ISSN 00978078, Water Resources, 2012, Vol. 39, No. 6, pp. 640–647. © Pleiades Publishing, Ltd., 2012. Original Russian Text © A.A. Svitoch, R.R. Makshaev, 2012, published in Vodnye Resursy, 2012, Vol. 39, No. 6, pp. 590–597.
WATER RESOURCES AND THE REGIME OF WATER BODIES
Hydrological Benches on Manych A. A. Svitoch and R. R. Makshaev Moscow State University, Moscow, 119991 Russia Email:
[email protected] Received May 31, 2011
Abstract—The structure and development of hydrological benches, which regulate water discharge from Caspian transgressions into the Black Sea are considered. Keywords: Manych straits, benches, development history, Pleistocene, PontoCaspian DOI: 10.1134/S0097807812060061
INTRODUCTION The Manych depression, extended in latitudinal direction and lying between the Caspian Sea and the Black Sea, in Pleistocene repeatedly served as a dis charge site for waters of Caspian transgressions into pontic basins. By now, reliable signs of existence have been found for four straits: bakinskii (~500 thous. years ago), early khazarian (~250), late khazarian (~100), early khvalynian (~12 thous. years ago), as well as burtasskoe lake, which discharged into the Azov water body and Prikaspiiskaya Lowland. The bed of the straits is uneven, governed by the structural fea tures and neotectonic regime of Manych flexure. The lower areas are confined to local depressions, while higher areas to tectonic highs. In the epochs of Cas pian transgressions, the highs of depression bed served as benches, regulating the opening and closing of straits and the entire system of Caspian water dis charge into the Black Sea. G.I. Popov [10] was the first to turn attention to this circumstance, and D.D. Kva
sov [6] evaluated the volume of annual discharge at 90 km3. DESCRIPTION OF BENCHES In the history of Manych straits, the first reliable signs of the existence of benches were found in the structures of ZundaTogla and Sal’skii swell (Fig. 1) [6, 10, 11]. They are determined by the following fac tors: the positive deformation of the base and roof of the reference horizons of marine deposits relative to the nearby areas of depression (Fig. 2) less the values of deformation of all subsequent epochs; the presence of deep incisions, detected in paleorelief, and an increase in the thickness of sediments; the presence of traces of interruptions and erosions; the features of geomorphological and geohydrological structure of areas.
n Do
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Fig. 1. Schematic map of Manych benches. (1) ZundaTogla, (2) Sal’skii, (3) ManychBalabinka.
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m 10 0 –10 –20 –30 –40 –50 20 10 0 –10 –20 –30 –40 –50 10 0 –10 –20 –30 40 30 20 10 0 –10 –20 40 30 20 10 0 –10 –20 –30 м
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Fig. 2. Hypsometry of (1) the roof and (2) the bed of reference horizons of Pleistocene straits in Manych: (A) bakinskii–late chau dinskii, (B) early khazarskii–ancient euxine, (C) late khazarskiikaraganatskii, (D) burtasskoe lake, (E) early khvalynian. (1) Established (full line) and supposed (dashed line) position; (2) the direction (sign) of deformations; (3) reference geological pro files [10]; (4) benches: (I) ManychBalabinka, (II) Sal’skii, (III) ZundaTogla.
ZundaTogla Bench ZundaTogla bench is situated in the eastern part of Manychskaya depression. Structurally, this is a tec tonic high, separating the ManychGudilovskoe and KumaManychskaya depressions. In the relief, the high is marked by outcrops of Lower Sarmatian lime stones. Geomorphologically (Fig. 3), this is a narrow (2–15 km) ridge of bars with steep sides, which repeat edly served as a bench in the flow of waters of Caspian transgressions through Manych into Azov–Black Sea basin. The available materials on ZundaTogla [10, 11] allow us to adequately describe the structure and development of the bench in the Pleistocene straits of Manych. Its typical features are deep incisions filled with various aqueous and continental deposits, which form “plugs” (Fig. 4). The largest (70 m in depth) incision at ZundaTogla was established before the early khazarian epoch, and it seems to have been asso ciated with the existence of a high bench and with the low position (–30 m) of the bed of the Manych depres sion. Another deep (30 m) and narrow (1 km) incision WATER RESOURCES
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occurred in the postkhvalynian time, seemingly, because of river erosion of paleoKalaus R. The formation of incisions took place mostly in the beginning of the flow of ancient Caspian waters when the transgressing sea reached and tided over the bench. Obligatory conditions for the formation of incisions were the presence of a bench and a dynamic water flow. In this case, the energy of flow could be due to differ ent causes: the steepness of the bench, an abrupt drop in sea (water body) level, active neotectonic elevations of the bench or sinking of the adjacent depressions. The incisions of ZundaTogla in the epochs of attenu ation of erosion (abrasion) into strait beds and after their closing were rapidly filled by various sediments, which formed “plugs,” i.e., the benches of the future straits. The plugs in their base and the lower part are composed of marine deposits of previous straits, and rarely, by sediments of flowthrough lakes. The formation conditions of the upper parts of the plugs, which determine the height of the bench, are not clear. According to [1], plugs at ZundaTogla formed because of the protrusion of the delta of paleo Kalaus R. This assumption contradicts to the follow
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III
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Fig. 3. Geomorphological scheme of ZundaTogla bench. (1) The bed of straits; (2) waterdivide slopes; (3) water divides; (4) territorial areas: (I) ZundaTogla, II Caspian depression. (III) ManychGudilo depression.
