Palynostratigraphy of Oligocene-Miocene continental deposits in Southwestern Siberia

540

ISSN 0869-5938, Stratigraphy and Geological Correlation, 2008, Vol. 16, No. 5, pp. 540–552. © Pleiades Publishing, Ltd., 2008.Original Russian Text © O.B. Kuz’mina, B.S. Volkova, 2008, published in Stratigrafiya. Geologicheskaya Korrelyatsiya, 2008, Vol. 16, No. 5, pp. 87–100.

INTRODUCTION

The Paleogene and Neogene deposits are wide-spread in West Siberia, although they are usually con-cealed under Quaternary sediments, being accessiblefor investigation in drill holes only. Palynological anal-ysis is so far the most productive method for subdivi-sion of these deposits containing diverse assemblagesof palynomorphs. First palynological data used to getinsight into the Paleogene–Neogene palynostratigraphyof West Siberia have been obtained in the 1960s–1970s(Panova, 1971). Afterward, the main attention was paidto investigation of the Paleogene marine deposits con-taining dinocysts, which enable distant correlations andcoordination with subdivisions of the Internationalscale (Kul’kova, 1998; Akhmet’ev et al., 2004; Benia-movski et al., 2002; Volkova et al., 2005). At present,continental deposits are characterized in detail from theside of paleocarpology and paleomagnetic data (Gni-bidenko, 2006; Nikitin, 1999). Spores and pollen arewell studied in the composite section of the Tomskregion near the Ob River (Il’enok et al., 1989). In south-ern part of West Siberia, new extensive data obtained bydrilling in 1999–2001 and their analysis considerablyenhanced our understanding of palynostratigraphy incontinental sequences of the Oligocene and Miocene.The expectable innovations are especially significantfor the Baraba and Kulunda lithofacies zones of theplain. This work is continuation of previous studieddedicated to investigation results of recent years andtheir generalization.

MATERIALS AND INVESTIGATION METHODS

We studied 650 samples in total, which have beencollected from 16 localities situated largely in southernpart of West Siberia (Ishim, Baraba, and Kulunda litho-facies zones) and from three section of the Centrallithofacies zone of the plain (Fig. 1). Kuz’mina sam-pled five borehole sections directly during the processof drilling (fieldworks of 2000–2001 in the Novosibirskand Omsk oblast and in the Altay krai). In addition, westudied core samples collected by C.P. Kaz’min fromboreholes 10 and 15 (Novosibirsk oblast, collection of2000), by V.D. Dergachev, Zh.A. Dolya and T.M. Muratovfrom boreholes 01-BP, 07-BP, 011-BP, 2, 6, 9, and 13(Omsk and Novosibirsk oblast, collections of 1999–2000), and by T.A. Alekseeva from Borehole 13(Tyumen oblast, collection of 1999). Samples from nat-ural outcrops at the Tym (Belyi Yar site) and Irtysh(Zashchitino Village) rivers have been donated for ourstudy by Z.N. Gnibidenko and N.N. Semakov. Palyno-morphs are macerated using the conventional separa-tion method with preliminary ablution and acetolysis inacetic anhydride (Grichuk and Zaklinskaya, 1948).Careful descriptions of all the borehole sections andassociated palynological diagrams are published in ourearlier works (Kuz’mina and Volkova, 2001, 2004;Volkova et al., 2002, 2005; Kuz’mina et al., 2003).

Palynostratigraphic subdivisions considered in thiswork are “palynozones” and “beds with assemblages ofpalynomorphs.” Palynozone is biostratigraphic subdi-vision of a complex substantiation (

Practical Palynos-tratigraphy

, 1990). At present, this term is introduced

Palynostratigraphy of Oligocene–Miocene Continental Deposits in Southwestern Siberia

O. B. Kuz’mina and B. S. Volkova

Institute of Oil-and-Gas Geology and Geophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia

Received October 10, 2006; in final form, January 28, 2008

Abstract

—Data on spores, pollen, and dinoflagellate cysts studied in composite section of Oligocene–Miocenedeposits in southern part of West Siberia are presented. Eleven biostratigraphic units distinguished in the sectionare ranked as palynozones and beds with palynological assemblages. Palynological data substantiate age ofdeposits and specify ranges and boundaries of palynozones. Based on dinocyst assemblages first studied in sed-iments of the Zhuravka and Abrosimovo horizons (upper Oligocene, lower Miocene), the

Pseudokomewuia

Beds are included into local stratigraphic scheme. According to results of comparative analysis, similar and dis-tinctive features of Oligocene–Miocene dinocyst assemblages from West Siberia, China and North America areelucidated. Based on palynological data, the local stratigraphic scheme of higher resolution is suggested forsubdivision of Oligocene and Miocene deposits in southern part of West Siberia (Baraba and Kulunda lithofa-cies regions).

DOI:

10.1134/S0869593808050079

Key words

: pollen, spores, dinocysts, Oligocene, Miocene, West Siberia, palynostratigraphy.

STRATIGRAPHY AND GEOLOGICAL CORRELATION

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PALYNOSTRATIGRAPHY OF OLIGOCENE–MIOCENE CONTINENTAL DEPOSITS 541

into the regional stratigraphic scheme of West Siberiato designate the respective zonal biostratigraphic unit(

Unified Regional…

, 2001). Palynozones are recogniz-able within the West Siberian Lowland and sometimesin adjacent regions. They correspond to section inter-vals containing particular palynological assemblagesdiffering in structure and taxonomic composition fromassemblages in overlying and underlying strata. Spe-cies with narrow stratigraphic ranges are commonlyabsent in the Oligocene and Miocene palynologicalassemblages, and groups of forms having broad agediapason are of prime stratigraphic significance in thiscase. Accordingly, it is necessary to distinguish sepa-rate section intervals, where these forms occur in cer-

tain quantitative proportions, which do not repeatbelow and higher, thus characterizing taxonomic com-position of zonal assemblage persistently recognizablewithin the study region (

Practical Palynostratigraphy

,1990). Distinguishing beds with particular assemblages ofpalynomorphs, we also paid principal attention to all thespores and pollen taxa specific of the beds’ assemblages.As subordinate biostratigraphic subdivisions, the bedswere distinguished in those cases, when it was impossibleto establish the successive change of palynological assem-blages in the section, and when the respective depositsappeared to be undetectable in all the sections.

Morphologic examination and microphotography ofmicrophytofossils were carried out using microscope

100 0 100 200 300 km

55°50°65°

60°

55°

65°60° 70° 75° 80° 85° 90°65°

60°

55°

3

2

1

Taz R.

