RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 8, ES2002, doi:10.2205/2006ES000200, 2006
Upper Carboniferous--Permian stratigraphy and fusulinids from the Anarak region, central Iran
E. Ja. Leven
Geological Institute, Russian Academy of Sciences, Moscow, Russia
M. N. Gorgij
Department of Geology, Faculty of Sciences, Sistan and Baluchistan University, Zahedan, Iran
Contents
Abstract
[1] The section of Upper Carboniferous (Gzhelian) and Lower Permian (Asselian-Sakmarian)
sediments in the Anarak region of central Iran was first thoroughly studied.
The sediments are subdivided into two units, the lower, 95-m-thick, significantly
calcareous Zaladou Formation and the upper, 100-m-thick, dolomitic Tighe-Maadanou
Formation. The formations are united in the Anarak Group separated from the under- and
overlying deposits by stratigraphic hiatuses. The Zaladou Formation contains fusulinids
from top to bottom. At the base they are represented by species characteristic equally of
the uppermost Kasimovian and the lower zone of the Gzhelian. The middle Gzhelian
species were encountered at 70 m above the base and still higher the typical uppermost
Gzhelian forms referred to the Ultradaixina bosbytauensis Zone, occur. The upper 6 m of
the section are assigned to the Asselian including its lower and middle zones. Dolomites
of the Tighe-Maadanou Formation lack faunal remains. According to the position in the
section they are referred to the uppermost Asselian and to the Sakmarian. The described
section is similar to that in the Ozbak-Kuh Mountains north of Tabas, where the both
formations of the Anarak Group are recognized. West of Tabas, in the Kalmard region,
the Khan Formation can be correlated with the group; in the Alborz, the Dorud Formation;
and in northern Zagros (Abadeh region), the Vazhnan Formation, respectively. The
fusulinid assemblage recorded in the studied section includes 70 species referred to 21
genera and 12 families. They are illustrated in 10 paleontological plates. Seven new
species and subspecies Schwageriniformis acutatus, Rauserites stepanovi, R. (?)
persicus, Rugosofusulina (?) iranica, R. (?) anarakensis, Ultradaixina bosbytauensis distincta, and Likharevites gracilis are described.
Introduction
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Figure 1
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[2] The area of investigation is situated nearby a small town Anarak, between the
Dashte Kavir Desert in the north and the Kuh Rud Range in the south, and occurs within
the Yazd block, one of the large, curved to the west submeridional fault blocks
recognized in the structure of central Iran (Figure 1). The Carboniferous and Permian
sediments were discovered there during the geological survey conducted in the 1970s by
geologists from the USSR under the contract with the Iran government. Findings of
brachiopods, bryozoans, cephalopods, and foraminifers permitted the recognition of the
Visean-Namurian, the non-identified more precisely Carboniferous-Permian, and Lower
and Upper Permian units. By analogy with the sections of eastern Iran
[Stepanov, 1971;
Stöklin, 1971],
the Shishtu (Famennian-Namurian), Sardar (Carboniferous-lowermost
Permian), and Jamal (Asselian-Upper Permian) formations were distinguished
[Sharkovski et al., 1984].
We started a thorough investigation of the discussed section
few years ago. In so doing a large stratigraphic hiatus was recorded within the Sardar
Formation. Therefore it was subdivided into two separate units, namely, the Ghaleh
(upper Serpukhovian?-Bashkirian) and Absheni (Moscovian) formations
[Leven et al., 2006].
The Gzhelian sediments were also recognized and united together with the
Asselian rocks in the Zaladou Formation. It was believed that the Kasimovian
Stage is missing in the section
[Leven and Gorgij, 2006].
Upward from the base the new dolomitic, presumably Sakmarian, Tighe-Maadanou
Formation was distinguished. It is overlain by the Upper Permian Jamal Formation
and is separated from it by a thin sandstone and shale sequence conventionally
correlated with the Baghe-Vang Formation of eastern Iran, which is referred to
the Bolorian Stage. The Anarak section is in general very similar
to those from eastern Iran, namely, from the Ozbak-Kuh Mountains, Shirgesht, and
Shotori. This permits the proposition of a single scheme for subdivision of the
Carboniferous and Permian in central and eastern Iran, where these sediments are
subdivided into three groups and several formations
[Leven and Gorgij, 2005]
(Table 1).
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Figure 2
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[3] All the above reported age determinations of stratigraphic units were inferred from
foraminifers, mainly fusulinids that occur throughout the section. Their comprehensive
descriptions were made only for the Bashkirian and Moscovian stages
[Leven et al., 2006].
The first findings of the Gzhelian and Asselian fusulinids were also described
[Leven and Gorgij, 2006].
This paper contains the characteristics of the Gzhelian
(Kasimovian?)-Asselian part of the Anarak section referred to the Zaladou Formation,
and of the encountered fusulinids twice collected by M. N. Gorgij. The samples numbered
AC and P were collected initially, then followed by samples C. The relation of samples to
the section is shown in Figure 2. Additionally, the samples PR, R, RL, Rup, and ML were
derived from certain outcrops. Their precise relation to the section is not assured though
its degree is rather high, which is indicated by the involved fusulinids. Over 800 oriented
thin sections bearing fusulinids were produced from the samples. They were described by
E. Ja. Leven. The thin sections are deposited in the Laboratory of Micropaleontology in
the Geological Institute, Russian Academy of Sciences under the number 4781.
Brief Characteristics of the Section
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Figure 3
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[4] The discussed section is located on the southern slope of Mount Kuh-e-Bande
Abdulhussein, 1625 m high, about 25 km southeast of the Anarak town (Figures 1 and 3).
At the base of the slope there is a small separate outcrop of limestone bearing the
following fusulinids from the lower zone of the Gzhelian: Schubertella sp., Ozawainella
sp., Schwageriniformis sp., Triticites aff. ishimbaji, T. ex gr. simplex, T. ex gr. secalicus, T. nefandus, T. aff. samaricus, Rauserites rossicus, R. ex gr. postarcticus, R. variabilis, R. persicus, Rauserites sp. 1, Rugosofusulina aff. elliptica, and Rugosofusulina sp. 1
(Sample RL). Upward the slope the limestone likely related to the Upper Permian Jamal
Formation is recovered, which is evidenced by the involved small foraminifers Geinitzina, Pachyphloia, Langella, and others. Further upward from the base the uninterrupted
sequence of limestones of the Zaladou Formation occurs (Samples AC9-P13 and C1-C47).
