CC BY
19GEOLOGICAL AND MINERALOGICAL SCIENCES
RELATION OF MUD VOLCANISM AND SEISMICITY WITH OIL AND GAS ACCUMULATION
ZONES IN THE SOUTH CASPIAN HOLLOW
Pogorelova E.
Associate Professor Azerbaijan State University of Oil and Industry, PhD
Bakhtiyarov A.
4th year undergraduate student of Azerbaijan Oil and Industry University
Gasimov B.
4th year undergraduate student of Azerbaijan Oil and Industry University
Abstract
Mud volcanoes serve as direct indicators of deep deposits of oil and gas, and often accumulations of iron, mercury, arsenic and other elements.
Mud volcanoes in Azerbaijan are occured in groups or detached in the area of Southeast immersion of the Greater Caucasus and in the foothills of the Kura depression and in adjacent waters of the Caspian Sea.
Mud volcanoes are located mainly within the mobile belts of the globe with a high level of seismic activity, the intensity values of speeds of neotectonic and contemporary movements, etc.
For seismically active zones are rifts and subduction zones, and the second - the most active areas.
As is well known, the zone associated with oil and gas well above the crust elements.
On the other hand, all the mud volcanic and seismic phenomena are confined to fault zones of different depths of burial and age, which on one hand are conducting channels, on the other - screens for hydrocarbon accumulations.
High seismic area of mud volcanoes may be considered zones of hydrocarbon accumulations.
Keywords: Mud volcanoes, South Caspian, Absheron Peninsula, tectonic, Scythian-Turanian plate, Gil Adasi, seismic
In terms of the number of mud volcanoes, Azerbaijan ranks first in the world, on whose territory exist more than 300 volcanoes out of about 800 known
(Fig.l).
In the Baku archipelago of South Caspian hollow, 8 islands (Khara-Zira, Zenbil, Garasu, Gil Adasi, etc.) are of mud volcanic origin.
Fig. 1. Location of mud volcanoes in the South Caspian depression
The upper structural layer of the earth's crust in the areas of development of mud volcanoes is composed of incompetent, plastic strata, where there is no possibility of long-term accumulation of high stresses, and tectonic activity is expressed in fast recent and modern geological movements (folding, shear and thrust deformations). These active tectonic processes, along with
the plastic state of geomaterials in the upper part of the earth's crust and the mud volcanism itself, provide a rapid discharge of accumulating stresses.
In Azerbaijan, mud volcanoes are found in groups or separately in the zone of the Southeastern immersion of the Greater Caucasus and its foothills (Absheron
Peninsula, Shamakha-Gobustan region, Caspian lowland), in the Kura-Araz lowland and in the adjacent waters of the Caspian Sea (Absheron and Baku archipelagos) [8,7].
Mud volcanoes are located mainly within the active belts of the Earth, which are characterized by a high level of seismic activity, intense rates of neotectonic and modern movements, etc.
Seismically active zones include rift and subduction zones, the latter being the most active zones. As known, the zones of oil and gas accumulation are also associated with the above-mentioned areas of the earth's crust. According to researchers, seismic tremors accelerate the creation of a favorable critical regime and may result in premature eruptions of mud volcanoes [2,10]. Seismic tremors are a consequence of the processes of displacement of the earth's crust, which are associated with the processes of oil and gas generation. Mud volcanoes are indicators of the location of hydrocarbon accumulations.
One or another earthquake force is considered a necessary precursor to the first eruption, i.e. the birth of a new volcano in general and a mud volcano in particular [4].
Thus, during the underwater eruption of the Ku-mani mud volcano on May 1, 1927, 41 shocks were noted. Seismic fluctuations were also noted during the eruption of mud volcanoes Shikhzagirli (12.24.1929), on the Sangi Mugan island (04.11.1932), Toragay (04.20-21.04.1932), etc.
Under the seismic regime of any territory is meant a set of earthquakes in this area, considered in space and time [11]. Modern and buried mud volcanoes are located in geosynclinal, epigeosynclinal orogenic belts, as well as in areas of reorogenesis. In general, there are areas of development of mud volcanoes of the Mediterranean and Pacific (Western and Eastern) tectonic belts, as well as areas of re-orogeny.
The Mediterranean belt [9] includes the Alpine folded region, of which Azerbaijan is also a part. The Alpine fold area, or, as it has recently been often called, the Alpine fold belt, stretching from Gibraltar through the Alps, Carpathians, Dinarids, Anatolia, Iran and Afghanistan, Hindu Kush, Pamir, Karakorum to the Himalayas. In general, it is an area of Neogene folding.
