirms the echo character of the high­resolution profiles. High quantities of sand occur in the Late Pleistocene deposits of the inner and middle fan, although the sand content may vary depending on whether channel or interchannel deposits (e.g. core 7) have been sampled (Fig. 6.4A and B). The Holocene deposits do not exhibit extensive sand-rich facies, perhaps because of the change of sedimentary regimes in postglacial environments. This may explain why core 7, which has only a slight penetration into Late Pleistocene sediment and is located in a slight swale between middle fan Iobes, does not show high sand contents (Fig. 6.4A).

Similar to the basin plain deposits downslope from aprons on the west side of the Iake floor (Fig. 6.3B) there are generally thick Holocene deposits in basin plain regions to the south of the Tompuda Fan; thus, Late Pleistocene basin plain facies are not penetrated by our cores (Fig. 6.4B, cores 9 and 10). Where Late Pleistocene facies are penetrated in basin plain areas near aprons or sand-rich fans, sand beds are common (Fig. 6.3B, core 4 and 6.4B, core 8) because of the numerous nearby turbidite systems in the base-of-slope areas that can feed laterally into the narrow basin plains (Fig. 6.1). More mud may pondagairrst recent fault scarps that cut the basin plain (Fig. 6.3A and B, core 2).

Selenga mud-rich fan The largest canyon draining north-eastward from the Selenga Delta is the main source for the largest sub­lacustrine fan in Lake Baikai (Fig. 6.1). This Selenga­fed fan extends 65 km in length to cover the south-western half of the Central basin (Figs 6.1 and 6.5). The high reflectivity echo character of the complete longitudinal profile suggests that sand is common throughout the entire fan and into the basin plain (Fig. 6.SA). The transverse profile shows that apparent channels of 5-20 m relief and 50-100 m width occur on the surface of the proximal fan. The better penetration and continuity of reflectors in overbank areas between channels and the high amplitude

reflectors in channel floors suggests the classical pattern of thin-bedded sands in overbank deposits and thicker sand beds on channel floors (Fig. 6.5B).

The single transect of cores that extends longitudinally down the fan cannot confirm the transverse channel and interchannel echo character (Figs 6.1 and 6.5). The proximal core 11, however, appears to be from an interchannel area on a bathymetric high and exhibits only thin-bedded sands (Fig. 6.5B). In addition, core 12 near an apparent channel (Fig. 6.5A) contains many sand beds, although neither core 11 nor 12 penetrates Late Pleistocene deposits. The lower fan cores do penetrate into Pleistocene sediment but contain only thin sand beds (Fig. 6.SA). The lower fan observations, and the shipboard descriptions of mainly silty turbidites in the proximal fan areas surrounding the Selenga Delta, suggest that the Selenga-derived fan is more mud-rich than the other smaller sand-rich turbidite systems of the Lake Baikai basins.

Acknowledgements The authors acknowledge the numerous other shipboard scientists and crew members for assisting with the collection of data. Susan Carter, ] im McRea, ]r, and M. Moffett helped complete Iabaratory analyses and compilation of data. Anne Felton kindly provided field descriptions of 1991 USGS Core Smear Slides. Helpful reviews were provided by Paul Carlson and Serge Berne. This study was supported by the USGS Global Change and Climate History Program and the Limnological Institute of the Siberian Branch of the Russian Academy of Sciences.

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900 ..

I ' I I

0 Skm I I - 1000

--------------------------------------------~~ 700m

A w

11 - BORDER FAULT

0 I

BASE-OF-SLOPE SAND-RICH APRON

Skm I

E

1-- 800

BASIN PLAIN

~ 1000

Fig. 6.3. Continuous seismic reflection profiles and core transects from a north basin apron and basin plain in Lake Baikal. (A) Longitudinal 3.5 kHz profilethat proceeds W-E from proximal to distal apron to basin plain environments (V.E. x 45). (B) Watergun profile of a complete north basin W-E cross-section that covers the same trackline as the 3.5 kHz profile in (A) (V.E. x 124). All piston core locations are keyed on (B), but interpretation of apron seismic facies is not relevant because of the small scale. Net sand percentage is calculated by summing the total thickness of sand layers (shown by the dark shading) and dividihg by the respective Holocene, Late Pleistocene or total Late Quaternary core length. See Fig. 6.1 for location of seismic profile tracklines and cores.

