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Middle Cambrian molluscs of ‘Australian’ aspect from northern Siberia a
Alexander P. Gubanov , Artem V. Kouchinsky a
Peeland & Stefan Bengtson
a b
, John S.
c
a
Department of Earth Sciences (Palaeontology), Uppsala University, Norbyvägen 22, SE-752 36, Uppsala, Sweden E-mail: b
Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, 90095-1567, USA c
Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05, Stockholm, Sweden E-mail: Published online: 27 Nov 2008.
To cite this article: Alexander P. Gubanov , Artem V. Kouchinsky , John S. Peeland & Stefan Bengtson (2004) Middle Cambrian molluscs of ‘Australian’ aspect from northern Siberia, Alcheringa: An Australasian Journal of Palaeontology, 28:1, 1-20, DOI: 10.1080/03115510408619272 To link to this article: http://dx.doi.org/10.1080/03115510408619272
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Middle Cambrian molluscs of 'Australian' aspect from northern Siberia ALEXANDER P. GUBANOV, ARTEM V. KOUCHINSKY, JOHN S. PEELAND STEFAN BENGTSON
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GUnANOV,A.P., KOUCHINSKY,A.V., PnEL,J.S. &; BENGTSON,S., 30.4.2004. Middle Cambrian molluscs of 'Australian type' from northern Siberia. Alcheringa 28, 1-20. ISSN 03115518. An assemblage of silicified helcionelloid molluscs is described from the Kuonamka Formation (Middle Cambrian Amgan Stage) of the Bol'shaya Kuonamka and Malaya Kuonamka rivers, northern Anabar Shield, northern Siberia. In addition to the new genera Kuonamkaella and Anabaroconus, the assemblage contains species of Yochelcionella, Eotebenna, Pseudomyona, and Protowenella. These latter genera were previously unknown from the Middle Cambrian of Siberia and indicate a strong affinity with coeval molluscan faunas from the Australian Middle Cambrian. The fauna provides evidence for close palaeogeographie links to East and West Gondwana, Baltica, and Laurentia during the Middle Cambrian, and facilitates biostratigraphiccorrelation between these crustal blocks. Alexander P. Gubanov [
[email protected]], Artem V. Kouchinsky [
[email protected]], John S. Peel [
[email protected]], Department of Earth Sciences (Palaeontology), Uppsala University, Norbyviigen 22, SE-752 36 Uppsala, Sweden [present address of A. E Kouchinsky: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA]; Stefan Bengtson [
[email protected]], Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE- I 04 05 Stockholm, Sweden;received l 4.11.2002, revised 17.4.2003.
Key words: Mollusca, helcionelloids, Middle Cambrian, Siberia. VARIATION in our knowledge of Early and Middle Cambrian molluscs from different regions adversely affects the utility of molluscs for biostratigraphic and biogeographic purposes and impedes the discrimination of evolutionary lineages. Siberian helcionelloid molluscs from the Early Cambrian, especially from the Tommotian and Atdabanian, have been intensively studied (Vostokova 1962, R o z a n o v et al. 1969, Missarzhevsky 1989, Vassiljeva 1990, 1996), but the molluscs from overlying strata have received little attention. In contrast, molluscs from the late Early and Middle Cambrian in Australia, New Zealand and elsewhere exhibit an array of new morphologies (Runnegar & Jell 1976, MacKirmon 1985, Geyer 1986, Bengtson et al. 1990, Partdaaev 2001). However, the paucity of descriptions o f the earlier Cambrian molluscs from these 0311/5518/2004/01001-20 $3.00 ©AAP
localities makes it difficult to trace the ancestry of these faunas. A silicified Middle Cambrian molluscan fauna, described herein from the Kuonamka Formation of northern Siberia, contains helcionelloids such as Eotebenna Runnegar & Jell, 1976, Protowenella Runnegar & Jell, 1976, Pseudomyona Runnegar, 1983, and Yochelcionella Runnegar & Pojeta, 1974, all previously unknown from the Middle Cambrian of Siberia. The fauna p r o v i d e s e v i d e n c e for closer palaeogeographic links to East (Australia and New Zealand) and West (Spain and M o r o c c o ) Gondwana, Baltica and Laurentia in the Middle Cambrian, and facilitates direct biostratigraphic correlation between these crustal blocks.
