The Zaza Formation is a geological formation located in

Buryatia Buryatia, officially the Republic of Buryatia (russian: Республика Бурятия, r=Respublika Buryatiya, p=rʲɪsˈpublʲɪkə bʊˈrʲætʲɪjə; bua, Буряад Улас, Buryaad Ulas, , mn, Буриад Улс, Buriad Uls), is ...

( Russia). It dates to the Lower Cretaceous period. It is

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

in age and consists of sandstones, siltstones, marls and bituminous shales, deposited in a stratified lake. It is situated on a large granite plateau in the NE of Buryatia.Zherikhin, V.V., Mostovski, M.B., Vrsansky, P., Blagoderov, V.A. and Lukashevich, E.D. 1999
The unique Lower Cretaceous locality of Baissa and other contemporaneous insect-bearing sites in North and West Transbaikalia
''Proceedings of the First Palaeoentomological Conference, Moscow, 1998''. Bratislava: Amba Projects, pp. 185-192. The formation is known for its numerous compression fossils of many varieties of insect found predominantly at the Baissa locality, located on the banks of the Vitim River. Insects are found in multiple beds throughout the succession, predominantly in the finer grained facies, the preservation of insect fossils is variable between beds, with good preservation in marl and poor preservation in shale beds.

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