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.
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:
[email protected] Received September 15, 2003
Abstract—The paper presents results of the comparative analysis of organic matter (OM), mineralogical characteristics, 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 ForeTalysh 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.
1.40 1.78
0.990
‡
b
1.39
c
1.41
0.714
0.495
0.423
0.334
b 0.423
1.77 1.39
(b)
0.357
0.990
‡
1.40
0.423 0.445 0.494
0.357
0.423
0.303
0.303
0.318
0.714
0.334
(a)
BRIEF GEOLOGICAL CHARACTERISTICS OF THE STUDY AREA The territory of Azerbaijan, a constituent of the mobile Alpine–Himalayan tectonic belt, structurally corresponds 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 orogenic massifs is attributed to the beginning of the Oligocene 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 southeastern margins of the Greater Caucasus and Talysh are char-
0.318
During last decades, rocks from many natural exposures of eastern Azerbaijan were subjected to geochemical, 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 Oligocene clayey rocks of the Greater Caucasus and Talysh characterized by several distinctive features of geological setting and evolution.
c
Fig. 1. Diffractograms of Oligocene clays of the (a) Greater Caucasus and (b) Talysh regions. (a) Air-dry sample; (b) glycerin-saturated sample; (c) sample heated at 580°C. 0024-4902/05/4004-0376 © 2005 åÄIä “Nauka /Interperiodica”
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Table 1. Quantitative characteristics of the hydrocarbon potential of Oligocene clays in the Greater Caucasus and Talysh Composition, % Section
1
Number of examined samples
TOC, %
S1, mg/g
S2, mg/g
S3, mg/g
S1 + S2
S1 + S2 ---------------íéë
2
3
4
5
6
7
8
Greater Caucasus Sumgait-chai
5
2.2–12.8 --------------------6.3
0.03–2.77 -----------------------0.87
3.1–68.8 --------------------27.5
1.71–8.95 -----------------------3.64
3.1–71.5 --------------------28.4
1.5–5.6 -----------------3.7
Perekeshkyul
4
0.2–1.6 -----------------0.7
0.01–1.55 -----------------------0.48
1.2–5.3 -----------------3.2
1.45–1.92 -----------------------1.60
1.2–5.5 -----------------3.7
3.2–7.4 -----------------5.9
Average
9
0.2–12.8 --------------------3.8
0.01–2.77 -----------------------0.70
1.21–68.77 --------------------------16.7
1.45–8.95 -----------------------2.73
1.2–71.5 --------------------17.4
1.45–7.41 -----------------------4.7
Talysh Perembel
1
0.8 ------0.8
0 --0
0.4 ------0.4
1.09 ---------1.09
0.4 ------0.4
0.5 ------0.5
Yardymly
4
0.6–3.3 -----------------1.5
0.09–0.42 -----------------------0.25
0.4–2.0 -----------------1.2
0.05–0.96 -----------------------0.32
0.5–2.1 -----------------1.4
0.6–1.7 -----------------1.1
Dashkend
3
0.5–2.2 -----------------1.2
0.14–1.4 --------------------0.62
0.48–3.86 -----------------------1.7
0.03–0.18 -----------------------0.11
0.6–5.3 -----------------2.3
1.2–2.4 -----------------1.6
Surrug
2
1.2–3.3 -----------------2.3
0.08–0.12 -----------------------0.1
0.4–2.0 -----------------1.2
0.34–1.37 -----------------------0.86
0.5–2.1 -----------------1.3
0.4–0.6 -----------------0.5
Arus
1
0.7 ------0.7
0.21 ---------0.21
0.3 ------0.3
0.09 ---------0.09
0.5 ------0.5
0.7 ------0.7
Vilesh-chai
10
0.5–1.0 -----------------0.7
0–0.36 ---------------0.17
0.1–0.4 -----------------0.2
0.09–0.35 -----------------------0.18
0.1–0.8 -----------------0.4
0.1–1 ------------0.6
Average
21
0.5–3.3 -----------------1.1
0–1.4 ------------0.24
0.1–3.9 -----------------0.7
0.03–1.37 -----------------------0.3
0.1–5.3 -----------------1.1
0.1–2.4 -----------------0.8
Note: Numerator shows content variations; denominator, average value.
