sikhote-alin, russia

323GEODIVERSITAS • 2001 • 23 (3) © Publications Scientifiques du Muséum national d’Histoire naturelle, Paris. www.mnhn.fr/publication/

Structure and genesis of the lower structural unitof the Samarka Jurassic accretionary prism(Sikhote-Alin, Russia)

Igor’ V. KEMKINAnatoliy N. FILIPPOV

Far East Geological Institute, Far Eastern Branch,Russian Academy of Science, Prospect 100-letiya Vladivostoka,

159, Vladivostok 690022 (Russia) [email protected]

[email protected]

Kemkin I. V. & Filippov A. N. 2001. — Structure and genesis of the lower structural unit of theSamarka Jurassic accretionary prism (Sikhote-Alin, Russia). Geodiversitas 23 (3) : 323-339.

ABSTRACTBased on a study of several cherty-terrigenous sequences of the Samarka ter-rane in Sikhote-Alin, comprising lithologic and paleontological analysis, thedifferent age of the transitional layers from marine formations to paleo-continental-margin deposits was established and the succession of marinefragments accretion was restored. The obtained data shows that low structurallevel of the Samarka accretionary prism is composed of a minimum of foursuccessive tectonostratigraphic units that differ both in age of accreted marinefragments and time of their accretion. Each unit consists of deposits of apaleo-oceanic plates gradually changing above on a section by terrigenousrocks, which further are replaced by an olistostrome. The relatively youngpelagic rocks and overlapping terrigenous deposits occur structurally belowolder deposits. Such structure of the Samarka prism results from a consecutiveaccretion of the fragments of a different-age sites of a paleo-ocean plate.Radiolarian age data for the accretionary prism indicates that fragments of aLate Permian-Triassic, Early Triassic-Early Jurassic and Early Triassic-MiddleJurassic paleo-oceanic plate were consecutively accreted into the prism.

KEY WORDSSikhote-Alin, Russia,

terrane, accretionary prism,

accretion, tectonostratigraphy,

radiolaria, olistostrome.

INTRODUCTION

Modern geological structure of the northeasternpart of the Asia-Pacific margin is a collage of ter-ranes that have various age and genesis. Finalaccretion of the terranes was finished at the end ofthe Cretaceous (Natal’in & Faure 1991; Faure &Natal’in 1992; Faure et al. 1995; Sokolov et al.1997; Parfenov et al. 1998; Nokleberg et al.1998). According to Nokleberg et al. (1998), aterrane is a fault-bounded geologic entity or frag-ment that is characterized by a distinctive geologichistory that differs markedly from that ofadjacent terranes. Among the terranes there arefragments of ancient passive continental margins,volcanic island and continental-margin arcs,accretionary prisms, backarc and turbidite basins.Accretionary prisms are important for reconstru-tion of geodynamic evolution, as well as correla-tion of geological events in a continent-oceantransition zone. Accretionary prisms form alonginternal slopes of modern convergent margins(Seely et al. 1974; Karig & Sharman 1975;Huene et al. 1982; Ogawa 1985; Fujioka et al.1988; Matsuda & Isozaki 1991) during subduc-tion of an oceanic plate under continent or islandarc by means of consecutive accretion of a frag-

ments of oceanic plate sedimentary cover andseamounts. Older units are accreted first and areunderplated by accreted younger units. Thisresults in the formation of a package of tectonicslices. Each structural slice composed of pelagicdeposits from central areas of ocean floor,hemipelagic deposits of marginal parts of ocean,and of bottom and slope facieses of trenchdeposits. These repeating stratigraphic sequencesreveal a history of sedimentation of an oceanicplate, from a spreading zone to a subduction zone(Piper et al. 1973; Berger & Winterer 1974;Matsuda & Isozaki 1991; Nakae 1992). Thetransitional layers from marine to continental-margin deposits of these stratigraphic sequencestestify to gradual change of geodynamic condi-tions of sedimentation, and fix an approach of anoceanic plate to convergent boundary. Thus, theage of transitional layers provides a timing ofapproach of any site of an oceanic plate to a sub-duction zone and, correspondingly, the beginningof its subsequent accretion. Knowing the age of atransitional layers of these stratigraphic sequencesin a various tectonic slices of an ancient accre-tionary prism makes possible to specify the timeof subduction of separate paleo-oceanic frag-ments. Based on this data, it is easy to restore a

Kemkin I. V. & Filippov A. N.

