Recycling of clastics and detrital zircon during the formation of the riphean stratotype’s sedimentary sequences

The lithochemical features of clastic rocks of a number of stratigraphic levels of the Riphean stratotype (Ai, Bakal, Zigalga, Zilmerdak and Uk formations), as well as the distribution of detrital zircon populations in the sandstones composing them, are analyzed. Two main trends have been outlined in the formation of clastics that make up the stratotype section of the Riphean – the entry into the sedimentation area of material of the first cycle (petrogenic) and recycled (redeposited, lithogenic) material. It has been suggested that detrital zircon, which came from protosources into the sandstones of the Ai stratigraphic level, was then, apparently, repeatedly subjected to redeposition: crystals with close maxima on the probability density curve are present in sandstones of younger stratons of the Riphean type section, up to the Uk Formation. The most striking renewal of detrital zircon protosources occurs at the beginning of the Late Riphean. The arkosic and subarkosic sandstones of the Biryan Subformation of the Zilmerdak Formation contain both detrital zircon with ages similar to those we see in the sandstones of the Lower and Middle Riphean, and new zircon, characterized by Paleo- and Mesoproterozoic maxima on the probability density curve. A small part of them is repeated in the oolitic limestones of the Uk Formation, but some renewal of the proto-sources is also recorded here. Thus, the boundary of the Middle and Late Riphean was marked probably by a radical change in the age populations of detrital zircon, which can be associated with the formation of a fundamentally new system for transporting clastics from sources to sink.