The Silurian of the northern Caucasus, Russia

Northern Caucasus is one of the regions within the Greater Caucasus where the Silurian strata have been recorded. Rocks of this age are not particularly widespread, and are usually metamorphosed.

Silurian strata in the northern Caucasus were examined during CASP fieldwork in July 2013. The main objective of fieldwork was to characterise the Silurian stratigraphy, to restudy sections described earlier by Chegodaev in 1977 and Obut et al. in 1988, and to collect samples for follow-up analyses including biostratigraphy, organic geochemistry, whole rock geochemistry, petrography and provenance. Areas visited include Bichesyn (i.e. Malka River) and Fore Range (i.e. Teberda River, Kyaphar River) tectonic zones.

In the Malka sections, the Silurian comprises the Ullu-Lakhran and Manglai formations. The Ullu-Lakhran Formation, which is 300 m thick, consists mostly of grey to black clayey and siliceous shales. The shales include sandstone intercalations, as well as sandy limestone, which are more developed near the top of the formation. Shales, at some levels, are rich in graptolites (Obut et al. 1988). Biostratigraphically, they range from Llandovery to mid Ludlow in age. The overlying Manglai Formation is up to 22 m thick. It is a carbonate unit with several intercalations of black siliceous shales. Limestones yield conodonts (Obut et al. 1988), cephalopods, bivalves, trilobites and gastropods. Their occurrence established the late Ludlow to Pridoli age of the formation.

In the Teberda sections, the Silurian comprises the Achkhiminar Formation. It is a 420 m thick clayey unit with several sandy beds and siliceous shales yielding cherts. In the Kyaphar sections west of the Teberda sections, the 900 m thick Silurian succession is more metamorphosed and is represented by quartz-chlorite-sericite schist with interbeds of fine-grained metasandstone and graphite-bearing chert. Limestones are found in some sections. Silurian graptolites and radiolarians were found in the chert (Somin 2011).