Material and methods Material described herein was obtained in 1996
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2
GUBANOV, KOUCHINSKY, pEEl.& BENGTSON
Fig. 1. Map of the Siberian Platform, showing the distribution of facies zones in the basin during the Early Cambrian and the localityfor Middle Cambrian molluscs. 1, lagoonal facies zone; 2, transitional facies zone; 3, open-marinefacieszone; B - Bol'shayaKuonamkaRiver, M - Malaya Kuonamka River. during fieldwork by AVK and SB in northern Siberia (Fig. 1). The fossils are derived from limestone beds in the bituminous Kuonamka Formation (Fig. 2) and occur within the Amgan Stage of the Siberian Middle Cambrian. Acrolretid and lingulid brachiopods, polymerid trilobites and agnostids, simple phosphatic tooth-like and tubular structures, chancelloriids, net-like Microdictyon, button-shaped palaeoscolecid sclerites, hyoliths and ossicles of echinoderms co-occur with the molluscs described here. Section 1 of the Kuo,amka Formation (Fig. 2) crops out along the left bank of the Malaya Kuonarnka River, near and downstream o f the village of Zhilinda (70°02'N, 114°42'E). The lowermost part of the section belongs to the Emyaksin Formation and is composed o f bioturbated fossiliferous greenish-grey, glauconitic, lime mudstones with wacke- and packstones, interbedded with greenish-grey shale, especially in the upper 3 m of the formation. The Kuonamka Formation is overlain by yellowish-grey lime mudstones of the basal Olenyok Formation; sample 1/22 was collected
ALCHER1NGA
from the upper part o f member 6 (top of bed 12 o f Val'kov 1975, p. 28). Because of its proximity to the northern part of the transitional facies zone of the Siberian Platform, the Kuonamka Formation in section 8 (Fig. 2) is considerably more calcareous than in section 1. Section 8 is exposed along the left bank of the Bol'shaya Kuonamka River, ca. 7 km downstream from the mouth o f the UlakhanTjulen Brook (Val'kov 1975). Sample 8/18.5 is from the upper part of member 5; sample 8/23.3 is from a lime mudstone layer near the middle of member 6; sample 8/32 was collected from the top o f member 7. Silicified fossils were initially extracted from the limestones using a buffered solution o f 10% dilute acetic acid. Mud was removed from the resultant insoluble residues by heating to boiling point in water and immediately decanting the suspension. Sample 8/32 was additionally treated with 10% diluted hydrochloric acid to remove calcite crystals, leaving the silicified fossils intact.
Systematicpalaeontology Figured material is housed in the type collection o f the Swedish Museum of Natural History in Stockholm, Sweden (SMNH Mo 160563-615). AM F refers to the collections o f the Australian Museum, Sydney; and ANU refers to collections in the Department of Earth and Marine Sciences, Australian National University, Canberra. Phylum MOLLUSCA Cuvier, 1797 Class HELCIONELLOIDA Peel, 1991a Order HELCIONELLIDAGeyer, 1994 Family HELCIONELLIDAEWenz, 1938 K u o n a m k a e l l a gen. nov.
Derivation of name. From the Kuonamka River. Type and only species. Kuonamkaella oliva sp. nov. Diagnosis. Small, bilaterally symmetrical univalve
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SIBERIAN MIDDLE CAMBRIANMOLLUSCS
Borshaya Kuonamka River section 8 Olet
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Malaya Kuonamka River section 1
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8
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30
2
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