The top of the mountain is composed by dolomites of the Tighe-Maadanou Formation.
[5] Below is a brief characteristics of the sequence of the Zaladou Formation (upward
from the base).
[6] 1. Light grey clayey shale bearing beds of shaly, silty and sandy, biomicritic,
biosparitic, and oobiosparitic limestone, rarer of coarse-grained sandstone. Numerous
Reitlingerina bradyi and scarce, non-identified more precisely Triticites occur
(Samples AC9-AC13). The total thickness is 15.5 m.
[7] The relationship of the member with the sediments located down the slope is
unclear. Considering the probable relation of the latter to the Jamal Formation, the
contact between them should be of tectonic origin. However, this was not recorded in
describing the section.
[8] 2. Clotted, thin- or medium-bedded limestone (silty and sandy biosparite,
oobiosparite, packstone, scarcely grainstone); small coral bioherms (Samples AC14-AC16,
C1-C12). The limestones bear single corals, bryozoans, brachiopods, and
fusulinids. Among the latter Eostaffella aff. acuta, Seminovella ex gr.
carbonica, Eoschubertella obscura, Schubertella sp., Quasifusulina sp.,
Schwageriniformis aff. perstabilis, Sch. ex gr. kairakensis, Sch. aff.
gissaricus depressa, Sch. cf. perlongus, Triticites aff. ishimbaji, T. globoides, T. ex gr. ohoiensis, Rauserites variabilis, R. aff.
samaricus, R. (?) persicus, Rugosofusulina uralica, R. (?) iranica, and
R. (?) elongata were encountered at the base of the member (Samples AC14, C1, C2).
The overlying sediments yield Eostaffella sp., Eoschubertella obscura, Reitlingerina aff.
tachtavica (Sample AC16), and fragments of ferruginated and likely redeposited
Schubertella ex gr. kingi, Schwageriniformis (Tumefactus) sp., Montiparus (?) sp.,
Triticites sp., and Pulchrella sp. (Sample C12). The thickness is 16.5 m.
[9] 3. Grey medium- and coarsely bedded limestone (biomicritic or dismicritic
packstone) with two thick beds, at the base and in mid-member, of coral prereef breccia
(boundstone) (Samples AC17-AC21, C13-C16). Fusulinids are missing. The total
thickness is 22.3 m.
[10] 4. Grey, brownish, coarsely bedded, in places dolomitized limestone (biomicritic or
sparitic, sometimes oomicritic packstone, rarer grainstone and rudstone) (Samples
AC22-AC26, C17-C24). Small mud mounds of algae-fusulinid limestone occur in the
upper part. The limestones of the member are mostly poor in organic remains, however,
certain beds are overfilled with fusulinids. One of them is in the middle part of the
member and contains numerous Schwageriniformis acutatus n. sp. (Sample AC25). The
limestone mud mounds located slightly above yield Rauserites elongatissimus, R. cf.
erraticus, and Jigulites cf. formosus (Samples C20-C24). Reitlingerina bradyi, Triticites aff. shikhanensis, Rauserites aff. postarcticus, R. karlensis,
and R. (?) stepanovi were found nearby the top of the member (Samples AC22-AC26).
The total thickness is 15.6 m.
[11] 5. Rose-colored marl, 4.3 m thick.
[12] 6. Light grey, brownish, medium bedded
limestone (biomicritic and biosparitic floatstone
and rudstone) bearing numerous fusulinids and
fragments of bryozoans, crinoid columns, algae,
corals, and echinoid spines. At the base the
limestone is overfilled with Ruzhenzevites ferganensis (Samples AC27 and R-3). The
overlying beds contain Reitlingerina sp.,
Anderssonites aff. zarjae, A. aff.
nanus, U. bosbytauensis distincta, and
Ultradaixina (?) aff. kozui (Samples AC28,
AC29, and C27). The thickness is 3.7 m.
[13] 7. Grey, medium- and coarsely bedded, in
places dolomitized, ferruginated and
recrystallized algae-fusulinid limestone
(biosparitic wackestone, packstone, occasionally
floatstone); coral bioherms at the base of the
member. Small foraminifers, brachiopod valves,
and bryozoans occur together with fusulinids and
algae. Among fusulinids Eostaffella sp.,
Schubertella sp., Ozawainella (?)
sp., Ultradaixina bosbytauensis distincta, U. kosvaensis, U. (?) kozui, Likharevites esetensis, L. aff. paranitidus, Anderssonites anderssoni, A. pseudoanderssoni latiterminosa, A. paraanderssoni, and A. nanus were identified; nearby the top Rugosofusulina directa and R. mutabilis
were recorded (Samples P1-P9, C29, C30, ML, and
others). The thickness is 11.4 m.
[14] 8. Algae-fusulinid limestone analogous to that of Member 7. In the lower part
fusulinids Sphaeroschwagerina sp., Ruzhenzevites subcylindricus, R. zaladuensis zaladuensis, R. zaladuensis brevis, and Praepseudofusulina kljasmica were found
(Samples P10, P11). The overlying beds yield Eoschubertella sp., numerous Likharevites gracilis, and L. kokpectensis and Pseudofusulina aff. conspiqua (Samples C38, C39,
P12, R1, R2, RupA, Rup2, Rup3). The uppermost beds contain Schubertella sp.,
Boultonia sp., Ozawainella sp., Quasifusulina longissima, Rugosofusulina cf.
directa, Likharevites inglorius, Pseudoschwagerina ex gr. extensa, Ps. robusta, Ps.
sp. n., Sphaeroschwagerina shamovi primitiva, Sph. shamovi gerontica, Sph. pavlovi, Sph.
ex gr. sphaerica, Sph. moelleri, Sph. notabilis, Sph. ellipsoidalis, Sph. fusiformis, Pseudofusulina (?) narjanmarica, Rugosochusenella paragregaria, and Praeskinnarella
(?) huangchuigouensis (Samples P13, Rup, C42-C47, PR1). The thickness is 5.85 m.
[15] The total (incomplete) thickness of the Zaladou Formation is 95 m.
