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1.3 Geology, economic minerals and seismicity 1.3.1 TECTONIC ZONATION The describing territory is corresponded to the eastern part of the Caucasian segment of the Mediterranean folded belt. The typical feature of structure of the region Earth crust as well as Caucasus the whole is its tectonic heterogeneity, it expresses in presence of structural-formational units with different degree and character of determination, content of composing rocks and history of geological development. The description of the region geological structure is based on materials of fundamental geological studies of Azerbaijan, South Caspian and the Caucasus the whole. The main structural elements of the described territory are the mountain-folded systems of the Lesser and Greater Caucasus and Kura intermontane depression dividing them (Fig. 3). Along the north-eastern side of azerbaijanian part of the Greater Caucasus there is Gusar-Devechi foothill trough. The structural-matter complexes composing of the Greater Caucasus and troughs outlining it on the north and south submerge in the south-eastern direction and go under the modern deposits of the Caspian Sea meridional depression. In coastal zone the Lesser Caucasus system, is represented by the Mountain Talysh folded system restricted on the north-west from the main structural zones of the Lesser Caucasus by Lower Araz superposited depression. The Mountain Talysh adjoins to the north-eastern side of the mountain-folded system of Elburs which frames the South Caspian deep-water depression on the south-west and south. The modern structure of the region had formed on the Alpine stage of the tectogenes in spatial limits covering the southern flank of the Eurasian continent (North-Caucasian plate), Trans-Caucasian plate, the northern flank of the South-Azerbaijan or Iran microcontinent (quasiplate form) and Greater Caucasian marginal-marine basin and Lesser Caucasian branch of Mesothetis locate between them. 1.3.2 TECTONIC ZONES STRUCTURE 1.3.2.1 Mountain-folded system of the Greater Caucasus The Greater Caucasus represents a complex folded-overthrust constriction consisting of three large structures. They are (from north to south) as follows: 1- Lateral Ridge uplift; 2 - Southern Slope trough; 3 - Balakan-Vandam uplift. In its turn each of the mentioned large geostructural units consists of some structural subzones consequently superimposed over each other from north to the south. The Lateral Ridge uplift locates on the south-eastern continuation of the Greater Caucasus Central Uplift and has a subplatformal basement. On the earth surface the Mesozoic formations of the Lateral ridge tectonic zones concentrate within three subzones: 1 - generally, the uplifted Tairjal subzone represents a meganticline turned southward. On sides it is complicated with little foldness and composed of relatively shallow sandstones and argillites of the Lower-Middle Jurassic; 2 - the transitional Sudur subzone locates on the southern side of the previous zone. Generally, it has a synclinorial structure and complicated by linear folds of the box-shaped form composed of evaporitic and carbon-bearing complexes of the Upper Jurassic-Neocomian in facies of the continental shelf and barrier reef. 3 - the lowered Shakhdag-Khyzy subzone is the extreme southern structural element of the Lateral Ridge. It is composed of the carbon-bearing-terrigenous-clayey formations of the Upper Jurassic-Cretaceous in facies of the continental slope and foothill. The overthrust of Sudur limestones into the limits of Shakhdag-Khyzy subzone took place in Austrian phase of the tectogenes (Early-Middle Cretaceous) along Siazan upthrust. This upthrust restrict Sudur and Shakhdag-Khyzy subzones. Gusar-Devechi trough had beef formed in the Middle Pliocene. It levels a structural plan of Tairjal and Sudur subzones in the south-eastern direction. On the north the trough formations are superposited on the south-eastern continuation of stripe of Dagestan Tertiary folds. Regionally the trough represents a western enclosure of large North-Apsheron depression of the Middle Caspian water area. It is composed of marine, continental-marine and continental molasses (clays, sands, pebbles-shingles, conglomerates) of the Middle Pliocene-Quaternary. The Southern Slope trough represented by subzone of Watershed Ridge on the north and Zagatala-Kovdag-Sumgayit subzone on the south. Subzone of Watershed Ridge (or Tufan) represents a stripe of uninterrupted development of the Lower-Middle Jurassic sandy-clayey series, added by the Upper Jurassic flyschoids to the subzone southern side. Zone is characterized by tense enough foldness and consists of very compressed linear often isoclinal stagnant folds. They undergo a southward overturn on the northern flank of Zagatala-Kovdag-Sumgayit subzone in the southern side along Malkamud upthrust. Zakatala-Kovdag-Sumgayit subzone represents a flyschoid trough and composed of southward overturned and fold crushed terrigenous-carbon-bearing-clayey deposits of the Upper Jurassic-Neokomian, Upper