324 GEODIVERSITAS • 2001 • 23 (3)

RÉSUMÉStructure et genèse de l’unité structurale inférieure du prisme d’accrétion duSamarka d’âge Jurassique (Sikhote-Alin, Russie).Basée sur l’étude de séries siliceuses et pélitiques des terranes de Samarka dansla région de Sikhote-Alin, les couches de transition entre les formationsmarines et les formations continentales ont été datées et l’histoire des accré-tions successives a été établie (analyse lithologique et paléontologique). Lesrésultats montrent que le prisme est composé d’au moins quatre unités tectono-stratigraphiques qui diffèrent par leur âge et l’âge de leur accrétion. Chaqueunité consiste en une série océanique surmontée par des dépôts graduellementplus terrigènes pour finir par un olistostrome. De telles structures sont lerésultat d’accrétions successives de fragments de planchers océaniques. Lesâges fournis par les radiolaires montrent que ces fragments sont d’âge finPermien-Trias, Trias inférieur-Jurassic inférieur et Trias inférieur-Jurassiquemoyen.

MOTS CLÉSSikhote-Alin, Russie,

terrane, prisme d’accrétion,

accrétion, tectonostratigraphie,

radiolaires, olistostrome.

Samarka accretionary prism (Sikhote-Alin, Russia)

325GEODIVERSITAS • 2001 • 23 (3)

100 km

. . ..

.

.

.

.

.

.

Sibiria

Shantarskie Islands

AkademyBay

55°

Nizhneamursky T.

Sakhalinsky Bay

Ulban T.

Galam T.

Dshagdy-Kerby T.

Kema T.

Bureya-Khanka superterrane

Khabarovsk

Sovyetskaya Gavan'

Zhuravlevka T.

Samarka T.

Khanka Lake

Laoelin-Grodekov T.

Kavalerovo

Taukha T.

Sea of Japan

I I I I I I I I I I I I I I I I I I I I I I I I I I I I

I I

I I I I I I I I I I I I I I I I I I I I I

I I I I I I I I

I I

I I

I I I I I I I I I I I

I I I I I I I I

I I

I I

I I I I I I I I

I I I I I I I I I I I I I

I

I I I

Vladivostok

130°135°

140°

45°

50°

UdylLake

Pre-Mesozoic terranes

Paleozoic continent

Paleozoic accretion prism(Galam terrane) and island arc (Laoelin-Grodekov terrane)

Mesozoic Sikhote-Alin superterrane

Middle-Late Jurassic terranes

turbidite basin (Ulban terrane)

accretion prism (Samarka,Nadankhada-Bikin, Khaba-rovsk and Badzhal terranes)

Early Cretaceous terrane

near-continental turbiditestrike-slip basin (Zhuravlevkaterrane)

accretion prism (Taukhaterrane)

island arc (Kema terrane)

Early-Late Cretaceous terrane

accretion prism (Nizhne-amursky terrane)

Late Jurassic - Early Cretaceous

subduction volcanite

Early Cretaceous

turbidite post-accretionalcover

Faults

strike-slip

thrust

with unclear motions type

supposed

Uda R.

Amgun R.

Bureya R

.

Amur River

Naoeli

n R.

Bikin R.

Ussury R.MFF

Amur

Rive

r

CSA

F

FIG. 1. — Tectonostratigraphic terranes of the Sikhote-Alin and adjacent areas. After Khanchuk (1994). Abbreviations: CSAF, CentralSikhote-Alin fault; MFF, Mishan-Fushung faults.


326 GEODIVERSITAS • 2001 • 23 (3)

2

Paleozoic continent:Khanka-Bureya superterrane

Jurassic accretionary prism:Samarka (Sm), Nadankhada-Bikin (Nb),Khabarovsk (Kh), Badzhal (B) terranes

Early Cretaceous terranes:Taukha accretionary prism,Zhouravlevka turbidite basin and Kema volcanic arc

Sergeevka terrane of theKhanka-Bureya superterrane

Paleozoic ophiolite of theSamarka terrane

Left-lateral strike-slip faults

Location of cross-sectionsshown in Fig. 5

A

C

C

M

MF

Vladivostok

50°

45°

45°

140°

50°

140°135°

135°

100 km0

Ussuri R

iver

Big Ussurka River

Komsomolsk

Olga

Sea of Japan

Khanka lake

B

Sm

Sm

Kh

Nb

Amur River

Khabarovsk

15

4

2

3

FIG. 2. — Location of studied areas. Abbreviations: A, Arsen’evsky; C, Central Sikhote-Alin; M, Meridional; MF, Mishan-Fushungfaults.