[16] The Zaladou Formation grades into the dolomitic Tighe-Maadanou Formation of
about 80-100 m thick. It is overlain by the 8-10-m-thick loose quartz sandstone and the
2-m-thick shaly argillite. The latter is sharply unconformably overlain by the limestone
Jamal Formation that bears the Upper Permian fusulinids ( Staffella, Nankinella, and
Chusenella) and small foraminifers, which are going to be described later.
Analysis of Foraminiferal Assemblages and Age Determination of the Sediments
[17] The discussed section is strongly unevenly characterized by foraminifers. They
mainly occur in the upper portion of the sequence.
[18] Fusulinids from Member 1 are mostly represented by Reitlingerina bradyi,
a species of wide stratigraphic range from the Bashkirian of the Upper Carboniferous to
the Permian inclusive. Additionally we encountered several poorly preserved, likely
Triticites tests chiefly ranging from the uppermost Kasimovian to the Gzhelian
(Late Carboniferous).
[19] A significantly richer fusulinid assemblage was found at the base of Member 2.
It includes 9 genera and 18 species. Most of the encountered species are endemics and
their identification with the known forms is difficult. The species of Triticites
and Rauserites are most similar to that of the uppermost Kasimovian Triticites
quasiarcticus-Tr. acutus Zone and of the lowermost Gzhelian Rauserites rossicus-R.
stuckenbergi Zone. One of the three species Rugosofusulina (R. uralica) was described
by Mikhailova [1967]
from the lowermost Gzhelian in the Northern Urals. Two other, which
assignment to Rugusofusulina is doubtful, resemble "Triticites arcticus" and
Rugosofusulina scaphulaeformis described by G. P. Zolotukhina from the upper
zone of the Kasimovian in the southern East European Platform. The Schwageriniformis
species indicate the same age. For instance, Sch. perstabilis is characteristic of
the Kasimovian and Gzhelian of the Caspian syneclise
[Scherbovich, 1969].
The rest forms were described by
Bensh [1969, 1972]
from the upper Kasimovian beds of the southern Gissar and southern Fergana region.
However, according to V. I. Davydov (personal communication), in southern Fergana the
Schwageriniformis forms referred by Bensh to the Kasimovian, were recorded in the lower
part of the Uchbulak Horizon together with the Gzhelian ammonoids
[Popov et al., 1989].
[20] Based on the reported data the age of the discussed assemblage can be roughly
estimated as the latest Kasimovian and earliest Gzhelian. According to the general
development of Triticites and Rauserites, it is similar to the association
derived from the isolated limestone outcrop located on the slope downward from the base
of the above-discussed section (Sample RL). Among its forms Rauserites rossicus,
the index species of the Gzhelian lower zone, occurs. The concurrent fusulinids more
likely confirm the early Gzhelian age of the sediments than contradict it. We are not
aware to what part of the described section the R. rossicus-bearing limestone
corresponds. Most likely it is close to the base of Member 2. If so, the assemblage
from its lower part is Gzhelian as well. In that case the question of the presence
of the Kasimovian sediments in the section remains open. True, the upper portion of
Member 2 contains the Kasimovian-like fusulinids, as Schwageriniformis (Tumefactus), Montiparus (?), and Pulchrella. However, these identifications are not quite reliable
owing to a poor preservation of the forms. Additionally all of them have traces of redeposition.
[21] Member 3 lacks fusulinids. They occur in the middle of Member 4 and are
represented there by Schwageriniformis acutatus, the new species similar to the forms
encountered by V. I. Davydov in the uppermost Gzhelian of Darvaz and the Chios Island,
Greece (personal communication). Although the species differs in lesser number of
whorls and accordingly in smaller size, its Gzhelian age is beyond question. Fusulinids
from the upper portion of Member 4 are also estimated as Gzhelian. The species
Triticites shikhanensis, Rauserites erraticus, R. elongatissimus, and R. postarcticus
are characteristic of the lower zone of the Gzhelian in the East European Platform and the
South Urals. However, the concurrent occurrence of Jigulites cf. formosus suggests
the successive, Jigulites jigulensis Zone of the Gzhelian.
[22] Marls of Member 5 are barren of fusulinids. Ruzhenzevites ferganensis encountered
immediately above, at the base of Member 6, is known in Central Asia in the uppermost
Gzhelian, beginning at the beds correlated with the Daixina sokensis Zone of the East
European sections
[Bensh, 1972;
Davydov, 1986].
Anderssonites and Ultradaixina first occur in the upper portion of Member 6.
The former is characteristic of the lower zone of the Asselian in a great deal of
East European sections but first occurs in the uppermost
Gzhelian Ultradaixina bosbytauensis Zone. Precisely this zone is indicated by the latter
genus that is represented by the new subspecies of the index form and by the Indo-Chinese
species described by
Deprat [1914]
as Fusulina kozui, which is transitional between the typical Ultradaixina and
the genus Likharevites.
[23] The assemblage of Member 7 differs from the previous one in a greater number of
diverse Anderssonites forms and in the Likharevites first occurrence.
The species L. esetensis and L. paranitidus are known in the South Urals and
northern Fergana region, where they are associated with the beds underlying the Asselian.
This fact and the presence of Ultradaixina bosbytauensis distincta indicate that
the discussed assemblage should be referred to the U. bosbytauensis Zone, i.e. it is still
Gzhelian. It is not therewith improbable that the uppermost part of Member 7 is referred
to the Asselian.
[24] Member 8 is undoubtedly of Asselian age, which is evidenced by the finding of
Sphaeroschwagerina at its very base. Despite a small (under 6 m) thickness of the bed,
three significantly distinct fusulinid assemblages can be recognized in it. The first one in
addition to few Sphaeroschwagerina includes Praepseudofusulina kljasmica, Ruzhenzevites subcylindricus, R. zaladuensis zaladuensis and R. zaladuensis brevis.
The former species is characteristic of the uppermost Gzhelian and the lower zone of the
Asselian in the East European Platform and Darvaz. R. subcylindricus was described
from the Asselian of the southern Fergana region. Both subspecies of Ruzhenzevites
were recorded in the Asselian part of the Zaladou Formation in the Ozbak-Kuh
Mountains, eastern Iran.
[25] The second assemblage mainly includes numerous Likharevites gracilis and scarcer
L. kokpectensis and Anderssonites pseudoanderssoni. L. gracilis is the new
species and it is hard to judge of its age. However, it is similar to the form described as
Paraschwagerina acuminata uralensis from the lower half of the Asselian in the Nikol'skii
section of the South Urals
[Rauzer-Chernousova and Scherbovich, 1949].
