Early Palaeogene siliceous microfossils of the Middle Volga Region: stratigraphy and palaeogeography

23 Pages·1999·6.7 MB·English

by  Tatiana V Oreshkina

Early Palaeogene siliceous microfossils
of the Middie Volga Région: stratigraphy
and palaeogeography
Irina E. KHOKHLOVA & Tatiana V. ORESHKINA
Geological Institute, Russian Academy of Sciences,
Pyzhevsky per. 7, Moscow, 109017 (Russie)
[email protected]
[email protected]
Khokhlova I. E. & Oreshkina T. V. 1999. — Early Palaeogene siliceous microfossils of the
Middie Volga Région: stratigraphy and palaeogeography, in Crasquin-Soleau S. & De
Wever P. (eds), Peri-Tethys: stratigraphie corrélations 3, Geodiversitas 21 (3) : 429-451.
ABSTRACT
The Sengiley section (Middie Volga Région» Russia) provides one of the
most complété late l’alaeocene sedimentary sequence wirh well-preser\^ed dîa-
toms, silicoflagellates, and radiolarians. I hree zones of régional zonal scheme
(Kozlova 1994) based on radiolaria werc distinguished In the sédiments:
Buryella tetradicUy Tripodiscinus sengilensis^ Petatospyris foneolam zones. Based
on diatom régional scheme (Strelnikova 1992) Trinacrtii venîriculosa and
Hemiaiilus periptertis zones were recognised. Aithough assemblages of siii-
ceous microfossils strongly differ front the oceanic coeval associations, the
précisé âge of the boréal zones was determined on the basis of direct corréla¬
tion wich standard zonal scales of diatoms, silicoflagellates and radiolarians.
For example, from sédiments of Petalospyris foveoUita zone, severai spccies
described by Nishimura (1992) from ihe upper part of the Bekoma campe-
chemis standard radiolarian zone of the North-West Atlantic were found and
allowed us to corrclate thèse rwo zones. Two zones of the standard oceanic
diatom scheme (Bai ron ik Baldauf 1993) {Hem/aulus peripterus and
Hemianlus incurvus zones) and standard silicofiagellate Maviculopsis constricta
zone w'ere distinguished in the Sengiley section, Siliceous-terrigenous
ICEYWORDS Palaeogene sédiments of the Middie Volga can be considered as rypical sédi¬
Palaeogene,
ments of the marginal epicontinenial bavSÎn. Siliceous assemblages of the
bioÿiratigraphy,
raoiolaria, Sengiley section are ver)' close to assemblages from Lulinvorr and Serov for¬
silicoflaeellates, mations of the West Siberia and the eastern Unils slope, Fur Formation and
oiatoms,
Sambian Formation of North-Easc Europe» aithough the geometry of
Middie Volga,
East European Platform. connections berween these basins during late Palaeocene is siill not ciear.
GEODIVERSITAS • 1999 • 21 (3) 429
Khokhlova I. E. &C Oreshkina T. V.
RÉSUMÉ
Microfossiles silicetix paléogènes de la région de Li moyenne Volga : stratigraphie
et paléoécobgie.
La coupe de Sengiley (région de la moyenne Volga, Russie) présente une des
séquences scdirnentaires les plus complètes du Paléocène supérieur avec des
diatomées, radiolaires, silicoflagellés bien con,servé.s. Trois zones de la zona¬
tion régionale (Koziova 1994). fondée sur les radiolaires, sont distinguées
dans Ica sédiments (cid:9632)* zones à Bitryclla tettadica^ Tripodheinus sengHensis,
Petalospyris fbveolata. Dans l.a zotration régionale à diatomées (Srrelnikova
1992), les zones à Trinacria mnrtadosa and Hetniaulns peripicriis sont recon¬
nues. Bien que les assemblages à microfossîles siliceux dilïèrent fortemenr des
équivalents océaniques, Tige précis des zones boréales a éré déterminé sur la
base de corrélation.s directes avec les échelle.s régionales standard a diatomées,
silicoflagellés et radiolaires. Par exemple, pour les sédiments de la zone
Petalospyris joveolata, plusieurs espèces décrites par Nishimura (1992) dans la
partie supérieure de la zone sc-andard à radiolaires à Bekotna campechensis du
Nord Ouest de l'Atlantique ont été trouvées et nous permettent de corréler
ces zones. Deux zones de la zonation océanique standard à diatomées (Barron
&: Baldâuf 199^) (zones à Hemiimlus peripterus and IJemiaulus im'unms) et la
zone standard à silicoflagcllés à Naviculops'ts constricta ont été trouvées dans la
coupe de Scngiley. Le.s sédiments paléogènes siliceux-terrigènes de la moyen¬
MOTS CLÉS ne Volga peuvent être considérés comme typiques de bassin marginaux épi-
Paléogène,
continenraux. Les assemblages siliceux de la coupe de Sengiley sont très
biostratigraphy,
radiolaires, proche.s des assemblages des formations de Lulinvorr et Serov de Sibérie occi¬
silicoflagclJcs, dentale et du versant est de l’Oural, des formations de Fur et Sambian du
diatomées,
Nord Est de FEurope, bien que la géométrie des connexions entre ces bassins
Moyenne Volga,
Plate-forme est-curopéenne. durant le Paléocène ne soit pas clairement établie.