Pur. R

.

Salekhard

Ob. R.Ir

tysh

R.

4

56

Khanty-Mansiisk

Section near Zashchitino

Tym RiverSections at the

Yenisei R.

Tomsk

Novosibirsk

8

9

7

(Chelyuskintsev)

Section near Isakovka

Omsk

10

11

A B

C

1 2 3 4 5

A

61

Borehole 13

Fig. 1.

Localities of the studied boreholes: (1) state boundary; (2–3) boundaries of (2) West Siberian plate, (3) lithofacies zones, and(4) distribution area of the Paleogene deposits; (5) study areas: (A) borehole 01-BP (Neverovka Village), borehole 07-BP (Pobo-chino Village), borehole 011-BP (Achair Village); (B) borehole 13 (Chistoozernyi Settlement), borehole 2 (Novomikhailovka Vil-lage), borehole 6 (Lebyazh’e Village), borehole 9 (Orlovka Village); (C) borehole 2 (Ozeryanka Village), borehole 4 (Novopescha-noe Village), borehole 10 (Urozhainyi Village), borehole 15 (Kur’inskii Village); (6) lithofacies zones by names: (1) Yamal-Taz,(2) Trans-Uralian, (3) Central, (4) Narym, (5) Tomsk, (6) Yenisei, (7) Ishim, (8) Baraba, (9) Ob River, (10) Kulunda, (11) Cis-Altai.

542


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KUZ’MINA, VOLKOVA

Pale

ogen

eN

eoge

neSy

stem

Eoc

ene

Olig

ocen

eM

ioce

neSe

ries

uppe

rlo

wer

mid

dle

Subs

erie

s

Pria

boni

anR

upel

ian

Cha

ttian

Aqu

ita-

Bur

di-

Lan

g-Se

rrav

a-T

orto

nian

Mes

si-

Stag

e

NP

NP25

NP24

NP23

NP22

NP21

NP20

NP19

NP18

Unified

Mammals,

Forami-

MN13MN12

MN11

MN10

MN9

MN7+8

Globigerina

Globigerina

Turborotalia

Globigerina

Globigeri-

Tav

daA

tlym

Nov

omik

hailo

vka

Zhu

ravk

aA

bros

imov

oB

eshc

heul

Tav

olzh

anPa

vlod

ar

Hor

izon

Tav

da (

uppe

r su

bfor

mat

ion)

Kur

gan

Zhu

ravk

a T

urta

s

Form

atio

n

low

erup

per

uppe

r

nian

galia

nhi

anlia

nni

an

zones

MN

nifers

officinalis

tapuriensis

centralis

corpulenta

nathekatropicalis

Nov

omik

hailo

vka

Nov

omik

hailo

vka

Atly

mA

bros

imov

o

Abr

osim

ovo

Tav

da (

uppe

r su

bfor

mat

ion)

Bed

s

Form

atio

n

not established

Regional

Palynozones

Chenopodiaceae,

Ulmus – Betula

–

Alnus

–

Quercus sibirica –

Pterocarya

Fagus

Betula gracilis –

Carya

Pinaceae –

Quercus gracilis –

Palynozones and beds with

Baraba

Castanea – Quercus sibirica

Quercus sibirica –

Alnus – Betula

Kulunda

Atremisia

–Chenopodiaceae

Pinaceae –

Dinocyst zones

Central,

Pseudokomewuia

Pseudokomewuia

Charlesdowniea

stratigraphicsubdivisions

(

UnifiedRegional…

, 2001)

Poaceae,Apiaceae,

Artmisia

,

Ephedra

Polypodiaceae

Polypodiaceae

Ulmus crassa

Quercusgraciliformis

Quercusgraciliformis

spackmania –Pinaceae

Juglanssieboldianiformis

stenopteroides –

grandifoliiformis

palynomorphs (this work)

lithofacieszone

Alnus

–Polypodiaceae

Quercus sibirica –Ulmus crassa

Fagusgrandifoliiformis

gracilis – Juglanssieboldianiformis

Alnus – Betulagracilis – Juglanssieboldianiformis

Betula gracilis –Juglans

sieboldianiformis

Carya spackmania

–Pinaceae

Quercus gracilis –Quercus

graciliformis

lithofacieszone

Ulmus – Betula

–Polypodiaceae

Alnus

–Polypodiaceae


Castanea – Quercus sibirica

Quercus sibirica –Fagus

grandifoliiformis

Betula gracilis –Juglans

sieboldianiformis

Castanopsis

–

Quercus gracilis

Carya spackmania

–Pinaceae

Quercus gracilis –Quercus

graciliformis

and beds

Baraba,and Kulunda

regions

aff.

laevigata

aff.

granulata

clathrataangulosa

Pavl

odar

Pavl

odar

Tav

olzh

an

Tav

olzh

an

Bes

hche

ul

Bes

hche

ulZ

hura

vka

Tur

tas

Atly

mK

urga

nB

eds

Fig. 2.

Local stratigraphic units (Southwest Siberia) correlated with the Eocene–Miocene general scale based on palinological data.


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JENAVERT CARL ZEISS (object lens

50

×

, oculars

12

×

)and digital camera KODAK DC280, or microscopeLeica with stationary digital camera Leica DC500, res-olution up to 12 megapixels.

BRIEF STRATIGRAPHIC REVIEW OF OLIGOCENE–MIOCENE DEPOSITS

IN WEST SIBERIA

The Oligocene Series of the Paleogene is repre-sented in West Siberia by deposits of three regional sub-divisions: the Atlym, Novomikhailovka, and Zhuravkahorizons (Fig. 2). Age of their sediments is substanti-ated by correlation of respective palynological assem-blages with those known from the Turgai depression,North Aral and North Ustyurt regions, where palyno-morphs from marine deposits were found in associationwith diverse groups of fossil fauna and flora (Panova,1967).

The Atlym Horizon

includes the synonymous for-mation resting with scouring on marine deposits of theTavda Horizon. The formation is composed of sandswith clay and aleurite interlayers from 16–30 to 120 mthick. It corresponds in range to the

Carya spackma-nia–Pinaceae

palynozone (Fig. 2). Based on composi-tion of spores and pollen these deposits are correlatedwith the Aishcheairyk Formation of the lower Oli-gocene of the North Ustyurt region (Boitsova andPanova, 1973). The horizon corresponds in age to theearly Oligocene (Rupelian Stage).