Cretaceous flysch, and terrigenous deposits of the Paleocene-Miocene in coastal line. Comb-like foldness with numerous dislocations prevail here. On he east the Southern Slope trough is traced within Caspian as Apsheron-Pri-Balkhan depression. On its continuation there is Pri-Balkhan folded zone of the west Turkmenia. Balakan-Vandam uplift exposes near the foothill of the southern slope of the Greater Caucasus. It is the northern near-flank structural element of the Trans-Caucasian plate. Basement and Alpine volcanogenic-sedimentary complex of the uplift are moved far northward, under the southern side of the Southern Slope, putting Zakatala-Kovdag-Sumgayit zubzone of the latter one into the paraaautochthonous position. Balakan-Vandam tectonic zone represents a geoanticlinal uplift. In its arc the formations of volcanogenic Bajocian and Neokomian flyschoids expose there, sides are composed of volcanogenic-sedimentary complex of the Upper Cretaceous complicated by comb-like foldness. In interfluve of Girdimanchai-Aghsuchai the Mesozoic core of Balakan-Vandam uplift closures (flexural submerge) on the Girdimanchai right-displacement zone of cross faults. On its south-eastern continuation a wide Shamakhy-Jeirankechmez depression opens, mainly composed of terrigenous-clayey sediments of the Paleocene-Pliocene. The latter are gathered into small sharp and isoclinal folds often overturned southward. The depression northern flank is blocked by Baskal-Pirekishkul allochthonous complex of schtiritc and attic phases of tectogenes, composed of deposits from the Aptian till Miocene inclusively and moved off the limits of Zakatala-Kovdag-Sumgayit zone with amplitude 25 km and more. On the east the allochthonous complex submerges under the Pliocene-Quaternary deposits of Apsheron periclinal trough. Southward from the overthrust front the gentle upthrust of rodan phase of foldness (the Middle Pliocene) complicate the inner structure of Shamakhy-Jeirankechmez trough, practically leading to double of the Cenozoic deposits thickness. At the same time in valakh phase of tectogenes the trough southern flank tectonically cuts the northern flank of the Lower-Kura depression with allochthonous ceiling amplitude reaching 15-20 km and more along Ajichai-Alyat upthrust. 1.3.2.2 Kura intermontane depression Kura depression takes the eastern more submerged part of the Trans-Caucasian plate and represents within the shore zone of the Lower-Kura trough. On the east Kura depression hoes into the sea opening and deepening. Pre-Jurassic basement of Kura depression undergoes the step submersion from flanks to axial line and from the west to the east. Depression is the superposited structure because the sedimentary cover, consisting of molasse series, blocks unconformitly the sedimentary and volcanogenic complexes of different age of the Mesozoic and Paleogene dislocated sediments. Lower-Kura depression is cut off the more western Middle Kura depression by zone of West-Caspian submeridional fault. Talysh-Vandam Mesozoic uplift is confined to the latter one. On the Mesozoic uplift the Cretaceous top occurs on depth 3000-3500 m, and the Pre-Jurassic basement - about 9000 m. Within Lower-Kura depression the Mesocenozic thickness increases sharply towards Caspian shore up to 16-20 km, from which about a half is on share of the Pliocene-Quaternary complex. Lengebiz-Alyat zone of uplifts, restricted by Ajichai-Alyat upthrust, is the north-eastern margin of the depression. Some anticlinal and synclinal structures are distinguished under the recent deposits in the depression cross section. At the same time the tectonic tension increases with depth. Anticlinal lines are complicated by lengthened upthrust-overthrusts. 1.3.2.3. Mountain Talysh The Mountain Talysh zone locates in lane of lateral transition from the mountain-folded system of Iranian Elburs to the Lower-Kura depression and represents a paleorift superposited on the Cretaceous volcanic island-arc of the Trans-Caucasian plate southern flank. Middle and Upper Eocene subalkaline and alkaline volcanites of the andesit-basaltic composition play a main role in Talysh tectonic zone. Paleocene-Lower Eocene tuffogenous flysch and Dutch limestones come out the volcanites on the south. Within the folded system of the Mountain Talysh one can distinguish the following from the south to north: 1 - Astara uplifted composed of the Cretaceous-Paleocene; 2 - Kosmolyan-Lerik trough, composed of the Eocene; 3 - Burovar uplift, composed of the Upper Eocene and cut by Pre-Talysh deep fault on the north-east; 4 - Bilasuvar trough, composed of molasse of the middle and Upper Miocene; 5- South Mugan uplift buried under the recent deposits. These structures are characterized by moderate-compressed foldness, on the north-east complicated by upthrusts towards the Lower-Kura depression. 