INTRODUCTION
In the Ulyanovsk'Saratov syncline of the Middle
Volga Région (Fig. 1) widespread early
Palaeogene seqiience (approximately .300 m
thick) is represented by marine siliceous-terrige-
nous deposits widi lilgli faciès diversity. Previous
srratigrapliic subdivision ot Palaeogene séquences
was based in most cases ori the liihological data.
The âge of these subdivisions and relations bei-
ween them hâve bcen révisée! by different investi-
gators more than once (Milanovsky 1940;
Leonov 1961; etc.). The high abundancc of sili-
ceous faciès, opokas (kryptogenc sUlceous depo¬
sits), the diatomites, siliccous clays and sands
offer advantage for siliceous microfossils study.
430 GEODIVERSITAS • 1999 • 21 (3)
Palaeogene siliceous microfossils of Volga Région
Fig. 2. — Lithology and lithostratigraphy of the Sengiley section, stratigraphie ranges of siliceous microfossils, and zonation.
Schemes of Strelnikova (1992) (diatoms), Locker & Martini (1987) (silicoflagellates) and Koziova (1994) (radiolarians) were used.
l’his paper seeks to examine the evidence provi- SENGILEY SECTION
ded by siliceous microfossils — dnitoms, silico-
flagcllates and radiolarians which occur in the The Sengiley section (Figs 1, 2) is located 7 km
Sengiley section. Scudy of siliceous micro- north-west of the Sengiley (Ulyanovsk Région).
organisms from this section is very crucial for On chc right bank ofthe Volga River, at an éléva¬
précisé âge déterminations of Palaeogene sedi- tion of approximatcly 300 m above sea level, a
mentary cycles and for revealing conditions of section of 40 m high cliff so-called "Granoe
silica accumulation on the northern Peri-Tethyan üklto” was scudied. Up ro the section the follo-
margin. The problem of relations between thcsc wing Uthological units were disringuished in the
early Palaeogene biosilica accumulation events studied interval:
and régional and global geologlcal events is also - at the river bank below the clifF siliceous grey
of great interesi. clays of 7 m thickness; no microfossils found.
GEODIVERSITAS • 1999 • 21 (3) 431
Khokhlova I. E. & Oreshkina T. V.
- siliceous dark-grey sandstones, thin-layered, Russian Academy of Sciences Geological Institute
with silica clays lenses, lie at the base of thc in 1994. 81 samples were examined for diatom
diatomite clifF; thickness 4-4.5 m; no microfossil and radiolarian biostratigraphy, but siliceous
found. micro-organisms were found only in 55 samples
- white massive diatomires with layers of lighr- from che diaromite units of the section. Sampling
grey diatomires, sometimes with glauconite; interval wa-s approximately 50 cm.
thickness 22 m; in samples 930109-930072 Approximately 5 g of sample was crushed
abundant siliccous microfossils werc found. mechanically and placcd into an 400 ml bcalcer.
