ISSN 01458752, Moscow University Geology Bulletin, 2014, Vol. 69, No. 1, pp. 11–16. © Allerton Press, Inc., 2014. Original Russian Text © L.V. Panina, V.A. Zaitsev, 2014, published in Vestnik Moskovskogo Universiteta. Geologiya, 2014, No. 1, pp. 17–23. The Recent Tectonics of the Caspian Sea Region L. V. Panina and V. A. Zaitsev Department of Geology, Moscow State University, Moscow, Russia email: [email protected] Received May 28, 2013 Abstract—Recent uplifts and depressions complicated by lineaments, many of which are faults, were found within the Caspian depression using complex structural and geomorphological studies, which included visual interpretation of differentscale topographic maps, as well as an analysis and computer processing of radar satellite images. In many respects, the latest dislocations correlate with the structures and sedimentary cover of the basement and are also determined by salt tectonics. Their formation is substantially influenced by the Ural Orogen and the Scythian plate is involved in the entire uplift at the latest stage. Keywords: recent tectonics, structural and geomorphological analysis, radar image, lineament, fault DOI: 10.3103/S0145875214010074 INTRODUCTION most elevated structure (with occurrence depths down to –8 km) in the tectonic map of the basement (Inter The Caspian depression, which is located in the national map…, 2003) is the Astrakhan–Aktyubinsk southeast of the Russian plate, is part of the entire system of block uplifts, which is confined to the Cas Caspian megadepression, which also includes the pian Sea and further extends along the eastern periph depressions in the Middle and Southern Caspian. Tec ery of the Caspian depression. The most subsided por tonically it corresponds to the East European platform tions are the Central Caspian depression and the syneclise of the same name, which is the structure with Sarpin downwarp with basement occurrence depths the most subsided basement. The area under study down to –22 km. The thick sedimentary cover formed covers the Caspian Sea region that is traditionally during the long–term downwarping of the Caspian called the Caspian lowland; it underwent negative Sea region consists of the presalt Paleozoic–Early movements during the entire Phanerozoic. Its recent Permian, saliferous Kungurian and abovesalt Upper relief is a poorly broken plain with the dominant abso Permian–Cainozoic complexes. These rocks form lute marks of <100 m down to negative values of –28 m rootless folds complicated by diapirs and ruptures that increasing to the eastern periphery to 200 m and frequently inherit the basement faults. greater in the area of the Underural plateau. In the The recent structure of the Caspian depression has north and northwest, the boundary structures are the been studied by many scientists, including I.P. Gerasi recent uplifts that develop on the slopes of the Volga– mov, Yu.A. Meshcheryakov, V.S. Zhuravlev, and Ural and Voronezh anticlises, in the west and southwest L.B. Aristarkhova. Many dislocations of the Caspian they are the structures of the Scythian plate, such as the Sea region are not shown at the 1 : 5000000scale neo Yergeninskoye uplift and the zone of subsidence of the tectonic maps edited by N.I. Nikolayev and Karpinsky ridge, and in the northwest, the near Volga A.A. Naimark (1979), and by A.F. Grachev (1998) due uplift. The northeastern margin is the Obshchiy Syrt to their small scale. The latest geological–geophysical uplift, and the eastern one is the structures of the pied data and the materials of the satellite images, in partic mont downwarp of the Ural Mountains. In the south, ular, radar images, and the procedures of their pro the lowland is bounded by the Caspian Sea depression. cessing, created a necessity for new studies that would According to the recent studies, the occurrence substantially expand the concept of the regional tec depth of the basement in the Caspian depression tonics. The purpose of this work is to study the recent reaches 22 km and the basement itself is a series of tectonics of the Caspian depression using the latest blocks of continental crust that were consolidated at materials and procedures for their processing. different times and separated by the zones of long Procedures of studies. It is always difficult to carry existing faults (Astrakhanskii…, 2008). The Archean– out a structural and geomorphological analysis under Proterozoic, the oldest age of the basement, is identi conditions of flat and poorly broken relief. Developing fied for the Central–Caspian block; southward within structures are traditionally discovered by indirect geo the Eastern Caspian geoblock the basement is morphological features, such as contouring of uplifts younger, viz., the Late Proterozoic–Riphean. The by river valleys and erosion depressions, a typical radi 11 12 PANINA, ZAITSEV ally divergent pattern of a hydrographic network, a Ink submontane trough in the east, which is developed change in the slopes and elevations of a relief, a reduc by the valley of the Ink river. Located