Within the considered regions, mud volcanoes are developed in the border zone of Eastern Georgia and Western Azerbaijan (Kura and Gabirri interfluve), Eastern Azerbaijan (Shamakha-Gobustan region, Ab-sheron peninsula, Low-Kura lowland, Caspian lowland), Absheron-Cheleken threshold, Baku archipelago and Western Turkmenistan. Tectonically [10], the noted areas are located within the South Caspian region of the earth's crust trough, including the Kura, South Caspian and West Turkmenian intermontane depressions, the Absheron-Pre-Balkhanian interpericlinal and Shamakha-Gobustan rear troughs. Earthquakes in this area have been known since ancient times. Here they manifested themselves with varying strength, both from local foci located within the territory itself, and
from remote foci of folded structures of the Greater Caucasus, Lesser Caucasus, Kopetdag and Albours.
The main seismogenic zone of the Caspian region is the Agrakhan-Turkmenbashi (Krasnovodsk) marginal seismogenic zone, caused by the junction of the epigercynian Scythian-Turanian plate with the alpine folded system, which is associated with the catastrophic Krasnovodsk earthquake of 08.07.1895. This zone along its entire length is characterized by a complex structure, predetermined by the presence of a transverse fault in the central part of the South Caspian depression, traces of which are noted in the structure of the upper mantle [12]. The southern boundary of the Eurasian (Scythian-Turanian) plate within the Crimean-Cauca-sian-Kopetdag region is drawn by most researchers along a series of large crustal faults extending in a sub-latitudinal direction from the Kubadag-Greatbalkan dislocations in the east to the meganticlinorium of the Mountainous Crimea in the west through the Caspian Sea, the Greater Caucasus, Gagra-Javy zone, northwestern side of the Tuapse trough.
In fact, this boundary is a paleosubduction zone [6], along which horizontal movements continue to the present day. The specified border does not have a uniform expression along its entire length. Three large troughs of the transverse trough - the Caspian, Azov and North Black Sea troughs - have a significant impact on the character of its severity. The peculiarity of the interaction of these zones with the subduction zone is that the latter at the intersection nodes loses its clear expression.
The South Caspian depression is of the greatest interest in terms of oil and gas. The southern and western boundaries of the South Caspian depression (microplates) are characterized by increased seismicity and young Neogene-Quaternary volcanism. Despite the fact that, in general, the Caspian Sea region is characterized by a scattered distribution in terms of seismicity sources, typical for zones of collision of continental plates, separate zones of increased seismicity are outlined here, which can be linked to plate boundaries. These are the Albours-Talysh zone, along which the South Caspian microplate borders on the Lesser Caucasian and West Iranian microplates. The zone of increased seismicity also includes the northern border of the South Caspian microplate. The central zone of the latter is characterized by a low density of earthquakes (Fig. 2).
Sedimentary formations of the Cenozoic are represented mainly by clay-carbonate sediments [5] with plastic properties. The Mesozoic in the considered zone is represented by terrigenous-carbonate and volcanic-sedimentary formations. The extreme eastern end of the Agrakhan-Turkmenbashi zone is characterized by an increased density of formations [14], which, by their physical and mechanical properties, can generate earthquakes.
Areas of development of mud volcanoes in Azerbaijan and the Caspian region are located south of the Agrakhan-Turkmenbashi seismogenic zone.
0, S32 [S3 H34
Figure 2. Geodynamic model of the South Caspian hollow (by N.R. Narimanov, 1998)
The Shamakha-Gobustan area of development of mud volcanoes is associated with the rear trough of the same name, which is a structural element of the southeastern subsidence of the Greater Caucasus. According to [13], a significant part of the trough, represented by Cenozoic deposits, rests on the volcanogenic-sedimen-tary formations of the Vandam zone. The near-crest of the folds are complicated by mud volcanoes or mud volcanic manifestations. The pre-Alpine basement is divided by transverse faults into a series of protrusions and troughs with depths of 9-12 km in the west, up to 15 km in the central part and 20 km in the extreme eastern part near Cape Alat.
The structure of the Maraza zone is mainly composed of clayey and sandy-clayey sediments of the Paleogene and Miocene. They are unconformably overlapped by a stratum of Pontician and Akchagylian weakly dislocated deposits. Miocene-Paleogene deposits are intensively dislocated. The Central Gobustan zone is represented mainly by Paleogene-Miocene deposits, which are replaced by the Pliocene to the outskirts, completely representing the Maraza trough and the Jeyrankechmez depression. This is the most uplifted block and the thickness of the Paleogene-Miocene complex here reaches 4-4.5 km. The Shamakha-Go-bustan area of mud volcano development spatially coincides with the segments of the Main Caucasus, Gai-nar-Zangin, Vandam, Ajichay-Alat, Khankendi-Devechi, Palmir-Absheron and Yashma seismogenic zones.