- light-grcy massive clayey diaromites lying l'hcn samples wctc processed by 15'mJnutes boi-
conform.ibly on the uudcdying unie; thiclcness ling in hydrogen peroxide. The procedure of
7 m; samples 930072-93057 contatn abundant cepcatedly filling and decanring the bcakers with
siliceous microfo.ssils. distillcd waicr and allowing 2 hr scctling was
- the unconformity separates thc diatomite unit.s used to remove Chemicals and clay minerais.
from ovcrlying sediment.s; they arc represented Slides for radiolarian study were prepared on
by sandy brownish-green cla\^, siliceous greenish- 24 X 24 mm cover glasscs and mounted in
grey sands, brownish sandy opokas, silica dark- Canadian balsam on 24 x 80 mm glass slides.
grey opokas; thickness about 11m. Microfossils Radiolarians wcrc examined at X 400. Spccies
were not found. wcrc rccorded as abundant (A) if more titan
10 spécimens were présent in the slide, common
(C) if 3'10 specimeits occurred in the slide and
PREVIOUS STUDY OF SILICEOUS rare (R) if 1-3 .spécimens were found.
MICROFOSSILS Strevvn slides for diatoms werc prepared by sam-
pling che suspended residuc with a pipette sprea-
Zonal subdivision of rhe Sengiley section on the ding il on 18 X 18 mm covet slide and mounting
basis of radiolarians bas been proposed by in Elyashev moumirig medium, iliatoms were
Kozlova (1984). The age was considered as late examined ar X 500. Species identification was
Palaeocene. Radiolarian zones of diis scheme are checked at X 1250. Somc .samples wcrc studied
undoubiedly régional and can be traced in ihc in SEM *T.’arnbridgc Srcrcoscan" microscope.
boréal epiconcinental Palacogenc of the Volga Relative abundance of taxa represented in the
and UraJ régions. range charr is reported as abundant (A) when
The study of diaroins of thc Middle Volga 20 spccimens are présent in one horizontal tra¬
Région vtas starred in 19th century by Ehrenberg verse ac X 500, common (C) when 3-19 spéci¬
(1854), Grunow (1884) and Wirt (18%). Pater, mens are présent at each traverse, few (F) -
diatoms and silicoflagellates Irom tbis location 1-2 specimens in each traverse, rare (R) — less
hâve been studied by Leonov (1961), Jousé chan one specimen in each traverse.
(1979, 1982), Gleser (1993, 1995; Gleser et aL
1977) and Srrelnikova (1990^ 1992). The lower
part of the diatomite unie is cerrainly related to STRATIGRAPHY
the Palaeocene by ail invesrigators, but an early
Eocene age is srill nor excliided for the upper Rapiolaria
part of diatomires. Silicoflagellare assemblages Using radiolaria, the section was subdivided on
from several separated samples from ihe Sengiley che basis of rhe boréal zonal scheme of Kozlova
section were studied and dated by Locker 6c (1994). The zonal succession is Palaeocene
Martini (1987) as early Eocene. (Fig. 1, Table 1 ).
Buryell/t tetradica zone
MATERIAL AND METHODS The assemblage is moderately preserved and
contains Buryella tetradica Foreman, Theco-
Samples were collected during a field trip of sphaera rottmda Borissenko, Spongotrochus puter
432 GEODIVERSITAS • 1999 • 21 (3)
G Table 1. — Stratigraphie distribution of radiolaria in Sengiley section. A. abundant (20 specimens are présent in one horizontal traverse examined at x 500); C, common (3-19 spé¬
E
O cimens are présent at each traverse); F, few (1-2 specimens In each traverse); R, rare (less than 1 specimen in each traverse).
