Abstract

Devonian deposits are found to be widespread within the Greater Caucasus and the adjoining part of the Scythian platform.

In Devonian time, the Caucasus was part of the geosynclinal area of the Tethys sea. Eight geosynclinal and geanticlinal belts can be discriminated. No Devonian deposits are known on the geanticlines (except in the case of the Glavnokavkazskaya) and the Upper Palaeozoic or Mesozoic strata lie directly on pre-Silurian beds. There are signs of intensive development of Middle Palaeozoic gabbro-plagiogranite magmatism, with an absolute age of up to 360–365 million years. A shortened sequence with lavas and limestones (thickness — up to 1 km) is known to be present in the northwestern subsidence of the Glavnokavkazskaya GA belt.

The Predkavkazskiy depression (as shown by borings) is probably of miogeosynclinal character. The geosyncline of the Peredovoy Range includes deposits of slate (D₁-2), diabaseplagioliparite D₂), clastic tuffs (D₂-3), and terrigenous and carbonate sediments (D₃fm) (thickness 5.7 km). This is an eugeosynclinal depression, the development of which began in the Silurian and continued through the Early Carboniferous. The formation of the chalcopyrite ores of exhalation-sedimentary genesis was an important feature of the Middle Devonian volcanism.

The Yuzhnokavkazskaja geosyncline was a sub-rhiogeosynclinal depression of moderate depth (the thickness is more than 1-1.5 km) with an insignificant development of basic volcanic activity.

The tectonic disturbance in the form of vertical movements of large longitudinal blocks, partially delimited by suture zones, is expressed in the formation of extensive consedimentation anticlinal and synclinal belts.

Palaeogeographically, the Caucasus during the Devonian was a marine basin, deep-water at times, manifesting a connection with the basin of the south Urals, Russian platform and western Europe, with their intensive Middle Devonian volcanism. Mountainous island elevations appeared in Frasnian time and disappeared by the beginning of the Famennian.

The initial and middle phases of the main stage of the geosynclinal development of the Hercynian orogeny in the Caucasus took place in Devonian time.