L. kokpectensis is known from the Caspian and southern Fergana sediments correlated with
the middle zone of the Asselian in the Urals
[Bensh, 1972;
Scherbovich, 1969].
[26] The latter assemblage recorded in Member 8 is typical just for that zone. This is
evidenced by the occurrence of numerous Sphaeroschwagerina, namely, Sph. shamovi, Sph. moelleri, and Sph. pavlovi, and of characteristic species of Pseudoschwagerina
and Likharevites.
[27] The dolomitic Tighe-Maadanou Formation lacks faunal remains. Its late Asselian-Sakmarian
age is indicated by the position in the section above the beds bearing the middle Asselian
fusulinids. Recall that limestones of the Zaladou Formation grade into the dolomites.
Correlation
[28] Eastern Iran. In eastern Iran the sediments synchronous to that discussed
above were reliably recorded only in the Ozbak-Kuh Mountains of the Tabas region,
where the Zaladou Formation was first recognized
[Leven and Taheri, 2003].
The formation is subdivided there into two parts. The 50-m-thick lower unit is mainly
composed of terrigenous sediments bearing few faunal remains. Its age is conventionally
estimated as Kasimovian-early Gzhelian. The overlying 35-m-thick part of the formation
is carbonate in composition. Fusulinids were encountered in the upper 15 m of the
section. This faunal bed yields in its lower part Ruzhenzevites ferganensis and
numerous Rauserites including the characteristic Gzhelian forms. The upper 5 m of
the section contain Pseudoschwagerina, the genus typical for the middle zone of
the Asselian. Limestones of the Zaladou Formation are overlain by the dolomite sequence
over 100 m thick.
[29] In the Anarak section the terrigenous portion of the Zaladou Formation is missing,
probably cut by the fault. The Gzhelian-Asselian Anarak limestone is as a whole
correlated with the carbonate portion of the Zaladou Formation in the Ozbak-Kuh section.
In both sections the beds bearing the upper Gzhelian Ruzhenzevites ferganensis, and
the overlying layers with the Asselian Pseudoschwagerina are recorded in the upper part
of the limestone sequence (Table 2). Also in both sections these beds are extremely thin (15-20 m)
and embrace two or three Gzhelian and two Asselian fusulinid zones. It is hardly the
result of a low sedimentation rate, which is evidenced by the occurrence of coarsely
detritic facies of fusulinid limestone, from a wackestone to rudstone. The most likely
reason is the short-term, non-identified hiatuses that are quite probable considering the
shallow character of the limestones. This inference is indirectly confirmed by frequently
occurring sharp differences between fusulinid assemblages in adjacent beds without any
succession.
[30] In both the Anarak region and Ozbak-Kuh Mountains the Zaladou limestones are
overlain by dolomites that we distinguish as the Tighe-Maadanou Formation. These units
make up the Anarak Group. The latter unconformably overlies the Moscovian Absheni
Formation and is also unconformably overlain by the Bolorian-Upper Permian Shirgesht Group
[Leven and Gorgij, 2006;
Leven et al., 2006].
All these facts underline the similarity
of the discussed sections and indicate that at least in the second half of the
Carboniferous and in the Permian the sedimentary sequences in the studied areas were
accumulated in a single basin with like conditions of sedimentation. In the current
structure these regions are referred to the different, namely, Yazd (Anarak region) and
Tabas (Ozbak-Kuh region), fault blocks (Figure 1).
[31] The Carboniferous-Permian sections in the Shotori Mountains are also referred to
the Tabas block. The sediments in part or completely synchronous to the Zaladou and
Tighe-Maadanou formations, i.e. to the Anarak Group, are likely represented there by
a white quartz sandstone sequence, 60 m thick, that occurs between the shaly Sardar
Group and the Jamal Formation's limestone and is separated by stratigraphic
unconformities. The unconformity at the base of the quartz sandstone is underlined by
the presence of coal beds.
[32] The sediments that can be referred to the Anarak Group are recorded in the
Pashte-Badam block (Kalmard region) west of the Tabas block. According to
Arefifard and Davydov [2004]
and to our observations, they are represented by the 300-m-thick Khan
Formation composed of interbedded conglomerates, quartz sandstones, shales, and
limestones. Fusulinids derived from the middle and upper portions of the section indicate
the Asselian and Sakmarian age. The lower part of the formation is probably Gzhelian or
Kasimovian, which is evidenced by the findings of Ferganites and Daixina,
not related to the section
[Kahler, 1977].
[33] Alborz. The analogue of the Anarak Group in the central and eastern Alborz is
the Dorud Formation distinguished by
Assereto [1963].
In the type section north of Teheran he subdivided it into four parts. Subsequently
Bozorgnia [1973]
separated its lowest part as the Dozdeband Formation based on findings of
the Visean-Serpukhovian conodonts and Bashkirian foraminifers
[Ahmadzadeh, 1971;
Bozorgnia, 1973].
According to our preliminary data, the Dozdeband Formation includes the Moscovian sediments
as well. If this will be confirmed, the formation can be correlated with the Sardar Group of
the central and eastern Iran, whereas the Anarak Group will correspond to Beds 2-4 of the
Dorud Formation in its initial interpretation. The age of the Dorud Formation is commonly
estimated as the Asselian-Sakmarian or even Asselian-Artinskian. In so doing the
records by
Kahler [1976]
are cited. In the middle of the formation (Bed 3 after Assereto)
he encountered the Asselian Pseudoschwagerina and numerous fusulinids that he
referred to different species of the Lower Permian, including the Artinskian, Triticites
and Pseudofusulina. These species are closely similar and certain of them actually resemble
the Sakmarian and Yakhtashian Darvazites. However, they are no less related to
Praepseudofusulina reported from a great deal of Asselian sections, including the Anarak
section discussed in this paper.
[34] Unlike the central Iran sections, where the Dorud Formation includes sandstone
beds, in the eastern Alborz, namely, in the Gheselghaleh section nearby Gorgan, it is
mainly composed of limestone. Its age without the proper substantiation, mostly based on
the geologic position and by analogy with the western sections, was determined as the
middle Asselian-Sakmarian
[Lys et al., 1978].
