The results of U–Pb isotope dating (LA-ICP-MS) of zircons from metatuffaceous sandstones of the Shidzhatmaz (sample DN223A) and Dolina Narzanov (sample DN224A) Formations within the Bechasyn Zone on the northern slope of the Greater Caucasus are presented. The minimum age estimates for zircons from the studied metatuffaceous sandstones of the Shidzhatmaz and Dolina Narzanov Formations, taking into account the error, are very similar. The weighted mean of the youngest coherent zircon dates from metatuffaceous sandstones of the Dolina Narzanov Formation is 544 ± 5 Ma (based on 5 dates), while that from the Shidzhatmaz Formation metatuffaceous sandstones is 545 ± 5 Ma (based on 6 dates). The weighted mean of the 9 youngest coherent dates of zircons from both samples is 544 ± 4 Ma. The Shidzhatmaz and Dolina Narzanov Formations are assigned to the Upper Riphean on the certified second-generation State Geological Map. Our results reliably constrain the ages of the Shidzhatmaz and Dolina Narzanov Formations not older than the latest Vendian (Ediacaran). The zircons extracted from the metatuffaceous sandstones of both formations are dominated by age groups ranging from ~700 to ~540 Ma, with distinct frequency peaks at ~557 and ~630 Ma, which are nearly identical for samples from both formations. This pattern of zircon age distribution is highly typical of clastic rocks from Upper Precambrian and Lower Paleozoic sequences that form tectonic blocks interpreted as Peri-Gondwanan terranes and widespread in Western and Central Europe, on the Atlantic coast of North America, in North Africa, Anatolia, and Arabia. In this context, it is concluded that the metatuffaceous sandstones of the Dolina Narzanov and Shidzhatmaz Formations were most likely formed in close proximity to a large volcanic edifice that developed on the Northern periphery of Gondwana (in Peri-Gondwana) with enhanced magmatic activity occurring at approximately 630 and 557 Ma. The Dolina Narzanov Formation is composed of the erosion products of the upper part of the volcanic edifice, while the structurally overlying Shidzhatmaz Formation is made of the erosion products of its lower part and the basement.
Кузнецов et al. (Thu,) studied this question.