D
IV
E
R
S
IT AGE ZELANDIAN
A
S ZONE BuryeUa Tripodiscinus sengilensis

• tetradica
19 ' Species / sampla number 109 108 107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92
99 ' Burva'da teuadea C C C R
(cid:9632) LophophsôTxa curta R R C C R R
21 (3 PSloeocntoodoidsicçuciü: Sïo a\cnh\\elni(crn3an us A CA CA CA CR R
) ' SDOnoüdi^cuii vlina C R C C C R
SpoDQOirrichijs C C R R
SpoDQotrocttus sp ah Trainodiscus cleve A C
SponaQirocnus aH heiinr/BS A A A A A A C C C
Sponpninychus pacfani’i R R R R
Spongcfnjchu^:, polcr C C C
Thecosonacra rviunda R R R
Tripodiccinus- seupiten^i^ C C C C C R R R
1 Tripodiscinus Slbirii Üf^ R R R R R R R R R R ,
Tripodiscinus irifcpalus’ R R _ R
AGE ZELANDIAN-THANETIAN
ZONE Tripodiscinus sigilensis
specles/sampie number 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74
Anthoevrtoma fr/zzetf R R
LarnocatpiS smih C R R
Lophophasna curta -1 R -- R
Phormocv*tis- ^ailcuia C R
Plectodtscus t0tc^i//nae C R R
Sponaoftoenue atf tietioides C R C C
SponQomeits&a tamaria R R R
Tropodiscinus UHobafa^ C C C R C R R R R R R R C
Tripodisanus sengilensis 1 H 1 R R
species/samZpAOlGeN EnE_u_mber ^73 _7Z2TE rLipAoNdDi7sI1Ac iNnu-TsH sAi7gN0i lEeTn,I sAiNs6__9 68 _67^ _66 ; 65_ _64 Pe6t3a TloHsApyN6rEi2sT HfoiAveNo 6î1a ta 60 59 58 57 Palaeog
BCCoifaaitrihhvrroocfycrevj'icçrJiaaX se esiinxpimss n^nsüs ^ I ' CRR CR CCR R C R ene siliceo
DDC/iiapprii/oojccrovycccvtiaacsst ôcpsos lemounu(aStaljsù oriulcnnoaire ovnaae C R AR A R C -1C -1 us micro
Dseudobiccrone R C C R C fo
PPeetnav/oiasoiuvrruis'/ taouvmeoifm^icad v R R C C C CR RR R ssils o
SoonQaetôTiscuç- otnziipfm R R C R f V
SSSppDooonnnaodùponimfioeeîe/vnissuassaa nnîêau/tpmivàaur isnd pi /rmaea cox R CC A RC R R R C olga R
uj STtrvilpooddyicstc\>inau hs atrdUaosbtoàtnueSn sh R R R AR R C R egioi 3
Khokhlova I. E. & Oreshkina T. V.
Kozlova, Trifwdiscinîis sibiricus Kozlova, Spongo- Sengiley diatomites (Eig. 1, Table 2) allow us to
discus americamis Kozlova, Spongodisms phrix distinguish frum the base and upsection two
Gorboveiz and Lophophaena curta Kozlova. The zones of the zunal scheme for the Northern
base of rhe zone was tint oKserved in the section. Hemisphere sensu Srrelnikova (1990, 1992).
The upper boundary is deterinined by the appea- Trinacria ventrkulosa zone is represeiited bv com¬
rance of Trîpodischms sengilensis Kozlova and mon TriceTatium mirabiU' Jousé, Trinacria ventri-
Plectodisciis totchUinae Kozlova. culosa {A. Schmidt) Gteser, Pyxidicula ferox
(Grevillc) Strelnikova & Nikolacv, Crunôwiella
Tripodhcintis sengilensh zone gernmata (Grunow) Van Heurck. The assemblage
Radiolarians are abundant and wcll-preserved. of the flemiaulus proteus zone consists of
The most common are: Tripodiscimts sengdemii FJendaulns inatrms Shibkova» H. proteus Heiberg,
Kozlova, T. trilohatm Kozlova, Lophophaena H. incisus Hajos, H. frrgidtts (Grunow) Fenner,
curta Kozlova, Spongotrochus paciferus antiquus Soleufii eX'SCulptum Heiberg, Taceratiurn heihergii
Kozlova, 5. atf. Troehodiscus clevêl (Ko7.1ovâ), Gombos, Craspcdodiscus moelleri A. Schmidt,
S. aff helioidei Clcve, Spongodlscus americü^ius Aulacodiscus suspectus A. Schmidt, Grunowiella
Kozlova & Gorbovetz and Pl^ctodiscus tochilinae palaeocaenica Jousc and Cyiindrospira sirnsi
Kozlova. Sponolrocbus alveatui Riedel & Mirlehner.