The limestone is overlain by dolomites of the Kuh-e-Sariambar Formation presumably dated as
the Artinskian and Kubergandian. In our opinion, considering the records on the Anarak and
Ozbak-Kuh sections, both units correspond to the Zaladou and Tighe-Maadanou formations, i.e.
to the Anarak Group. The additional collections of fossils in the Gheselghaleh section will
permit the more valid conclusion.
[35] Zagros. The stripe of mainly Upper Permian sediments stretching along the
Shahreza-Abadeh-Hambast Range is commonly referred to central Iran. However, they
strongly differ from the deposits of the Anarak section primarily in a greater abundance
and diversity of fusulinids, among which the Eopolydiexodina members dominate. In this
regard they are similar to the sections described from certain Zagros regions.
Undoubtedly the Late Permian basin located in the modern Zagros area differed in
environmental conditions from the basin that occupied central and eastern Iran and
Alborz. These basins were likely separated from each other, which explains the above-
mentioned difference in benthic fauna. It is not, however, improbable that the basin was
single though relatively deeper in the northern part, where the Late Permian benthic biota
was oppressed and did not evolve.
[36] The sediments that can be correlated with the Anarak Group were studied by
Baghbani [1993]
in the vicinity of Shahreza town, in the Tang-e-Darchaleh section. They
were distinguished as the Vazhnan Formation represented by the 142-m-thick variegated
interbedded sandstone and limestone sequence. Bearing the basal conglomerates at its
base the formation overlies the Moscovian sediments yielding Ozawainella mosquensis
and with no visible unconformity but with a probable hiatus is overlain by limestones of
the Surmaq Formation that bears the Kubergandian fusulinids slightly above its base. The
lower portion of the Vazhnan Formation contains the Asselian Pseudoschwagerina and
Sakmarian Robustoschwagerina. Based on this fact Baghbani estimated the age of the
formation as the Asselian-Sakmarian. However, on the photos in his paper the forms
identified as "Robustoschwagerina" possess distinct septal flutings, which are not
characteristic of this genus as its septa are completely straight. Thus we assign these
forms to Pseudoschwagerina; if so, the Sakmarian age of the sediments is not proved.
However, considering that Pseudoschwagerina and "Robustoschwagerina" were
found at the base of the formation, the assignment of its upper part to the Sakmarian cannot be
excluded. In that case the Vazhnan Formation can be correlated with the Asselian-Sakmarian
portion of the Anarak Group and we can state that despite the relation of the
discussed sections to different biogeographic provinces, they are characterized by the
same transgressive-regressive cycle of sedimentation in the time span between the
Moscovian and Kubergandian (Bolorian-Kubergandian) ages.
[37] In a vast territory of southern Iran from Luristan on the west to Iranian Baluchistan
on the east the Sigillaria persica-bearing sandstone that overlies various horizons of
the Lower Paleozoic and is transgressively overlain by the Upper Permian limestones, most
likely corresponds to the Vazhnan Formation.
Conclusions
[38] The major results of our investigation can be summarized as follows.
[39] 1. The Anarak section is nowadays the most complete and well-studied among the
Gzhelian and Asselian sequences that are known in Iran. The Gzhelian Stage is
represented there in a full range; the Asselian, by two lower fusulinid zones.
The uppermost Asselian is likely characterized by dolomite facies and lacks fauna.
[40] 2. Despite certain peculiarities, the Gzhelian and Asselian fusulinid assemblages of
the discussed section are quite correlative with that from classic East European sections
and from sequences located in the Tethian northern margin, namely, in the Carnic
Alps, Fergana, and Darvaz. This indicates the occurrence of free connections between
the basin in central and eastern Iran and Alborz and the major Paleotethys basin.
[41] 3. The single Gzhelian-Sakmarian (Kasimovian?-Sakmarian) sedimentation cycle is
recorded in the territory of Iran. The sediments of the Anarak Group accumulated
during that time - continental on the south (Zagros) and shallow marine on the north
(central and eastern Iran and Alborz) - overlie the Sardar Group and older deposits
and are overlain by the Shirgesht Group with stratigraphic but not angular unconformities.
[42] 4. The attribution of the Shahreza-Abadeh-Hambast region to central Iran is controversial,
as the biofacies peculiarities of the Upper Permian sediments distributed there
indicate that they are more similar to the synchronous sediments of Zagros than to
those from central and eastern Iran and Alborz.
Systematic Descriptions
[43] The described fusulinid collection is sufficiently numerous and diverse, which
primarily results from a significantly large studied interval spanning the whole Gzhelian
and most of the Asselian Stage. At the same time the small size of the available samples
and poor preservation of some shells do not permit the complete enough characteristics
of the fusulinid assemblages in certain beds and the reconstruction of their evolution.
The Iranian fusulinids are still extremely poorly studied. Therefore, their species
identification is significantly difficult, since we have to be oriented to fusulinids
from other than central Iran biogeographic provinces. This results in incompletely reliable
certain species identifications that we are led to give in an open nomenclature, which in
turn produces the non-confident age determinations. Many specimens by convention referred
to certain known forms, should be likely recognized as separates species. However,
the limited amount of material generally prevents from doing it.
[44] In the discussed part of the section we identified 70 fusulinid species referred to 21
genera and 12 families. Among them six species and one subspecies are new. They are
described below (Plates 1-10).
Genus Schwageriniformis Bensh, 1996
Subgenus Schwageriniformis
Bensh, 1996
Schwageriniformis (Schwageriniformis) acutatus
Leven, n. sp. Plate 1, figs 23, 25, 27, 28
Etymology.
[45] Acutatus - acutate (Lat.).
Holotype.
[46] GIN 4781/20. Axial section; Iran, Anarak, Zaladou Formation,
Sample AC-25; Late Carboniferous (Pennsylvanian), Gzhelian.
Material.
[47] 9 axial and subaxial sections.
Description.
[48] Shell moderate in size, slender fusiform, with straight to
slightly convex lateral slopes and acutely pointed poles. Mature shells have 7 to 8 whorls
and measure 3.5 mm to 4.8 mm in length and 1.3 mm to 1.6 mm in diameter; form ratio 2.7 to 3.
