Nummulitic Banks of the Crimean-Caucasian Regionтезисы доклада

Дата последнего поиска статьи во внешних источниках: 28 мая 2015 г.

Работа с тезисами доклада


[1] Nummulitic banks of the crimean-caucasian region / L. F. KOPAEVICH, P. A. FOKIN, E. A. LYGINA et al. // 19 ISC 2014 Abstract book. — Universite de Geneva, 2014. — P. 354–355. Introduction. Nummulitic facies are widely distributed from Pyrenees to Caspian region. Within the Eastern Black Sea area they are dated as Late Ypresian-Early Lutetian. Nummulitic limestones could be good collectors in certain geological situations having high porosity and permeability. Therefore they acquire a great interest in the region. Material and Methods. Detailed lithologic and sedimentological description of 10 sections of Crimea and 4 outcrops of South-Western Caucasus (North-Western part of Georgian massif) was done. More than 100 thin sections of Crimean samples and 15 thin sections of Caucasian rocks were described. At that the classification of R.J. Dunham supplemented by A.P. Embry and J.E. Klovan was used. Data of porosity and permeability of rocks of 6 Crimean sections and Caucasian outcrops were defined instrumentally with kerosene impregnation technique. Sampling was carried out by drilling in the outcrops oriented cylinders of 4 sm diameter with different lengths. Also porosity percentage was determined visually in thin sections. 17 thin sections of Crimean limestones were made with epoxy impregnation. Ratio of various genera of Larger Benthic Foraminifera (LBF) and an analysis of distribution of their micro- and macrospheric forms in the sections were studied using published data. Results. Nummulitic limestones of studied area construct nummulitic banks and were formed in shallow warm-water sea basins. Crimean nummulitic bank assessed size reaches 120-150 km and it is assumed as a single isolated carbonate platform. It was relatively flat forming within quiet hydrodynamic conditions at mean depth below fairweather wavebase (less than 50 m). Рщцумук аacial changes reflect variations in water depth. Different facies of the Crimean bank are clearly distinguished: a shoal, its lee- and weather side slopes, a shelf plain in the rear of the bank and a relatively deep basin-ward slope with predominantly terrigenous sedimentation. Among LBF of Crimea Nummulites, Operculina, Assilina are the most typical. Discocyclina and Actinocyclina are less distributed, their appearance indicates a deepening of the basin. Georgian nummulitic banks (Sukhum-Novy Athon, Bzyp and Tquarchal structures) are differed from Crimean bank by smaller sizes and composition of rocks. Banks each were about 25-30 km in diameter. The main components among LBF are Discocyclina, Nummulites with total absence of Operculina and Assilina and among other bioclasts are red algae, echinoids, bryozoans. These may mean deeper conditions than of the Crimean bank. Abundance of bioclastic limestones in structure of banks is a mark of higher hydrodynamic activity, presumably storm-induced. They were formed upon local basement uplifts within the shelf basin of Georgian massif edged by deep troughs with active terrigenous supply. Georgian massif acted as a carbonate platform with local nummulitic banks within it. Reservoir properties of nummulitic limestones are very good to excellent within Central and to a lesser extent South-Western Crimea. The same time nummulitic limestones of Caucasus do not possess such properties as they are strongly condensed in the post-diagenetic changes. Conclusions. Appearance and position of Crimean and Georgian banks were predetermined tectonically. Tectonic movements of Palaeocene-Eocene transition and early Eocene known in Crimea and Caucasus may be related to the main compressional event in Pontides. Subsequent rifting within Pontides was accompanied with broad Middle Eocene transgression in adjacent regions. Within Georgian massif stress tectonics resulted in blocky movements, which created uplifts favourable for the origin of nummulitic banks.

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