.Sanfilippo, Tripodiicinus sibirirus Kozlova, Bcsides thé siratigaphically important species
Stylodiciya churlestonemis (Clark Campbell), enumcraicd above, diversifîed représentatives of
Anthocyrtoma frizz-eli Nishimura and PeriviaMri^.) the neritic diatom flora of epicontinental basins
dumitriiae Nishimura occur rarely. Common .ire présent in both zonal assemblages. A lull ILst
Larnocalpis smill Middour and Phoonocyrtis reti- is shown in the Table 1 and in the taxonomie
cula Kozlova & Gorbovetz were found in rhe appendix.
upper part of the zone. The upper boundary of Silicoflagellates (about 10 taxa) are common
the zone is very sharp and determined by the throughout the wholc section. For stratigraphie
appearance of Petalospyrh fnveolata Ehrenberg, subdivision, the zonation of Locker & Martini
Diplocyclas cornuta runjetw Kozlova, D. pseudo- (1987) is applied. The appearance of memhers of
bicorana pseudobkorona Nishimura, Spongo- the ITavicttlopsis genus (including N. constricta
melissa numa numa Kozlova, Clathrocyclas (Schulz) Frcnguclli, N. robusta Deflandre,
longispina Clark & Campbell and Spongotrochus N. danica rcrch-Nielsen) defines Naviculupsis
nativuspraecox Kozlova, constricta zone (upper Palaeocene-eavly Eocene).
Corhîsema disymmeiricû Bukry is présent ihrou-
Petalospyris fbveolnta zone ghout the whole section. According to Locker &
Radiolarians are diversifîed and well-preserved. Martini (1987), this stratigraphie inrerval corres¬
The most abundant are: Petalospyris foueolata ponds to the NP4-NP9 nannoplankion zones
Ehrenberg, Dyplotyelns cormaa nmjevae Kozlova, and so gives as the po5.sibiIiry to restnet the âge
D. pseudobicorona pseudohicorona Nishimura, of the diaiomite unit by the Palneocene. Less
Antocyrtoma pizzeli Nishimura, Botryornetra osha pronounced chan diaroms one, change in taxo¬
Kozlova, Spongomelissn ternaria Kozlova, S. nurna nomie composition is related to the middle part
numa Kozlova. !n the lowct part ol rhe zone of the section. This reconstruction includes the
Clathrocyclas longispina Clark Ôc Campbell, and last appearance of Dittyocha elongata Gleser and
Spongotrochus nativus prnecox Kozlova are abun¬ the firsT appearance oï Naidculopsis punctilia
dant. Spongasteriscus cruciferus Clark & Perch-Nielsen.
Campbell, Clatrocyclas extensa Clark & Campbell
and C. lipmanii Kozlova are rather rare.
PALAEOECOLOGY
Diatom.s and silicoflacellai ks
Pronounced taxonomie changes in diatom Radiolarian assemblages are well preserved and,
assemblages observed in the middle part of for the epicontinental setting, diversifîed (33 spe-
434 GEODIVERSITAS * 1999 • 21 (3)
G Table 2. — Stratigraphie occurrence of diatoms and sillcoflagellaîes in Sengiley section. Legend: see Table 1.