The Novomikhailovka Horizon

includes forma-tion of the same name that is represented by alternatingrusty-brown clay, aleurite and sand with brown coalseams, all deposits from 30–50 to 120 m thick. The for-mation spanning the

Betula gracilis–Juglans siebold-ianiformis

palynozone is correlated with the ChiliktaFormation of the Turgai depression and brackish-waterdeposits of the North Aral and Ustyurt regions (Boits-ova and Panova, 1973). The horizon is of the early Oli-gocene (Rupelian) age.

The Zhuravka Horizon

includes deposits of syn-onymous formation on the south of West Siberia, whichare defined as coastal facies of a lacustrine basin. Incentral part of the plain, the deep-water equivalent ofthe Zhuravka Formation is the Turtas Formation.Greenish gray clays, sands, and aleurites of the latterare from 20–25 to 80 m thick and overlie, conformablyor with partial scouring, the Novomikhailovka Forma-tion. Being within the range of the

Fagus grandifolii-formis–Pterocarya stenopteroides

palynozone (Fig. 2),these sediments are correlated with the lower BaigubekSubhorizon of the North Ustyurt region (Panova, 1971)and attributed to the late Oligocene (Chattian Stage).

The Miocene deposits of the West Siberian plain aredivided into the Abrosimovo, Beshcheul, Tavolzhan,and Pavlodar horizons (Fig. 2).

The Abrosimovo Horizon

and synonymous forma-tion 5–10 to 80 m thick are composed of clays and aleu-

rites with interlayers of sand, lignite and brown coal.The formation conformably resting on the ZhuravkaHorizon corresponds to the

Quercus sibirica–Ulmuscrassa

palynozone (Fig. 2). Being correlated with theAquitanian Baigubek and Aral formations of theUstyurt and North Aral regions, it is conventionallyattributed to the lower Miocene and placed at the levelof the Aquitanian–lower Burdigalian (

Unified Regional…

,2001).

The Beshcheul Horizon

is equivalent of synony-mous formation (brownish gray sands with clay inter-layers 10–40 m thick) conformably resting on theAbrosimovo Formation. This subdivision, spanning the

Alnus

–Polypodiaceae palynozone (Fig. 2), is tenta-tively attributed to the early–middle Miocene (Burdiga-lian–Langhian–Serravalian) (

Unified Regional…

, 2001).

The Tavolzhan Horizon

is represented on the southby the Tavolzhan Formation (clays, sands with calcare-ous marly nodule; thickness up to 40 m) conformablyoverlying sediments of the Beshcheul Horizon. The for-mation corresponds to

Ulmus–Betula

–Polypodiaceaepalynozone (Fig. 2). Mammal remains suggest the mid-dle–late Miocene (Serravalian–Tortonian) age of theformation (

Unified Regional…

, 2001).

The Pavlodar Horizon

of the study region includessynonymous formation (variegate clays with carbonatenodules; thickness up to 50 m) overlying with scouringthe Tavolzhan Horizon deposits. Characteristic of sedi-ments is palynological assemblage exemplifying steppeand desert plant associations. The late Miocene (Torto-nian–Messinian) age of sediments is substantiated bydiverse remains of

Hipparion

fauna (

UnifiedRegional…

, 2001).

RESULTS

On the south of West Siberia, continental depositsrest on the Eocene marine sediments (Tavda Forma-tion). The

Quercus gracilis–Q. graciliformis

palyno-zone (PA1) is established in upper part of the TavdaFormation (bluish green compact clays and gray dustysands, thickness 88–97 m) penetrated by boreholes011-BP, 9, 2 (in reduced range, village of Ozeryanka),10, and 15 (Fig. 3). The PA1 includes diverse micro-phytoplankton, the Priabonian index species

Charles-downiea clathrata angulosa

inclusive, reliably definingthe late Eocene age of host sediments (Volkova et al.,2002). Only in Borehole 011-BP, Kul’kova identifiedthe Rupelian index species

Phthanoperidinium amoe-num

in terminal beds of the Tavda Formation (Akh-met’ev et al., 2001). However, this species was identi-fied with reservations, and Kul’kova listed it with ques-tion mark (Volkova et al., 2002).

In the studied borehole sections, the Atlym Forma-tion of continental deposits overlying marine sedimentsis lacking the palynozone established in the KurganBeds of the southern Trans-Urals (Panova, 1971; Akh-met’ev et al., 2001) and containing the

Pinaceae–Quer-

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KUZ’MINA, VOLKOVA

Bar

aba

litho

faci

es z

one

Kul

unda

lith

ofac

ies

zone

0 50 100

150

0 50 100

150

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e 01

1-B

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chai

r)al

t. 92

.5 m

200

250

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P3nm

P3nm

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P3at

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PA4

PA4

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6PA

6

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5

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nN

3pv

?

?

? ?

Q

Q50

50 100

250

?

PA4

PA4

150

150

PA10

PA10

PA11 PA7

PA3 PA1

350

350

N1-

2bs

P3zr

P3nm

P3at

P2tv

PA6

PA5PA7PA2

PA2PA3

PA5PA7PA9PA6

PA9

N2-

3tv

PA11

N3p

v

N3p

v

N1-

2bs

N1-

2bs

N2-

3tv

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N1a

b

P3nm

P3at

P3at

P2tv

P3nm

P3zr

P2tv

?

P2L

L

K2g

n

D

Hol

e 07

-BP

(Pob

ochi

no)

alt.

120

m

Hol

e 01

-BP

(Nev

erov

ka)

alt.

109.

2 m

Hol

e 9

(Orl

ovka

)al

t. 11

0 m

Hol

e 13

(Chi

stoo

zern

yi)

alt.

105

m

Hol

e 6

(Leb

yazh

’e)

alt.

120

m

Hol

e 2

(Pol

tavk

a)al

t. 11

5 m

Hol

e 2

(Oze

ryan

ka)

alt.

120

m

Hol

e 4

(Nov

opes

chan

oe)

alt.

118

m

Hol

e 10

(Uro

zhai

nyi)

alt.

214

m

Hol

e 15

(Kur

'insk

ii)al

t. 17

9 m

1 7

PA1

P2tv

D

?

2 8

3 9

4 10

5 11

6


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cus graciliformis

assemblage (initial Oligocene). Thesections are devoid of gradual transition from theEocene to Oligocene that is indicative of a break in sed-imentation (Fig. 2).