First 3 to 4 whorls make up tightly coiled juvenarium, which is followed by loosely coiled
adult stage. Thin in inner 4 to 5 volutions and thick in following ones spirothesa composed
of tectum and thin alveolar keriotheca, its thickness in last whorl 0.06 mm to 0.07 mm.
Septa essentially plane across middle of shell, becoming moderately fluted near poles.
Proloculus small, its outside diameter 0.04 mm to 0.05 mm. Tunnel about half as high as
chambers, narrow in the juvenarium, significantly widening outwards. Low and narrow
chomata developed in early 4 to 5.5 volutions.
Discussion.
[49] Schwageriniformis acutatus n. sp. is very similar to
Schwageriniformis schwageriniformis (Rauser-Chernousova) characteristic of the upper
zone of the Kasimovian and, to a lesser degree, of the lower zone of the Gzhelian in a great
deal of sections of the East European Platform, Urals, and Central Asia. The Iranian species
differs in a stronger isolated juvenarium and smaller chomata. The forms
similar to Schwageriniformis acutatus were recorded by V. I. Davydov in the uppermost Gzhelian of the
Darvaz region and Chios Island, Greece (personal communication). However, they
possess a greater number of whorls and greater size, which indicates their relatively
advanced character.
Occurrence and age.
[50] The same as holotype.
Genus
Rauserites Rozovskaya,
1950
Rauserites stepanovi Leven, n. sp.
Plate 4, figs 5, 7, 8
Etymology.
[51] The species named in honor of Professor D. L. Stepanov,
the outstanding investigator of the Carboniferous and Permian of Iran.
Holotype.
[52] GIN 4781/62. Subaxial section; Iran, Anarak, Zaladou Formation,
Sample C23; Carboniferous, Pennsylvanian, Gzhelian.
Material.
[53] 5 axial and subaxial sections.
Description.
[54] Shell small, fusiform, with bluntly rounded poles. Mature shell
has 5 to 5.5 volutions and measures 4.9 mm to 6.3 mm in length and 1.7 mm to 2.2 mm in diameter;
form ratio 2.7 to 2.9. First 3 to 3.5 whorls rather tightly coiled, after which coiling becomes
loose. Spirotheca composed of tectum and moderately coarse keriotheca, 0.07 mm to 0.08 mm thick
in last whorl. Septa rather strongly and very irregularly fluted from pole to pole.
Septal folds high and wide. Proloculus moderately sized, its outside diameter 0.125 mm.
Tunnel low and wide. Chomata weak, present only on proloculus and in 2 or 3 inner
whorls. Axial filling is absent.
Discussion.
[55] Rauserites stepanovi n. sp. is the most similar to
"Triticites" tabinicus Alksne from the boundary Kasimovian and Gzhelian sediments of the Urals,
but differs in a more elongated shell, particularly in the inner whorls, and in a more uniform coiling.
Occurrence and age.
[56] The same as holotype.
Rauserites (?)
persicus Leven, n. sp. Plate 3, figs 7-9
Etymology.
[57] The species name derived from the ancient name of Iran - Persia.
Holotype.
[58] GIN 4781/52. Axial section; Iran, Anarak, Zaladou Formation, Sample
AC14; Carboniferous, Pennsylvanian, late Kasimovian (?) or early Gzhelian.
Material.
[59] 3 axial sections.
Description.
[60] Shell small, fusiform, with straight to slightly convex lateral slopes
and bluntly pointed poles. Adult individuals have 4.5 to 5 volutions and measure 4.5 mm to 5.3 mm
in length and 1.5 mm to 1.9 mm in diameter; form ratio 2.7 to 3.3. Irregular undulated
spirotheca composed of tectum and fine textured keriotheca; thickness in last whorl 0.6 mm to
0.8 mm. First 1 or 2 whorls rather tightly coiled but later ones looser. Septa rather
strongly fluted from pole to pole. Septal folds irregular, high, usually reaching tops of
septa. Proloculus small, its outside diameter 0.05. Tunnel narrow and poorly observed.
Chomata weak, present only on proloculus and in first one or two whorls.
Discussion.
[61] The species differs from all the Rauserites members in a small
proloculus; irregular coiling, tight in the initial whorls and looser in the last whorl; and in
weakly developed chomata. The attribution of our species to Rauserites is not obvious,
however, it cannot be referred with enough reason to any other known genus.
Occurrence and age.
[62] Iran, Anarak, Zaladou Formation, Samples AC14 and RL;
Pennsylvanian, late Kasimovian(?)-early Gzhelian.
Genus
Rugosofusulina
Rauser-Chernousova, 1937
Rugosofusulina (?)
iranica Leven, n. sp. Plate 5, figs. 1, 2
Etymology.
[63] The species name is derived from the word Iran.
Holotype.
[64] GIN 4781/70. Axial section; Iran, Anarak, Zaladou Formation,
Sample AC14; Carboniferous, Pennsylvanian, late Kasimovian (?)-early Gzhelian.
Material.
[65] 2 axial sections.
Description.
[66] Shell moderately large, short fusiform in first 3 whorls
and elongate fusiform, with bluntly rounded poles in following ones. Mature individuals
4.5 to 5 volutions and measure 6.3 mm to 7.5 mm in length and 2 mm in diameter; form ratio
3.12 to 3.75. Shell loosely coiled except for first 2 to 3 whorls. Waved and here and
there corrugated spirotheca composed of tectum and thin alveolar keriotheca 0.07 mm to
0.08 mm thick in last volution. Septa strongly but irregularly fluted throughout shell;
septal folds of different height and shape. Proloculus moderately large, its outside
diameter 0.17 mm. Tunnel half as high as chamber, narrow in inner 2 to 3 volutions,
significantly widening outwards. Clear, narrow and high chomata developed in early 3 volutions.
Discussion.
[67] The species is referred to Rugosofusulina by convention, for its
spirotheca is not as waved and corrugated as described in the diagnosis of the genus. At
the same time the wavy spirotheca does not permit the assignment of the species to
Triticites, which forms are similar to it in all parameters excluding the character of
spirotheca. Rugosofusulina (?) iranica closely resembles R. scaphulaeformis
Semikhatova known from the Triticites quasiarcticus-Tr. acutus Zone of the Kasimovian
in the Donetsk basin, differing from it in a tighter coiling of inner whorls, their more
elongated form, and in slightly more fluted septa.
Occurrence and age.
[68] The same as holotype.