1.3.2.4. South-Caspian depression Generally the Caspian depression and the South-Caspian depression particularly are belonged to the superposited structures of the Earth crust, originating on the orogenic stage of Alpine folded area development. South-Caspian depression is in the system of Kura and Trans-Caspian intermontane troughs and separated by Apsheron rapids off the North-Apsheron (Middle Caspian) depression. The southern margin of the depression is Pre-Elburs trough in Iran. A sublatitudinal zonality is observed in the Earth crust thickness variations: it is maximal (45-50 km) in the southern and northern near-flank parts of the depression and reduces to 30-40 km in the central part, being the connected stage between Kura and Trans-Caspian intermontane troughs. Alpian sedimentary cover reaching up to 20 km in thickness, consists of 2 structural-matter complexes: the Mesozoic-Eocene and Oligocene-Anthropogen. Three zones of the different strike are distinguished in the structure of the Oligecene-Anthropogen formations of the sandy-clayey composition. These zones are caused by different ratios of structural plans of old and young foldness: Baku archipelago folded zone, zones of cross and latitudinal foldness. Anticlines can be divided into the inherited uplifts, consedimentational and diapiric folds, basically associated with ruptures and mud volcanoes manifestation. According to complex of the geophysical data three main zones are distinguished in structure of the buried Mesozoic-Eocene complex from north to south (Fig. 4). These zones are: Apsheron-Pri-Balkhan trough, South-Caspian uplift and Lenkaran-Gorgan trough. The first trough is the south-eastern continuation of the Greater Caucasus Southern Slope trough corresponded to the Mesozoic riftogenous marginal-marine basin between the Scythian platform and the Trans-Caucasian plate. The South-Caspian depression uplift is a sea continuation of the Trans-Caucasian plate and along the flanks it is complicated by Sangachal-Ogurchin (north) and Mil-Okarem (south) zones of the magnatic formations intensive development. These zones trace the axial parts of the buried continuations of Balakan-Vandam and Artvin-Garabakh island-arc uplifts accordingly. At last, Lenkaran-Gorgan trough reflects the location of formation of the Mesothetis Lesser Caucasus branch tectonically blocked on north and south. 1.3.3. MUD VOLCANISM Mud volcanism is closely associated with the tectonical, lithological, hydrogeological, geochemical, thermodynamic and other features of the depths and genetically a specific type of volcanism. It is confined to zones of the regional faults and alpine foldness and makes a unit genetic process of tectonics and oil-gas accumulations formation. There are about 240 mud volcanic shows in Azerbaijan from 700 modern mud volcanoes determined over the world. In Azerbaijan there are 202 onshore and 38 offshore shows (Fig. 5). The total volume of mud hill breccia of the separate volcanoes reaches some milliard m3. The summary volume of mud hill breccia only on the superconstructions of Azerbaijan main mud volcanoes is about 50 mlrd. m3 without accounting the periodical washing of islands of the mud volcanic origin and underwater banks, and also mud volcanic eruptions during the Neogene-Quaternary period. According to state of eruptive activity the mud volcanoes of Azerbaijan and South-Caspian water area are divided into: active (characterizing by one recorded eruption at least) and passive (the eruption of which were not recorded), and also the acting ones (characterizing by gryphon-mud hills activity), non-acting (characterizing by absence of gryphon-mud hills activity). More ancient eruptions are corresponded to V and X centuries and were observed in the South Caspian. But more or less systematic recording of paroxysms of their eruptions is since early XIX. Starting from 1810 there had been fixed about 200 eruptions of 74 modern continental and marine (island and underwater) volcanoes. At the same time 33 volcanoes erupted only one time, 25 volcanoes - 2-3 times, 16 volcanoes - 4 and more times; more eruptions falls to Lokbatana - 20 times! Intervals between separate eruptions of one and the same volcano is from some months up to 170 years and more. On the separate strong paroxysms of volcanoes eruptions the volume of emanated gases reach some milliard m3 (about 500 mln.m3 on average eruption), volumes of erupted hard rocks reach to some million m3 (about 0.5 mln.m3 on average eruption). Concerning the gryphon-mud hills activity. It is characterized by emanation of little (from 5-10, rare to some thousand m3 per day) quantity of hydrocarbon gases of various degree of waters mineralization (often accompanied with films or abundant oil shows) and fined rocks building salses, gryphons and mud hills bodies. Outbursts of volcanic breccia great volumes and blocks of different sizes during the mud volcanoes eruption shows the intensive generation and accumulation of great volume of hydrocarbon gases in depths under the strong pressure. The eruptions' periodicity proves an existence of uninterrupted flow of hydrocarbons into the eruptive apparatus, as a result of which the next eruption takes place when reaching the pressure critical point. Being the focuses of periodical gasodynamic unload of the sedimentary basins the mud volcanoes point to intensive generation of hydrocarbon gases in them and are reliable criteria of valuation of deep horizons oil-gas content. 