Aretz et al_2011.pdf - ORBi - Université de Liège

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Kölner Forum Geol. Paläont., 19 (2011)
M. ARETZ, S. DELCULÉE, J. DENAYER & E. POTY (Eds.)
Abstracts, 11th Symposium on Fossil Cnidaria and Sponges, Liège, August 19-29, 2011
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Middle Devonian reef facies in the Pistalitau and Khanbandy mountains,
Middle Tien Shan
Firdaus S. KARIMOVA & Firuza A. SALIMOVA
ОАО ‘Regional Geology’, State Committee of Geology and Mineral Resources, Akhunbabaev, 21, 111800,
Tashkent, Uzbekistan; Firdaus52@mail.ru; firuza_salimova@yahoo.com
The different types of biogenic carbonate build-ups and morphologically similar bodies are spread
widely in the Uzbek part of Middle Tien Shan, including Khanbandytau and Pistalitau mountains, which
probably reflect a former existence of a warm climate, small depth and normal salinity of the Devonian sea
in the region. The carbonate units range from a few tens to one thousand five hundred metres in thickness.
They are formed of interbedded siltstones with dolomites and clay limestones of the Lower Uchkulach
Formation (Eifelian-Lower Givetian), dolomite and dolomitic limestone of the Upper Uchkulach
Formation, organogenic limestone of the Khanbandytau Formation and limestone-dolomitic deposits of the
Pistalitau Formation (Givetian), organogenic limestone of the Ment, Ustkuruksay and Kolsuyuk formations
(Frasnian), and also bedded micritic limestones of the Semizsalpa Formation (Famennian). Among these
formations the Pistalitau and Khanbandytau formations are relatively rich in reefal faunas.
The Pistalitau Formation comprises from thin to thick-bedded dark-grey biomicritic and sparitic
limestone with singular thin beds of mudstones and lenses of cherts. The Pistalitau reef episode consists of
coral and stromatoporoid bioherms and biostromes with a local appearance of mud mounds. This
succession is a well exposed, continuous and fossiliferous limestone sequence is located on the southern
slopes of the Pistalitau Mountain. The thickness of the Formation is about 150-300 m. The carbonate buildups
are situated at some levels. In most cases there are monotaxonic bioherms and biostromes, combined
exclusively by numerous representatives of stromatoporoid genera such as Actinostroma, Idiostroma,
Syringostroma, Hermatostroma, Clathrocoilona, Anostylostroma, Simplexodictyon, Stromatopora, Trupetostroma,
Stachyodes, and Amphipora. Stromatoporoids are quite large, have dome-like skeletons and grow on each
other. Lagoonal facies are represented by biomicritic limestones and include layers with Amphypora,
colonies of tabulate and rugose corals and brachiopods. The amphyporal layers are stretched up to a few
tens kilometers. (KIM at al. 2007; SALIMOVA & KARIMOVA 2006).
The Khanbandytau Formation is formed of massive light-gray micritic and crinoid limestone with banks
of stryngocephalids and amphiporal interbeddings and also massive dolomites with rare stromatoporoid
and coral faunas. The deposits compose a watershed part of the Khanbandy Mountain. The thickness of the
Formation is about 500 m. Preliminary analysis of existing sedimentological data suggests that the
Khanbandytau-Pastalitau reef deposits represent a lateral row of reefogenic facies. The Khanbandytau
Formation may represent reef platform and the Pistalitau Formation probably belongs to a back-reef
lithofacies. Existing data require further confirmation and research.
The stratigraphic location of these deposits and also their relationships to the surrounding facies suggest
that the appearance, distribution and the architecture of carbonate build-ups were governed by eustatic
cyclicity with local tectonic movements (BURTMAN 2006). There are grounds to assume that the Khanbandy-
Pistalitau reef deposits were formed in conditions of an island-arc basin (TROITSKY 2005).
The research is supported by the Paleontological Society International Research Program - Sepkoski
Grants (RUG1-1648-XX-06).
BURTMAN, V. S. (2006): Tien Shan and High Asia. Tectonics and geodynamics in the Palaeozoic. - Trudy
Geologicheskogo Instituta, 570: 1-214. [In Russian].
KIM, A.I., SALIMOVA F.A., KIM I.A. & MESCHANKINA N.A. (2007): Palaeontological Atlas of Phanerozoic faunas and floras
of Uzbekistan. - Tashkent. IMR. 707 pp.
SALIMOVA F.A. & KARIMOVA F.S. (2006): Karbonatnye postroyki Uchkulachskogo rudnogo polja [Carbonate frameworks of
the Uchkulach Ore Field]. – In: Problemy stratigrafii fanerozoya Uzbekistana i sopredel’nykh territorii. Tashkent: 16.
TROITSKY, V.I. (2005): Geodynamic zonation of Palaeozoic structures of Tien Shan and Pamir. - Vestnik NUUZ.
‘Universitet’, Tashkent: 5-13. [In Russian].
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