E
OD -r
IVE Diatoms/Samples 109 108 107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84
R Aulacodiscus distinquendus R i R R
S
IT Aulacodiscus probabfJis H H R
AS Briaaera sibirica R R F R R R F R R R R R R R R
• CostopyA^ arf/oua R R i
1 Eunotoqratr.rrs \/af4dbi1e R R R R R R R R R R R R 1 R R , R
9
99 Euno\Dgranirré weissU F F F R C 1
• ~3rün6w\eïîa ae<vmsi£ ~Ar ~C~~ "TT^ A C C F C F F ~F ~C C F F C “C A C C A A
21 (3 HHeemm^iaauu^KLJ•ss afrwiqbiQrga uus C R R R R R C R R R C R C R R R R R R R R R R R F RR
) HëmJa~üiu& daoïcus ~ir~ -p- R H R
Hemiaulos tncL'A'us- R
Hem}aulus rossfcus F F
Hyalodiscos radistt'S R R F R R R R F R R R R R R R R R -
Kentrodisevs fos$))is R H R R
Lisitz fi^a d^tancr/i' -1 R R
Odonîoîrctxs caftna^s R R R F F F F F F F F R F F R R R R R R R R R
! Odontatropis costara R R R R R R R R
Paralia CiV.nufata R F F R R R R R R R R R
Paralia orunewv/ F F R R R R R F R R R R R R R R R
Paralia sulcata R F R R R F F F F F F F F F F F F F F F
Probosàa cretacea F F F F F F F F F F F F F F F F F F F F R R R R R R
Pseodopodasira sp- 2 F R
Pseudopodos^xB rtesfV F R R R R R R R R R R R R R R F F F F F F
Pseudosticlod^cus argulaîus R R R F R R R R R R R R R R R R R R H H
Pterothecs maicr R R R R R H
Pyxid^-juia feroA C C C C C C C C C C F F F F F F F F F F F F
Rattrayalla oamarnensiS R R R
Rhaphoneis morsiana
Rhaphonbun simbirskiana R
Rhizosohnia hahblala R
Stellarifti<'i niiomtons, F R F F R R R F F F F F F F F F F F F F F F F F F F
Thalaa&fosiin 1 R R
Tbalar.sicslropsis yifUOana C C C C C C C C C C C C C C C 0 C C C C F F G C C C
P
TTrriicceerraaitiiuvmm kÛionak aïf R R F R R R R R R RR F F F F R R R R R R C C C C C C alaeo
TTTrrrioicnceahfcaontssaVu pdaH) skepo-i^nlu'o^sst na cvla^v CRF CCR CRRF CRF CARR ARF CRF ARRF ARF ARF ARFR AFF ARR ARR ARFF ARF ARF CFF CFF CFF (cid:9632)RRRR RR RFF RR RF RF gene siliceo
CoSribliicsoafmiaac dieislivamlems einca R F R F F F R F F F F F F F F F F R R R R R R R R R us m
commi/nis icro
Corbisema has^*at3 basfata F F F R R F F F F F C C C C C C C C C C fo
CCoorrbbiisS-esmpias inem^-s ionSe'ribnuiilsa ta R R R R R R R R R F F R R R R R R R R RF RF HF RR FR HF ssils o
Dictyoeba elonçafa C F F F F F F F F F C C C C C C C C C C F F R F R R f V
Dictyocha R R R R R R R R R R R R R R R R olg
DNNiaacvvtiiyccoiuicithooapp sspiirsse dccoaannrisectnna test a R R R R RR RR R R RR R RRR 1 R HR R R R a Régio
Navic\nopsis roDus\a R R l3_ R H H H H H H H R 1 R R n
4^
K
C^ ho
k
h
lo
v
11 ADAuuiallataocœomddsiis/s ccSüuaSsm pdprfvslbteiasnù gHuiesn dus 1 8R3 82 8R1 8RR0 79 7H8 7R7 7RR6 7H5 7H4 7RR3 7F2 7F1 7F0 6R9 68 6R7 6R6 6R5 64 6RR3 62 61 6R0 59 58 5R7 I. a E. &
Aulacodiscus schmidti ^ R H H F R R R O
ABruilqapoeordai sscibuiari sMu specfus 1 F R R R R H RR F F ^r~ CR C C ~cr~ ~c ~r~ A AR r~ reshk
Craspedodiscus moeliari F F F F F c A A C A A c C A A F ina
CEuynlionTdOroQsrpaimram saim vsair iabile H H R R R R C T. V
Eunotoprammà weissU R R .
