Moskvitin (1966) was the first to suggest an Akchagyl glaciation, but he miscorrelated it with the Oka glaciation (MIS 12). This author based on continuous PM, track and TL dated sequences of the Pont-Caspian region embracing 8 myr (Zubakov, Borzenkova, 1990) infers a hyperglaciation in the time span 3.6 to 2.044 myr.

Facts. Kochegura and I found that tills of the maximum Caucasian glaciation belong to the lower Matuyama zone. On the Taman Peninsula we found that Akchagyl water influx from the Caspian to the Black Sea, again in the lower Matuyama, was terminated during a double n-excursion unknown in those times. This excursion called the Kiziltash is now dated to 2.44 and 2.39 myr. Oskolkov (1992), described three cored sequences with 8 m thick till sandwiched between two red, obviously Neogene soils, in Vasilievka, the Lipetsk Region.

Regional background. The early Akchagyl-Zanclean ingression into the Caspian started in the lower Gilbert. The 'Break Formation" at its base is sandwiched between the track dates 5.19±0.89 and 5.4±0.6 myr. The sea incursion used the Sablya Strait along the Caucasus (Fig. 1) which is synchronous to the Gibraltar (5.33 myr). Thus, the Akchagyl ingression has nothing to do with the Kolva formation of the Pechora, even dated to Gauss as Yakhimovich suggested. During the Gauss chron the Barents and Kara seas were dry. During 1.7 myr the Caspian Sea was a bay of the Zanclean sea. It was isolated only 3.6 K/Ar myr ago as a result of the Chegem diastrophism when the Sablya Strait was closed (Fig. 1). Since that moment the Caspian level oscillations became an important palaeoclimatic archive.

Geographical prerequisites. Firstly, it was the isolation of the Arctic Ocean at 4.0-3.9 myr during the global diastrophism Skeifa-Baraolt-kepen and emergence of the bridge Faroes-Thule. The isolation is evidenced by: i) invasion of Equus stenonis from America into Eurasia. Its bones in Romania are synchronous to tufa dated by K/Ar to 3.92 myr; ii) invasion of Thuja from Labrador to northern Greenland, which could happen с 3.8 myr, prior to the Greenland glaciation; iii) dispersal of Pacific mollusks with Serripes groenlandicus who during the Beringian transgression crossed the iceless Arctic Ocean. These mollusks settled along the northern shores of Iceland but did not reach its southern shores. Secondly, it was the sudden uplift of mountains at 3.8 to 3 myr when their elevations grew up by twice initiating the monsoon circulation. Thirdly, the Panama closure at 3.1 to 2.9 myr activated the Gulfstream and cyclonic circulation.

History of the Barents Sea hyperglaciation embraces four 400 kyr cycles, i.e. four superglacials and eight orthoglacials. The beginning of the 1st superglacial is synchronous with the GSSP of the Piacenza-Pantikapei stage and was marked by the tundra appearance in the Urals. The 2nd Simbugino superglacial, 3.18-2.84 myr, coincides with the Panama closure at 2.9 myr and sharp increase of cyclones in the Atlantic. The 3d double superglaciation, called Elk Creek in America and Praetiglian in western Europe, became the culmination of the Barents Sea hyperglaciation when ice appeared in the Don valley 52°N (Fig. 1). The level of the Chistopol proglacial lake rose from 60 to 125 m, and с 2.54 myr its water found an outlet via the Manych Pass (Fig. 2). This event almost coincides with GSSP of the Gelasian and biozone Montopoli (2.6-2.58 myr). The 4th Domashka-Biklyan superglaciation was smaller, but at 2.13-2.044 myr meltwater again drained into the Black Sea which is evidenced by varves and fossils of the Meria formation in western Georgia.

The end of the Hyperglacial was predetermined by the Baksan diastrophism at 2.2 myr which is marked by ignimbrite volcanism in the Caucasus and ash in Iowa. It led to the collapse of the Faroe Bridge and the Gulfstream invasion into the Arctic Ocean. This is recorded by the Omar-Nogaret-Tiglian C5 interglacial.

Reference:

Zubakov V.A. Barents Sea Hyperglacial in the Akchagyl 3.6-2.05 myr ago. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 110.