The

Carya spackmania–Pinaceae

palynozone(PA2) is distinguished in lower clay–aleurite part of theAtlym Formation in boreholes 011-BP, 01-BP, 07-BP,4, and 9 (Fig. 3). Maximal thickness of this part is 37.5m (Borehole 4), minimal one is 2.6 m (Borehole 01-BP). Lower boundary of this palynozone is establishedat the occurrence level of considerably abundant pollenof the genus Carya (up to 40%), the characteristic spe-cies

Carya spackmania

Trav. Inclusive. In the studiedsections, this level is tentatively regarded as the AtlymFormation base (Fig. 2). Spectra of the palynozone aredominated (up to 60%) by pollen of Pinaceae:

Pinussibiriciformis

Zakl.,

P. strobiformis

Zakl.,

P. sylvestri-formis

Zakl. and others. Taxodiaceae are sufficientlyabundant also (up to 20%), while angiosperms (exceptforCarya) are subordinate components, and diversity oftheir pollen is not high.

The

Betula gracilis–Juglans sieboldianiformispalynozone (PA4, PA5) corresponds to upper part of theAtlym Formation coupled with whole range of theNovomikhailovka Formation (Figs. 2, 3). Deposits ofpalynozone are 60 to 96.3 m thick. Pollen of the familyPinaceae prevails in the palynozone (sometimes up to80%), and abundance of angiosperms is considerablyincreased at this level as compared to the previous one.Dominant angiosperm taxa are Betula gracilis Pan.,Betula trigonia Pan., Betula spp. (up to 40% in sum),Juglans sieboldianiformis Pan., J. sibirica Pan., J. poly-porata Pan., and Juglans spp. (up to 20% in sum).Carya is practically missing from palynospectra. Taxo-nomic composition of palynological assemblage is per-sistent in the study region, practically independent offacies affinity of host sediments. Only in sections ofboreholes 10 and 15 (Kulunda lithofacies zone), therewere distinguished the Pinaceae–Castanopsis–Quer-cus gracilis Beds (PA3) in sandy deposits of the AtlymFormation; thickness 5 to 8 m (Fig. 3). Pollen ofangiosperms prevails in palynological assemblage ofthe beds. Taxa dominant in this case are characteristicof the upper Eocene deposits. These are Quercus graci-

lis (up to 10 %), Castanopsis spp. (15–20 %), Castaneacrenataeformis (10–15 %), and Rhoipites sp.(Kuz’mina et al., 2003). Fairly abundant (10–15 %) ispollen of tropical plants: Hamamelidaceae, Rhus sp.,Platycarya sp., Ilex sp., Liquidambar sp., and Nyssa sp.Content of pollen representing Carya sp., Fagus sp.,Juglans sp., J. polyporata, Pterocarya sp., Alnus sp.,Carpinus sp., Corylus sp., B. trigonia, and Betula sp. isinsignificant. Pollen of conifers representing a highshare of the assemblage includes prevailing specimensof diverse genus Pinus (up to 37%), single grains ofTaxodiaceae, Glyptostrobus, Abies sp., Cedrus sp.,Picea sp., and Tsuga sp.

In upper part of the Betula gracilis–Juglans siebold-ianiformis palynozone, we distinguished the Alnus–Betula gracilis–Juglans sieboldianiformis Beds (PA5,Figs. 2, 3). The beds were established in upper part ofthe Novomikhailovka Formation (interlayering aleuriteand clay of rusty-brown coloration) in the followingboreholes: 01-BP, 9, 13 (Chistoozernyi settlement),2 near Poltavka village and 2 near Ozeryanka village, 4,and 10, i.e., the beds are recognizable in both theKulunda and Baraba lithofacies zones (Fig. 3). Theirthickness ranges from 3 to 28.4 m. The beds are dis-criminated within the Betula gracilis–Juglans siebold-ianiformis palynozone, as both subdivisions containspecies in common, while proportions between princi-pal taxa are variable. Dominant in the beds is Alnus pol-len (30–40%), contents of Juglans sieboldianiformis,Juglans spp. (up to 25% in sum), Pterocaryastenopteroides Pan. and Pterocarya sp. (up to 10% insum) are considerably higher, while abundance ofdiverse Pinus is sharply decreased (10–20% only).

The Quercus sibirica–Fagus grandifoliiformispalynozone (PA6, PA7) established in Zhuravka andAbrosimovo (lower part) formations (interlayeringgreenish gray aleurites and sands, gray aleurites withadmixture of plant detritus; total thickness from 25.4 to59 m) was recognized in all the studied sections(Figs. 2, 3). Characteristic of the palynozone is appear-ance of fairly abundant pollen representing familyFagaceae, first of all Quercus sibirica Pan. and associ-ated Q. mira Pan., Q. forestdalensis Trav., Fagus gran-difoliiformis Pan., Pterocarya stenopteroides Pan. and

Fig. 3. Borehole sections correlated based on palynological data: (1) clay; (2) sand; (3) aleurite; (4) loam; (5) buried soils; (6) coalseams; (7) break in sedimentation; (8) dinocysts (occurrence maximum); (9) formations: (P2tv) Tavda, (P3at) Atlym, (P3nm)Novomikhailovka, (P3zr) Zhuravka, (N1ab) Abrosimovo, (N1-2bs) Beshcheul, (N2-3tv) Tavolzhan, (N3pv) Pavlodar;(10) palynoassemblages: PA1, Quercus gracilis–Q. graciliformis (upper Eocene); PA2, Carya spackmania–Pinaceae (lower Oli-gocene); PA3, Pinaceae–Castanopsis–Quercus gracilis (with redeposited Eocene pollen); PA4, Betula gracilis–Juglans siebold-ianiformis (lower Oligocene); PA5, Alnus–Betula gracilis–Juglans sieboldianiformis (lower Oligocene); PA6, Quercus sibirica–Fagus grandifoliiformis (upper Oligocene); PA7, Castanea–Quercus sibirica (upper Oligocene); PA8, Quercus sibirica–Ulmuscrassa (lower Miocene); PA9, Alnus–Polypodiaceae (lower–middle Miocene); PA10, Ulmus–Betula–Polypodiaceae (middle–upperMiocene); PA11, Artemisia–Chenopodiaceae (upper Miocene), (11) not defined.PA1, Quercus gracilis–Q. graciliformis (PA2, Carya spackmania –Pinaceae (lower Oligocene), PA3, Pinaceae–Castanopsis–Quer-cus gracilis (with redeposited Eocene pollen), PA4, Betula gracilis–Juglans sieboldianiformis (lower Oligocene), PA5, Alnus–Bet-ula gracilis–Juglans sieboldianiformis (lower Oligocene), PA6, Quercus sibirica–Fagus grandifoliiformis (upper Oligocene),PA7, Castanea–Quercus sibirica (upper Oligocene), PA8, Quercus sibirica–Ulmus crassa (lower Miocene), PA9, Alnus–Polypodi-aceae (lower–middle Miocene), PA10, Ulmus–Betula–Polypodiaceae (middle–upper Miocene), PA11, Artemisia–Chenopodiaceae(upper Miocene), (11) palynoassemblage is not established.

