Main phytostratigraphic boundaries in the Jurassic deposits of Western Siberia

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  • ISSN 08695938, Stratigraphy and Geological Correlation, 2014, Vol. 22, No. 3, pp. 231238. Pleiades Publishing, Ltd., 2014.Original Russian Text N.K. Mogutcheva, 2014, published in Stratigrafiya. Geologicheskaya Korrelyatsiya, 2014, Vol. 22, No. 3, pp. 613.

    231

    INTRODUCTION

    A significant role in the remarkable legacy left byV.A. Vakhrameev belongs to the substantiation ofboundaries between Jurassic epochs in the continentaldeposits on the basis of paleobotanic data and the possibility of their stage subdivision. Certain success inthis direction was achieved by studying the Jurassicfauna of the IndoEuropean paleoflorisitic region(Vakhrameev, 1989). As Vakhrameev noted, the Jurassic flora in the Siberian region developed slowly andgradually, without sharp reorganization under warmand wet climatic conditions, and differed from theflora of the southern regions in the poorer taxonomiccomposition and stages of evolution. Therefore, it wasdifficult to distinguish phytostratigraphic units in theJurassic continental sediments of southern Siberia.Presently accumulated paleobotanic data are sufficient to substantiate a detailed phytostratigraphicscheme.

    Within the Siberian paleofloristic region, the Jurassic plantbearing continental sediments are widespread in the Kuznetsk, Irkutsk, ChulymYenisei,and KanskAchinsk basins. The study of these sediments and plant remains in them in natural exposureswas started as early as the end of 19th century. The firstbrief description of the Jurassic flora of the Irkutskcoal basin was conducted by Heer (1876) and Prynada(1962). The results of study of the stratigraphy and

    flora of the Jurassic deposits of Southern and WesternSiberia were generalized by Teslenko (1970) and laterby Kiritchkova et al. (1992). Teslenko (1970) recognized two floral assemblages in the Lower and MiddleJurassic. Kiritchkova et al. (1992) distinguished andcorrelated the main turnovers in the evolution of theJurassic flora of the Kuznetsk Basin, Krasnoyarsk krai,and Tomsk oblast. They distinguished two phytohorizons in the Kuznetsk Basin and Krasnoyarsk krai andalso determined the sequence of phytostratigraphiccomplexes and plantbearing beds, which are fairlyconditionally correlated with a general stratigraphicscale. As was correctly noted by Vakhrameev (1989),paleofloras can be reliably dated only by study ofsequences represented by alternating marine and continental sediments. Precisely these materials have beenobtained in recent decades during study of the Jurassicflora of Western Siberia, which can be presently considered as the reference flora for Jurassic sediments ofthe Siberian phytochoria.

    MATERIALS

    Owing to prospecting works carried out in recentdecades for discovery of the petroleum potential of theLowerMiddle Jurassic polyfacies terrigenous sediments of Western Siberia, a large collection of plantremains was bedbybed sampled from borehole coresby researchers from SNIIGGiMS. All finds have an

    Main Phytostratigraphic Boundaries in the Jurassic Deposits of Western Siberia

    N. K. MogutchevaSiberian Research Institute of Geology, Geophysics, and Mineral Resources (SNIIGGiMS), Ministry of Natural Resources,

    pr. Krasnyi 67, Novosibirsk, 630014 Russiaemail: mognk@mail.ru

    Received April 12, 2012; in final form, January 23, 2013

    AbstractThe study of the large collections of plant remains gained from cores of numerous boreholesdrilled in Western Siberia made it possible to determine the taxonomic composition of the Jurassic flora ofthis region, the stages of its evolution, and the sequence of floral assemblages, which characterize the regionalstratigraphic horizons indirectly correlated via series of parallel faunal, microfaunal, spore and pollen zonalscales with a general stratigraphic scale. The compositions of floral assemblages was established in the Hettangianlower part of the upper Pliensbachian, upper part of the upper Pliensbachian, lower Toarcian, upperToarcian, Aalenian, Bajocian, Bathonian, and CallovianOxfordian sediments. Criteria were elaborated tosubstantiate the TriassicJurassic and LowerMiddle Jurassic boundaries. Lithologically and biostratigraphically, the MiddleUpper Jurassic boundary is poorly expressed.

