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J.C. Gutiérrez-Marco, I. Rábano and D. García-Bellido (eds.),
Ordovician of the World.
Cuadernos del Museo Geominero, 14. Instituto Geológico y Minero de España, Madrid. ISBN 978-84-7840-857-3
© Instituto Geológico y Minero de España 2011
171
NEW DATA ON THE LATE ORDOVICIAN TRILOBITE FAUNAS OF KAZAKHSTAN:
IMPLICATIONS FOR BIOGEOGRAPHY OF TROPICAL PERI-GONDWANA
M. Ghobadi Pour
1
, L.E. Popov
2
, L. McCobb
2
and I.G. Percival
3
1
Department of Geology, Faculty of Sciences, Golestan University, Gorgan, Iran.
mghobadipour@yahoo.co.uk. m.ghobadipour@gu.ac.ir
2
Department of Geology, National Museum of Wales, Cardiff CF10 3NP, Wales, United Kingdom.
leonid.popov@museumwales.ac.uk, lucy.mccobb@museumwales.ac.uk
3
Geological Survey of NSW, 947-953 Londonderry Road, Londonderry 2753, New South Wales, Australia.
ian.percival@industry.nsw.gov.au
Keywords: Late Ordovician, Gondwana, Kazakhstan, trilobites, biogeography.
INTRODUCTION
During the Late Ordovician, microplates and volcanic arc systems presently incorporated into the
Kazakhstanian orogen converged to form a huge archipelago, which extended far into the ocean along
subequatorial latitudes west of the tropical Australasian sector of Gondwana (Popov et al., 2009). The
shelves of volcanic islands and microcontinents within this archipelago supported diverse benthic faunas,
with trilobites as one of the most important components. Kazakhstanian Late Ordovician trilobite faunas
have been documented in a number of publications (Ghobadi Pour et al., 2011; Koroleva, 1982 and
references therein). Koroleva (1982) gave up to date summaries with outlines of taxonomic diversity and
geographical distributions of trilobite taxa throughout Kazakhstan. A total of about 110 genera and more
than 200 species were counted, but their generic affiliation often requires revision. Apollonov (1975)
published a brief review of the Kazakhstanian trilobite biofacies, whereas Fortey and Cocks (2003) gave a
brief outline of biogeographic affinities of Kazakhstanian faunas throughout the Ordovician, mainly based
on personal assessment of unpublished collections by Richard Fortey. Nevertheless, existing data on
characters of trilobite faunas from individual terranes are still incomplete and there was little progress in
their study during the last 25 years.
In spite of significant losses of collections and geological information after the collapse of the Soviet
Union, there is a substantial amount of unpublished data which has been preserved and is available for
study. It includes an enormous trilobite collection assembled by the late Michael K. Apollonov, which covers
almost all areas in Kazakhstan where Ordovician deposits are present. In addition to published
information, new data are presented in this paper, mainly based on a preliminary assessment of the
samples available from Apollonov’s collections, which are currently under study.
ORDOVICIAN PALAEOGEOGRAPHY OF KAZAKHSTANIAN TERRANES
Three major clusters of early Palaeozoic terranes can be recognised in the Kazakhstanian orogen. The
southern cluster includes three major crustal terranes (i.e. Chu-Ili, North Tien Shan and Karatau-Naryn),
which were amalgamated together by the Late Silurian (Popov et al., 2009) (Fig. 1). The published record
of Mid to Late Ordovician trilobite faunas of Chu-Ili is the most complete in comparison with other regions
of Kazakhstan, whereas it is virtually nonexistent for North Tien Shan (Ghobadi Pour et al., 2009; Koroleva,
1982 and references here).
172
M. Ghobadi Pour, L.E. Popov, L. McCobb and I.G. Percival
Figure 1. Palaeogeographical reconstruction for the Upper Ordovician (Katian) showing geographical distribution of selected
biogeographically informative trilobite genera. Position of the major early Palaeozoic continents mainly after Fortey and Cocks
(2003) with emendations after Popov et al. (2009). Surface water circulation for a Northern Hemisphere summer is mainly after
Wilde (1991). Abbreviations for Kazakhstanian island arcs and microplates are as follows: A-Zh – Atasu-Zhamshi, Ak – Akbastau,
Ch-T – Chingiz-Tarbagatai, K-N – Karatau-Naryn, NTS – North Tien Shan.