546

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 16 No. 5 2008

KUZ’MINA, VOLKOVA

PaleogeneNeogeneSystem

OligoceneMioceneSeries

upperlowermiddleSubseries

ZhuravkaAbrosimovoBeshcheulHorizonTurtasAbrosimovoFormation

Depth, m

Lithology

Sampling

Spores

Gymno-

Angiosperms

Polypodiaceae

Sphagnum

PiceaAbies

Pinus

TsugaTaxodiaceaeGlyptostrobus

Alnus

Betulaceae

Carpinus, CorylusSalixUlmusJuglansCaryaPterocaryaCastaneaQuercusFagusTiliaGrasses, shrubs

Subtropical

Palynoassemblages

Quercus sibirica –Alnus – Betula –Alnus –Alnus –

Beshcheul

levels

40 46 51.4

56 59.8

61.8

67.8

020

4060

8010

0%

sperms

20%

40%

60%

Polypodiaceae Quercus sibirica –Ulmus crassa –Polypodiaceae


Fagusgrandifoliiformis –Pinaceae

Aquatic-paludal

12

34

Fig

. 4. P

alyn

olog

ical

dia

gram

for

Bor

ehol

e 13

(C

hely

uski

ntse

v): (

1) c

lay;

(2)

san

d; (

3) a

leur

ite; (

4) p

olle

n co

nten

t les

s th

an 1

%.



others. Lower boundary of the palynozone is taken con-ditionally for the base of Zhuravka Formation becauseof sediments’ erosion everywhere in West Siberia.Upper part of the palynozone is separated as the Casta-nea–Quercus sibirica Beds (PA7) confined to upperpart of the Zhuravka Formation (greenish gray aleuriteand clay) in most borehole sections and to lower part ofthe Abrosimovo Formation (gray clay with inclusionsof lignite clasts) in boreholes 011-BP, 2 (Ozeryanka),and 10 (Fig. 3). The beds are from 7.8 to 32.7 m thick,containing characteristic palynological assemblagewith considerable content of Castanea pollen often pre-vailing in palynospectra.

Beds with dinoflagellate cysts Pseudokomewuia aff.laevigata and P. aff. granulata are established in theZhuravka, Turtas (facies analog of the former in Cen-tral, Ishim, and Narym lithofacies zones), and Abrosi-movo (lower part) formations (Fig. 2, plate). The bedsare distinguished based on the first and last occurrenceof dinocysts in the composite section. They are recog-nizable in the following borehole sections: 01-BP, 07-BP,011-BP, 9, and 10 (Fig. 3), in addition to outcrops at theTym River and Zhuravka Formation stratotype nearZashchitino village (Kuz’mina and Volkova, 2008a, inpress). Acme of dinocysts (up to 35%) is confined to anarrow interval of the upper Oligocene not more than5 m thick (Kuz’mina and Volkova, 2008b, in press).Peak abundance of dinocysts is recorded in the follow-ing depth intervals of boreholes: 122.2–119 m, Bore-hole 01-BP; 120.1–115 m, Borehole 07-BP; 267 m,Borehole 10; 186.7–183.3 m, Borehole 9 (Fig. 3); and20.5 to 22.8 m above the water level near Zashchitinovillage. In southern sections, acme of dinocysts isestablished in basal beds of the Zhuravka Formation,whereas in Central lithofacies zone (Zashchitino vil-lage) this event is confined to middle part of the TurtasFormation. Probably this is a consequence of differencein either stratigraphic ranges of two formations attrib-uted to the Zhuravka Horizon, or of dinoflagellates’paleoecologic distribution in the paleobasin. Occa-sional single specimens of dinocysts were found in ter-minal beds of the Novomikhailovka Formation (inBorehole 01-BP only). Insignificant content of thesemicrophytofossils (not more than 3–5%) is establishedin the Zhuravka (upper part), Turtas, and Abrosimovoformations practically in all the studied sections.Pseudokomewuia aff. laevigata prevails amongdinocysts in the Turtas and Zhuravka formations,whereas Pseudokomewuia aff. granulata is more fre-quent taxon in the Abrosimovo Formation.

We distinguished at least four palynoassemblages inthe Abrosimovo Formation. Their succession estab-lished in Borehole 13 (Chelyuskintsev settlement) ofthe Ishim lithofacies zone, where the formation sectionis most complete, is as follows (Fig. 4): (1) Quercussibirica–Fagus grandifoliiformis–Pinaceae, (2) Alnus–Betula–Quercus sibirica–Ulmus crassa, (3) Alnus–Quercus sibirica–Ulmus crassa–Polypodiaceae,(4) Alnus–Polypodiaceae. In this succession, the for-

mation middle part (gray clay 9 to 27 m thick with aleu-rite laminae and lignite inclusions) corresponds to theQuercus sibirica–Ulmus crassa palynozone containingassemblages 2 and 3, because assemblage 1 is still char-acteristic of the upper Oligocene (Quercus sibirica–Fagus grandifoliiformis palynozone), whereas assem-blage 4 is already typical of the regional Alnus–Polypo-diaceae palynozone (lower–middle Miocene).Palynoassemblages 2 and 3 differ from each other inquantitative proportions of taxa, being practically indi-visible in sections of the Baraba and Kulunda lithofa-cies zones, where the Abrosimovo Formation is likelyincomplete. Accordingly, it is more reasonable to dis-criminate only one Quercus sibirica–Ulmus crassapalynoassemblage (PA8) typical of the AbrosimovoFormation middle part. This assemblage includes thediverse Quercus pollen, including that of guide speciesQuercus sibirica and associated Ulmus crassa. Bothtaxa are not dominant, however, and occur as insignifi-cant components (Panova, 1967). Abundance of small-leaved taxa, especially of Alnus, and Polypodiaceaespores is significant, whereas Taxodiaceae are notabundant and Castanea pollen is represented by singlegrains. In southern sections, percentage of pollen ofsubtropical plants is low, attaining maximum (13.7%)only in the Tym River sections. The Quercus sibirica–Ulmus crassa palynozone is established in boreholes011-BP, 01-BP, 07-BP, 6, 9, 13 (Chistoozernyi), 2 (Pol-tavka), 2 (Ozeryanka), and in sections of the IsakovkaVillage and Tym River.