~--------------------------------~~ 600m

8 w E

BORDER FAULT

I APRON BASIN PLAIN

RAMP

800 CORE 1

1000

·-----------~----

0 10km I

1200

NORTH BASIN APRON (1) & BASIN PLAIN (2-4) W-E TRANSECT 1 2 3 4

5.7

7.3 PHI MEAN DIAMETER

8.3

(NET SAND 5%)

HOLOCENE ..............• PLEISTOCENE ~

(NET SAND 33%) i

7.8 5.7

• I • I • • I I • • I I • I

~

(NET SAND 8%)

HOLOCENE

r············ : PLEISTOCENE

: (NET SAND I 7%) • • . . • • • • • . • • •

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\ 11,800 BP I I I . I • I I I I I I I I I

NET SAND 10% ~ (NET SAND 6%)

(TOTALCORE) L."!.~~9::.~: PLE.ISTOCENE (NET SAND 33%)

SAND LAYER

NETSANDO % NET SAND 14 % (TOTAL CORE)

NETSAND 23% (TOTAL CORE)

600 m

w A E CORE s

SAND-AICH FAN I tf. J

INNER FA 700 ;---·"-

800

0 Skm 900

~----------------------------------~~-----------------------------------r- 700m

8 s BASIN PLAIN SAND-AICH FAN LOBES

CHANNELS CORE 7

.......,,o_9 _ _ • _JJ--"':'::. I

0 I

Skm I

r---------------------- 600 m c s N

800

1000

0 5km 1200

L--l

N BASIN PLAIN 8

I- soo -- 900

~ 1000

c s N BASIN SAND-AICH FAN LOBES BASIN PLAIN

9 PLAIN CORE. 7 8

I I - I ..,.":::.. '-..:. - '-"""--~ ~ =-~_...::::::::::------=-- ~ ~ --~

--------------..__-=--------------~------~ ~~~ ~~~ -::-~-~ ~--------~ ~ - . =::::· . --------~~ .=-:::-:----:::

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~

NORTH BASIN SAND-AICH FAN LONGITUDINAL W-E TRANSECT

6 ~

= t: r.:l Q

7

3 .8 PHMEAH DIAMETER

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; I I :

I I

; (NET SAND 5") I

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(NETSAND"")

....

-:: NE.T SAND 5% -:: (TOT AL CORE)

-= 350-=

-= -= -= -= -= -= -=

6

(NETSANO""l HOLOCENE ····--------··· PLE.ISTOCENE '•

(NET SAND'"") •

5

(NET SAND 5") HOI.OCE.NE "Pt."Eis;ocEN·e·

(NET SAND 48%)

NE.T SAND 40% (TOTAL CORE)

SAND LAYER

-= NE.T SAND 13% (TOTAL CORE)

Fig. 6.4. Continuous seismic-reflection profiles and core transects from a north basin sand-rich Tompuda Fan in Lake Baikal. (A) Longitudinal 3.5 kHz profile (V.E. x 48) showing the E- W proximal to distal downfan cross-section and associated piston core transect. (B) Transverse N- S 3.5 kHz profile (V.E. x 36) and associated piston cores across the middle fan and adjacent basin plain. (C) Transverse N-S watergun profile across the middle fan and adjacent basin plain (V.E. x 45). See Fig. 6.1 for location of seismic profile tracklines and cores.

600 m NORTH BASIN SAND-AICH FAN TRANSVERSE S·N TRANSECT

10 9 7 (~.:., 8

800

G l 50 ~ NETSAND 15%

?

-= ... 1000 i5 -= \ (NI'T....., ... ,

200-= HOI.OCENE

t \~ r••••••••••• -:: • PI.EISTOCENE

-:: \ ,. i (NeT SAH[) No) oo

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-= . l Q

150-= \ ..

- "\. . NET SAND 111%

i (TOT AL CORE)

-= . 1200 300-=

,.\. ? -:: NETSAND 5%

NETSAND 5% (TOT AL CORE)

-350-=

(a) ~----------------------------------------------------------------------------------------------~800 m sw ~'

INNER FAN 11 I . .

0 I

10km I

SELENGA MUD-RICH MIDDLE FAN

CHANNEL / --

12 I

A

OUTER FAN 13

I ~- ---- -- .

CORE 14

..... __ ,..__ .. Js_·

NE

1200

BASIN PLAIN I

"'I'

1600

(b) -----------------------------------------------r-900m w E

Fig. 6.5. Continuous seismic-reflection profiles and core transects from Selenga Fan. (A) Longitudinal 3.5 kHz profile (V.E. X 15) SW- NE showing the proximal to distal downfan cross-section and associated piston core transect. (B) TransverseW-E 3.5 kHz profile across the inner fan (V.E. x 2.3). See Fig. 6.1 for location of seismic profile tracklines and cores.