The southern cluster of Kazakhstanian terranes is separated by an oceanic suture from the Atasu-
Zhamshi microplate (Apollonov, 2000; Popov et al., 2009) (Fig. 1). The area north-east of Atasu-Zhamshi
represents a complicated mosaic of island arc and continental fragments, separated by ophiolitic belts
associated with sutures and often strongly reworked since the Early Palaeozoic (for summary, see Popov et
al., 2009; Windley et al., 2007). At least three major island arc systems can be recognised, including
Akbastau, Chingiz-Tarbagatai and Boshchekul. Published information on the Late Ordovician trilobite
faunas of the Chingiz-Tarbagatai and Boshchekul regions was reviewed by Koroleva (1982 and references
here) and recently by Ghobadi Pour et al. (2011).
Another group of early Palaeozoic terranes are those of north-central Kazakhstan, i.e. the Kalmyk Kol-
Kokchetav unit of S
,
engör & Natal’in (1996) or Shatsk and Kokchetav microplates of Dobretsov et al. (2006)
and adjacent island arcs. Data on the Neoproterozoic to Early Palaeozoic geological history of this north-
central sector of the Kazakhstanian orogen, provided by Dobretsov et al. (2006), substantiates the idea
that these units did not interact with the south Kazakhstanian cluster of terranes throughout the
Cambrian-Ordovician. Koroleva (1982) published a detailed outline of Late Ordovician trilobite
distributions in the Selety, Ishim and Stepnyak regions, based in a significant part on her earlier
publications.
TRILOBITE BIOFACIES
In the late Darriwilian – Sandbian, asaphid-illaenid biofacies were characteristic for inshore
environments in almost all Kazakhstanian terranes, but they are well documented only for Chu-Ili. A good
example is the monotaxic ‘
Isotelus’ romanovskyi
Association of Apollonov (1975), which spread widely on
a shallow clastic shelf across Chu-Ili. It replaced the lingulid
Ectinoglossa
Association seaward and was
confined to a sandy bottom, nearshore setting, inhabited mainly by gastropods and bivalved molluscs.
‘
Isotelus’ romanovskyi
Weber, 1948 is probably assignable to
Damiraspis
(Fig. 2.11-13), but hypostome
morphology in this species is as yet unknown. On the shallow carbonate shelf of Chu-Ili, the asaphids
Damiraspis
and
Farasaphus
formed oligotaxic communities, usually in association with the endemic illaenid
Alperillaenus
(Fig. 2.1, 6-7) as a second major component. Other minor components comprised
Ceraurinella
?,
Eorobergia
,
Pliomerina
(Fig. 2.21) and
Sphaerexochus
(Ghobadi Pour et al., 2009).
The pliomerid-styginid biofacies first emerged during the Sandbian. At that time, it was most
characteristic for silty bottom, nearshore settings and probably occupied a quiet environment, affected
occasionally by seasonal storms. During the Sandbian, these biofacies were dominated by styginids, namely
Dulanaspis
,
Styginella
and
Bronteopsis
. Other common taxa are
Lonchodomas
,
Pliomerina
,
Remopleurides
and
Sinocybele
(Fig. 2.22), whereas asaphids are rare to almost absent. During the Katian, these
associations gradually replaced asaphid-dominated associations nearshore, and there were changes in the
taxonomic composition of the assemblages.
Pliomerina
and
Remopleurides
proliferated and became
dominant by the mid-Katian, whereas the proportion of styginids gradually declined.
The illaenid-cheirurid biofacies was confined to the carbonate build-ups, which became widespread
throughout Kazakhstanian island arcs and microcontinents in the Sandbian–Katian. This biofacies was
characterised by rich generic diversity, but remains very poorly known. In addition to the nominative
families, asaphids, lichids, pliomerids, remopleuridids, raphiophorids and styginids usually occur. Such
genera as
Acrolichas
(Fig. 2.5, 10),
Eokosovopeltis
,
Glaphurina
,
Holotrachellus
,
Metopolichas
and
Sphaerexochus
(Fig. 2.8-9) are the most characteristic. The nileid biofacies is known from the offshore
173
NEW DATA ON THE LATE ORDOVICIAN TRILOBITE FAUNAS OF KAZAKHSTAN: IMPLICATIONS FOR BIOGEOGRAPHY OF TROPICAL PERI-GONDWANA
environment of almost all major Kazakhstanian terranes. Faunas characteristic of this biofacies usually lack
distinct dominant taxa and may be rather diverse. For example, a nileid association recently described from
the lower Katian Karagach Formation of the Tarbagatai Range (Ghobadi Pour et al., 2011) contains 15
different trilobite genera, including leiostegiids (
Aegirina
), asaphids (
Birmanites
), encrinurids
(
Encrinuroides
,
Sinocybele
), remopleuridids, raphiophorids and shumardiids (Fig. 2.4, 17-19).