Fenestreila antiQua R R
Grunow/etta gemmata C G G F F F R F F F F F F F F F F F F c F F F F F F F
Grunowiella palaeocaenica R C C C C C C C c C C c C C C F
Hemiaulus ambtguus R R R R R R
Hemiaufus arcticus F R R R R C R R R R R R R R R R R R
var. bornholmensis
Hemiaulus cun/atuius F R R F T” F F F F R R
Hemiaulus danicus R R R R R R
Hemiaulus frigidus H R H R H R R R R
Hemiaulus incisus H H H R R R R R R R R R R R R R R R R R R R R R R
Hemiaulus incunfus R R
Hemiaulus protevs F C C C C C C C C C C C C C F A A A C A C c F
Hemiaulus rossicus R R R R -1
Hyalodiscus radiatus H H R R R R F R R R R F R R R R F R R R R R
Kentrodiscus fpssiiis R R
Lisitziniâ àtstanovlf R R R
OOddoonnttoottrrooppiiss ccannstnaattaa R R R R R R F F RR F R R RR R [ R • R R RF _R__. F ... R R
Paralia cronalala R h h G G C F F R R F “FT “FT" “R “F^ R : R “R R “Fr TT
PPaarraaihfaa gsûrulcnào'twa ii 1h- Gh GR AF AF AF AF AF GF GF GF RF R RA A A “A~ -pr— “FT- TAT (cid:9632)~RA “F^ “TT “R“
Probosda cretaceé 1 R R R “1^ R F R R ' F F R F F F R ~R "TT TT "TT ~R~ ir~
' PseudopDdosîra sp. 2 h h R^ R
Pseuoopodusira westii h h A A G G G F F R R R R R R F R ^R F R R R R R R R
PseLxicxstic^dsc'js arH^ulatus H H H H R R R F R R R R ~F~ “F R R ~r~ R R R R R
Pterorbecà major R R R “FT R
Pyxidlcülà môelhr! R F F F F F F F G C C C C F F F F ~u~ “cr C ~r~ R
G Rattrayella 3ansariMos\s F R F
EO Rattrayelia rcwndata R R R R R R
DIVE RRhhaapphhopnneeiiss smimorbsitresgkeia na F F RF F R F RF F F R RF F F F R F CR C C FF RF RR
RS Rhizosolenia hebetata R R R R
ITA Solium exsculptum R F F F F F F F F R R F F F R R F F F R R F F F R R
S Stellarima microtrias R h F F R R R F ^ F_ F R R F F R R R F F F R R R
•
1
9
9
9

•
21 (3)
Palaeogene siliceous microfossils of Volga Région
NLO CL CL X X cies were dctermincd). Different radiolarian spe-
cies dominatc the assemblage in spécifie strati¬
CUO) ÛC CE CL O CL CL X X X
graphie intervals. hor example, specimens of
Oin) CE LL LL U CL CE CL X X X X X Sporigodisciis umerivanus Kozlova & Gorboverz
dominatc in the lowcrmost part of section
O(O cr ü O CL CL LL X X
(samples 109-104), 'rripociiscinus sengilensis
to CE lE U U CL CL LL Kozlova in samples 106-101, Spongohvchin
C(OM X O U CL CL X X X helîoida (Cleve) in santplc.s 99-88, Tripodheinm
trilohntus Ko/lova in samples S7-75, Antho^
CCOO lE CE O O X X X cyrtonui frizzeli Noshiniura and Petahspym foi^ea'-
«(OT U_ CE CL ü O CL X X X lata Ehrenberg in samples 65-60. Generally, in
the lower part of diatomicc unit, représentatives
CtnO ü_ CL U ü CL LL X X X X
of the Spongodiscidac lamily (généra
(COO lj_ Ll ü X X X Spnngüdiscus and SpongoLrochuA and Irisso-
cyclinae iarnily (genus Tripodiicinus) are domi¬
hCO. CE CE tr LL O X X X X X X
nant, and in ihc upper part of diaromites speci¬
CCOO LL CE CL LL O X X X X X mens of tlie Cyrtidav (généra Diplocyclas^
5
Clathrocycla^ and Anîhocyrtoma) and ol the
oC>O LL CE CL CL ü CL X X X X X X
Spyridae (genus Petalospyris) dominatc. The
Oh- CE tr CE CL X X X X X X X X grcatest change of thé assvxiation can be obser-
ved at the stratigraphical level of samples 72-67
CE CE CL CL X X X X X X
(Fig. 2), on the boundary between the Tripo-
ChM. ΠLL CE CL X X X X X X dischius se7igilensis and Petalospyris fot'eolata
«hO. CE CE CL X X X X Œ X X X radiolarian zones.
Diatom assemblages are well preserved and taxo-
Vh- CL CE CE CL °= X X X X X X nomically diversified too. represented mainly by
lhO. CE CL CL X X X X X X X robusi, large frustules of diatoms. About 60 taxa
of diatom W'cre decennined. The diatom assem¬
(hO- CE CL X X X X blages arc dominated by species t)'pical tor neti-
fNs. CE CL X X X X X X tic environment. Fully planktonically living
species arc represented by généra TJemiaulus,
00 CE CL X X X X X Rhizosoletua, Proboscia. Thalussiosiropsis and
Or-) CE CL CL CL X X X X X Trkeratlnm.
