Along-strike variations in the composition of sandstones derived from the uplifting western Greater Caucasus: causes and implications for reservoir quality prediction in the Eastern Black Sea

Abstract

Abstract Oligo-Miocene outcrops along the southern margin of the western Greater Caucasus preserve a record of sediments shed from the range into the northern and central parts of the Eastern Black Sea. Sandstones in the Russian western Caucasus are significantly more quartz-rich than those located farther SE in western Georgia. The latter contain appreciably more mudstone and volcanic rock fragments. Oligo-Miocene turbidite systems derived from the Russian western Caucasus in the Tuapse Trough and central Eastern Black Sea may therefore form better-quality reservoirs at shallow to moderate depths than sediments derived from west Georgian volcaniclastic sources in the easternmost part of the basin. Palynomorph analysis indicates sediment derivation predominantly from Jurassic and Cretaceous strata in the Russian western Caucasus and from Eocene strata, and an increasing proportion of Cretaceous strata upsection, in western Georgia. An Eocene volcaniclastic source is proposed for the increased rock fragment component in west Georgian sandstones. Eocene volcaniclastic rocks are no longer exposed in the Greater Caucasus, but similar rocks form the inverted fill of the Adjara–Trialet Basin farther south in the Lesser Caucasus. The former presence of a northern strand of this basin in the west Georgian Caucasus is supported by earlier thermochronological work. Supplementary material: A sample data table, petrographic data table, petrographic key, QFL sandstone compositional plot and palynomorph reworking Stratabugs™ charts are available at www.geolsoc.org.uk/SUP18662 .