succession of accretion processes, to divide anaccretionary prism into separate tectonostrati-graphic units, and to specify a complete prismstructure and history of its development. Samarka terrane is a fragment of ancient (Jurassic)accretionary prism. In modern Sikhote-Alinstructure it is bounding the Khanka-Bureyasuperterrane from East (Figs 1; 2). Nadankhada-Bikin, Khabarovsk and Badzhal terranes are anal-ogous of the Samarka terrane in the Northwestand northern areas (Khanchuk 1994). It was ear-lier considered that the Samarka terrane depositsrepresents a section of single Paleozoic-Mesozoicgeosyncline stratigraphic sequence that werestrongly deformed by a thrusts (Mazarovich1985; Golozubov & Melnikov 1986). But ourresearches have shown (Khanchuk et al. 1988;Kemkin 1989; Khanchuk et al. 1989; Kemkin &Khanchuk 1992, 1993) that the Samarka terraneis a complex package of tectonic alternation ofdifferent deposits that were formed in varioustime, environmental and tectonic conditions.There are two groups of the Samarka terrane rockcomplexes that precisely differ from each other:1) Early-Late Jurassic turbidite-olistosromedeposits composing a matrix; and 2) older (fromLate Devonian (?) up to Middle Jurassic) oceaniccherts, limestones and ophiolites composing dif-ferent length and thickness slices at a variousstratigraphic levels among matrix deposits. A si-milar structure was revealed later for the Samarkaterrane in northern Sikhote-Alin (Natal’in 1991;Natal’in et al. 1994; Faure et al. 1995). Never-theless, there is a number of questions yet notanswered. In particular, what are the structuralpositions of various marine fragments within theterrane section? How many stratigraphic levelsare they made of? What was the timing and suc-cession of their accretion to a continental margin?How did the various structural slices form withinthe terrane? Answers to these questions will allowto carry out the decoding of the internal structure ofthe Samarka prism and history of its formation.The results of lithologic-biostratigraphic study ofcherty-terrigenous sequences of the Samarkaprism are given below, which allow to make clear,at least partly, the designated above questions.

BRIEF GEOLOGY OF THE SAMARKATERRANE

The Samarka terrane extends along the edge ofthe Khanka-Bureya superterrane in a Northeastdirection from southern coast of Primorye upto the right bank of Amur River by a width upto 100 km (Figs 1; 2). The large left-lateralstrike-slip Arsen’evsky and Central Sikhote-Alinfaults form its northwestern and southeasternboundaries in southern Sikhote-Alin and, cor-respondingly, Central Sikhote-Alin and Katen-Choukensky in northern Sikhote-Alin. The ter-rane is composed of rocks of various litho-logical composition, age and genesis. Sedimentarydeposits, which represent the majority of rocksare mainly represented by continental-margindeposits (turbidite and olistostrome) and pelagiccherts and cherty-clay deposits composed ofvarious panels and slices as well as different-sizelumps and block among terrigenous rocks.Besides, there are slices and blocks composed ofbasalts, limestones and ophiolitic rocks thatrepresents a fragment of seamounts andheights. The accreted marine deposits compriseextensive (up to 20 km long and more) slices,the thickness of which varies from several tensup to several hundreds meters. The separatecherty slices consist of 3-5 times of the tectonicrepetition of same-age fragments. Large slicesare usually underlied by the olistostrome thatcontains lumps and blocks of the same litho-logy.The strata of the Samarka terrane are crum-pled into asymmetric folds of variable ampli-tude that are often overturned and are trendedto the Northeast. The axial plains of the foldsexhibit Southeast vergence and the mirror offolding is sloping dip to the Northwest (Figs 3;4). Regional folding structure has resultedin exposing the lower structural units of theterrane to the Southeast and the upper struc-tural units to the Northwest. The accretedmarine formations of upper structural level ofthe Samarka terrane are as follows: 1) MiddlePaleozoic gabbro-ultramafic rocks (KalinovkaFormation); 2) basalts and overlying Late


328 GEODIVERSITAS • 2001 • 23 (3)

FIG. 3. — Geological map of the southern part of the Samarka terrane.

SmSm

Sm

Sm

50°

45°40°

60

70

60

60

85

40

50

Samarka

Kalinovka

Zhr

ZhrKh-Br

Kh-Br

Vladivostok

100 km

N

A

M

C

40Uborka

Ussu

ri R.