ing considerations: in the presence of a through valley, plugs would not form; in the Lake Pleistocene, the bed of the paleoKlaus R. never lied at elevations of the khvalynskii bench (more than +40 m) but lied much lower than that (less than +30). The existence of plugs at ZundaTogla suggests the absence of through river valleys here in the past, so the paleoKlaus R. flowed westward over the slope of the bed of straits. The postkhvalynian bench, which can be seen now, is very young and poorly developed. After drying out of ancient straits, their bed at ZundaTogla was filled mostly by deluvial and ravine–gully forma tions, delivered from steep northern or southern slopes of the Manych depression and forming the upper part of the plugs. Nowadays, the sides of the Eastern Manych Valley are covered by alluvial apron 10 m and more in thickness.
A widely accepted opinion is that the ZundaTogla bench showed high neotectonic activity. According to G.I. Popov [10], the total amplitude of its elevation was 60–70 m in Pleistocene, 30–40 m in postearly khazarian time, 20–25 m in postkarangatskoe (late khazarian) time, 8–18 m in postburtasskoe time, and 5–10 m in postkhvalynskoe time. Using comparative assessment of the deformation (x) of the base of refer ence stratigraphic horizons, the authors of this paper have obtained radically different estimates of the mod ern activity of ZundaTogla [11]. They suggest that, overall, the ZundaTogla bench showed relatively low total deformation—of the order of +5–10 m. The maximal rise (up to 20 m) was recorded for burtasskoe time; this seems to be a cause of the formation of eth eastern bench of a burtasskoe lake, situated further westward in the ManychGudilovskaya depression. WATER RESOURCES
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Fig. 4. Scheme of incisions of ZundaTogla bench [11]. (1) Paleogeographic epochs: (A) early khazarian, (B) late khazarian, (C) burtasskaya, (D) early khvalynian, (E) late khvalynian; (2) supposed level of reservoirs (benches); (3) deposits filling inci sions; (4) supposed depths of incisions.
The history of ZundaTogla bench in the epochs of Caspian transgressions is assumed as follows. A wide strait was situated here in the Early Pleistocene. Judg ing from the hypsometric position of bakinskie marine deposits, the height of the bench was at elevations of about +40 m. At the beginning of the early khazarian transgres sion, the height of the bench in the strait reached +40 m of absolute elevation. After Caspian water tiding over it, a deep incision appeared, whose forma tion was accompanied by complete washing out of the Quaternary deposits that composed the bar, and the width of the strait in this period was not more than 2– 3 km. Later, at the stabilization of the level regime, the incision in the strait was partially filled by early khaz arian clays with sand interbeds and shells of index mol lusks Didacna pallasi and D. subcrassa. In Late Pleistocene, because of the low level of the late khazarian sea, the height of the bench at Zunda WATER RESOURCES
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Togla was not greater than 10 m. At the beginning of transgression, an incision formed with partial erosion of early khazarian deposits in the strait bed, and strait width was not greater than 5 km. The subsequent fill ing of the incision has resulted in the accumulation of a thick stratum of faciesvarying upper khazarian deposits. In the epoch of existence of a vast burtasskoe lake in Manych depression, its level in the central part of the water body was in excess of +40 m, judging from the height of ridges composed on lacustrine deposits. At ZundaTogla, where lake waters flowed into Prikaspiiskaya lowland, the bench of the water body was about +20 m. At the end of the Late Pleistocene, water of a short (3–5 thousand years) early khvalynian depression was discharged through the Manych into the neoEuxine water body of the Pontian. At the beginning of the overflow, the ZundaTogla bench had an elevation of
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45–50 m. This can be reliably established by the height of the abrasion shelf of the khvalynian sea along Erge nei slope. The width of the strait in this area was ~5 km. Judging from the reference section of khva lynian deposits at ZundaTogla [11] and drilling data [10], we can conclude that the filling of the incision– bed by sediments consisted of two stages: in a dynamic situation and under relatively calm conditions. The khvalynian strait was closed ~10.5 thousand years ago when the Caspian Sea level dropped below 30 m. The bench at ZundaTogla dried and entered the zone of subareal processes. A deep erosion incision formed in its northern part, where the lower khvalynian, bur tasskie, and upper khazarian deposits were eroded. Later, the bench incision was filled by a stratum of Holocene lacustrine–alluvial deposits. Now, the bench at ZundaTogla is situated at an elevation of +26 m in the bed of Eastern Manych valley. Sal’skii Bench The Sal’skii Bench lies in the western Manych depression. It is confined to the Sal’skii Swell, separat ing the WestManych and ManychGudilovskaya depressions. This bench was described by G.I. Popov [10], who noted that the amplitude of its Pleistocene elevations was 20–25 m, and the width of the strait did not exceed 20 km. At the end of Late Pleistocene, the bench hampered the penetration of surozhskaya fauna to the east [10]. Geomorphologically, this is a segment of the steep bed of Manych depression and an abrupt (up to 90°) break of the main channel of Western Manych R. valley (Fig. 