    Keywords: Western Siberia, Jurassic, flora, phytostratigraphy, boundaries, floral assemblages

    DOI: 10.1134/S0869593814030083

  • 232

    STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 22 No. 3 2014

    MOGUTCHEVA

    accurate assignment to sections, formations, andregional stratigraphic horizons. The stratigraphicposition and stage dating of these horizons have beenreliably substantiated by macro and microfauna anddynocyst parallel zonal scales and reference palynspatic scale (Mogutcheva, 2000; Stratigrafiya, 2000;Kiritchkova et al., 2005).

    The study of collections sampled in sections of over170 boreholes allowed us to determine the taxonomiccomposition of the Jurassic flora of Western Siberia,including over 100 plant species from more than40 genera. The succession and stages in the floral evolution during the Jurassic have been investigated andfloral complexes typical of ten regional stratigraphicJurassic horizons have been recognized. The age offloral assemblages is determined by their assignmentto regional horizons. This made it possible for the firsttime to compile a detailed phytostratigraphic scheme(figure) for the southern West Siberian plate. In thisscheme, peculiar floral assemblages are demonstratedpractically for all stratigraphic regional horizons andseven floral beds are distinguished: five beds in theLower Jurassic, one phytostraton in the upper MiddleJurassic (Malyshevka Horizon), and one in the CallovianOxfordian (Mogutcheva, 2000; Geologicheskoe, 2005). Floral beds have not been recognized yet in the Laida, Vymskoe, and Leontevskiyhorizons, but floral beds characterized by the Verkhnepeshkovsky, Azharminsky, Malyshevsky, andNaunaksky floral assemblages were distinguished inthe Middle Jurassic by Kiritchkova et al. (2005).Established phytostratigraphic units play an importantrole in substantiating wide intra and interregionalcorrelations and determining criteria for the recognition of the Jurassic phytostratigraphic boundaries inthe West Siberian continental sediments and in specifying the age of the Jurassic continental plantbearingsediments in the Siberian coal basins (Mogutcheva,2009).

    Similar studies were conducted at the same time byA.I. Kiritchkova at the AllRussia Petroleum ResearchExploration Institute and by L.I. Bystritskaya atTomsk University. Their results were published in themonograph Phytostratigraphy and Flora of the WestSiberian Jurassic Sediments (Kiritchkova et al., 2005),which describes more than 100 species of plantremains, including first described epidermally studiednumerous Ginkgoales, Czekanowskiales, and conifers. This significantly expands our concepts concerning the taxonomic composition of the Jurassic flora ofSiberia. This work also presents materials of E.I. Kostina on the Jurassic phytostratigraphy of the KanskBasin. According to Kiritchkova et al. (2005), theJurassic succession is subdivided into three large phytohorizons: Lower Jurassic Urengoi, Middle JurassicTomsk, and CallovianOxfordian Naunaksky horizons. The former two horizons were subdivided into

    six floral beds correlated with regional horizons:(1) Levinskiy and Sharapovo horizons, (2) Kiterbyutand Nadoyakh horizons, (3) Laida Horizon, (4) Vymskoe, Leontevskiy and lower Malyshevka horizons;(5) Malyshevka Horizon, and (6) Vasyugan Horizon.Their correlation is complicated by different stratigraphic ranges determined by us and A.I. Kiritchkovaet al. for phytostratons.