Breevka

A

B

0 20 km

Early-Late Jurassic turbidite-olistostromedeposits of Samarka accretionary prism

Late Permian, Triassic and Early to Middle Jurassic cherts (Eldovaka Formation)

Middle Paleozoic gabbro-ultramafic rocks (Kalinovka Formation)

Late Permian green sandstonesand siltstones (Udeka Formation)

Basalts associated with Carboniferous-Early Permian cherts and limestones and Permian black mudstones (Sebuchar Formation)

Late Cretaceous volcanites

Late Cretaceous granites

Jurassic sandstones and siltstones(Ariadninskaya Formation)

Permian-Triassic shallow-water deposits ofKhanka-Boureya superterrane

Pre-Devonian gabbro-gneisses and overlying Permian toJurassic shallow-water deposits of Sergeevka terrane

Elements of rocks occurrence40

Faults. Figures in circles indicate faults:Arsen'evskyi, Meridianal'nyi and Central Sikhote-AlinskyiC

Quaternary deposits

Location of cross-sections shown on Fig. 4A



Devonian(?)-Early Permian cherts , EarlyCarboniferous-Early Permian limestones andPermian black mudstones (SebucharFormation); 3) Late Permian aleuro-psammiticrocks (Udeka Format ion) . The lowerstructural level of the Samarka terrane is com-posed of alternation of turbidite-olistostromedepos i t s and chert s s l ices (EldovakaFormation). The age of cherts changes fromLate Permian and Triassic up to Early andMiddle Jurassic (Mazarovich 1985; Volokhine t a l . 1990; Kemkin & Khanchuk 1993;Kemkin & Golozoubov 1996; Kemkin &Rudenko 1998; Phi l ippov e t a l . 2000a) .Basalts sometimes underlie the basis of sepa-rate chert slices. The age of terrigenous rocksis characterized by Middle-Late Jurassic radio-laria (Khanchuk et al. 1988; Kemkin 1989;Smirnova & Lepeshko 1991; Kemkin &Khanchuk 1992, 1993).Thus, the structure of the Samarka accretionaryprism looks like as “multi-layered cake” whererelatively young terrigenous deposits alternatewith more old marine rocks. The relationshipbetween various formations of the Samarkaprism in modern Sikhote-Alin structure are tec-tonic. The boundaries between them are thrusts.

STRATIGRAPHIC SUCCESSIONS

OF THE CHERTY-TERRIGENOUS SEQUENCES

AND AGE OF A TRANSITIONAL LAYERS

The fragments of primary section of paleo-oceanicplate sedimentary cover were investigated in vari-ous areas of the Samarka terrane. The contactsbetween chert slices and terrigenous rocks in mod-ern Sikhote-Alin structure are mainly tectonic (it isa result of accretionary and post-accretionaryprocesses). Conformable sedimentary contacts areextremely rare. Five localities with gradual transi-tion from pelagic cherts to continental-margin tur-bidites were found and studied. The transitionallayers of these cherty-terrigenous sequences arerepresented by cherty mudstones that gradesmoothly upward the section into mudstones,muddy siltstones, siltstones and, then, alternationof siltstones and sandstones. The description ofinvestigated prism sections is given below.

Katen River areaOn a right bank of the Katen River, areas ofDzhava and Dzho Creek (in the eastmost part ofthe Samarka terrane near the Central Sikhote-Alin fault, locality 1 on Fig. 2), the Samarkaterrane strata shows monoclinal dip to theNorthwest. The fragment of prism section recon-structed by four exposures, looks as follows(Fig. 5):

Grey clayish cherts 14 m

Alternation (1-5 cm) light grey clayish cherts 8 mand black clayish phthanite

Greenish grey different-bedded 75 m(1-3 - 3-7, less often up to 10 cm) cherts

Clayish jasper 5 m

Grey cherty mudstones 40 m

Dark grey mudstones 20 mand muddy siltstones

Alternation of siltstones 10 mand sandstones

Fine-medium-grained sandstones 200 m

Late Triassic part of cherty section is represent-ed in some exposures by an alternation of chertsand thin (1-3 to 7-10 cm) layers of grey lime-stones (Philippov et al. 2000a). The age ofcherts is characterized by an abundant con-odonts and changes from Olenekian stage ofEarly Triassic up to Bathonian-Callovian ofMiddle Jurassic (Philippov et al. 2000a). Thecherty mudstones contains radiolarians:Tricolocapsa fusiformis, Tricolocapsa ex gr. pli-carum, Tricolocapsa plicarum, Guexella nudata,Eucyrtidiellum unumaensis, Dictyomitrella (?)kamoensis, and Tricolocapsa sp., that indicate onage of Bathonian-Callovian. Mudstones andsiltstones according to radiolarians fauna(Phil ippov et al . 2000a) are Oxfordian-Tithonian in age. Thus, the age of transitionallayers from cherts to terrigenous rocks in KatenRiver area is Bathonian-Callovian.


