Baykonur Formation

The Baykonur Formation is an upper unit of the Ulutau Group and it outcrops in the mountains of Kazakhstan and Kyrgyzstan towards the border with China.^[1][4] It was formed during a period of heavy glaciation known as the Baykonurian glaciation which spread for at least 1,600 kilometres (990 mi),^[1] and it has been posited as a contributor to the Cambrian explosion.^[6] During the Ordovician and Devonian, the Baykonur Formation experienced faulting and folding during the Caledonian orogeny.^[4]

The Baykonur Formation is formed of diamictite and phyllite with dropstones,^[7] a shale layer and in some sections a feldspar layer and conglomerate layers increasing in abundance towards the western sections;^[8] it has unconformities between its upper and lower boundaries with Terreneuvian shale and granosyenite of Tonian-Cryogenian boundary age respectively, although in places it does comfortably underlie the Koktal, Kurumsak, and Kurmenty Formation and comfortably overlies the Kurayly, Aksumbe, and Dzakhbolot Formation.^[4] It is up to 600 metres (2,000 ft) in places with localised diamictite outcrops reaching 30 metres (98 ft) in thickness.^[2][9]

The age of the Baykonur Formation was initially suggested to be Late Paleozoic age in 1924 before the date was suggested to be Cambrian age by Borovikov (1953)^[10] and then Precambrian age by Korolev (1963).^[11] This was then changed to ?Ediacaran to Early Cambrian age by Chumakov (2011).^[4] Alexeiv (2025) refined the age to 556–540 Ma.^[1]

The Baykonur Formation constitutes margins believed to be related to the northern and eastern edges of the Syrdarya and Tarim microcontinents.^[12]