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| Figure 1 |
[8] At present Kerch-Taman depression is an area with the greatest abundance of mud volcanoes in the northern Black Sea coastal region. All known forms of mud volcano manifestations are found there: continental and marine, buried and exposed, extinct and active. Mud volcanoes and diapirs are grouped in anticline zones forming extended lines of ranges running to the Black Sea water. It is interesting to note that those anticline zones with general subparallel extension are abruptly cut by faults locating the borders of Kerch-Taman depression and specifically submeridional Dzhiginskiy fault. Diapir-forming complex in Kerch-Taman mud volcano province is a 3-4-km thick rock bed of Maikopian clays, which form mud volcano constructions and accumulate considerable amounts of coniform hill breccia. Diapir bodies forming a number of extended anticline zones close to parallel are linear clayey walls with symmetrical axes that, in structural geology terms, form in fact the injection filling of the system of extended syngenetic faults combined in an echelon-like manner, which are apparently separations as far as kinematics is concerned. Paragenesis of such ruptures (diapir walls - anticline zones) embraces the total Kerch-Taman province and is sharply limited by its borders. This fact is remarkable and apparently reflects features of late orogenic deformation of the thick body of Maikopian clays of the depression under consideration. The specified characteristics of the clayey-diapir formations mentioned above suggest shear stress distribution in lateral plane with respect to the complex being deformed. This assumption is to the point if we take into consideration echelon-like framing of the clayey Maikopian body of Kerch-Taman depression with the rigid blocks of the northern Taman spur in the northwest and Anapa spur in the southeast, which may produce shearing stress. This is corroborated by data on seismogenic ruptures orientation in the region in the upper area of the earth's crust [Pustovitenko and Kapitanova, 1997] with account for the directions of their cutting open. The general character of the structural relations described above allows us to define them as pronounced of Ridel paragenesis and to treat the system of clayey-diapir walls of Maikopian bed of Kerch-Taman depression as a wide zone of left lateral shift deformations.
[9] Considering the above-said it is reasonable to conclude that the total bed of Maikopian clays of Kerch-Taman depression reacts as a single whole to the applied force and the stress field formed by it, which caused the start of the processes of clayey diapirism and finally the appearance and development of mud volcanism. Volcanoes were most active in the Chokrakian, the Sarmatian, and the Kimmerian [Shardanov et al., 1962]. It is interesting to note that in the history of northwestern Caucasus and adjacent Ciscaucasia, these periods were associated with maximum manifestations of planation processes [Viginskiy, 1986] that completed tectonic cycles and immediately preceded the abrupt activation of tectonic movements in the Caucasian orogen. In this context, we may assume that mud volcano processes are of cyclic character owing to tectonic settings in the province under consideration. In this case the modern stage of mud volcano activation apparently started in the Kimmerian, which approximately corresponds to the age of Taman Peninsular [Viginskiy, 1997b].
[10] Oil and gas deposits located in Miocenic sediments are associated with clayey diapir structures of Taman Peninsula. Producing horizons are found in areas: Borisoglebskaya, Zaporozhskaya, Blagoveshchenskaya, Dzhiginskaya, Zapadno-Akhtanizovskaya, Severo-Neftanaya, Strelchanskaya, Belyi Khutor, Kapustina Balka and others. Mud volcanoes are located at some of the anticlines noted above.
[11] In the past in a number of mud volcanoes of Taman, repeated explosive-type eruptions were noted and here the high activity was most commonly observed in the last few decades. They are mud volcanoes Akhtanizovskiy, Mt. Karabetova, Shugo, Gladkovskiy, Mt. Gnilaya, Mt. Borisa and Gleba and sea volcanoes Golubitskiy, Temriukskiy and others, in the latter two volcanoes outbursts were noted that resulted in island formations in the sea. Earlier the outbursts were commonly accompanied by the release of explosive gases, probably hydrocarbon (hill Gorelaya). Among other things this phenomenon marks the activation of hydrocarbon generating processes in the eruptive deformation of Maikopian sediments saturated with organic matter. Such development is emphasized by the structural position of known deposits, which at least characterizes their Post-Kimmerian formation and, in our standpoint, accounts to a large extent for their location features.
[13] The axial part of the depression approximately coincides with the course of the Kuban riverbed. Approximately in the axial plane of the depression, Anastasievsko-Krasnodar anticline zone is located, which is a long clayey-diapir wall locally echelon-like, locally broken and locally crowned with mud volcanic formations (Kurchanskiy and Anastasievsko-Troitskiy). Other manifestations of mud volcanism are only recorded in this province in the southern area along Akhtyrskiy reverse fault and are characterized by distinct features of gravitational northern vergence [Burshtar et al., 1969].