    RESULTS

    Over the greater part of the territory of WesternSiberia, Jurassic sediments with erosion overlie different horizons of the Triassic, Paleozoic, and Precambrian. Only in the north of the region is the visible hiatus between Jurassic and Upper Triassic continentalsediments missing. Such uninterrupted successions ofthe boundary TriassicJurassic sediments were recovered in the Urengoi distinct, the north of WesternSiberia, and in the North Sosva district in the Uralianarea (Fradkina et al., 2003; Mogutcheva, 2011). Thefloral assemblages of the studied successions havesomewhat different composition. In the Urengoi district, the plant remains in the Upper Triassic Varengayakh (CarnianNorian) and Vityuta (Rhaetian)formations of the Tampei Group are mainly represented by large horsetails, mainly species Neocalamitescarrerei (Zeil.) Halle, sometimes with subordinateferns. The overlying Lower Jurassic rocks (BeregovayaFormation, Zimnyaya Horizon, Hettangianinitialupper Pliensbachian) also contain horsetails, but ofdifferent composition: Neocalamites pinitoides(Chachl.) Chachl. and Equisetites turgaicus (Vlad.)Kiritch., as well as Czekanowskiales, Ginkgoales, andconifers typical of the Siberian Jurassic flora. The TriassicJurassic boundary in this area is identified by achange in species composition of horsetails and fernsand by the first appearance of Jurassic gymnosperms.

    In the North Sosva district of the Uralian area ofWestern Siberia, the Triassic and Jurassic floral assemblages have richer taxonomic composition. The floralassemblage of the Raethian deposits (Yatrin Formation) bears 20 species, half of which (fern Cladophlebis, Czekanowskiales, and conifers) later receivedextremely wide development among Jurassic flora ofSiberia. Typical taxa of this assemblage (Cladophlebisstenolopha Brick, Scytophyllum, Tmematostrobus, Yuccites, Podozamites gutiformis (Migatch.) Stanisl., andothers) do not leave the Triassic and Jurassic boundaries. Jurassic deposits (Zimnyaya Horizon, Hettangianinitial upper Pliensbachian) in the studied successions yielded Equisetites turgaicus (Vlad.) Kiritch.,Osmundopsis plectrophora Harris, Podozamites sp., andElatocladus aff. manchuricus (Yok.) Yabe. In this partof Western Siberia, the TriassicJurassic phytostratigraphic boundary is identified by the complete disappearance of Triassic plants, decrease in horsetails

  • STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 22 No. 3 2014

    MAIN PHYTOSTRATIGRAPHIC BOUNDARIES IN THE JURASSIC DEPOSITS 233

    System

    Series

    Stage

    Substage

    Ho

    rizo

    nB

    eds

    wit

    h f

    lora

    Typ

    ical

    flo

    ral a

    ssem

    blag

    esJURASSIC

    Upper

    Oxfordian

    L.. U. L. . U.

    Geo

    rgie

    vski

    y

    Vas

    yuga

    n

    Co

    nio

    pte

    ris

    lati

    lobu

    s,

    C. d

    epen

    sis,

    L

    obi

    foli

    a aj

    aken

    sis,

    N

    ilss

    on

    ia m

    ajsk

    aja

    Equ

    iset

    ites

    late

    ralis

    (P

    hill

    .) P

    hill

    ., C

    onio

    pter

    is la

    tilob

    us B

    istr

    ., C

    . bur

    ejen

    sis

    (Zal

    .) S

    ew.,

    C. v

    sevo

    lodi

    i E. L

    eb.,

    C. d

    epen

    sis

    E.L

    eb.,

    Lob

    ifolia

    aja

    kens

    is E

    . Leb

    ., N

    ilsso

    nia

    maj

    skaj

    a B

    istr

    ., N

    . vitt

    aefo

    rmis

    Pry

    n.,

    Pag

    ioph

    yllu

    m s

    etos

    um (

    Ph

    ill.)

    Sew

    .

    Middle

    Callovian

    Bajocian

    Bathonian

    U. L. Middle U.

    Mal

    ysh

    evka

    Co

    nio

    pte

    ris

    sim

    ple

    x,

    C. f

    urs

    sen

    koi,

    C

    . via

    lovi

    i,

    Nil

    sso

    nia

    sp

    p.

    Equ

    iset

    ites

    late

    ralis

    (P

    hill

    .) P

    hill

    ., E

    . bea

    nii (

    Bun

    b.)

    Sew

    ., C

    onio

    pter

    is s

    impl

    ex (

    L. e

    t H.)

    Har

    r., C

    . fur

    ssen

    koi P

    ryn

    .,

    C. v

    ialo

    vii T

    ur.

