The upper portion of late Pre-Cambrian (or the Eocambrian in the former, narrower and more definite sense of this term) should become the basement of the Paleozoic, more precisely of the Lower Paleozoic group. The Upper Paleozoic group most probably commenced with the Middle (?) Ordovician and was terminated by the Middle Carboniferous. The boundaries of the Mesozoic must be expanded by the addition of Upper Carboniferous and Permian on the one side and nearly the entire Cenozoic on the other. Finally, the commencement of the Recent or Anthropogenic epoch should be situated in the Upper Pliocene, whose deposits exhibit, for the first time, traces of cooling of the climate — a precursor of the subsequent great continental glaciation, while the general character of its fauna and flora distinctly approach the Recent forms.
In all probability, the above statements do not exhaust the problem. Further investigations will aid in establishing a direct relationship between the geochronological subdivisions of the second and the third orders and the cosmic processes. Relationships of this kind have already been delineated with respect to periods of 38 to 45 million years, approaching the geological periods in their duration. The smaller subdivisions of the geochronological and stratigraphic scale (such as time units, stages, and zones) must also find direct analogues in the stages of cosmic evolution, provided they are correctly differentiated.
10. Geologists and paleogeographers may be considerable interested in the part played by the cosmic winters in the development of the Earth's climates and in the duration of glaciations. Data referring to the oldest (pre-Quaternary) glaciations suggest that the glacial epochs lasted millions of years, 10 million (and possibly even more) in certain cases.
The first, earliest signs of the Gondwanian glaciation were found in the Lower Carboniferous of South America, while the peak of glaciation was reached toward the end of the Upper Carboniferous and even the beginning of the Permian. Ordovician glaciation has been clearly traced, beginning with Tremadocian, and its maximum can probably be dated by the Middle Ordovician epoch. Glacial and conglacial Eocambrian deposits are often kilometers thick, (the Keweenawan period in North America, the Ust-Patom suite or the tillite series in the northern part of the Patom Plateau). Glacial strata proper and accompanying strata sometimes alternate with definitely interglacial lacustrine and shallow-water marine formations, with carbonate remains of algae (Australia; Eocambrian strata in the Polar basin, etc.).
Thus, it may be assumed that the Quaternary glaciation, whose overall duration does not exceed 600,000 to 700,000 years (including the interglacial epochs), marked only the beginning of the great terrestrial glaciations, while the present-day (historical) epoch must be regarded as an inter glacial epoch.
Glaciation traces are known in the deposits of many geological systems. However, it is only occasionally that they can indicate drastic climatic changes involving entire continents and even the entire planet. Local, orographic glaciations whose deposits have been discovered in Devonian, Jurassic, Cretaceous, Paleogene, etc., should probably be excluded. Caution must also be exercised with respect to certain unreliable data which call for most painstaking checks, such as the report on signs of glacial conditions in the Triassic deposits in the northeastern part of the Russian platform.
It was demonstrated earlier by this author (1956, 1957) that in addition to the Quaternary glaciation the great glaciations probably include those of the Upper Paleozoic and Eocambrian, and apparently also the glaciations of Ordovician, Lower Proterozoic, and possibly also Archean. General reviews of ancient glaciations were given by several authors (Coleman, 1926; Schwarzbach, 1950; Lungersgauzen, 1957, and others). Therefore we shall mention below only certain new or little-known facts.
Glaciation of southwestern Africa (Windhoek and Rehoboth) is usually cited as a classic example of the oldest glaciation known on Earth. This opinion is currently acceptable only with reservations. The Archean dating of the Chuos tillite is now open to doubt in connection with the recent revision of the age estimates of the Damara system which includes the tillite strata. There is a possibility that the tillites will prove to be post-Archean, and possibly even Eocambrian (?).
As yet, no authentic traces of Archean glaciation have been found in the USSR. On the other hand, certain recent findings may indicate a significant cooling of climate in the Archean time on the territory of present-day East Siberia. Southeast of the Aldan shield, in the Toko Lake area (eastern terminus of the Stanovoi Range), the geologist Yu. B. Kazmin of the All-Union Aerogeological Trust (VAGT) found rocks of peculiar habit occurring in the so-called "Ivakskaya" suite which forms part of the Dzhelatula series of the Upper Archean (in the new meaning of the scope of this term). Here, stratified marbles containing elastic materials occur amidst dark-gray marbles and calciphyres (Figure 10). The elastic material consists of graphite-pyroxene gneisses, pyroxene schists, granite gneisses, quartzites, and certain other rocks that are completely unknown among Archean deposits of the adjacent regions of the Aldan shield, i. e., they are of exotic nature.