[14] Generally Indol-Kuban province is characterized by significantly less abundant and much less pronounced manifestations of mud volcanism as compared to Kerch-Taman province discussed above. Three mud volcanoes are located at Anastasievsko-Krasnodar anticline zone and six mud volcanoes are situated at the folds of southern side of western Kuban depression (Figure 1). These mud volcano formations are associated with the development of clayey diapirism in the trough, which is apparently of arch origin [Burshtar et al., 1969; Grachev, 1998] and in the axial part is probably caused by gravitational pressure of Maikopian clayey mass at the walls of the depression. This assumption is corroborated by the abundance of pillow-form clayey cryptodiapiroids in the northern gentle slope of western Kuban depression [Viginskiy and Gromin, 1995]. In this case, a feature of intradepression clayey diapirism is its apparent linear confinement to the zones of large deep faults: Akhtyrskiy, Timashevskiy (pillow-form cryptodiapir) and assumed Zapadnokubanskiy fault, which may be intruded by hyperbasite [Viginskiy et al., 1988], that is positive linear magnetic anomaly. This fact can serve as a basis for the assumption of the triggering role of dislocations with a break in continuity in complexes underlying the diapir-forming layer.
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| Figure 2 |
[16] Especially interesting is oil and gas presence in the deposits overlying Maikopian deposits of cryptodiapiroid deformations band of the western Kuban depression northern side. Hydrocarbons are confined there to the Middle Miocene (gas condensate) and Upper Miocene-Lower Pliocene complexes (gas in Meotian-Pontian). In both cases, there is reason to assume a Maikopian source of hydrocarbon migration to deposits. The paths of such migration could have been subvertical faults, which, as a rule, reach the upper horizons of the sedimentary cover as fissuring or thinning zones [Viginskiy and Gromin, 1995].
[17] A significant feature of clayey-diapir formations of the province under discussion as well as of Kerch-Taman province is their active development at the recent stage. This is supported by both manifestations of mud volcanism and pronounced cryptodiapir folds in the topography (with marked weak capability of rocks composing them to stand denudation). In some cases, when we deal with cryptodiapiroid, we can easily reveal modern activity from Holocene sediments facial replacement. Activity of this kind as well as the empiric relation between maximum hydrocarbon resources in deposits and immediate contact of the latter with Maikopian core of the diapir tearing them (mud volcano vent) or wide development of tearing channels running from the core to the deposit suggest processes of recent oil and gas formation. Considerations of this kind are also supported by cases common in the last few years of flows from abandoned boreholes of the exhausted area of Kiev-Raznokolskaya band of deposits (locally after a rest period of 30-50 years).
[19] Maikopian beds are overlapped with a cover of Miocene-Quarternary sediments. In modern time owing to the Black Sea deep basin, Tuapse depression is drawn into the zone of progressive downwarping of the basin and is broken up as a preorogenic depression. Considerable deformation of Maikopian orogenic complex and post-orogenic sedimentary complexes of Tuapse depression [Viginskiy, 1997a; Viginskiy et al., 1997] is apparently caused by the structural position of the sedimentary body under the studiy on the slope of the Black Sea abyssal basin, which is being formed, and by Maikopian plastic clayey bed sliding to the basin center [Viginskiy et al., 1997]. The more active process went on from the beginning of the neotectonic stage when Tuapse depression was drawn into the process of the Black Sea basin formation and reformed in the deep-sea basin conditions causing active subsidence of the Black Sea basin floor.
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| Figure 3 |
[21] The assumed mud volcanoes are characterized by anomalous seismicity record in the form of a hill of chaotic reflections at a conventional boundary from where the inphase state regular axes stop to be traced (Figure 3). Such form of record was identified with clayey diapir with sufficient reliability; forms like this are revealed in the northern half of the profiles up to the structure line limiting the prevalence of intensive deformations of sediments overlying Eocene bed. As for seismic horizon "B" (Sarmatian sediments top), these forms are either enveloped in it or underlain it, locally they tear off the horizon and are traced to the floor surface. In the latter case they were interpreted as mud volcanoes. Nine exposures of the floor in the surface were recorded (Figure 1). Most northern mapped mud volcanoes are located at the sea floor depths of 1800-1900 m and northern volcanoes are at the depth of 1200-1400 m. Apical parts of clayey diapirs are revealed at depths ranging from 1500 m to 2800 m.
[22] Morphologically the assumed mud volcanoes are objects weakly manifested in the topography and characterized with exposures on the sea floor surface of head parts of Maikopian clayey diapirs. A likely explanation of missing cones of breccia in the relief is in the undersea position of assumed mud volcanoes, which provide high mobility of erupted mass apparently forming extensive mantle-form "covers" characterized by a random-layer pattern of seismic record similar to a record pattern typical of submarine landslides. The form of diaper-forming complex injection, that is Maikopian diapir body can vary from classical channel-like form to mushroom-shaped form fixing the break through of the extended head part of Maikopian "scales" forming upthrust hanging sides on the sides thrusted under gravitational folds.
