The role of conodonts in the global stratigraphic correlation on example of southern Siberia (Russia) and eastern Serbia

Conodonts are very precise tools for global stratigraphic correlation of Devonian deposits. They can be correlated at the level of standard conodont zones even for basins having very different geological structure. In this paper Devonian conodont correlations between north-western margin of the Kuznetsk Basin (Siberia) and eastern Serbia are demonstrated. The geology of both regions is quite different. East Serbian zone is the southern tip of the Carpathian folded area (Carpatho-Balkanides). Middle Paleozoic carbonate and terrigenous deposits (Silurian, Devonian and Lower Carboniferous) are replaced by Hercynian molasse, and sedimentation continued throughout the Mesozoic and Cenozoic Eras. Rocks were exposed to repeatedly tectonic effects, olistoliths, olistostromes are widespread. Middle Paleozoic sediments, including Devonian, are localized within separate small tectonic blocks, often shifted from its place and form allochthons. In the western part of the Altai-Sayan folded area the Middle Paleozoic sediments have undergone folding and orogeny during the Hercynian phase of tectonic and magmatic activity, but since that time the continental conditions have been dominant in this region. The Devonian deposits are well represented in the marginal parts of the Kuznetsk Basin. In both regions the Devonian rocks have been well studied and the standard conodont zones varcus, gigas (rhenana) – linguiformis, crepida, expansa and praesulcata were established.

remain the major biostratigraphical correlation tools. By studying the distribution of conodonts in certain sections, every specialist tries always to tie their subdivisions to zones of the standard conodont scale and to implement the inter-regional and global correlation of strata. The Devonian subdivisions of southern Siberia and eastern Serbia can serve as an example of such correlation (RODYGIN 2014).

Methods
Ten years ago during geological excursions in eastern Serbia the author could see that the geology of this area is very differing from the geology of southern Siberia. East Serbian zone is the southern tip of the Carpathian folded area (Carpatho-Balkanides). Middle Paleozoic carbonate and terrigenous deposits (Silurian, Devonian and Lower Carboniferous) are replaced here by Hercynian molasse, and sedimentation continued throughout the Mesozoic and Cenozoic Eras (ĆIRIĆ 1996). Rocks were exposed to repeatedly tectonic effects, particularly strong in Alpine phase of tectonic and magmatic reactivation. Overthrusts, olistoliths, olistostromes are widespread there; Middle Paleozoic sediments, including Devonian are localized within separate small tectonic blocks, often shifted from its place and formed allochthons. Tectonic blocks are interpreted as terranes, significantly changed its initial spatial position (KRSTIĆ et al. 2004).
In the western part of the Altai-Sayan folded area the Middle Paleozoic sediments have undergone folding and orogeny during the Hercynian phase of tectonic and magmatic activity, but since that time the continental conditions have been dominant in this region. The Kuznetsk coal basin (Kuzbass) began to form. The Kuznetsk Basin is an intermountain depression filled in its middle part by coal-bearing Carboniferous and Permian sediments. The Devonian deposits are well represented in the marginal parts of the Kuzbass. They are confined to the Givetian Stage of the Middle Devonian, to Frasnian and Famennian of the Upper Devonian. The studied sections are located in the vicinity of the town of Anzhero-Sudzhensk, in the Yaya, Barzas rivers basins, in the Tom' basin downstream of the city of Kemerovo (the northern district of the Kemerovo Region) and in the vicinity of village Vassino of the Novosibirsk Region (Type sections, 1992;RODYGIN 2011RODYGIN , 2014. The sections are composed of terrigenous and carbonaceous, mainly shallow deposits bearing rich associations of benthic fauna with brachiopods, rugoses, tabulates and stromatoporoids predominantly. Crinoids, ostracodes, tentaculites, bivalves are encountered; less common are gastropods, cephalopods, trilobites and fish integument fragments. Along with the fauna, stromatolites, algae, vegetable debris and spores were found from certain of the sections.
For many years these sections were tested for conodonts being of great stratigraphic importance. Representative conodont assemblages were established, which enabled the stratigraphical position of horizons to be defined more precisely and the correlation between the sections and the Standard Conodont Scale to be made. L.M. Aksenova and V.G. Halymbadzha took part in studying conodonts jointly with the present author (AKSENOVA et al. 1994;Type sections.., 1992;RODYGIN 2011RODYGIN , 2014.   (GUTAK et al. 2004;2007;GUTAK & RODYGIN 2011;RODYGIN 2011RODYGIN , 2014.

Lower Devonian and
Consequently, the deposits of the northern margin of the Kuznetsk Basin represent the section that is almost continuously characterized by conodonts and confidently comparable with the Standard Conodont Zones Scale. M. SUDAR during 1989-1994 made efforts on the conodonts study of the Devonian in Eastern Serbia. These researchers had complexes similar to those that we have been identified in Kuzbass. This is particularly important, given that both regions have quite different geological history (KRSTIĆ & SUDAR 1989, 1990a, b, 1991, 1992, 1993, 1994.
In the south-eastern Serbia, near the spa Zvonačka Banja in a small interlayer of dolomitic limestone among clastic rocks, quite a rich conodont complex was found: Palmatolepis gigas MILLER et YOUNG-

Conclusions
Eastern Serbia and Kuznetsk Basin with their margins both have different geological structure and history. Devonian terrigenous-carbonate deposits on Kuzbass margins were mainly deposited in shallow marine conditions, with often reef constructions, brachiopod banks and rich benthic fauna. Along Devonian sections near the town of Anzhero-Sudzhensk, rivers Yaya and Tom, representative conodont complexes were collected and standard conodont zones of Middle and Upper Devonian and regional stratigraphic horizons were established. But in the north-western margins of Kuzbass a complete stratigraphic Devonian succession was not preserved. In the absence of zonal conodont species, the age was sometimes determined on benthic fauna (RODYGIN 2011(RODYGIN , 2014. In the Eastern Serbia the Devonian sediments are preserved in separate tectonic blocks. There are both autochthonous and allochthonous blocks. From rare limestone beds the representative collection of conodonts con-taining many zonal species was obtained (KRSTIĆ & SUDAR, 1995;RODYGIN, 2014). Standard conodont zones were established for the Devonian beds of Eastern Serbia. Conodonts have high correlation potential, whereby the opportunity to compare the Devonian of Eastern Serbia with many regions around the world, in particular, with the margins of the Kuznetsk Basin in southern Siberia, where similar conodont complexes were also found and the standard conodont zones were established. KRSTIĆ, B. & SUDAR, M. 1990b