The Ajichay-Alat seismogenic zone is caused by an interblock deep fault that extends along the northern side of the Kura depression. The western component of the fault is known as the North Ajinohur fault, and the eastern component as the Ajichay-Alat fault. The Ajichay-Alat seismogenic structure is associated with
the Shamakha-Gobustan area of development of mud volcanoes. The fault causing this structure has a gentle dip of 20-30°, the displacement amplitude along it is 57 km [3].
The Caspian region of the development of mud volcanoes is associated with the Kusar-Devechi superimposed trough, filled with a thick layer (10-12 km) of terrigenous and carbonate rocks of the Cenozoic and Mesozoic age, and is one of the elements of the Terek-Caspian trough. Within the Kusar-Devechi trough, the Yalama-Khudat zone of uplifts, the Zeykhur trough, the Kusar zone of uplifts and the Kainarja trough are distinguished. Slips along the Samur and Khankendi-Devechi faults may be associated with a somewhat isolated character of the spatial position of the Gusar-Devechi trough. Mesozoic carbonate-terrigenous rocks in the crest of the Yalama-Khudat anticlinal zone are complicated by a seismogenic fault zone identified in Azerbaijan according to geophysical data [1].
Within the Kura intermontane depression, mud volcanoes are known in the Middle-Kura and Low-Kura depressions. In the Middle Kura depression (between the Kura and Gabyrri rivers), they are confined to the Mirzaany-Areshy synclinorium and the Chatma-Geychay anticlinorium. In the Mirzaany-Areshy synclinorium, which is the most submerged part of the depression, the Mesozoic surface lies at depths of 7-8 km, and the consolidated crust at depths of up to 15 km. In the zone of development of mud volcanoes, the geosynclinal formations of the Mesozoic and Paleocene-Eo-cene are filled with carbonate and terrigenous deposits. Molasse sandy-clayey varieties of the Oligocene and Lower Miocene have a thickness of 2-3 km. The thickness of the Miocene terrigenous strata is 3-4 km. The Miocene-Pliocene and Quaternary deposits of the Mir-zaany-Areshy synclinorium are strongly dislocated and
complicated by thrusts and uplifts. In this area, several anticlinal zones are noted, separated from each other by wide synclines filled with Upper Pliocene-Quaternary formations of the continental type. In this part of the Middle Kura depression, a number of transverse structures are noted, along which the tectonic block, where mud volcanoes are developed, is elevated in relation to adjacent ones.
Through the considered area of mud volcanoes, the Kura seismogenic zone is traced, caused by the interblock deep fault of the same name. This zone is divided by transverse faults into separate structures of various lengths.
In the Low-Kura depression, mud volcanoes are spatially related to its northeastern margin. In general, the basin is a synclinorium filled with a thick stratum of Pliocene and Anthropogenic formations about 8 km thick. A significant number of mud volcanoes are associated with this section of the depression, which is characterized by a high slope of the consolidated crust surface. The most well-defined structural element of the depression is the Kharami-Salyan anticlinorium, which consists of lower-order anticlinal structures: Kurovdag-Neftchala and Kalamadyn-Bandovan, complicated by extended fold-type faults of the fault type. The surface of the Mesozoic rocks occurs within this area at depths of up to 8 km. Local seismogenic zones for this area of development of mud volcanoes are regarded West Caspian and Kurovdag-Neftechala.
The seismogenic zones of the Absheron-Pre-Balkhanian uplift region of mud volcanoes are due to the mobile system of the same name, bordering in the south with the stable South Caspian basin. The mobile system has a W-NW (Caucasian) strike. In the direction from the Cheleken Peninsula to the Neft Dashlary Islands, here at the bottom of the sea stretches the Ab-sheron-Cheleken uplift zone - expressed in the relief of individual anticlines and active mud volcanoes: the banks of Zhdanov, Gubkin, Livanov, Bezymyannaya, etc.
At a depth, according to geophysical data [12], the mobile system is built by several narrow tectonic steps of the Caucasian strike, forming a grandiose graben 3050 km wide in section. The steps are a continuation of the well-known zones of Western Turkmenistan and the South-Eastern Caucasus at the bottom of the Caspian Sea. Thus, the northernmost step is the western continuation of the Kubadag-Big Balkhan uplift and the eastern marine analogue of the Tengiz-Beshbarmak horst-anticlinorium. The central step is the Khizi-Kel-kor trough, as well as the southern step - the so-called Absheron-Cheleken sill. The steps are separated by longitudinal deep faults, the largest of which is Absheron-Cheleken.