in the east, the tion in lake areas, etc., which are not always shown in Orenburg uplift (12) is confined by the Sakmara and the topographic maps and ordinary spectrozonal satel Ural nearfault troughs in the north and south, respec lite images. The use of radar images significantly tively (Naumov, 1981). Partial dislocations are identi expands the possibilities for interpreting a flat relief. fied within these first rank structures, which tend to The Global Mapper software makes it possible to rise in general. identify an erosion network via radar images; when The Caspian depression itself is also complicated generalized, it provides a better view of the structures by uplifts of different ranks and amplitudes. Among that are weakly reflected in the relief. Therefore, the them there are highamplitude uplifts with the abso structural and geomorphological interpretation of the lute marks of 100–250 m; lowamplitude uplifts, topographic maps and Landsat7 spectrozonal satellite whose relief altitudes are no more than 100 m, as well images is supplemented by a visual analysis of detailed as buried uplifts that are not reflected in the relief. The radar images that allow detection of buried structures highamplitude uplifts are confined to the northern in the areas that have negative values of the relief’s and eastern peripheries of the Caspian depression. As absolute marks. This especially concerns the central a rule, they are structures that are somewhat elongated part of the Caspian depression, which has been sub in the sublateral and submeridional directions, are jected to substantial downwarping in the latest period separated by narrow valleylike troughs, and corre from the Oligocene until recently. spond to the relatively elevated zones of the basement: the Astrakhan–Aktyubinsk system of uplifts and the ASTER GDEM radar images were also automati TransVolga PreUral fault zone in the east and south cally processed by the LESSA and Global Mapper east, respectively, as well as the northwestern flank in software. The LESSA software, which was developed the north. The occurrence depth of the basement roof by A.A. Zlatopolskii (Zlatopolskii, 1998), automati ranges here from –4 to –10 km. It is important to indi cally detects watersheds and valleys as socalled dashes cate the increase in the contours of the recent uplifts as and calculates their statistical characteristics in a slid compared to the structures of the basement of the ing window. As well, it can determine the general den same name (Ashchikolskoye, Enbekskoye, and sity of dashes, the density of dashes of different direc Karaulkel’dinskoye). tions, create rose diagrams of the distribution of Lowamplitude (up to 100 m) and buried uplifts are dashes by their directions, and obtain the degree and confined to the central western and southern parts of direction of the elongation of rose diagrams and other the Caspian depression (Fig. 1). A few of them, viz., parameters. A pattern of lines of elongation in the rose Munailinskoye (44) and Opornoye (45), are located in diagrams was constructed for the relief elements with the southeast. The uplifts, as a rule, have an isometric an averaging window of 135 km, which was further shape that may be determined by salt diaperism. compared to the results of the structural and geomor Among them there are the Chkalovskoye (47), Yustin phological interpretation and dislocations of deep skoye (49), Oktyabrskoye (52), Bulukhtinskoye (53), structural plans, mainly of the basement surface. The and Eltonskoye (54), which develop on the western data that were obtained as a result of such complex and northwestern Caspian slopes, and the structural and geomorphological studies were com Yulayevskoye (61), Shalkarskoye (62), and Buldyrtin pared to the geological and geophysical materials. skoye (63), which are confined to the central part of Recent tectonics. The structural and geomorpho the depression. logical studies showed that the Caspian depression The Azhbaiskoye (56), Taldykudukskoye (57), bounds a series of the recent first rank uplifts with an Satybaldukskoye (58), Kozhantaiskoye (59), Mokrin amplitude ranging from 150 to 400 m (Fig. 1). Some of skoye (60), and other uplifts are developed within the them develop on the young Scythian and Turanian Central Caspian depression, which is the most sub plates (Yergeninskoye, Donyztausskoye, Turushskoye, sided with respect to the basement (down to –22 km) et al.); the others develop on the slopes of the Voron and are inversion structures. The radar images in the ezh and VolgoUral anticlises of the ancient East south of the Caspian depression revealed a series of European platform (nearVolga, Mokrousskoye, Pere buried uplifts, which in general correspond to the lyubskoye, Sorochinskoye, Nazykskoye, and Oren uplifts of the Astrakhan–Aktyubinsk system base burgskoye) and some form a system of uplifts within ment. The buried uplifts located there, viz., Astra the PreUral foredeep (Chebogarovskoye, Kuvandyk khanskoye (73), Northern Caspian (74), and skoye, and Poltavskoye).