330 GEODIVERSITAS • 2001 • 23 (3)

500

500 500

250 250

500

0 m

0 m 0 m

L

L

L L

L

LL

Ã

Ã Ã

Ã Ã

Ã Ã

ÃÃÃ

LLL

L

0 m

0

0

NW

NWSE

SE335°

350°

T-J2

P2

P2P2 P2 P2 P2

P2

T-J2T-J2 T-J2T-J2

J2-3

J1-2J1-2 J1-2

J2-3 J2-3

km

m

1

400

chert gabbro-ultramafic rocks

olistostrome deposits

siltstone sandstone alternation

black mudstone

basalt

A

B

FIG. 4. — Cross-sections across the Samarka terrane in the Samarka village (A) and Uborka village (B) areas.

Medvedka River areaOn a right bank of Medvedka River (a south-ern margin of Breevka village, locality 2 onFig. 2), other fragment of the Samarka prismsection is detail investigated. The Breevka sec-tion occur structurally higher then Katen sec-tion. It is represented in ascending order by(Fig. 5):

Olistostrome formations occur above the terrige-nous rocks, but the contact between them are notcroped out. The majority of the outcrop is repre-sented by grey bedded cherts. The bedding iscaused by thin (1-3 mm) clayey interbeds.Thickness of the chert beds varies from 1-2 cmin low and upper parts of the section up to 3-5 -7-10 cm in middle. Within the exposure, thestrata shows monoclinal dip to the Northwest(dip azimuth, 345°, angle 50°-60°). In the lowerpart of chert section the clastic layer (about10 cm of thickness) is embedded within the greybedded cherts. The clastic layer shows gradedbedding. Grain size of the lower part is more then0.5 mm, whereas that of the upper part is about0.1-0.3 mm. The clastic grains are composed

Grey and yellowish-grey cherts 70 m

Greenish-yellowish-grey cherty mudstones 3 m

Dark grey mudstones 5 mand muddy siltstones

Siltstones changing upward the section 65 minto an alternation of siltstonesand sandstones



250

200

150

L L

Age My

phthatites cherts limestones chertymudstones mudstones siltstones basic

volcanitesolistostromesilt. & sand. alternation

Late Permian

Tria

ssic

mid

dle

mid

dle

late

late

early

early

Per

iod

Epo

ch StageMatay River area

Ussuri River area

MedvedkaRiver area

Bikin River area

Katen River area

Tithonian

Kimmeridgian

Oxfordian

Callovian

Bathonian

Bajocian

Aalenian

Toarcian

Pliensbachian

Sinemurian

Hettangian

Rhaetian

Norian

Carnian

Ladinian

Anisian

Olenekian

Induan

Jura

ssic

5 4 3 2 1

FIG. 5. — Stratigraphic columns of cherty-terrigenous sequences of the Samarka prism. See location on Fig. 2.

mainly of basalt, volcanic glass, chert, chertymudstone, and plagioclase. Cherts are changessmoothly to terrigenous rock through chertymudstone. The data of micropaleontologicalstudy have shown (Kemkin & Rudenko 1998)that the age of chert part of the Breevka sectionchanges from Anisisan stage of Middle Triassicup to Aalenian-Bajocian of Middle Jurassic. Thecherty mudstone contain radiolarians:Tricolocapsa ruesti Tan Sin Hok, 1927, Tricolo-capsa sp., Hsuum medium (Takemura, 1986),Hsuum fukazawaense Sashida, 1988, Hsuum cf.fukazawaense Sashida, 1988, Hsuum sp., Sticho-capsa convexa Yao, 1979, and Milax sp., that indi-cates their Bajocian age. The mudstones andsiltstones are characterized by Bajocian-Bathonian and Callovian radiolarians corre-spondingly (Kemkin & Rudenko 1998). Thus,the age of transitional layers from cherts to ter-rigenous rocks of the Breevka section is Bajocian.

Ussuri River areaOn the left bank of Ussuri River, opposite ofSaratovka village (locality 3 on Fig. 2), other frag-ment of the Samarka prism section composingmore higher structural level is detail investigated.Within this exposure the 18-meters fragment ofthe Samarka prism crops out. It is as follows:

1985, Hsuum altile Hori & Otsuka, 1989,Hsuum sp., Parvicingula sp., and Tricolocapsa sp.,is Aalenian-Early Bajocian. The mudstones andsiltstones contain radiolarians that specifies theirage as Middle Bajocian-Bathonian andBathonian-Callovian correspondingly (Kemkin& Golozoubov 1996). Thus, the age of transi-tional layers from cherts to terrigenous rocks ofthe Saratovka section is Aalenian-Early Bajocian.