    Kel

    ., C

    . em

    bens

    is P

    ryn

    ., C

    . lat

    ilobu

    s B

    istr

    ., C

    . ner

    ifolia

    Gen

    ., C

    . sni

    gire

    vska

    e Te

    sl.,

    Cla

    doph

    lebi

    s w

    illia

    mso

    nii

    (Bro

    ngn

    .) B

    ron

    gn.,

    C. d

    entic

    ulat

    a (B

    ron

    gn.)

    Fon

    t., R

    apha

    elia

    dia

    men

    sis S

    ew.,

    Nils

    soni

    a po

    lym

    orph

    a S

    chen

    k, N

    . vitt

    aefo

    rmis

    P

    ryn

    ., N

    . maj

    skaj

    a B

    istr

    ., N

    . gra

    cilli

    ma

    Pry

    n.,

    Hei

    lung

    ia c

    f. a

    mur

    ensi

    s (N

    ovop

    .) P

    ryn

    ., P

    agio

    phyl

    lum

    set

    osum

    (P

    hill

    .) S

    ew.,

    T

    axoc

    ladu

    s si

    biri

    cus

    (Ch

    ach

    .) T

    esl.,

    Ela

    tocl

    adus

    man

    chur

    ica

    (Yok

    .) Y

    abe,

    Bra

    chyp

    hyllu

    m s

    p.

    Leo

    nt

    evsk

    iyE

    quis

    etite

    s as

    iatic

    us P

    ryn

    ., C

    onio

    pter

    is h

    ymen

    ophy

    lloid

    es (

    Bro

    ngn

    .) S

    ew.,

    C. b

    urej

    ensi

    s (Z

    al.)

    Sew

    ., N

    ilsso

    nia

    maj

    skaj

    a B

    ist.

    Aalenian

    Upper

    Vym

    sko

    e

    Hep

    atic

    ites

    won

    naco

    tti H

    arr.,

    Equ

    iset

    ites

    late

    ralis

    (P

    hill

    .) P

    hill

    ., E

    . bea

    nii (

    Bun

    b.)

    Sew

    ., C

    onio

    pter

    is h

    ymen

    ophy

    lloid

    es

    (Bro

    ngn

    .) S

    ew.,

    C. m

    aaki

    ana

    Hee

    r, C

    lado

    phle

    bis w

    illia

    mso

    nii (

    Bro

    ngn

    .) B

    ron

    gn.,

    C. n

    ebbe

    nsis

    (Bro

    ngn

    .) N

    ath

    ., C

    . kam

    enk

    ensi

    s T

    hor

    n.,

    C. b

    iden

    tata

    Tur

    .K

    et.,

    Cze

    kano

    wsk

    ia r

    igid

    a H

    eer,

    Pho

    enic

    opsi

    s an

    gust

    ifolia

    Hee

    r, P

    ityop

    hyllu

    m n

    orde

    nski

    oldi

    i (H

    eer)

    Nat

    h.

    Lower

    Lai

    da

    Equ

    iset

    ites l

    ater

    alis

    (P

    hill

    .) P

    hill

    ., E

    . asi

    atic

    us P

    ryn

    ., C

    onio

    pter

    is p

    orci

    na B

    rick

    , C. s

    pect

    abili

    s B

    rick

    , Cla

    doph

    lebi

    s kam

    enke

    nsi

    s T

    hom

    ., G

    inkg

    o si

    biri

    ca H

    eer,

    Pse

    udot

    orel

    lia s

    p., P

    odoz

    amite

    s sp

    ., P

    ityop

    hyllu

    m s

    p., C

    zeka

    now

    skia

    , P

    hoen

    icop

    sis

    Lower

    Toarcian

    Upper

    Nad

    oya

    kh

    Phlebopteris polypodioides

    NeokoretrophyllitesClathropteris obovata

    Neo

    kore

    trop

    hylli

    tes

    linea

    rifo

    rmis

    Tes

    l., N

    eoca

    lam

    ites

    sp.,

    Ann

    ular

    iops

    is s

    p., E

    quis

    etite

    s la

    tera

    lis (

    Phi

    ll.)

