Nummulitic facies of the Crimean-Caucasian Region

Abstract

The nummulitic limestones of Crimea and the southwestern Caucasus, often interpreted as "nummulite banks", formed carbonate platforms throughout most of the Ypresian-Lutetian. Such deposits were accumulated in shallow warm-water basins of Crimea and the Caucasus, which differed from each other by the structure of the basement and the hydrodynamic regime. The Crimean carbonate platform was relatively flat and was formed mainly within quiet hydrodynamic conditions below the fair-weather wave base (less than 50 m). The facies changes within it reflect variations in water depth. Facies distinguished there form the nummulite bank, its lee-side slope, the shelf plain in the rear of the bank (back-bank), and the relatively deep basin-ward slope with predominantly terrigenous sedimentation (fore-bank). Among larger benthic foraminifera (LBF), Nummulites, Operculina, and Assilina are the most typical. Discocyclina is less common; its increase in abundance is interpreted as deepening of the basin. Nummulitic limestones and marls reappear in the southwestern Caucasus within the shallow-marine deposits of the Georgian massif shelf basin. It was bordered with the Great Caucasus deep-water flysch basin in the north and the rift-related volcanic area of the Achara-Trialeti in the south. Nummulitic limestones of the Bzyp and Kodori river valleys and the Novy Afon district formed the "nummulite banks" upon the local basement uplifts within the Georgian massif shelf basin. The main components among the LBF are Discocyclina, Nummulites, and Operculina; Assilina is absent.