acterized by not only common features of evolution, but also several differences in the geology, facies characteristics of Paleogene rocks, and geochemistry of fluids. For instance, in contrast to the southeastern margin of the Greater Caucasus, the Talysh segment demonstrates a large positive gravity maximum. Eocene rocks are composed of only sedimentary terrigenous facies in the Greater Caucasus, but they also include volcanogenic rocks in Talysh. Oligocene sequences are also different in terms of facies composition. The Greater Caucasus is marked by wide development of mud volcanism, which is missing in the Talysh region. Finally, the Talysh region incorporates all types of natural gas shows (hydrocarbon, nitrogen, and carbonic acid), whereas only methane and LITHOLOGY AND MINERAL RESOURCES
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nitrogen–methane seepages are known in the Greater Caucasus. All these features stimulate interest to geochemical, mineralogical, and radioactive properties of Oligocene rocks in the Talysh and Greater Caucasus regions that serve as oil-bearing formations in the South Caspian Basin (SCB) (Feyzullayev et al., 2001). OBJECTS AND METHODS The present work is based on the study of 93 rock samples from 8 natural outcrops in the Greater Caucasus and Talysh. They were subjected to geochemical No. 4
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FEYZULLAYEV et al.
Table 2. Quantitative characteristics of OM from Oligocene clays of the Greater Caucasus and Talysh Section 1
Number of examined samples 2
Composition, % HI, mg/g
OI, mg/g
PI
Tmax , °C
R0 , %
3
4
5
6
7
Greater Caucasus Sumgait-chai
5
143–539 --------------------355.8
24–107 -----------------62.8
0.01–0.04 -----------------------0.02
408–428 --------------------416.6
0.22–0.29 -----------------------0.26
Perekeshkyul
4
212–708 --------------------546.5
94–690 -----------------348
0.01–0.32 -----------------------0.11
401–472 --------------------445
0.53 ---------0.53
Average
9
143–708 --------------------440.6
24–690 -----------------189.6
0.01–0.32 -----------------------0.06
401–472 --------------------429.2
0.22–0.53 -----------------------0.33
Talysh Perembel
1
47 -----47
129 --------129
0 --0
446 --------446
Yardymly
4
56–131 -----------------81.5
4–29 -----------17.3
0.04–0.31 -----------------------0.21
457–477 --------------------465
0.57–0.73 -----------------------0.65
Dashkend
3
90–177 -----------------120.3
5–15 -----------9.3
0.23–0.29 -----------------------0.26
464–466 --------------------465
0.65–0.83 -----------------------0.72
Surrug
2
35–60 --------------47.5
28–41 --------------34.5
0.06–0.16 -----------------------0.11
487–496 --------------------491.5
0.71–0.82 -----------------------0.77
Arus
1
39 -----39
13 -----13
0.46 ---------0.46
482 --------482
0.69 ---------0.69
Vilesh-chai
10
6–51 -----------32.6
14–46 --------------26.5
0–0.5 ------------0.35
467–494 --------------------479.88
0.73–1.39 -----------------------0.9
Average
21
6–177 --------------56.9
4–129 --------------27.3
0–0.5 ------------0.28
446–496 --------------------474.0
0.57–1.39 -----------------------0.81
Note: Numerator shows content variations; denominator, average value.