1.3.4. ECONOMIC MINERALS The coastal zone is characterized by development of various types of economical minerals mainly hydrocarbons and building materials (Fig. 6). 1.3.4.1. Oil and gas Azerbaijan is one of the oldest oil producing regions worldwide. Oil industry had organized not only the economics structure, but had played a crucial role on all stages of the country economic industry the whole. Role and meaning of this industry in the country economic industry complex is still significant. For over 120-year history of oil production there had been discovered 68 oil-gas fields in country territory, including 42 fields onshore (only 8 fields of them are beyond the coastal zone) and 26 fields in Azerbaijan Caspian sector. 61 fields were in industrial exploitation, among them 40 onshore and 21 offshore fields. Degree of production of preliminary produced oil reserves is 87% onshore and 59% offshore. At present 33 oil-gas fields onshore and 16 offshore fields are under exploitation now. They are subdivided on the following oil-gas bearing regions (OGR): Apsheron, Baku archipelago, Lower-Kura, Shamakhy-Gobustan, Pri-Caspian-Guba (Fig. 7). The South-Caspian perspective OGR has a great potential. Here a significant volume of prospecting works are conducted there. Reserves distribution according to categories is given in Table 1-1. Total area of coastal parts which of interest for oil-gas search is over 50 thous. km2, of them 35 thous. km2 falls to Azerbaijan sector of the Caspian Sea. Oil-gas bearing regions with qualitative valuation of prognosticated resources take an area of 47.1 thous.km2, including 21.4 thous.km2 offshore. The main oil-gas bearing complex is the productive series (the Middle Pliocene) containing 81% of preliminary potential oil resources and about 90% of natural gas. In spite of high degree of investigation the productive series is still the main perspective complex and contains 72% of unexplored oil resources and 85.5% of natural gas. Table 1-1. Reserves distribution of oil+condensate and gas according to categories, %
Thus, the perspectives of geologic-prospecting works are not exhausted yet and about 30% prospective areas had not got a proven value because of weak geologic-geophysical investigation. Structures and oil-gas content of deep horizons of the developed and explored areas are not studied yet enough. In its turn these areas increase the reserve of raw material base of oil industry. At present the majority of onshore and offshore fields are in the late stage of development and characterized, since 1961, by reduce of hydrocarbons production, which up to 90s was compensated mainly by exploitation of explored offshore fields. But in 90s the tendency of reduction of hydrocarbons production totality was kept on and only starting 1997 the stable increase of indicators is observed. It is associated with intensification of the technological processes and of foreign investments in oil fields development. At present the contracts with leading overseas companies had been signed for joint prospecting and development of some prospective structures (onshore and offshore as well) and produced oil share. At the same time the expected total volume will be over 1.5 milliard t. of oil and 1 trillion m3 of natural gas. 1.3.4.2. Glassy sands Deposits of quartzy sands suitable for glass production are known in Guba and Apsheron regions as well and have the Neogene age. They are suitable for bottle glass, and after the enrichment - for window glass and thin ceramics. They also can be used while production of autoclave concrete and silicate brick. Total reserve of raw material is over 14 mln.t. 1.3.4.3. Benthonic clays Deposits of the benthonic clays have the Eogene age, locate in the North Gobustan on territories of Gobustan and Khyzy regions, differ with high quality and can be used as a raw material for drilling solutions, whitening of petroleum and vegetative oils, in metallurgic and other industries. Total explored reserves of 7 deposits are 82 mln.t. 1.3.4.4. Construction materials The coastal zone is rich with various fields of construction materials having considerable reserves. Cement raw material is represented by limestone deposit with reserves over 110 mln.t., clay deposit with reserves over 30 mln.t., which used in cement production on Garadag plant. Sawing stones are represented by limestones-shells of the Pliocene-Holocene age mainly located within Apsheron peninsula and Gobustan as well. Here 24 deposits with total reserves 202.5 mln.m3 are known. All these are developed at present. Facing stones are represented by Budug deposit of marbleized limstones of the Upper Jurassic age (Guba region) with approximate reserves over 6 mln.m3, and Gyulbakht deposit of detrital and sandy limestones, calcareous sandstones of the Pliocene-Pleistocene age, located in Gobustan with reserves over 9 mln.m3. Construction sands have a coastal-marine origin and located along the shore in Devechi region, Apsheron peninsula and the South-Eastern Gobustan. Totally 8 deposits with summary reserves over 38 mln.t. are explored and exploited. Clays for brick-tile production are explored on territory of Guba, Khachmaz, Siazan, Neftchala, Masalli, Lenkaran, Astara regions, and on Apsheron peninsula and Gobustan as well. Their age varies from the Oligocene to the recent one. Totally 24 deposits with summary reserves 60.8 mln.m3 had been explored. 