    Phi

    ll., C

    onio

    pter

    is la

    tifo

    lia B

    rick

    , C. s

    pect

    abili

    s B

    rick

    , C. k

    irgi

    sica

    Bri

    ck, C

    lath

    ropt

    eris

    obo

    vata

    Ois

    hi,

    Gin

    kgo

    sibi

    rica

    Hee

    r, G

    . dig

    itata

    (B

    ron

    gn.)

    H

    eer,

    Pte

    roph

    yllu

    m te

    slen

    koi B

    at.,

    Cze

    kano

    wsk

    ia, P

    hoen

    icop

    sis,

    Kov

    alia

    gra

    ndifo

    lia T

    esl.

    Lower

    Kit

    erby

    ut

    Equisetites turgaicus

    Oto

    zam

    ites

    Neo

    kore

    trop

    hylli

    tes

    linea

    rifo

    rmis

    Tes

    l., N

    eoca

    lam

    ites

    sp.,

    Equ

    iset

    ites

    turg

    aicu

    s (V

    lad.

    ) K

    irit

    ch.,

    Con

    iopt

    eris

    maa

    kian

    a H

    eer,

    C

    . ner

    ifolia

    Gen

    k., C

    lath

    ropt

    eris

    sp.

    , Phl

    ebop

    teri

    s po

    lypo

    dioi

    des

    (Bro

    ngn

    .) B

    ron

    gn.,

    Tod

    ites

    prin

    ceps

    Pre

    sl, C

    lado

    phle

    bis

    den

    ticul

    ata

    (Bro

    ngn

    .) S

    ew.,

    C. d

    elic

    atul

    a Ya

    be e

    t Ois

    hi,

    Oto

    zam

    ites

    cf. l

    atio

    r S

    apor

    ta, C

    zeka

    now

    skia

    , Pho

    enic

    opsi

    s

    Pliensbachian

    Upper

    Sh

    arap

    ovo

    Co

    nio

    pte

    ris

    zin

    dan

    ensi

    s

    Neo

    cala

    mite

    s sp

    ., E

    quis

    etite

    s tu

    rgai

    cus

    (Vla

    d.)

    Kir

    itch

    ., C

    onio

    pter

    is m

    aaki

    ana

    Hee

    r, C

    . zin

    dane

    nsis

    Bri

    ck, C

    . por

    cina

    Bri

    ck,

    C. s

    pect

    abili

    s B

    rick

    , Phl

    ebop

    teri

    s po

    lypo

    dioi

    des

    (Bro

    ngn

    .) B

    rong

    n., C

    lado

    phle

    bis

    will

    iam

    soni

    i (B

    ron

    gn.)

    Bro

    ngn

    ., G

    inkg

    o si

    biri

    ca H

    eer,

    Sph

    enob

    aier

    a cz

    ekan

    owsk

    iana

    (P

    om.)

    Flo

    r., C

    zeka

    now

    skia

    , Pho

    enic

    opsi

    s

    Lev

    insk

    iy

    Ric

    ciop

    sis

    tom

    iens

    is B

    at.,

    Neo

    cala

    mit

    es p

    init

    oide

    s (C

    hac

    hl.

    ) C

    hac

    hl.

    , E

    quis

    etit

    es tu

    rgai

    cus

    (Vla

    d.)

    Kir

    itch

    .,

    E. g

    raci

    llis

    (Nat

    h.)

    Hal

    le,

    Sph

    enob

    aier

    a sp

    ecta

    bili

    s (N

    ath

    .) F

    lor.

    , C

    zeka

    now

    skia

    , P

    ityo

    phyl

    lum

    , S

    amar

    opsi

    s pl

    icat

    ifor

    mis

    , C

    arpo

    lith

    es iv

    anov

    skyi

    Tes

    l.,

    C. t

    rico

    stat

    us T

    ur.

    Ket

    ., P

    ityo

    sper

    mum

    par

    vum

    Tu

    r.K

    et.

    L.

    Zim

    nya

    ya

    HettangianSinemurian

    L.

    Jur

    assi

    c ph

    ytos

    trat

    igra

    p

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