The raphiophorid biofacies probably occupied the disphotic zone in deeper water offshore. Trilobite
taxa characteristic of this biofacies are often blind (many raphiophorid genera), or possess hypertrophic
eyes (e.g.
Arator
and
Telephina
). Trilobite associations of this biofacies may be oligotaxic (e.g.
Bulbaspis
Association from the Dulankara Formation of Chu-Ili terrane), or display remarkable taxonomic diversity
with more than 25 genera (
Caganaspis
Association from the Bestamak Formation of the Chingiz Range).
The list of characteristic genera includes the three-segmented raphiophorid
Caganaspis
(Fig. 2.14) and
remopleuridids (e.g.
Arator
,
Eorobergia
,
Robergia
?) (Fig. 2.16) that are widespread in the Chu-Ili,
Boshchekul and Chingiz-Tarbagatai terranes, but are as yet unknown outside Kazakhstan. There are also
more widespread taxa, e. g.
Ampyxinella
,
Bulbaspis
,
Endymionia
,
Birmanites
,
Dionide
and
Telephina
(Fig.
2.2, 3, 15), which are also documented from the Australasian sector of Gondwana. A significant proportion
of Kazakhstanian faunas characteristic of the raphiophorid biofacies remain formally undescribed.
The deepest water olenid biofacies was not previously documented from Kazakhstan. In Atasu-
Zhamshi, the olenid
Porterfieldia
occurs in association with
Endymionia
in black limestones of the Shundy
Formation (Sandbian). The only other fossils to occur at that locality are radiolarians. In Chu-Ili, olenid
trilobites occur in black graptolitic shales of Katian age, exposed on the Akkerme Peninsula on the western
coast of Balkhash Lake. In this locality, the olenid
Triarthrus
(Fig. 2.20) occurs in association with
Dionide
,
Caganaspis
and a new, as yet undescribed, harpetid genus.
IMPLICATIONS FOR BIOGEOGRAPHY
In spite of incomplete knowledge of Kazakhstanian trilobite faunas, there is good evidence that during
the Late Ordovician they exhibited similar biogeographical signatures, suggesting affinity to the
Eokosovopeltis-Pliomerina
Province of Webby et al. (2000). Indeed,
Eokosovopeltis
and
Pliomerina
proliferated on the shallow shelves of all major Kazakhstanian terranes. However, significant work is still
needed to establish the faunal signatures of individual Kazakhstanian island arcs and microplates.
174
M. Ghobadi Pour, L.E. Popov, L. McCobb and I.G. Percival
Figure 2. Selected Ordovician trilobites from Kazakhstan. Specimens deposited in the National Museum of Wales Cardiff (NMW), and
F.N. Chernyshev Central Geological Scientific Research and Exploration Museum (CNIGR), St Petersburg. 1, 6, 7,
Alperillaenus
intermedius
Ghobadi Pour and Popov, 2009; Darriwilian, Kypchak Limestone, northern Betpak-Dala; 1, NMW 2008.34G.3, cranidium,
x2; 6, NMW 2008.34G.11, hypostome, x5.5; 7, NMW 2008.34G.9, pygidium, x5.5. 2, 3,
Ampyxinella balashovae
Koroleva, 1965;
Sandbian, Sarytuma, West Balkhash Region; 2, NMW2008.34G.150, internal mould of cranidium, x3; 3, NMW2008.34G.151, internal
mould of pygidium, x3. 4,
Agerina acutilimbata
Ghobadi Pour et al., 2011, Katian, Karagach Formation, east side of the Ayaguz River,
about 7 km north of Akchii village, Trabagatai Range; NMW 2005.32G.135, holotype, articulated exoskeleton, latex cast, x5. 5, 10,
Acrolichas clarus
Koroleva, 1959, Sandbian, Myatas Formation, northern coast of Atansor Lake; 5, NMW2008.34G.155, cranidium,
x4; 10, NMW2008.34G.156, incomplete pygidium, x4. 8, 9,
Sphaerexochus conusoides
Koroleva, 1959; age and locality as Fig. 2.5;
8, NMW2008.34G.157, cranidium, x2.5, 9, NMW2008.34G.158, pygidium, x2.2. 11-13,
Damiraspis margiana
Ghobadi Pour and
Popov, 2009, age and locality as Fig. 2.1; 11, NMW 2008.34G.46, cranidium, x4. 12, NMW 2008.34G.42, holotype, hypostome, x1.1;
13, NMW 2008.34G.48, partly exfoliated pygidium, x2.5. 14,
Caganaspis unica
Kolobova, 1985, area about 7 km south-west of
Alakul Lake, West Balkhash Region, NMW2008.34G.149, articulated exoskeleton, latex cast, x4.5. 15,
Telephina omega
Koroleva,
1982, age and locality the same as Fig. 2.2; NMW2008.34G.152, internal mould of cranidium, x 3.5. 16,
Robergia
? sp., age and