Rugosofusulina (?)
elongata Leven, n. sp. Plate 5, figs 3-6
Etymology.
[69] Elongata - elongated.
Holotype.
[70] GIN 4781/88. Axial section; Iran, Anarak, Zaladou Formation,
Sample AC14; Carboniferous, Pennsylvanian, late Kasimovian (?) or early Gzhelian.
Material.
[71] 5 axial sections.
Description.
[72] Shell fairly large, elongated, subcylindrical, with bluntly
rounded to bluntly pointed poles. Mature shell has 4 to 4.5 volutions and measures 5 mm to
7 mm in length and 1.4 mm to 1.7 mm in diameter; form ratio 3.5 to 4.1. Spirotheca waved
in first two whorls and more or less corrugated in following ones. Spirotheca composed
of tectum and thin alveolar keriotheca; its thickness 0.07 mm in outer volution. Septa strongly
and irregularly fluted; septal folds of different height and shape. Proloculus moderately large,
its outside diameter 0.17 mm. Tunnel half as high as chamber, narrow in inner two
volutions, significantly widening outwards. Clear rounded chomata developed in
proloculus and two early volutions.
Discussion.
[73] Rugosofusulina (?) elongata n. sp. differs from R.
(?) iranica n. sp. in its subcylindrical shape of shell and more pronounced corrugation
of spirotheca.
Occurrence and age.
[74] The same as holotype.
Genus
Ultradaixina Davydov, 1982
Ultradaixina bosbytauensis distincta Leven, n. subsp.
Plate 5, figs 7-9, 11, 13, 14, 18
Etymology.
[75] Distincta - distinct.
Holotype.
[76] GIN 4781/77. Axial section. Iran, Anarak, Zaladou Formation;
Carboniferous, Pennsylvanian, latest Gzhelian.
Material.
[77] 10 axial and subaxial sections.
Description.
[78] Shell of moderate but variable size, fusiform to inflated fusiform,
with convex lateral slopes and bluntly pointed poles. Adult shells of 4.5 to 5 volutions measure
5.0 mm to 7.2 mm in length and 2.5 mm to 3.9 mm in diameter, form ratio 1.8 to 2.4. First 1 to 2
volutions constitute tightly coiled juvenarium, followed by more or less abrupt expansion
into loosely coiled adult stage. Spirotheca composed of tectum and thin alveolar
keriotheca, 0.1 mm to 0.125 mm thick in outer whorls. Septa irregularly fluted from pole to
pole or only slightly wavy across middle of shell. Proloculus medium-sized, its outside
diameter 0.15 mm to 0.21 mm. Tunnel low or narrow. Chomata narrow and developed only in
juvenarium. Axial fillings are absent.
Discussion.
[79] Ultradaixina bosbytauensis distincta n. subsp. is similar to
Ultradaixina bosbytauensis bosbytayensis (Bensh) but differs from it in a slightly isolated
juvenarium, presence of chomata, and generally in lesser size.
Distribution and age.
[80] Iran, Precaspian syneclise; Carboniferous, Pennsylvanian,
latest Gzhelian.
Occurrence.
[81] Iran, Anarak, Zaladou Formation, Samples P3, P6, C1, C27, AC29.
Genus
Likharevites Davydov, 1987, emend. Leven
Remarks.
[82] A great deal of Permian sections in the Tethys and South Urals regions
contain fusulinids characterized by a more or less inflated fusiform shell, extremely small
proloculus, tightly coiled juvenarium, widely and loosely coiled following whorls, and thin
septa strongly and as a rule irregularly fluted throughout the whole width and length. Over
many years these fusulinids were referred to the American genus Paraschwagerina
Dunbar et Skinner, 1936. A lot of researchers continue doing this up to now. After the
distinction of Occidentoschwagerina
[Miklukho-Maclay, 1959]
and Alpinoschwagerina
[Bensh, 1972]
some of like fusulinids were assigned to these genera. The above-mentioned genera were
mainly described from the Asselian and Sakmarian, though their
first members were recorded in the upper Gzhelian Ultradaixina bosbytauensis Zone and
the last ones, in the Yakhtashian sediments. Fusulinids of this type were recently found in
the lower Gzhelian in the Darvaz and Donetsk basin and were recognized as a new
genus Darvasoschwagerina
[Leven and Davydov, 2001].
[83] The above-reported major morphologic characters of the discussed fusulinids
remained almost unchanged with time. Only juvenarium was progressively altered. In
Gzhelian forms, for instance,
( Darvasoschwagerina donbassica Leven et Davydov, 2001 and others),
it resembles that of the Kasimovian Montiparus in the wall structure and
massive chomata. Juvenarium of the late Gzhelian, Asselian, and, partly, Sakmarian
forms, namely, of "Alpinoschwagerina" paranitida Besh, 1972,
"Occidentoschwagerina kokpectensis" Bensh, 1972, "Paraschwagerina" pseudomira M.-Maclay, 1949, and others, is similar to that of the Gzhelian
Triticites and Rauserites. Beginning with the Sakmarian time, it gained
features of Pseudofusulina s. l. characterized by strongly and
regularly fluted septa, sometimes with pronounced axial fillings, as in
"Paraschwagerina" kanmerai
[Nogami, 1961], "P." akiyoshiensis
[Toriyama, 1958], and "P." zhen'anensis
[Xia et al., 1996].
According to the biogenetic law, at early stages of ontogeny the
organisms bear ancestor characters. If so, the marked differences in the juvenarium
structure of the discussed fusulinids mean that different ancestors repeatedly and
at different times produced morphologically similar forms that, despite their general
similarity, should be interpreted as separate taxa. At first sight the current taxonomy
fits this requirement, keeping in mind that these forms are referred to different genera,
namely, D arvasoschwagerina, Occidentoschwagerina, Alpinoschwagerina, and
Paraschwagerina. However, on distinguishing these genera (excluding the former) no
particular significance was attached to differences in the juvenarium structure. Moreover,
the validity of Occidentoschwagerina and Alpinoschwagerina can be questioned
following
Forke [2002],
based on their diffuse diagnosis and undoubted similarity of the
genotypes with the genus Pseudoschwagerina. As for Paraschwagerina, judging from
the juvenarium with strongly fluted septa and general habitus, it can be compared only with
relatively young, Sakmarian-Yakhtashian members of the discussed fusulinid group.
