Progress in the study of the Devonian–Carboniferous boundary sections in the Berchogur Depression (Mugodzhary Mountains, western Kazakhstan)

The Devonian–Carboniferous boundary beds in the Berchogur (Birshogyr) sections in the Mugodzhary (Mugalzhary) Mountains in western Kazakhstan, known to contain various fossil groups, including ammonoids, conodonts, foraminifers, corals, crinoids, and trilobites, are re-examined. The siliciclastic-carbonate succession of the Zhangana Formation reveals the presence of several ammonoid, conodont, and foraminiferal zones. The succession contains the Acutimitoceras ammonoid Genozone, equivalent to the level of the Stockum ammonoid fauna of Germany, with the conodont Siphonodella sulcata appearing within the Genozone. The same beds show mass occurrences of the foraminifer Tournayellina pseudobeata. The study of the Berchogur sections began in the 1980s; these sections are among very few successions globally with ammonoids of the Acutimitoceras Genozone in association with conodonts and foraminifers. At that time, several outcrops in a small area in the upper reaches of Burtybai (Zhangansai) Creek and two boreholes drilled near the sections were studied, and new taxa of ammonoids, foraminifers, ostracods, conodonts, algae, and spores were described. New excavations in 2018–2020, in conjunction with a search for a new definition of the Devonian–Carboniferous boundary, provided abundant new information on these taxa, on the lithology, and on crinoids, trilobites, and corals. The exact position of marker fossils and lithological changes are documented in several sections along Burtybai Creek allowing an amended correlation with sections of the D–C boundary beds in Western Europe.