Conodont characteristic of the Lochkovian-Pragian boundary interval in the Mindigulovo section (western slope of the Southern Urals)
Tóm tắt
Conodonts from the Sherlubay (upper Lochkovian) and Kulamat (lower Pragian) Horizons of the Mindigulovo section (western slope of the Southern Urals) were studied in detail. The conodont sequence can be globally correlated. The sequence contains important cosmopolitan taxa. The taxon index of the global zone gilberti was discovered at the top of the Sherlubay Horizon. Overlying Kulamat Horizon in the lower Pragian is characterised by the proliferation of typical species of the irregularis Zone in addition to the taxon index. Almost all characteristic Lochkovian species completely disappear. The observed successive morphological changes in Masaraella pandora: Mas. pandora morphotype alpha → Mas. pandora morphotype beta → Mas. pandora cf. morphotype zeta and Eognathodus: Eognathodus cf. irregularis → Gondwania cf. profunda are close to the development of Masaraella pandora → Eognathodus phyletic lineage, proposed by Murphy (2005). In the revealed evolutionary lineage of Mas. pandora–Eognathodus, the starting of eognathodontid from Mas. pandora is a biostratigraphical criterion for the establishment of the Lohkovian/Pragian boundary, along with lithological and macrofaunal control. Together with the deep-sea eognatodontid fauna, another index taxa as Caudicriodus steinachensis morphotype eta and Pelekysgnathus cf. serratus brunsvicensis of the alternative scale (Slavik 2004; Slavík et al. 2007) were recorded. The parallel presence of shallow-water icriodontid and deep-water eognathodontid biofacies at the lower part of Kulamat Horizon of the Pragian sediments in the Southern Urals is relevant for interregional correlations.
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