Bikin River areaThe next fragment of the Samarka prism sectionwith gradual transition from pelagic deposits tocontinental-margin formations is investigated onthe right bank of Bikin River area, on theNorthwest slope of Amba Mountain (locality 4on Fig. 2). The Amba section is a more highstructural level of the Samarka prism thenSaratovka section. Geological structure of theAmba Mountain area are similar to describedabove areas and represented by an alternation ofturbidite-olistosrome deposits and cherts slices.These strata are also crumpled into asymmetricfolds that are often overturned and are trend tothe Northeast. However, the age range of chertslices differs from the Katen River, MedvedkaRiver and Ussuri River areas. Late Permian chertslices are also established here besides Triassic andJurassic cherts (Philippov et al. 2000b). The rela-tionship of Permian and Mesozoic pelagicdeposits is unclear. The contacts between them,as well as terrigenous rocks are tectonic. On acontrary, Mesozoic pelagic formations are con-formable grade into turbidite (Fig. 5). Here areobserved:


332 GEODIVERSITAS • 2001 • 23 (3)

Grey bedded cherts 4 m

Greenish-grey cherty mudstones 3 m

Dark grey massive mudstones 3 m

Black bedded muddy siltstones 8 mand siltstones

Greenish-grey bedded cherts 6 mwith a lens of calcarenite (up to 30 cm)

Grey bedded cherts changing into 14 mthe reddish jaspers

Clay bedded jaspers 4 m

Brown and greenish-grey cherty mudstones 22 m

Dark grey mudstones and muddy siltstones 8 m

Black bedded siltstones changing 30 minto the alternation of siltstonesand sandstones

The strata of Saratovka section shows similarmonoclinal dip to the northwest. According toradiolarians fauna data the age of cherts withinthe exposure is Pliensbachian-Toarcian (Kemkin& Golozoubov 1996). The age range of chertymudstones, according to the extrated radiolari-ans, Parahsuum officerence (Pessagno & Whalen,1982), Parahsuum sp., Hsuum medium (Take-mura), Hsuum hisuikyoense Isozaki & Matsuda,

Late Triassic radiolarians were extracted fromchert (Philippov et al. 2000b). Clay beddedjaspers and cherty mudstones contains radio-larians: Bagotum cf. modestum Pessagno &Whalen, 1982, Bagotum sp., Broctus cf. ruestiYeh, 1987, Broctus sp., Canoptum anulatumPessagno & Poisson, 1981, Canoptum aff.dixoni Pessagno & Whalen, 1982, Canoptumpoissoni Pessagno, 1979, Canoptum cf. rugosumPessagno & Poisson, 1981, Canoptum sp.,Drulanta (?) sp., Eucyrtidiellum sp., Gorgansiumsp., Ka-troma sp., Lantus sixi Yeh, 1987, Meso-saturnalis sp., Orbiculiforma sp., Parahsuum cf.kanyoense Sashida, 1988, Parahsuum ovale Hori& Yao, 1988, Parahsuum simplum Yao, 1982,Parahsuum takarazawaense Sashida, 1988,Parahsuum sp., Praeconocaryomma sp., Santo-naella sp., Staurolonche sp., Tetratrabs sp.,Tricolocapsa sp., and Trillus sp., based on whichthe age of these rocks is determined as latePliensbachian-early Toarcian. Same radiolarianspecies were found in the first layers of mud-stones. The age of muddy siltstones and silt-stones is not known, because we could notextracted any fossils from them. Thus, the ageof transitional layers from cherts to terrigenousrocks of the Amba section is late Pliensbachian-early Toarcian.

Matay River areaOne more fragment of the Samarka prism sec-tion is described on a right bank of Matay River(locality 5 on Fig. 2). Accreted marine frag-ments here are also represented by slices of LatePermian and Triassic-Early Jurassic cherts(Philippov et al. 2000a). The relationship ofPermian and Mesozoic pelagic deposits is alsounclear, but taking into account their jointoccurrence it is considered that they are frag-ments of a single sequence of sedimentary coverof a paleo-oceanic plate. The gradual transitionfrom pelagic deposits to continental-marginturbidites is investigated on a right bank ofLyamfana Creek (inflow of Matay River). Thefragment of the prism section here looks as fol-lows (Fig. 5):



Phthanites and clayish cherts 12 m

Grey-dark grey thin and medium bedded 30 m(1-7 cm) cherts

Greenish-grey clayish cherts 6 m

Dark grey cherty mudstones with a 6-meter 18 minterbed of hyaloclastite

Dark grey mudstones and muddy siltstones 40 m

Greenish-grey hyaloclastite 50 m

Siltstones changing above the section 50 minto alternation of siltstones and sandstones

Greenish-grey hyaloclastite 20 m

Alternation of siltstones and sandstones 40 m

Basalts and diabases 100 m

Olistostrome formations containing 150 mdifferent-size lumps and blocks of siltstones,sandstones, basalts, Early Permian chertsand Carboniferous-Permian limestones

