--> Early and Middle Jurassic basins of Great Caucasus (Northern margin of Tethys)

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Early and Middle Jurassic basins of Great Caucasus (Northern margin of Tethys)


Lower and Middle Jurassic sediments traced a narrow strip between the Black and Caspian seas., in various structural-facies zones have their own characteristics. Lower and Middle Jurassic of Greater Caucasus are presented by sedimentary and volcano-sedimentary rocks. They overlies with unconformity on ancient complexes and deposited in marginal sea. History of sedimentary basin include two main stages: Sinemurian-Aalenian, and Bajocian-Bathonian.

The Sinemurian-Aalenian section is presented by rhythmical alternation of sandstones, aleurolites and mudstones. On a northern margin of the Caucasian basin terrigenous rocks deposited on the shelf with delta and pro-deltic fans. In axial part of the basin are reconstructed facies of a continental slope and deep-water sediments, with turbidites and contourites. On the northern slope of the Greater Caucasus lithic sandstones are presented arenites and greywackes, their mineral composition due to the arrival of the debris mainly of metamorphic rocks from the north, from the Scythian plate.

On the southern margin monotonous terrigenous sediments deposited on the shelf of Transcaucasian continental massif. The Lower and Middle Jurassic sandstones are mainly to the greywacke or arkose. Arkoses traced the south-eastern Caucasus (rivers Alazani and Kurhumchai). Their formation is due to erosion of the Transcaucasian massif (granitoid, granodiorite and granite-gneiss). Sandstones contain plenty of fresh feldspars and with west to east in the composition of sandstones increases the amount of feldspar and quartz content decreases, suggesting some brings erosion products igneous rocks in the east of the study area.

In Bajocian-Bathonian time on the northern margin shelf and more deep-water deposits (greywacke) continued to deposit. For the Southern margin volcanoclastic turbidites are characteristic rocks. Sedimentological data show that at an Aalenian and Bajocian boundary there was a change of the geodynamic settings. The passive continental margin setting transformed into the active margin. Transformation was happened quickly – during 3 million years.