locality the same as Fig. 2.14; NMW2008.34G.153, cranidium, latex cast, x5. 17,
Nileus
sp., age and locality the same as Fig. 2.4;
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NEW DATA ON THE LATE ORDOVICIAN TRILOBITE FAUNAS OF KAZAKHSTAN: IMPLICATIONS FOR BIOGEOGRAPHY OF TROPICAL PERI-GONDWANA
NMW 2005.32G.193, cephalon with attached thoracic segments, latex cast, x6. 18,
Aethedionide
sp., Sandbian, Karagach Formation,
locality as Fig. 2.4; NMW 2005.32G.191, pygidium, internal mould, x4. 19,
Birmanites akchiensis
Ghobadi Pour et al., 2011, age and
locality the same as Fig. 2.4; NMW 2005.32G.181, holotype, cranidium, latex cast of external mould, x1.5. 20,
Triarthrus
sp., Katian,
Ak-Kerme Peninsula, west coast of Balkhash Lake, NMW2008.34G.154, cranidium, x9. 21,
Pliomerina
aff.
sulcifrons
(Weber, 1948),
age and locality as Fig. 2.1; NMW 2008.34G.25, cranidium, x5. 22
, Sinocybele weberi
(Kolova, 1936), Katian, Besharyk Formation,
Dzhebagly Mountains; CNIGR 60/4263, lectotype, incomplete dorsal exoskeleton, latex cast, x1.8.
Recent studies also demonstrate that the asaphid trilobites
Basilicus
and
Basiliella
were probably
confined to peri-Iapetus settings, while the Kazakhstanian and Australasian species traditionally assigned
to these genera in fact belong to separate asaphid lineages (Ghobadi Pour et al., 2009), which evolved
independently in tropical peri-Gondwana and should be assigned to different genera (i.e.
Damiraspis
and
Farasaphus
). Remarkably, although these asaphids commonly occur in the Australian sector of Gondwana,
they are absent from the Darriwilian–Katian rocks of South China, where they are replaced by genera of
the Subfamily Nobiliasaphinae (e.g.
Liomegalaspides
). A similar pattern was observed for
Eokosovopeltis
,
which is absent from the Sandbian to early Katian of South China (Zhou and Zhen, 2009). Zhou and Zhen
(2009) recently suggested that Australian trilobite faunas had closest affinities with those of North China
during the Arenig-Caradoc interval (=Sandbian–early Katian). It is likely that there was a continuous belt
of tropical peri-Gondwanan, shallow water faunas during the Sandbian-early Katian, which included
Kazakhstanian terranes, North China and the Australian sector of Gondwana.
The most likely explanation can be found in features of oceanic surface circulation along the western
coast of Gondwana (Fig. 1). It is well established that the Australian sector of Gondwana, North China and
Kazakhstanian microplates and island arcs occupied a subequatorial position in the Ordovician, whereas
a more temperate latitude is evident for South China during the Early to Mid Ordovician, based on
palaeomagnetic data, characteristics of shallow marine benthic communities and sedimentation (Fortey
and Cocks, 2003). In particular, the occurrence in South China of trilobites from the Family
Reedocalymeninae and
Taihungshania
represents a distinct link with temperate to high latitude
Gondwanan faunas (e.g. Armorica, Turkish Taurids, Iran), whereas they are virtually absent from
Kazakhstanian terranes and the Australian sector of Gondwana. It is probable that a cool water, South
Subpolar Current, running along the western Gondwanan coast (Wilde, 1991), might have an effect on
climate comparable to the present-day Humboldt Current. As a result, average annual temperatures of
surface waters along the coasts of the South China continent during the Early to Mid Ordovician were
considerably lower than in subequatorial peri-Gondwana, which prevented the immigration of some warm
water taxa. Only in the Katian, when South China entered low latitudes, did affinity with the shallow shelf
faunas of the Kazakhstanian terranes become firmly established.
Acknowledgements
The research of Mansoureh Ghobadi Pour was supported by the Golestan University, Gorgan. Leonid
Popov and Lucy McCobb acknowledge support from the National Museum of Wales. Ian Percival publishes
with permission of the Director, Geological Survey of New South Wales.
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