Age of cherts of the Matay section ranges fromOlenekian stage of Early Triassic to Rhaetian stageof Late Triassic according to conodont fossils(Buriy et al. 1990; Klets 1995). Clayish cherts (lay-ers 3) contain only two radiolarian species:Parahsuum simplum and Parahsuum ovale thatspecify Early Jurassic (Hettangian-Pliensbachian)age of these deposits. Cherty mudstones containParahsuum simplum, Parahsuum ovale, Tricolocapsasp. and Canoptum sp., that indicate an EarlyJurassic age. Mudstones and muddy siltstones arecharacterized by Toarcian-Aalenian radiolarians:Parahsuum cf. cruciferum Takemura, 1986, Transh-suum medium Takemura, 1986, Hsuum hisuiky-oense Isozaki & Matsuda, 1985, Hsuum matsuokaiIsozaki & Matsuda, 1985, Hsuum sp., Tricolocapsasp., Laxtorum (?) jurassicum Isozaki & Matsuda,1985, and Katroma sp. Bajocian-Bathonian radio-larians Hsuum cf. primum Takemura, 1986,Hsuum cf. belliatulum Pessagno & Whalen, 1982,Transhsuum medium Takemura, Stichocapsa con-vexa Yao, 1979, Stichocapsa japonica Yao, 1979,Parvicingula sp., and Tricolocapsa sp. were extractedfrom siltstones. Taking into account the age data ofunderlying cherts and overlying mudstones, the ageof cherty mudstones can be determined asPliensbachian-Toarcian. Thus, the age of transi-tional layers from cherts to terrigenous rocks of theMatay section is Pliensbachian-Toarcian, that coin-cides with that of Amba area.

DISCUSSION

The age of transitional layers from cherts to ter-rigenous rocks in various marine fragments of theEldovaka Formation change from Pliensbachian-Toarcian of Early Jurassic up to Bathonian-Callovian of Middle Jurassic. It indicates forthem a different timing of approach to a subduc-tion zone and, correspondingly, accretion.

Taking into account data of the transitionallayers age, it is possible to conclude that the sub-duction of the paleo-oceanic plate and, corres-pondingly, accretion of marine fragments ofEldovaka Formation were carried out continu-ously during approximately 25 my. During thistime, a minimum of four different fragmentscoming from different sites of the oceanic platewere accreted to the Samarka prism. However,actually more numerous entities could be disco-vered, if new (intermediate) data of age of transi-tional layers in other chert slices can beestablished. Thus, the Eldovaka Formation of the Samarkaterrane consists of a minimum of four structuralunits that differ both in age of accreted marinefragments and timing of subduction. Each unitsconsists of marine deposits that grade smoothlyupward into terrigenous rocks of continental-margin origin that are replaced by olistostromes.Figure 6 shows a geological reconstruction at theend of Early Cretaceous. It is time of left-lateralmotions along the Central Sikhote-Alin fault.The estranged blocks of the Sergeevka terranewere used as markers of amplitude of motions. Itis possible to see, that the age of transitional lay-ers, and, correspondingly, timing of accretion ofmarine formations are younged (rejuvenate) tothe Southeast. The growth (or younging) of theSamarka prism section is also realized to theSoutheast. But prevalent (principal) dip of theprism strata is realized to opposite side, i.e. to theNorthwest (see Figs 3; 4; 7). In other words, as awhole, the apparent stratigraphy of the EldovakaFormation of the Samarka terrane is structurallyinverted. The relatively younger units composethe lower structural level of the Samarka prismwhereas older units compose the higher structurallevels of the Samarka prism. But within eachstructural units the stratigraphic succession isnormal (from older to younger). Such structureof the Samarka terrane is consistent to that of themodern accretionary prisms and permits us toidentify the Samarka terrane as an ancient accre-tionary prism.In spite of identity of both lithological composi-tion and structure of each tectonostratigraphic


334 GEODIVERSITAS • 2001 • 23 (3)

Olga

Vladivostok

Amur River

Komsomolsk

Khanka lake

100 km0

A

C

M

B

Sm

Sm

Kh

Nb

MF

Khabarovsk

2

3

5

4

1

FIG. 6. — Geological reconstruction of the Sikhote-Alin region atthe end of Early Cretaceous; A, Arsen’evsky; C, Central Sikhote-Alin; M, Meridional; MF, Mishan-Fushung faults.



2

3

1

5

4

A

A

B

B

100 km0

T1 ol - J2 bat

T1ol - J1 plin

T2 an - J2 baj

J1 plin - J2 aal

J3 kim-tit

J2 cal

J2 bat-cal

J2 baj-bat

J1 (?)C1 - P1

D3 (?) - P1

P2?

