The study of volcanic-sedimentary rocks of the Dzykhra sequence within the Abkhazian zone of the Gagra-Java uplift, Northwestern Caucasus

The authors discuss the results of studying the composition of the volcanogenic-sedimentary rocks of the Dzykhra sequence, which come to the surface in the upper reaches of the river Bolshaya Khosta (Khostinsky district, Krasnodar territory). In the rocks of the Cretaceous age of the Akhun series, composed of limestones of the Dzykhra sequence and the Kazachy Brod suite, an outcrop of clastic rocks was found. The structure and mineral composition of the rock sample, as well as its chemical composition according to X-ray fluorescence analysis, were studied in detail. In the sequence, two layers are distinguished: the lower (3 m) cream-brown and the upper (0.05 m) green. Macroscopically, it is a lenticular-layered, fine-grained, lithocrystal-clastic, polymictic sandstone with carbonate cement. The sequence is underlain by interbedded dark gray limestones and black siltstones of the Lower Cretaceous Agur Formation, and overlain by cream limestones with interlayers of brown cherts of the Upper Cretaceous Kazachy Brod Formation. The data of microscopic studies, as well as X-ray fluorescence analysis, made it possible to establish the following minerals in the composition of sandstones: quartz, potassium-feldspar and plagioclase, less often amphibole, as well as a large amount of carbonate matter, and to conclude that in composition they correspond to tuffs of medium composition (andesite-dacite).