Stratigraphic distribution of stromatoporoids in Silurian Subpolar Urals and their significance for correlation

Category Paleontology and Stratigraphy
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Antropova, Evgeniya
Holding Date 04 October 2008

The established succession of stromatoporoids in the Silurian section of the Subpolar Urals makes it possible to single out stratigraphic intervals, characterized by stable associations, retraced in the investigated sections. These intervals are marked out as local zones, which reflect a certain stage of fauna development in the range of the investigated part of the Ural basin. As a basis for the dissection of Silurian sedimentation there’s been used a stratigraphic scale of the western slope of the Urals, approved by the International Commission on Stratigraphy and supplemented with the additions of T.M. Beznosova (2006).
Ecclimadictyon microvesiculosum (Riab.) - local zone corresponds to the Yarenej and lower part of Lolachor horizons (Llandovery). Besides E. microvesiculosum, there also are widely spread the species of Ecclimadictyon genus.
Clathrodictyon variolare (Rosen) - local zone corresponds to the upper part of Marshrutny horizon (Llandovery). Among the typical species of this interval are Ecclimadictyon cylindricum (Riab.), Symplexodictyon uralicum (Yavorsky).
Araneosustroma astroplexa Antr. - local zone corresponds to the upper part of Padymejtyvis horizon (Ludlow). There are some other species here, e.g. Plexodictyon latilaminatum (Bogoyavl.), Stromatopora uralicum Yavor.
The established local zones are correlated with the zones singled out by T.M. Beznosova (2006) in this region according to brachiopods underlying the dissection of Silur.
Stromatoporoids define the whole silurian section considered in this work. In stratigraphic succession, besides the above-listed local zones, there also exist inter-zones, corresponding to Yunkochor layers and for the most part of Lolachor horizon. Some species have a wide stratigraphical range and are therefore of little stratigraphic value. For example, species Symplexodictyon kyssuniense (Riab.) was known from Fillip’’el’ time to Padymejtyvis time. Local zone species-indexes have well-defined stratigraphic range and narrow stratigraphic spreading interval.
These singled out zones helped to establish likeness of stromatoporoid complexes in even-aged sedimentation of the Subpolar, North and Middle Urals, Baltics, Gottland island, Podolia. In Silurian time fauna development took place under reiterated shift of facies conditions, out of which openshelf facies were the most optimal. Palaeobasin was open to fauna migration, which is proved by the presence of species widespread in even-aged sedimentation of Baltic, Podolia, Arctic islands of Russia and North America.
References: Beznosova T.M. Development of Brachiopods in Late Ordivician-Devonian in North-East part of Baltica palaeocontinent. Syktyvkar, 2006. 48 p.