The Alnus–Polypodiaceae palynozone (PA9) isestablished in upper part of the Abrosimovo Formation,boreholes 011-BP, 07-BP, 2 (Ozeryanka), 10, 13 (Che-lyuskintsev), and also in the Beshcheul Formation(almost in all boreholes, Fig. 3) and basal beds of theTavolzhan Formation (boreholes 011-BP and 9), thelatter composed of gray aleurite, sand, and greenishgray grumous clay 9 to 38.2 m thick in total (Figs. 2, 3).Lower boundary of the palynozone is well recognizablein all borehole sections owing to prevalence of Alnuspollen (20 to 60%) and Polypodiaceae spores (up to60%) in palynoassemblage, characteristic of which isalso increased abundance of herbaceous and shrubs'pollen (Fabaceae, Cyperaceae, Ericaceae, etc.) and ofpaludal plants (up to 25% in sum). The assemblage alsoincludes pollen of small-leaved Salix, Carpinus, Cory-lus, and Betula. Pollen of broad-leaved, moderatelythermophilic Quercus, Tilia, and Juglans still occurs,though in minor amount. Content of conifers corre-sponds to 10–20%; these are Pinus sibiriciformis,P. sylvestriformis, Tsuga sp., and Picea sp.

The Ulmus–Betula–Polypodiaceae Beds (PA10) arerecognized in middle part of the Tavolzhan Formation,boreholes 4 and 10 (Figs. 2, 3). Sediments of the beds11 m thick are gray sand and greenish gray clay. Thepalynoassemblage includes equally abundant Ulmusand Betula pollen and Polypodiaceae spores (up to 20%per each group). Pollen of herbs and shrubs is diverse,representing 20% in sum. Alnus pollen is subordinate

548


KUZ’MINA, VOLKOVA

(10–15%), whereas pollen of broad-leaved Quercus,Carya sp., C. ordinaria Pan., and C. glabraeformis Pan.is of low abundance (up to 5 % in sum). Conifers are notnumerous also (5–6%).

The Artemisia–Chenopodiaceae Beds (PA11) corre-spond to variegate clays and micaceous sands (1 to18.8 m thick) of the Pavlodar Formation in boreholes 4,15 (Figs. 2, 3) and in the Isakovka section, Depositsunderlying and overlying the beds are barren of sporesand pollen. Characteristic of the palynoassemblage isprevalence of angiosperm pollen, primarily of domi-nant Chenopodiaceae (up to 71.6%) and associatedAsteraceae (up to 6.4%), Artemisia, Cichoriaceae,Poaceae, Polygonaceae, Ephedra, and others. Singlepollen grains represent broad-leaved Quercus sp.,Ulmus sp., Juglans sp., and Carya sp. Not abundantsmall-leaved taxa are represented by Betulaceae, Alnussp., and Salix sp. Abundance of conifers is low (up to6.4%), and taxa identified among them are Pinus sp., P.sibiriciformis, Picea sp., Abies sp., Tsuga sp., and Glyp-tostrobus sp.

DISCUSSION

During the last 30 m.y., sedimentation in West Sibe-ria progressed in continental environment, being undercontrol of tectonic and climatic factors. Glacioeustaticsea level drop at the beginning of the Oligoceneresulted in seawater recess from inland basins of theNorthern Hemisphere (Akhmet’ev et al., 2004). TheTavda sea of West Siberia ceased existence, and marinesedimentation eventually gave way to continental one(fluvial and lacustrine). Characteristic features of con-tinental sediments in the plain are facies variability andcomplicated stratification because of lateral unconfor-mities and local hiatuses. All these features are typicalof all borehole sections, investigation of which wasaimed at getting the higher-resolution subdivision offluvial and lacustrine deposits. Valuable data on distri-bution of palynoassemblages are sustained by paleo-magnetic investigations. Parallel paleomagnetic andpalynological analyses (boreholes 011-BP, 9, and 10)enhance validity of distinguished palynoassemblagesfor the high-resolution subdivision of deposits (Volk-

ova et al., 2002, 2005; Kuz’mina et al., 2003; Gni-bidenko, 2006). For separate stratigraphic units, theresults obtained are sustained by data on distribution ofcarpolites (Nikitin, 2006).

As a result of research, we established the upwardsuccession of 11 palynoassemblages used to distin-guish in continental sequence of Southwest Siberia fivebiostratigraphic units in the rank of palynozones andsix in the rank of beds with assemblages of palynomor-phs and dinocysts (Figs. 2, 3).

Lower Oligocene. In one of two palynozones char-acterizing the lower Oligocene, we discriminated bedswith palynoassemblage.

The Carya spackmania–Pinaceae palynozoneestablished in lower part of the Atlym Formation corre-sponds in range to synonymous palynozone of theregional scale and the Atlym Horizon of the early Oli-gocene (Unified Regional…, 2001). In the studied sec-tions, the palynozone is concurrent only to lower part ofthe Atlym Formation, i.e., the top of the Atlym sandsdoes not coincide with the base of the next palynozoneas in the regional scale, where upper boundary of theCarya spackmania–Pinaceae palynozone is placed atthe top of the Atlym Formation (Fig. 2). We traceduninterrupted succession Carya spackmania–Pinaceaeand Betula gracilis–Juglans sieboldianiformis palyno-zones in the Atlym Formation of boreholes 01-BP, 4,and 9 (Fig. 3), and this position of boundary betweenthe designated palynozones is characteristic of sectionsin the Kolpashevo area near the Ob River (Il’enok et al.,1989; Geologic and Biotic…, 1996). The range ofpalynozone is at the Mezhovka level of carpofloras(Nikitin, 2006). The data obtained should be taken intoaccount in the case of interregional and local correla-tions.