[23] It is interesting to note that in spite of the fact that mapped mud volcanoes are located at pronounced clayey diapir walls extended for tens of kilometers (gravitational "scales"), as it was mentioned above, they are spatially organized in line structures with orientation different from diapir ridges extension (Figure 1). In the western part of the depression, a line of northeastern strike is pronounced, which apparently fixes the marine continuation of Krasnodar fault transverse to western Caucasus fault. The heat flow contrasting anomaly, which did not receive any explanation until recently coincides with this line [Grachev, 1998; Viginskiy, 1997a]. In the northern area of Tuapse depression, the assumed mud volcano formations evidently retain the linearity caused by the structural plan of gravitational diapir folding. One more structural line cutting the strike of Tuapse depression is formed by volcanoes St. Voskreseniya, St. Vitalia and Velesova Pad' (Figure 1). It is characteristic that on its continuation on land (northwestern Caucasus) it is located at structural forms testifying to active shifts on it. Earlier this fact allowed the authors [Viginskiy et al., 1998] to separate active neotectonic Shepsinskiy fault (Figure 1).
[24] Thus in this case as well as in the mud volcano provinces described above, faults in the bed underlying the major diapir-forming complex to a large extent have the role of controlling mud volcano activity. At the same time a characteristic feature of Tuapse province is the discordance of the disjunctive structure of the base under diapirs and the inner structure of complexes dislocated by clayey diapirism processes. This fact emphasizes secondary tectonic origin [Shults, 1979] of clayey diapirism and correspondingly mud volcanism of Tuapse depression. Evidently tectonogenic air lift does not take place in this case and therefore its manifestations seem doubtful in other situations either.
[25] We can estimate the role of Tuapse province mud volcanism in oil and gas geology only from general considerations. As it is known the prevailing part of mud volcanism manifestations is genetically associated with structures bearing oil and gas. Similarly to mud volcano provinces described above, possible manifestations of mud volcanism of Tuapse depression initiated by Maikopian clayey diapirism suggest that the water area under investigation is favorable for searching for considerable hydrocarbon deposits. The more so, that there are good foundations for such statements [Meisner et al., 1996; Viginskiy et al., 1997]. At the same time areas of wide-spread direct manifestations of mud volcanism are less interesting because the conditions of conservation are partially upset. Besides as the research in the conditions of deformation of Tuapse depression complexes overlying Eocene complex showed [Viginskiy et al., 1999] the development of mud volcanoes activity is related to the active change of volumes with sedimentary base deformation (Figure 1). In this connection, most favorable conditions of elite oil and gas presence are found in beds that show deformation that is uniform (without volume variation) or close to it. Such areas are located out of the zones of mud volcanism intense manifestations or are close to them.
[27] Mud volcanoes of the Caucasus province are revealed in the band where Lower Cretaceous and Jurassic sediments for the major part clayey are abundant. All of them are confined to faults on conjugation with anticline faults. The latter are complicated by regional faults of the general extension of the Caucasus. It can be seen most evidently from the example of Semigorskaya anticline zone, which is apparently of diapir origin, confined to a fault of the same name; four of six mud volcanoes of the province known at present (Semigorskiy, Manzhosova, Khomiakova, Beregovoy) are located on the fault at its considerable length.
[28] Mud volcano manifestations are for the major part small cone-form structures of a height of up to 1.0-1.5 m. The diameter of the largest gryphon in Shapsugskaya village (mud volcano Manzhosova) reaches 3.5 m. Mud cone sediments make breccia of clays of black color with fragments of sandstones and siderite exposed in steep slopes of the ravine pattern in the area of the volcano. Mud cone breccia apparently dates back to the Jurassic-Lower Cretaceous (the mud-forming complex is Jurassic-Lower Cretaceous flysch).
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| Figure 4 |
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| Figure 5 |
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| Figure 6 |
[31] The studies of the mud volcanoes structure of the Caucasus province allow us to conclude that they are formed of Jurassic-Lower Cretaceous clayey stocks and are evidently the result of compression thick Jurassic-Lower Cretaceous clayey (terrigenous flysch) beds, which may develop "in passing the chord" as a result of isostatic floating of the orogene construction of northwestern Caucasus (by the type of F. V. Meinesz tectogene).
[32] It is interesting to note that active mud volcanoes in the province are characterized by noticeable manifestations of increased concentrations of such useful components as mercury and hydrocarbons. Thus anomalous cinnabar ore manifestations accompanied by increased bitumoid content (Voskhod and Aprelskoye) are associated with mud volcano Manzhosova; mud volcano Poleshchuka controls similar ore shows of Adova Shchel. This is not surprising that mercury and hydrocarbon in combination occur in anomalous concentrations in mud volcano activation zones in the Caucasus mud volcano province. Similar facts are noted in Kerch-Taman and Indol-Kuban provinces (mud volcanoes Borisoglebskiy and Shugo respectively). This stable bimodal mineragenetic combination (with different weight ratios of useful components) in mud volcanism zones suggests its paragenetic dependence. These paragenetic correlations are apparently associated with deformation processes activation up to maximum level with forming mud volcanic structures and reflect miragenetic zonality manifestations in the lateral distribution of useful minerals [Viginskiy et al., 1997]. In this case, typically metallogenetic zones of meganticlinorium, which in fact are areas of erosional truncation, are followed by areas of bitumen manifestations commonly enriched with vanadium, nickel, cobalt and others [Kandaurov, 1995].
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