9 deposits with production to 0.2 mln.m3/year are developed. 1.3.4.5. Iodine-bromine waters There had been explored and accepted for balance 5 deposits of iodine-bromine waters with total reserves 938778 thous.m3/year located on Apsheron peninsula and Neftchala region. Baku and Novo-Neftchala iodine-bromine plants act on their base. 1.3.4.6. Thermal waters There had been explored and accepted for balance only 1 deposit of thermal waters in Khachmaz region (Gusar-Devechi trough) with reserves 12500 m3/day or 4562.5 thous.m3/year which can be used for medical and industrial needs. 1.3.5. SEISMICITY The described territory is one of the more seismoactive areas in Azerbaijan, representing a zone of possible show of the destructive seismic events with effect 8 and more (hereinafter the shocks intensity is given according to scale MSK-64). During the historical period of time many earthquakes of different intensity (up to destructive ones) took place in this zone and adjacent regions. It was the reason to construct the first seismic stations "Baku" and "Balakhani" in 1903. At present there is a net of seismic stations to record local, near and distant earthquakes and to study the seismicity of shore zone (Fig. 8). They are equipped with seismographs of general, regional type and to record strong movements. During the period of instrumental observations (1903-1999) onshore and offshore 424 events with intensity 4-9 and magnitude 3.0-6.6 took place within coastal zone. Spatial-time analysis of Azerbaijan and neighbour territories seismicity allow judging about the seismic activation in region and predict the further seismicity growing. In this connection there increases a possibility of strong and destructive earthquakes' appearance, including the territories considered before as weakly-active. The available seismogeological and geologic-tectonical information allow divide the continental part of the described territory into two seismic hazard areas: 1) high mountain areas and the southern slope of the Greater Caucasus (including more seismoactive Shamakhy area) where earthquakes with magnitude (M) to 6.1-7.0 and hypocentres within 1-15 km (to 75% of seismic events) take place; 2) area covering the south-eastern submersion of the Greater Caucasus (including Apsheron peninsula), Gusar-Devechi and Kura depressions, Mountain Talysh where the depth of much earthquakes is within 21-50 km (over 60%), and magnitude doesn't exceed 4.5. National sector of the Caspian Sea water area is characterized by very uneven spread of the earthquakes focuses. The increased density of focuses is concentrated in zone of Apsheron rapids uplift, about 160-170 km southward from Baku. Within the North-Apsheron (Middle Caspian) depression the focus area are characterized by less density, and the separate focuses of the earthquakes are typical for the South-Caspian depression. Hypocentres are spread in wide range of depths - from 5 to 80 km with magnitude reaching 6.5-6.6. Region seismic activity onshore and offshore as well is associated with continuing intensive re-construction of the structural plan with significant amplitudes of the newest and modern movements. The carried out researches lead to conclusions that periodically activating focus areas of strong and moderate earthquakes are confined to the Earth crust faults, having "general-Caucasian" (NW-SE) and "anti-Caucasian" (SW-NE) strike. At the same time the hypocentres mainly concentrate within and exocontact parts of two submeridional zones - South-Caspian-Apsheron and Talysh-Samur having 80-100-km width. Proceeding from available seismological information some maps of various usage had been compiled for Azerbaijan territory including the coast zone and the national sector of the Caspian Sea. These maps are as follows: 1) general seismic zonation, 1989 (Fig. 9); 2) general isonet of strong earthquakes for 427-1978; 3) epicentres and seismic activity A10 for 1859-1965 and 1951-1982 (Fig.10); 4) Kmax of maximal possible earthquakes for 1951-1982 (Fig. 11); 5) prediction of long-term seismic activity on AT and Ag ; 6) long-term prediction of maximal possible earthquakes Kmax; 7) earthquakes epicentres M>5.1 for 1939-1982, zones of possible strong earthquakes appearance (AIC) and semsic zonation; 8) seismic shacking, etc. Based on materials on the geologic-tectonical zonation, deep structure, newest and modern movements in correlation with available seismological information there had been conducted a separation of the described territory into the seismotectonical (seismoactive) zones and a scheme of region seismotectonical zonation had been compiled (Fig. 12). Reference
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