Abstract:

Arabika is an outstanding high-mountain karst massif in the Western Caucasus composed of Lower Cretaceous and Upper Jurassic limestones continuously dipping southwest to the Black Sea shore and plunging below the sea level. The central sector (elevations within 2000-2700 m) is characterized by pronounced glacio-karstic landscape and hosts several deep caves including the deepest cave in the world (Krubera-Voronja Cave) recently explored to the depth of -2191 m.  Dye tracing experiments conducted in 1984-1985 revealed that the Krubera Cave area is hydraulically connected with major springs at the Black Sea shore and the submarine discharge, with the flow directed across major fold structures. Krubera Cave has an extremely steep profile and reveals a huge thickness of the vadose zone. Its lower boundary is at elevation of about 110 m, which suggests a very low overall hydraulic gradient of 0.007-0.008. Reported low salinity groundwater tapped by boreholes in the shore area at depths 40-280, 500, 1750 and 2250 m, which suggests the existence of deep flow system with vigorous flow. Submarine discharge in the Arabika coast is reported at depths up to ca. 400 m bsl. Huge closed submarine depression is revealed at the sea-floor in front of Arabika with the deepest point of ca. 400 m bsl. These facts point to a possibility that the main karst system in Arabika could have originated in response to the Messinian salinity crisis (5.96 – 5.33 Myr) when the Black Sea could have almost dried up, similarly to the adjacent Mediterranean where the sea level drop up to 1600 m is well established. Further development of the huge vadose zone and a super-deep cave have been caused by subsequent uplifts during Pliocene-Pleistocene, highly differential between the shore sector (0.1-0.2 km of total uplift) and the central sector (2-2.5 km) of Arabika.