The Betula gracilis–Juglans sieboldianiformispalynozone (early Oligocene) is correlated with synon-ymous regional palynozone characteristic of theNovomikhailovka Horizon of West Siberia (UnifiedRegional…, 2001). According to our data, however, thispalynozone in sections of the Baraba and Kulundalithofacies zones spans, in addition to the Novom-ikhailovka Formation, also the Atlym Formation upper

Palynomorphs from upper Eocene, Oligocene, and Miocene deposits of southern West Siberia:(1) Quercus gracilis Boitz., Borehole 011-BP (Achair), depth 265.3 m, Tavda Formation; (2) Quercus graciliformis Boitz., Bore-hole 011-BP, depth 265.3 m, Tavda Formation; (3) Carya spackmania Trav., Borehole 4 (Novopeschanoe), depth 293 m, Atlym For-mation; (4) Juglans sieboldianiformis Vojc, Borehole 011-BP, interval 264.5–265 m, Atlym Formation; (5) Betula gracilis Pan.,Borehole 011-BP, depth 246.9 m, Atlym Formation; (6) Quercus forestdalensis Trav., Borehole 9, depth 184.3 m, Zhuravka Forma-tion; (7) Quercus sibirica Pan., Borehole 10, depth 267 m, Zhuravka Formation; (8) Pterocarya stenopteroides Pan., Borehole 9,depth 184.3 m, Zhuravka Formation; (9) Fagus grandifoliiformis Pan., Borehole 9, depth 184.3 m, Zhuravka Formation; (10) Cas-tanea sp., Borehole 2 (Ozeryanka), depth 165.5 m, Zhuravka Formation; (11) Ulmus crassa Pan., Borehole 9, interval 137.1–137.2 m,Abrosimovo Formation; (12) Polypodiaceae, Isakovka section, depth 40.7 m, Beshcheul Formation; (13) Alnus sp., Isakovka sec-tion, depth 40.7 m, Beshcheul Formation; (14) Chenopodiaceae, Borehole 15, interval 140.6–135.5 m; (15) Artemisia sp., Borehole15, interval 140.6–135.5 m; (16–19) Pseudokomewuia aff. laevigata He 1980: (16, 18) Borehole 10, depth 267 m, slide 1481/3,Zhuravka Formation; (17) Borehole 9, depth 184.3 m, slide 117/4, Zhuravka Formation; (19) Borehole 01-BP, depth 119 m, Zhurav-ka Formation; (20–24) Pseudokomewuia aff. granulata He 1980: (20, 23, 24) Borehole 9, depth 184.3 m, slide 117/1; (21) Borehole9, depth 184.3 m, slide 117/3; (22) Borehole 9, depth 184.3 m, slide 117/4, Zhuravka Formation; (25–27) Pseudokomewuia sp. A:(25, 26) Borehole 9, depth 184.3 m, slide 117/4; (27) Borehole 9, depth 184.3 m, slide 117/1a, Zhuravka Formation.



Plate

10 µm

1 2

3 45

6 7 8 9

10

11 12 1314 15

16 1718 19

20 21 2223

24 25 26 27

550


KUZ’MINA, VOLKOVA

part (Fig. 2). In some sections, the Betula gracilis–Juglans sieboldianiformis palynoassemblage from theAtlym Formation upper part is replaced along the strikeby the Pinaceae–Castanopsis–Quercus gracilispalynoassemblage containing a considerable share ofredeposited Eocene pollen. In view of this, we distin-guished the Pinaceae–Castanopsis–Quercus gracilisBeds of the Betula gracilis–Juglans sieboldianiformispalynozone in the Kulunda region (Fig. 2).Occurrenceof the above beds evidence most likely a considerablethickness variation of continental formations in theKulunda region, where stratigraphic range of the AtlymFormation is reduced, and it overlies the Eocene TavdaFormation with a large hiatus. In this region, clayeydeposits characteristic of the Atlym Formation lowerpart and containing the Carya spackmania–Pinaceaepalynoassemblage (Kuz’mina et al., 2003) are oftenmissing from the sections. Mixed palynological spectrawith a considerable admixture of Eocene elements havebeen identified earlier in sandy deposits of the Atlymand Novomikhailovka (lower part) formations in sev-eral boreholes drilled in the Tym and Ket river basins,the southeastern part of West Siberia (Il’enok et al.,1989). In opinion of Il’enok, taxonomic composition ofthese spectra evidences scouring of underlying marinesediments and redeposition of Eocene pollen. Il’enok(1989) also reported that the Betula gracilis–Juglanssieboldianiformis palynoassemblage (early Oligocene)was found in the same sands farther along their strike inthe study region.

In upper part of the Betula gracilis–Juglans siebold-ianiformis palynozone, we distinguished for the firsttime the Alnus–Betula gracilis–Juglans sieboldianifor-mis Beds (Fig. 2). Palynoassemblage of the beds char-acterizes the uppermost part of the NovomikhailovkaFormation, which corresponds to the early Oligoceneperiod of lacustrine sedimentation. Fossil flora of thispalynoassemblage and its stratigraphic range should beadditionally studied. The beds correspond in part to thelate Mikhailovka level of carpofloras (Nikitin, 2006).The distinguished beds can be useful for high-resolu-tion correlations within West Siberia.

Upper Oligocene. In the upper Oligocene, onepalynozone, beds with palynoassemblage characteristicof the zone upper part, and beds with dinocysts areestablished. The Quercus sibirica–Fagus grandifolii-formis palynozone is correlative with the regionalFagus grandifoliiformis–Pterocarya stenopteroidespalynozone characteristic of the Zhuravka Horizon ofWest Siberia (Unified Regional…, 2001). In the studyregion, the palynozone spans not only the ZhuravkaFormation, but also the Abrosimovo Formation lowerpart. As it was stated earlier based on palynologicaldata, lower part of the Abrosimovo Formation wasdeposited in the early Oligocene (Kul’kova and Volk-ova, 1994). The early Oligocene age of these depositswas substantiated by correlation of their palynologicalspectra with spectra of the lower Baigubek Subhorizon(North Aral and Ustyurt regions) bearing Cardium

abundans Lev. and with very diverse palynoassemblagecontaining Fagus grandifoliiformis (Boitsova et al.,1968). As for the difference in names of palynozone,we should note that steady appearance of Quercussibirica in palynospectra is very characteristic of theZhuravka Formation in southern West Siberia, whereasFagus grandifoliiformis and Pterocarya stenopteroidesare not as indicative here as in central areas of the plain(Panova, 1971). Appearance of diverse Quercus pollenin deposits of the Zhuravka Formation was also notedby Boitsova (1966). The Fagus grandifoliiformis–Quercus sibirica Beds are distinguished also in localscheme of the southern Trans-Urals (Vasil’eva, 1990).

Beds with Castanea prevailing in spectra are distin-guished for the first time in upper part of the Quercussibirica–Fagus grandifoliiformis palynozone. They arecharacteristic of sections in the Kulunda and Barabalithofacies zones, being appropriate for the high-resolu-tion regional correlation. The beds correspond in part tothe Koshkul level of carpofloras (Nikitin, 2006). In sec-tions of Central and Ishim regions, the beds have notbeen recognized probably because of geographic zon-ing in distribution of vegetation that could already existat that time in the plain (Boitsova and Panova, 1973).

