0024-4902/05/4004- © 2005 åÄIä “Nauka /Interperiodica” 0376 Lithology and Mineral Resources, Vol. 40, No. 4, 2005, pp. 376–385. Translated from Litologiya i Poleznye Iskopaemye, No. 4, 2005, pp. 430–439. Original Russian Text Copyright © 2005 by Feyzullayev, Kheirov, Ch. Aliyev, Abbasova, K. Aliyev. During last decades, rocks from many natural expo- sures of eastern Azerbaijan were subjected to geochem- ical, mineralogical, and radiometric investigations (Aliyev and Zolotovitskaya, 2002; Ali Zade et al., 1971; Kheirov, 1979; Abrams and Narimanov, 1997; Feyzullayev et al., 2001). They were, however, carried out in different years for different purposes. No special works aimed at the study of relationships between these parameters were performed until recently. Our paper presents results of the comparative analysis of OM, mineralogical characteristics, and radioactivity in Oli- gocene clayey rocks of the Greater Caucasus and Talysh characterized by several distinctive features of geological setting and evolution. BRIEF GEOLOGICAL CHARACTERISTICS OF THE STUDY AREA The territory of Azerbaijan, a constituent of the mobile Alpine–Himalayan tectonic belt, structurally cor- responds to the Kura–South Caspian intermontane depression bounded by orogenic massifs of the Greater and Lesser Caucasus, Talysh, Elburs, Kopet Dagh, and Greater and Lesser Balkhan. The formation of these oro- genic massifs is attributed to the beginning of the Oli- gocene phase in tectonic reactivation of the basin (Azizbekov et al., 1972), which was accompanied by their uplift and exhumation of Mesozoic–Pliocene rocks. This process was developed in the Greater and Lesser Caucasus, as well as in Talysh. However, the southeast- ern margins of the Greater Caucasus and Talysh are char- Comparative Characteristics of Composition and Radioactivity of Oligocene Clays in the Greater Caucasus and Talysh A. A. Feyzullayev, M. B. Kheirov, Ch. S. Aliyev, S. B. Abbasova, and K. A. Aliyev Institute of Geology, National Academy of Sciences of Azerbaijan, H. Javid pr. 29A, Baku, AZ 1143 Azerbaijan e-mail: afeyzullaev@gia.ab.az Received September 15, 2003 Abstract—The paper presents results of the comparative analysis of organic matter (OM), mineralogical char- acteristics, and radioactivity in Oligocene clayey rocks from the Greater Caucasus and Talysh, which bound the South Caspian Depression on the southeast and northwest, respectively. It is established that Oligocene clays of the Greater Caucasus and Talysh substantially differ in terms of quantitative and qualitative parameters of OM, its maturity, integral radioactivity, and composition of radioactive elements. At the same time, the mineral composition of clays from these mountainous massifs shows a certain similarity. It is concluded that the Fore- Talysh subsidence zone and adjacent areas of the Caspian Sea are characterized by a lower oil and gas potential as compared with Oligocene rocks developed at the southeastern margin of the Greater Caucasus. (a) (b) ‡ b c ‡ b c 0.303 0.303 0.318 0.334 0.357 0.423 0.423 0.445 0.494 0.714 0.990 1.40 1.39 1.77 0.318 0.334 0.357 0.423 0.423 0.495 0.714 0.990 1.40 1.41 1.78 1.39 Fig. 1. Diffractograms of Oligocene clays of the (a) Greater Caucasus and (b) Talysh regions. (a) Air-dry sample; (b) glycerin-sat- urated sample; (c) sample heated at 580°C.