However, they are also most likely of independent origin considering the attribution of
typical Paraschwagerina to the other, significantly isolated from the Tethys,
Midcontinent-Andean biogeographic region.
[84] All the above suggests the necessary distinction of Paraschwagerina-like fusulinids
with a simple juvenarium structure, such as "Alpinischwagerina" paranitida Bensh,
"Occidentoschwagerina" kokpectensis Bensh, "Paraschwagerina" acuminata uralensis
Rauser-Chernousova, "P." inflata Chang, and a lot of others, in a separate genus. This
conclusion was previously made by V. I. Davydov who recognized the new genus
Likharevites. Unfortunately its diagnosis was published in the Deponent of VINITI and
was almost beyond the reach of most of researchers. Owing to this, though the author
repeatedly used the name Likharevites, it actually remained nomen nudum. With the aim
of securing this name we give below the diagnosis of the genus similar to that by the
author, however, with certain refinements produced by the latest available records.
Diagnosis.
[85] Shell small to moderately large, fusiform to nearly spherical,
with bluntly pointed poles. Mature individuals usually possess 5 to 6 whorls. First three
of them constitute very tightly coiled juvenarium, which is followed by abrupt expansion
into loosely coiled adult stage. Spirotheca composed of tectum and thin alveolar keriotheca.
Septa thin, rather strongly but irregularly fluted throughout the shell. Septal folds variable
in height; some involve only lower third of septa, whereas others extend to tops of
chamber. Regularity of septal flutings increases from ancient to more developed species.
In juvenarium septa wavy or gently fluted in the highly developed species. Axial filling is
absent. Tunnel low and feebly marked. Chomata weak but clear, present only in
juvenarium.
Discussion.
[86] The discussed genus differs from Paraschwagerina Dunbar
et Skinner (s.s.) in a more simple juvenarium, which indicates that it originated from
a relatively primitive ancestor. This is also confirmed by the older, late Gzhelian-Sakmarian
age of our genus. The typical American Paraschwagerina members are dated as the
Sakmarian-Artinskian
[Wardlaw and Davydov, 2000].
Likharevites generally differs from Alpinoschwagerina (Bensh) (s.s.)
in a fusiform shell, significantly stronger fluting of septa, and in smaller size.
The author of the genus referred to it fusulinids from the Triticites (?)
fornicatus Kanmera group, which was in our opinion untrue, since they correspond to the
above diagnosis neither in shell size nor in coiling and septal fluting and most likely
should be recognized as a separate genus.
[87] Type species - Pseudoschwagerina (?) sartauensis
[Davydov, 1986, p. 92-93, Plate 14, fig. 11].
Likharevites gracilis , n. sp.
Plate 6, figs 2-11a
[88] Paraschwagerina inflata Chang.
[Kahler, 1989, Plate 5, fig. 2, p. 224].
[89] Alpinoschwagerina confinii F. et G. Kahler. [Chen Genbao et al., 1992, Plate 28, figs. 5, 6].
[90] Paraschwagerina bianpingensis Zhang et Dong.
[Chen Genbao et al., 1992, Plate 28, fig. 9].
[91] Paraschwagerina aff. toriyamaia (Igo).
[Forke, 2002, Plate 38, fig. 11, p. 250].
Etymology.
[92] Gracilis - slender, slim (Lat.).
Holotype.
[93] GIN 4781/95. Axial section. Iran, Anarak section,
Zaladou Formation, Unit 8; Permian, Cisuralian, Asselian.
Material.
[94] 25 axial sections.
Description.
[95] Shell moderately large, fusiform to nearly spherical,
with bluntly pointed poles. Mature individuals usually possess 5 to 6 whorls. First
three of them constitute very tightly coiled juvenarium, which is followed by abrupt
expansion into loosely coiled adult stage. Spirotheca composed of tectum and thin
alveolar keriotheca. Septa thin, rather strongly but irregularly fluted throughout
the shell. Septal folds high and broad. In juvenarium septa wavy or gently fluted.
Axial filling is absent. Tunnel low and feebly marked. Chomata weak but clear,
present only in juvenarium.
Variability.
[96] The outer shape of shell and juvenarium are primarily
subject to variations. Juvenarium is particularly variable: from elongated fusiform
to short oval. The degree of septal fluting slightly varies as well. Variations are
sometimes so significant (for instance, between figs. 4 and 5, Plate 6) that
the affiliation of certain forms to the same species casts some doubt. However,
the concurrent occurrence of numerous intermediate forms permits the consideration
of these variations as a result of intraspecific variability.
Discussion.
[97]
The species is similar to Likharevites kokpectensis
(Bensh) but possess a shorter and more inflated shell. In this respect it can be compared
with Likharevites inflatus (Chang). However, this Chinese species has a more elongated
juvenarium, looser coiling, and slightly stronger and more regular septal fluting. The
tighter coiling and lesser septal folds differentiate the discussed species from the
Japanese Likharevites shimodakensis (Kanmera). Likharevites gracilis is very similar
to the species described by Rauser-Chernousova as Paraschwagerina acuminata var.
uralensis from the Asselian of the South Urals
[Rauser-Chernousova and Scherbovich, 1949].
However it differs from the Uralian form in a somewhat looser coiling and less
strong septal fluting.
Distribution and age.
[98] Iran, Carnian Alps, China; Permian, Cisuralian, Asselian.
Occurrence.
[99] Iran, Anarak, Zaladou Formation, Samples P4, P8, P12, C25, C38,
C39, RupA, Rup2, Rup4, R1, R2.
Acknowledgments
[100] This work was supported by the Russian Foundation for Basic Research,
project no. 06-05-65201
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Received 10 March 2006; revised 15 April 2006; accepted 20 April 2006; published 3 May 2006.
Keywords: Carboniferous, Permian, stratigraphy, fusulinids, Iran.
Index Terms: 0999 Exploration Geophysics: General or miscellaneous; 1165 Geochronology: Sedimentary geochronology; 1705 History of Geophysics: Biogeosciences.

Citation: Leven, E. Ja., and M. N. Gorgij (2006), Upper Carboniferous--Permian stratigraphy and fusulinids from the Anarak region, central Iran, Russ. J. Earth Sci., 8, ES2002, doi:10.2205/2006ES000200.
Copyright 2006 by the Russian Journal of Earth Sciences
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