(30 samples), radiometric (30 samples), and mineralogical (33 samples) examination. All the three analytical measurements were carried out for the same samples. Analysis of OM included pyrolysis of clayey rocks, assessment of total organic carbon (TOC) content in them, and evaluation of vitrinite reflectance (R0). The TOC content was determined using a LECO CS-444 equipment after the removal of carbonate fraction from the preliminarily crushed rock. Programmed pyrolysis of crushed rock was performed using a LECO THA-200 equipment. We determined the following parameters: S1 (free and absorbed HC in rocks); S2 and S3 (HC and ëé2, respectively, produced as a result of the thermal destruction of OM); Tmax (temperature corresponding to the S2 maximum); hydrogen index (HI)
and oxygen index (OI) that designate types of hydrocarbons and are determined as mgS2/gTOC and mgS3/g TOC, respectively; and productivity index (PI) determined as S1/(S1 + S2). The vitrinite reflectance (R0) was determined by the optical examination of the polished rock surface. Radiometric studies were carried out using a SRP68-01 field radiometer to measure integral radioactivity of rocks. The rock samples were subjected in a laboratory to gamma-spectrometric analysis using a SARI-2 equipment. Mineralogical studies included the X-ray diffraction analysis of clayey rocks using the DRON equipment. The qualitative assessment of the mineral composition of clayey rocks was based on diffractograms of
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Table 3. Quantitative characteristics of the mineral composition in Oligocene clays of the Greater Caucasus and Talysh Section 1
Composition, %
Number of examined samples
H
K
Ch
S
Quartz
Feldspar
Calcite
2
3
4
5
6
7
8
9
–
Greater Caucasus Sumgait-chai
8
28–42 --------------35
14–29 --------------19.5
3–5 --------4.8
0–7 --------3.3
28–35 --------------30.9
3–13 -----------6.5
Perekeshkyul
4
27–38 --------------34.3
15–28 --------------22
6–8 --------6.8
5–6 --------5.3
27–31 --------------29.3
3–3 --------3
12
27–42 --------------34.8
14–29 --------------20.3
3–8 --------5.4
0–7 --------3.9
27–35 --------------30.3
3–13 -----------5.3
Average
Talysh Perembel
1
26 -----26
24 -----24
5 --5
3 --3
32 -----32
10 -----10
0 --0
Yardymly
4
18–41 --------------30.3
14–32 --------------20.3
3–7 --------5.8
0–3 --------0.8
18–31 --------------26
12–15 --------------13.5
0–9 --------3
Dashkend
3
30–35 --------------32
11–17 --------------14.3
3–4 --------3.7
0 --0
29–36 --------------33.3
10–12 --------------11
0–9 --------5.7
Surrug
2
36–44 --------------40
15–19 --------------17
3–14 -----------8.5
3–3 --------3
24–25 --------------24.5
10–11 --------------10.5
0–3 --------1.5
Arus
1
14 -----14
42 -----42
3 --3
5 --5
20 -----20
11 -----11
5 --5
Vilesh-chai
10
30–38 --------------33
8–28 -----------21.8
3–6 --------4.9
0–3 --------0.9
24–32 --------------26.1
8–17 -----------11.5
0–8 --------1.8
Average
21
14–44 --------------31.8
8–42 -----------21.1
3–14 -----------5.1
0–5 --------1.2
18–36 --------------27.0
8–17 -----------11.6
0–9 --------2.6
Note: (H) Hydromica; (K) kaolinite; (Ch) chlorite; (S) smectite. Numerator shows content variations; denominator, average value.
oriented preparations obtained by the precipitation of their dense suspension on slides with the registration of not only basal reflections of clay minerals, but also main diffraction lines produced by nonclay minerals, such as quartz (at 0.334 nm), calcite (0.303 nm), and feldspars (0.318 nm). In order to specify the qualitative mineral characteristics of each sample, we analyzed diffractograms corresponding to three states of sediments (air-dry, glycerin-saturated, and heated at 580°ë). The samples were saturated with glycerin to specify the parameters of smectite, whereas the heating was carried out for identification of kaolinite and chlorite. These procedures were necessary, because first-order reflections of chlorite and smectite in diffractograms of LITHOLOGY AND MINERAL RESOURCES
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air-dry samples overlap each other and are registered at 1.40 nm. In diffractograms of glycerin-saturated samples, reflection (001) of smectite shifts up to 1.77– 1.78 nm, while d(001) of chlorite is retained at 1.40 nm. In diffractograms of heated samples, reflections of kaolinite disappear because of its transformation into amorphous state and d(001) of chlorite is retained at 1.39 nm. Figure 1 exemplifies diffractograms of oriented samples. The content of clay minerals was determined by comparing areas of first-order basal reflections in diffractograms obtained for oriented preparations of 550
400–450 450–500 500–550
mg/g
200–250 250–300 300–350 350–400