(c) SELENGA MUD-RICH FAN SW-NE TRANSECT SELENGA MUD-RICH INNER FAN

CHANNELS

/ I

0 SOOm 8

Heferences Colman, S.M. and Lake Baikai Paleoclimate Project Members.

1992a. Initial Results of the Joint American-Russian Project on the Paleoclimate Record of Lake Baikal, Southeastern Siberia. EOS Transactions, American Geophysical Union, 73, 457, 460--462.

Colman, S.M. , Karabanov, E.B., Williams, D.F. , Hearn, Jr, P.P. , King, J.W., Oren, W.H., Bradbury, J.P. , Shanks, III, W.C., Jones, G.A. and Carter, S.W. 1992b. Lake Baikai Paleoclimate Project, Southeastern Siberia: Initial dating and paleoenvironmental results. In: Horie, S. (ed.) Intemational Profeeton Paleolimnology and Late Cenozoic Climate News/etter, Kyoto University, Japan, 6, 30-39.

Damuth, J.E. 1980. Use of high frequency (3.5-12 kHz) echograms in the study of near-bottom Sedimentation processes in the deep sea. A review. Marine Geology, 38, 51-75.

Hutchinson, D.R., Golmshtok, A.]., Zonenshain, L.P. , Moore,

1000

1 100

1200

T.C., Scholz, C.A. and Klitgord, K.D. 1992. Depositional and tectonic framework of the rift basins of Lake Baikai from multichannel seismic data. Geology, 20, 589-593.

Karabanov, E.V., Bezrukova, E., Granina, L. , Inouchi, Y. , Lazo, F., Letunova, P., Mukhina, V., Shimaraeva, M. and Stolbova, E. 1992. Climatic Sedimentation rhythms of Baikai sediments. In: Horie, S. (ed.) Intemational Profeet on Paleolimnology and Late Cenozoic Climate News/etter, Kyoto University, Japan, 6, 21-30.

Karabanov, E.V. and Fialkov, V.A. 1987. Baikat Canyon Morphology. Academy Nauk Siberian Branch Limnological Institute , Novosibersk, Russia, 104 pp.

Mats, V.D. 1992. The Structure and Evolution ofthe Baikat Rift Depression. Baikai Center for Ecological Research, Reprint 1, Irkutsk, Russia, 70 pp.

Nelson, C.H., Meyer, A.W. , Thor, D. and Larsen, M.L. 1986. Crater Lake, Oregon: A restricted basin with base-of-slope aprons of nonchannelized turbidites. Geology, 14, 238-241.

Nelson, C.H., Maldonado, A., Barber, Jr, J.H. and Alonso, B.

1991. Modern sand-rich and mud-rich siliciclastic aprons: Alternative base-of-slope turbidite systems to submarine fans. In: Weimer, P. and Link, M.H. (eds) Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Systems. Springer-Verlag, New York, pp. 171-190.

Ogura, K. 1992. A preliminary report on ,.,C ages of a 4.6 m long core sample of Lake Baikal. In: Horie, S. (ed.) Intemational Profeet on Paleolimnology and Late Cenozoic Climate News/etter, Kyoto University, Japan, 6 , 123-124.

Qui, L. , Williams, D.F. , Gvorzdkov, A., Karabanov, E.V. and Shimaraeva, M. 1993. Biogenie silica accumulation and paleoproductivity in the northern basin of Lake Baikai during the Holocene . Geology, 21, 25-36.

Takemura, K., Marui, A. and Horie, S. 1992. Comments on the core sample 323-PC1 of Lake Baikai from the sedimentary viewpo int. In: Horie , S. (ed.) International Profeet on Paleolimnology and Late Cenozoic Climate News/etter, Kyoto University, Japan, 6, 72- 79.

11 o--

25 -

so -15 -

I -125 -

ISO -

115-

200 -

225 -

250 -- NETSANO 6%

275 -

12

= NETSAND 39%

(NET SAND 11%) HOLOCENE

~-------······· . PLEISTOCENE . . (NET SAND 5%) . . i :

i : : !

300 -= .. SAND LA VER 325-

JSO -

JS3-

400-

425-

450 -

415 -

525-

550-S1S-

600-

NET SAN06'4 (TOTAL CORE)

13 14

···• ... .. ··-. ~-~

NETSAND 14%