The Pseudokomewuia Beds are established in WestSiberia for the first time. The discovered dinocystassemblage is unique in certain aspects for the entireNorth Eurasia. The close Pseudokomewuia–Bose-dinia–Granodiscus assemblage is known from depositsof the lower (second half)–upper Oligocene in China(Bohai Bay), which accumulated in a large lake nearseacoast (He, 1980). In northern Canada, monospecificPseudokomewuia aff. granulata assemblage is con-fined to the Miocene continental deposits of the ClarkiaLake (Batten et al., 1999). In West Siberia, thePseudokomewuia correspond to the Quercus sibirica–Fagus grandifoliiformis palynozone, which spans theZhuravka, Turtas, and Abrosimovo (basal beds) forma-tions (peak abundance of dinocysts is in the zone lowerpart), and to lower part of the Quercus sibirica–Ulmuscrassa palynozone (middle part of the Abrosimovo For-mation). According to palynological data, the beds cor-respond in age to the late Oligocene–early Miocene.Significant abundance rate of dinocysts in lower part ofthe Zhuravka Formation and in lower–middle intervalof the Turtas Formation can be reliable criterion for cor-relation of regional sections. Data on paleoecology ofthe genus Pseudokomewuia are not unambiguous.Dinocyst assemblages from three aforementionedlocalities are different in composition. The marine gen-esis of the genus has been argued for in China. In NorthAmerica, there are no sufficient data for such a conclu-sion and assemblage from the Clarkia Lake is mostlikely of the freshwater origin. We tend to consider thedescribed dinocysts as remains of freshwater organismsprobably tolerant to brackish-water environment, asdata on chemical composition of minerals from theZhuravka and Turtas formation are in favor of this



hypothesis (Dargevich et al., 1969; Kuz’mina and Volk-ova, 2008a, in press).

Differentiated tectonic movements of differentamplitude and climatic fluctuations with general ten-dency of climate cooling were characteristic of theNeogene period in evolution of southern West Siberia.Continental regime of sedimentation was still inprogress during the Neogene. Activation of positivetectonic movements commenced in the terminal Oli-gocene and gave rise to areal reduction of the Turtaslake-sea. The latter turned into a system of small lakesin the initial Miocene.

Miocene. In the studied sections, the Miocene inter-val spans the Abrosimovo, Beshcheul, Tavolzhan, andPavlodar horizons. In first two horizons, we distin-guished two palynozones, whereas two beds withpalynoassemblages have been established in the othertwo horizons.

The Quercus sibirica–Ulmus crassa palynozone iscorrelative with the regional palynozone characterizingthe Abrosimovo Horizon of West Siberia. The respec-tive deposits correspond in age to the early Miocene. Inthe adopted stratigraphic scheme (Unified Regional…,2001), the Quercus sibirica–Ulmus crassa palynozonespans entirely the Abrosimovo Formation (Fig. 2).According to our data, it corresponds only to middlepart of the formation (Fig. 2). Palynospectra from theformation base are identical to those from the underly-ing Zhuravka Formation, whereas the formation upperpart yields already the Alnus–Polypodiaceae palynoas-semblage (lower–middle Miocene). Nikitin (1999) dis-tinguished four levels of carpofloras in the AbrosimovoFormation, and we similarly established four palynoas-semblages in this subdivision (Fig. 4). Unfortunately,we failed so far to correlate data of palynology and car-pology for this intricate part of the Neogene successionthat is an intriguing topic for subsequent investigations.

The Alnus–Polypodiaceae palynozone is equivalentof synonymous palynozone in the regional scale of theearly–middle Miocene (Unified Regional…, 2001). Inthe studied sections, nevertheless, upper and lowerboundaries of palynozone do not coincide with litho-logic boundaries of the Beshcheul Formation, as it isadopted in the stratigraphic scheme (UnifiedRegional…, 2001). In addition to the Beshcheul Forma-tion, the palynozone spans upper part of the Abrosi-movo and basal part of the Tavolzhan formations.

Palynoassemblage of the Ulmus–Betula–Polypodi-aceae Beds (PA10, Figs. 2, 3) is also characteristic ofsynonymous regional palynozone of the middle–lateMiocene (Unified Regional…, 2001). Composition ofpollen assemblage from the Artemisia–Chenopodi-aceae Beds (PA11, Figs. 2, 3) is close to that ofpalynoassemblage from regional palynozone at thelevel of the late Miocene Pavlodar Horizon (UnifiedRegional…, 2001). The designated beds have beenestablished in the Kulunda lithofacies zone only. Bothbiostratigraphic units are ranked as beds, because in the

studied sections the respective deposits are barren ofspores and pollen, and it was impossible in such a situ-ation to reveal the palynological succession of PA9,PA10, and PA11 (Fig. 3).

CONCLUSION

Based on successive palynoassemblages distin-guished in the Oligocene–Miocene section of continen-tal deposits in southern West Siberia, 11 biostrati-graphic units ranked as palynozones and beds withassemblages of palynomorphs are established; three ofthese units are distinguished for the first time (Fig. 2).The first discovered Pseudokomewuia assemblage ofmicrophytoplankton characterizes the Zhuravka, Tur-tas, and Abrosimovo (lower part) formations. Generali-zation of extensive materials showed that boundaries ofpalynozones established in southern sections of WestSiberia not always coincide with lithologic boundariesof formations, as it is adopted in the regional strati-graphic scheme of West Siberian plain (UnifiedRegional…, 2001). Changes introduced into thescheme of subdivision of the Oligocene and Miocenedeposits in the study region provide grounds for subse-quent palynological investigations and preparation ofregional stratigraphic schemes of new generation. Thedistinguished palynoassemblages can be used in inter-regional and local correlations and for the Late Ceno-zoic paleoclimatic and paleogeographic reconstruc-tions.

ACKNOWLEDGMENTS

We are grateful to G.N. Aleksandrova, from theLaboratory of Paleofloristics, GIN RAS, for valuablerecommendations and assistance during preparation ofmanuscript. The work was supported by the RussianFoundation for Basic Research, project no. 08-05-00344-a.

Reviewer G.N. Aleksandrova

REFERENCES

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Documents

Palynostratigraphy of Oligocene-Miocene continental deposits in Southwestern Siberia