The graben of the mobile system is made by a layer of loose clayey, carbonate and detrital rocks of the Cenozoic with a total thickness of up to 10-12 km. The bottom of the Lower Pliocene is located at depths of 57 km. The Pre-Cenozoic complex of rocks is represented by flysch and terrigenous-carbonate, as well as volcanic-sedimentary formations of relatively high density.
The surface of the Paleozoic crystalline basement within different structures of the region is characterized by different depths. In the Karabogaz arch, it is located at a depth of 2-5 km, gradually sinking to the south. In the Kubadag-Big Balkhan step, the foundation is submerged by 18-20 km, in the Khizi-Kelkor trough by 25 km, at the Absheron-Cheleken sill 20-22 km, and finally under the South Caspian depression - more than 25 km. In parallel with the subsidence of the basement to the axial part of the graben, the surface of the Meso-zoic rocks, corresponding in its physical and mechanical properties to the upper horizons of the consolidated crust, also subsides. At the same time, such a clear gra-ben-like subsidence in the axial zone of the mobile system is no longer typical for the surface of the Lower Pliocene loose deposits. On the surface of these rocks, geophysical methods established the presence of the aforementioned local anticlines, which are also very clearly manifested on the surface of the Upper Pliocene rocks and are confirmed by drilling in Quaternary rocks, and are also often expressed in the bottom topography in the form of individual banks. The systems of such brachyanticlines extend in chains within the Absheron-Cheleken threshold and the Tengi-Beshbarmak stage. Moreover, the first chain extends far to the east-southeast to the territory of the West Turkmen lowland, tracing the Cheleken-Kumdag deep fault. In the eastern part of the bottom of the Caspian Sea and in Western Turkmenistan, the near-fault brachyanticlines substitute each other en-echelon and are disturbed by numerous faults and local dextral strike-slip faults.
In agreement with tectonic data, the so-called Northern seismogenic zone has been identified within the Absheron-Pre-Balkhanian mobile system, stretching for more than 500 km from the northern edge of the Absheron peninsula to the northern coast of the Cheleken peninsula and further to Western Turkmenistan.
In the modern structural plan of the South Caspian Basin, zones of near-longitudinal (the Baku archipelago and the adjacent deep-water part of the South Caspian), transverse (the area of intersection of the Baku archipelago and the basins) and the Pre-Albours trough.
The seismogenic zones of the area of development of mud volcanoes of the Baku archipelago been caused by the massif of the same name in the South Caspian block of the ancient middle massif, bordering in the north with the Absheron-Pre-Balkhanian trough and Lankaran-Gorgan in the south.
The linearly elongated anticlinal zones of the Baku archipelago, which have a predominantly northwestern-southeastern strike, are complicated by large longitudinal ruptures, the amplitude of which in places reaches 1.2 km, and a series of transverse faults. The islands and banks of the archipelago are associated with these rifts, most of which are of mud volcanic origin. The en-echelon folds of the Baku archipelago in the shelf zone occupy a higher hypsometric position in comparison with the folds of the Lower-Kura depression. They are sharply dislocated, the dip angles on the wings vary from 10-15° to 40-50°.
The western deep-water part of the South Caspian depression is distinguished by a sharper subsidence of
the Mesozoic and Cenozoic deposits, caused by the large subsidence of the massif of the Baku archipelago. This difference emphasizes its similarity with the southeastern part of the Kura depression. In relation to the eastern part of the South Caspian depression (Godin massif), the zone of the Baku archipelago is lowered along the transverse fault, which predetermined [12] in this area of the South Caspian basin a calm subplatform structure of the sedimentary cover.
According to calculations [12], igneous rocks of the Mesozoic reach 10-12 km within the Baku archipelago. It is obvious that the block of the Baku archipelago underwent greater subsidence in the Mesozoic than the Godin massif.
The thickness of sedimentary deposits within the West Turkmenian region of development of mud volcanoes is 14 km. The geosynclinal stratum is represented mainly by clay, sandy-clay and limestone rocks. The orogenic complex is expressed by clayey sediments in the lower part (Oligocene-Lower Pliocene), sandy-silty in the middle (Pliocene), and clayey sediments in the upper part of the section. The southern boundary of the trough is the Pre-Albours trough, where the basement surface is traced at a depth of up to 20 km.