L L

L

FIG. 7. — Generalized section of the Samarka prism and stratigraphic columns of allocated tectonostratigraphic units. See legend onFigs 2 and 5.

unit, there are small differences reflecting a faciesfeatures of different sites of paleo-oceanic plate.For example, Katen section is characterized bypresence of limestones interbeds within the chertlayers. The Breevka section cherts contain clasticlayers consisting of the clasts of basalts, cherts,cherty mudstones, volcanic glass and plagio-clases. In Amba and Matay area there are LatePermian cherts slices. It should be noted, that

the accumulation of terrigenous part of theMatay section was periodically accompanied bybasaltic volcanism (see Fig. 5). The geodynamicnature of it is not clear. Probably modes ofpaleo-oceanic plate subduction of early and latestages were a little different, in terms of both themorphology of subducted paleo-oceanic plateand the direction of subduction (frontal oroblique).


336 GEODIVERSITAS • 2001 • 23 (3)

LLL

L

L

L

L

LL

L

L

FIG. 8. — Model of the mechanism of olistostrome formation. See legend on Fig. 5.

The monotony of lithological composition ofaccreted marine fragments of Eldovaka formationof the Samarka prism, which are representedmainly by pelagic cherts, indicates that in theMiddle-Late Jurassic the sediment cover of theabyssal plain of a paleo-oceanic plate (withoutany seamounts and heights) was accreted. On acontrary, the upper structural level of the

Samarka prism is composed mainly by fragmentsof ophiolitic association interpreted as a paleo-oceanic plateau (Khanchuk & Panchenko 1991;Kemkin & Khanchuk 1993) with relativelyraised sites (where reef-like knolls were formed)and plain-like sites (where cherts and cherty-claydeposits were formed). The lithological differ-ences of accreted marine fragments reflecting the

morphological features of subducted paleo-oceanic plate allow to subdivide the Samarka ter-rane into the two subterranes called hereSebuchar and Eldovaka, which characterize, cor-respondingly, upper and lower structural levels.Similar structure is established also for a terranesof the Jurassic accretionary prisms of Japan(Kojima 1989; Mizutani & Kojima 1992; Isozaki1997). Tamba, Mino and Ashio terranes are alsodismembered by the Japanese geologists on a sep-arate tectonostratigraphic units, which are char-acterized by own oceanic plate stratigraphy(Nakae 1993). The sliding age of transitional lay-ers in various tectonostratigraphic units andyounging (rejuvenating) of deposits age to thedirection of the lower structural levels are charac-teristic of them. The set of these data allows toassume a single mechanism of the Samarka andJapanese accretionary prisms formation and toconsider them as a fragments of single Jurassicconvergent margine (arc-trench system).

CONCLUSION

It is possible to conclude that the lower struc-tural unit of the Samarka terrane consists ofunits of various ages and facies that representalternations of paleocontinental-margin andmarine rocks. The age of marine fragmentsranges from the Late Permian up to the MiddleJurassic, whereas the age of terrigenous rocks isEarly to Late Jurassic. The age data for themarine rocks supports the interpretation that theLate Permian-Triassic, Triassic-Early Jurassicand Triassic-Middle Jurassic fragments ofmarine plates were consecutively accreted intothe Eldovaka Formation of the Samarka accre-tionary prism. The time of beginning of sub-duction and, correspondingly, subsequentaccretion of each marine structural slice are cor-related with the age of overlapping terrigenousrocks. The Late Permian-Triassic marine platefragments were accreted in the Early-MiddleJurassic. The Triassic-Early Jurassic and Triassic-Middle Jurassic marine plate fragments wereaccreted in Middle-Late Jurassic. Thus, lower

structural unit of the Samarka terrane are apackage of successive tectonostratigraphic slicesconsisting of a paleo-oceanic plate formationsgradually changing above on a section by ter-rigenous rocks. In the accretionary prism, thestructural units are separated by horizons of olis-tostrome (accretionary melange), which formedduring the underplating of a relatively youngermarine slices under an older marine slices (Fig. 8).

AcknowledgementsThe authors thank A. I. Khanchuk (director of FarEast Geological Institute) for valuable advice andremarks. We are grateful to Dr. M. Caridroit(France) and Dr. L. Jolivet (France) for criticalreading of the manuscript and their constructivecomments. Special thanks are due to Dr. Joyce R.Blueford (USA) for revision of the English text.This work was done with partial financial supportof Russian Fund of Fundamental Researches(Grant No. 98-05-65346).

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Submitted on 9 August 2000;accepted on 16 January 2001.



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