The Geological Evolution of West Georgia and the Petroleum Potential of the easternmost Black Sea

CASP has undertaken extensive fieldwork in West and Central Georgia. Two hundred outcrop localities were visited and over 400 outcrop and subsurface samples collected. The resultant outcrop observations and analytical results, when combined with published data, have enabled us to re-construct the tectonostratigraphic evolution of the region and delineate and characterise sediment pathways and source rock intervals. These provide insights into the likely hydrocarbon potential of the adjacent easternmost Black Sea.

Westernmost Georgia comprises three tectono-stratigraphic elements. From north to south these are: (1) The southern slope of the Greater Caucasus that comprises the Jurassic and Cretaceous relatively deep-water fill of the inverted Greater Caucasus Basin; (2) the Transcaucasus, a continental fragment that continues offshore as the Shatskiy Rise and whose basement is represented by the Dziruli Massif. This is overlain by (a) a syn-Greater Caucasus Basin carbonate-dominated succession isolated from siliciclastic input from the East European Craton because of the rift basin to its north and (b) a syn-compressional siliciclastic-dominated succession, largely derived from the inverting Greater Caucasus Basin / uplifting Greater Caucasus. The Transcaucasus cover sequence includes the Kuma Formation and Maykop Series source rock intervals. (3) The Adjara-Trialet Belt, a transtensional basin largely filled by Eocene volcanic rocks and volcaniclastic sediments, which, like the Greater Caucasus Basin, probably began to invert in the Late Eocene.

A source prone mudstone interval in the lower part of the Maykop Series has good to very good source potential, a Type II source quality and is at least 60 m thick. The Kuma Formation may form an important secondary source of hydrocarbons. Sands derived from the western Greater Caucasus and routed either through the Rioni Basin or directly offshore are typically lithic rich and contain abundant mudstone and volcanic rock fragments. Those derived from the Adjara-Trialet Belt almost wholly comprise volcanic rock fragments. Relatively quartz-rich sands derived from the Dziruli Massif are largely shed eastwards, away from the eastern Black Sea. As a consequence, reservoir quality is the critical risk in the Eastern Black Sea. Thermochronometric studies indicate low to moderate punctuated exhumation of the western Greater Caucasus during the Oligo-Miocene. Exhumation rates increased in the West Georgian sector of the range during the Plio-Pleistocene.