In the upper part of the section (samples 80-71)
O00 Œ. CE CL X X X a taxonomie turnover in diatom assemblages cor¬
CO O CE CE CL CL X X X X X X X rélâtes wiih relative increase of the Paralia sulcata
(Ehrenberg) Cleve group. le is possible diai ihese
CCMO Ü LL CE CL CL X X X X X changes restify the transition to the coastal, .shal-
0C0O O LL CE CL CL X X X X O X X low'er environment. The same trend is reflected
in the increasing of clayey material content in
the upper part of the section and in the change
43
Diatoms/ Samples iO<wCSO05 •etVî§at§CCcto:DOJ:-S 1E5S s%1(£E5Qb <1S1CO<l I51SI! ' iS5j5Çn3SJjr ’ ; Tnceratium veotneubsum 10i?} i15bQS. 11SO2ü) ëS1sgg 1icCVOii 1 18t51$fsse 1 8tct-j J8Ü4scsUria2J.. -IaiCtoii •811LÇ1D1e c1Q10tCa9O1 Q4J«.i3müO8 Q1e8QLOVn9I . NaviculQpS!S constficta 1S§Î(aaO2 Naviculopsfs punctiha Navfculopsis robusta oSTDfthI rdSeaiC atpitUpgrméSracSiiptIseOhés iNccâo gilseos uudre éfsrt oemrm winhaittei oton gorefy siliceous
GEODIVERSITAS • 1999 • 21 (3) 437
Khokhlova I. E. & Oreshkina T. V.
Fig. 3. — The stratigraphie position of the diatomites of the Sengiley section and corrélation to standard and régional zonal schemes.
microfossil.s associarion.s from the diatomite unit the associations Irom the Guif Mexico
of the Sengiley section is very important to (Foreman 1973).
understand the stratigraphie position oF the \Ve suggesr thar the Bi^ryella tetradica and
Middle Volga sÜiceous sediment.s (Fig. 3). Tripodiscinus sengilensis zones are relaied to the
Présent knowledge of stratigraphie ranges of lower Bvkouta campvchensh zone of ihe standard
Palaeoccne dratoms and radiolarians is very liini- radiolarian icale. in regard of the presence of
ted, espccially for the epieontinentaJ basitis. As a Buryella ttimdicd Foretnan, l'hecdsphiiera ronwda
rule sediment.s do not contain any calcareou.s BorLssenko, Spangodisetis amerîcanuy Kozlova ÔC
plankton and do not hâve not any pulaeomagne- Gorhovetz, Spoiigotrot'hui ttlpcdtus Riedel 6c
tic data. Sanlllippo and Penviator (?) dumitricai Nishimura.
Bcsides in the Volga Région, rhe Bnryelld tetnl- Bascd on the presence of DiplinycLîs pseudvbi-
dica radiülarian zone can be distinguished in chc coninn pseudobicorona Nishimura, Spoitgasttriscus
North Prccaspian Basin; the Tripodiscinm sengi- rruciferus Clark ÔC Campbell and Antho-
lensis zone can be observed in rhe Serov cyrtoniit (?) frizzelli Nishimura, the Petalospyris
Formation of tlie eastern Ural slopc and of the foveoLtta zone .seems lo correspond to the upper
western Siberia; and the Petidospytis faveolata part of Bekoma cdmpechensis zone of the
radiolarian zone can bc recognised in the Irbii Northwest Atlantic and, cornespondingly, to the
Formation of ihc eastern Ural slope (Kozlova CP5-CP6'lower CP7 nannoplankron zones
1984). These radiülarian zones are ihus régional (Nishimura 1992).
and can be traced across a wide lerritory. A similar piciurc is obiaincd Irom the diatom
Radiolarian zones distinguished in this paper stratigraphy. 'fhc samc succession of diarom
were referred to the upper Palaeoeeiie by Kozlova assemblages ( Trinacria venlriculosa and
(1994) on the basis of a few species common to Hemiaulus protem zones) is typical for the whole
438 GEODIVERSITAS • 1999 • 21 (3)