Mud volcanoes in Western Turkmenistan are associated with individual anticlinal uplifts, in the spatial distribution of which a regional interblock fault can be traced, disrupting the Mesozoic and Cenozoic complexes of deposits and falling to the west. This fault within the present area of mud volcanoes is responsible for the local seismogenic zone.
The depths of the foci of the volcanoes under consideration correspond to the thickness of the productive strata. The maximum thickness is noted in the area of the Garasu and Ayrantokan mud volcanoes, in the area of the Dashmardan, Lokbatan and Ajinohur mud volcanoes, shallower depths are noted. The centers of mud volcanic earthquakes can be associated with the thickness of the productive strata. The depths of the sources of mud volcanic earthquakes under consideration are the greater, the greater the thickness of the productive strata. In this regard, it is enough to recall the existing connections between the magnitude of the earthquake and the thickness of the rocks overlying the focus of a tectonic earthquake [3]. Presumably, the above assumption suggests itself due to the fact that the overlying complex is unambiguously represented by a productive stratum, which is exposed on the Earth's surface in the section of the considered mud volcanoes. Thus, it can be assumed that sources of shaking of active mud volcanoes are developed in the upper parts of sedimentary basins in the depth interval up to 1.5-4.5 km.
Conclusions
For understanding the relation between seismicity and activity of mud volcanoes it is necessary to being addressed to nature of that occasion. Apparently, the development of zones of mud volcanism is mainly confined to the areas of molasse troughs that have experienced subsidence at the latest stage, and is associated with their surface filling, represented in the territory of the South Caspian depression by the Cenozoic (Ya-gubov and et.al., 1983). It means that their roots do not
penetrate into consolidated geosynclinal complexes. It has been established [10] that the Upper Cretaceous are the most ancient rocks participating in the composition of mud volcanoes in depression zones, which makes it possible to estimate the maximum depth of penetration of their roots in the territory of the South Caspian depression, not exceeding 10-15 km.
On the other hand all seismic and mud volcanic occasions are confined to the zones of faults with different depths of deposits and age which on one hand considered as conductive channels, on the other hand -screens for accumulation of hydrocarbons.
Taking all above-mentioned data into account with a higher share of probability may be meant that high-seismic zones of development of mud volcanism are thickly correlated with zones of accumulation of hydrocarbons.
References
1. Abdullayev R.A., Jafarov Kh.D. Geological-geophysical characteristics of Caspian oil-bearing region of Azerbaijan//Baku, Azerneshr, 1962, p.5-13
2. Akhmadbeyli F.S. Modern activity of mud volcanoes in the eastern part of Azerbaijan and its relationship with seismicity. Azerb. SSR, vol.31, № 8, 1975, p. 61-64
3. Agamirzoyev R.A. Seismotectonics of Greater Caucasus part of Azerbaijan. Baku, Elm. 1987, 124 p.
4. Bunyatzadeh Z.A. Gas-oil volcanism of the South Caspian depression and earthquakes. // In collection. Modern seismic dislocations and their significance for seismic microregioning. М., MSU, 1977, p. 33-40
5. Lebedev L.I. Construction and oil-gas bearing content of modern heterogenic depressions. М., Science, 1978, 111 p.
6. Lebedev L.I. Impact of tectonic factors on oil-gas bearing content of inland seas. - 1988.- 120 p.
7. Map of mud volcanoes of oil-gas bearing areas of the Azerbaijan SSR. Edited by A.A.Alizadeh, E.M.Shekinsky, А.А. Yagubov. L., Airgeology, 1979.
8. Map of the deep structure of the Black Sea-South Caspian zone of regional subsidence//Karimov К.М., Shikhalibeyli E.Sh., 1:1000000, 1992
9. Muratov M.V. Origin of mainlands and ocean troughs. М., Science, 1975, p. 176
10. Rakhmanov R.R. Mud volcanoes and their importance in predicting gas and oil-bearing capacity of the subsoil. М., Subsoil, 1987, 174 p
11. Riznichenko Yu.V., Drumya A.V., Ste-panenko N.Ya. Seismicity and shaking in the Carpathian-Balkan Region. Shtiintsa, Kishinev, 1976, p.118
12. Shikhalibeyli E.Sh., Hasanov A.G. and oth. On the issue of formation of the South Caspian basin (according to new data) // Essays on the geology of Azerbaijan. Baku: Azerneshr, 1984, p. 61-84
13. Shikhalibeyli E.Sh. Shamakha-Jeyrankechmez superimposed deflection.IGANA, N 25, Баку, Elm, 1995, p. 218-236
14. Shtanko Ye.V. Deep structure of the earth's crust in northwestern Turkmenistan according to geophysical data. Cand. diss. Ashkabad. 1984, 127 p.
