Geological Setting

The collection comes from a large territory of over 500,000 square miles in the Urals and Kazakhstan (Fig. 15.1) and covers the three Famennian ammonoid genozones: Prolobites-Platyclymenia, Clymenia-Gonioclymenia, and Kalloclymenia-Wocklumeria as defined by Bogoslovsky (1969, 1971) (Fig. 15.2). The genozone concept, definition, correlation, and distribution of Devonian genozones in the world are discussed in detail by Bogoslovsky (1969) and Becker and House (2000). For the purpose of this study, the subdivision of the Famennian into three stages is adopted in the sense of Sandberg et al. (2002) rather than into four substages, as ruled by the International Commission on Stratigraphy (2004).

The area studied includes several large regions each containing ammonoid assemblages of differing abundance [west to east direction - Bashkortostan, western Kazakhstan, Chelyabinsk Region (these three within the South Urals), and two regions in central Kazakhstan] (Fig. 15.3). The borders of these regions do not conform to political boundaries (e.g., the western Kazakhstan Region, as defined here, includes some localities that are politically in the Orenburg Region, Russia). The central Kazakhstan Region, as defined here, includes the southwestern margin of the Chingiz Mountain Range, which is politically in the former Semipalatinsk Region. The Uralian-Kazakhstanian Region includes several tectonic zones existing in the Famennian, i.e., the eastern slope of the Baltica Craton [the Volga-Ural Carbonate Platform on the eastern margin of the Euramerica (Laurussia) Continent], remains of the Magnitogorsk Island Arc, the slope of the Kazakhstania Continent, and that of the submarine Mugodzhar Microcontinent (Puchkov, 2000; Mizens, 2004; Veimarn et al., 2004). The complex tectonics of this region, with highly variable depths, facies, and currents are reflected in the variety of ammonoid communities, which included clyme-niids and goniatitids. The differences in the abundances of specimens and in

Fig. 15.1 Map showing ammonoid localities in the Uralian-Kazakhstanian Region. Major localities are at the southern termination of the Urals and Kazakhstan.

the taxonomic structure of the assemblages are believed to reflect different habitats within the basin of the Uralian Ocean.

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