5) with a change from south western to northwestern orientation. The bench, as a small elevation, certainly existed in the prebakinskoe time and in the beginning of the formation of bakinskii strait, when incisions of 15 m and more took place and it was filled with a stratum of Caspian deposits with a thickness twice as large as the coeval deposits in nearby parts of the depression. In the early khazarskaya epoch, a deformation of the base of the reference horizon by 3–5 m was estab lished along with the existence of a deep incision (down to 20 m), filled with a 40m stratum of lower khazarian deposits. In the following (late khazarian) time, the Sal’skii Bench was morphologically insignificant, it did not contain a considerable incision, and the thickness of the karangat–upper khazarskie deposits was half that in nearby depressions. The Sal’skii Bench seems to have not existed in the burtasskoe time. A vast lake bed, filled with a thick mass of silt–clay deposits, was situated in its place. No proofs of Sal’skii Bench existence in the epoch of khvalynian transgression are also available. Judging by drilling data [10], in that time, two small arms of
khvalynian strait were situated here; the incision and the thickness of sediments in them were less than 10 m. A hypothesis regarding the great role of Sal’skii Bench in the history of khvalynian Caspian Sea was suggested in [7]. It is substantiated by data on the existence in ManychGudilovskaya depression of many accumulative forms that appeared in khvalynian flow. Indeed, ridge relief forms are widespread here, though they have nothing in common with the khva lynian strait, but rather they represent prekhvalynian formations, composed of burtasskie lacustrine depos its—in the case of Manych, this is an axiom, estab lished in [2, 4, 5, 8, 10, 11]. There is no evidence for the existence of kvalynian bench in drilling data as well [10]. Thus, the facies composition of khvalynian deposits in the bench is not different from the compo sition of sediments in the downstream and upstream segments of the strait. ManychBalabinka Bench Geological and geomorphological materials [9– 11] suggest the existence of an elevation in the western part of Manych depression near ManychBalabinka and Spornyi settlements; this elevation served as a bench for some straits of Manych. Geologically, ManychBalabinka bench lies on the northern margin of Mechetkinskoe transverse elevation (identified in the midXX century by seismic exploration [12]), sep arating the Tuzlovskii and WestManychskii flexures. Earlier, before seismic exploration, they were identi fied in the composition of a single TuzlaManychskaya depression [3]. The bench can be clearly seen in the surface relief (Fig. 6)—it lies in an area of narrowing and abrupt (90°) change of the planar configuration of the valley of the Western Manych R. and, possibly, it is associated with rupture dislocations. In the elevation zone, the valley of the Western Manych cuts a narrow (0.3–0.4 km) long ridge (swell) with smooth summits 13–15 m in height, which forms the right side of Sad kovskaya gully. The left side of the gully is low, it grad ually passes into a vast flat bed of the WesternManych flexure. Judging from drilling material [10], the bench existed as a small elevation in the bakinskii strait, though it is not impossible that the positive deforma tion of the roof and floor established in its reference horizons can be younger. The abrupt increase in the thickness of the lower khazarskie deposits and a small rise in their foot unambiguously suggest the neotec tonic activity and the presence of a bench in the water of early khazarian strait. Its highest area lied 5 km westward near Krasnyi Kut V. The existence of the bench in khazarskoe time is also confirmed by the configuration of the early and late khazarian straits— an appreciable (2 and more times) decrease in its width [11]. In the burtasskoe time, the foot of the bench was hypsometrically higher than that in the nearby parts of WATER RESOURCES
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Fig. 5. Geomorphological scheme of the Sal’skii Bench. (1) Depression sides, (2) depression (strait) bed, (3) lower parts of the bed, (4) water bodies.
the depression, allowing us to suggest its existence in the Late Pleistocene, in the epoch of existence of bur tasskoe lake. The bench also existed in the khvalynian and postkhvalynian epochs. This can be seen from the decrease in the thickness of khvalynian deposits and the presence in them of traces of repeated scours of more ancient deposits, detected in a reference sec tion of the khvalynian deposits of ManychBalabinka [10, 11] and the presentday structure of relief in the bench segment (Fig. 6). CONCLUSIONS The existence of three benches—ZundaTogla, Sal’skii, and ManychBalabinka—is determined in the history of Pleistocene straits of Manych depres sion. They are identified by different features and sig nificantly differ in their structure, the time and dynamics of development, and the role in the history of the straits. The ZundaTogla bench is unanimously believed by researcher to be the key link in the entire system of Caspian–Black Sea straits, which controlled the upper level of Caspian transgressions and the entire system of Caspian water discharge. Its history features WATER RESOURCES
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stagetype processes of active incision and subsequent filling of the incision by sediments. The beginning of each stage coincides with the time when the trans gressing Caspian water flowed over the bench and its incision into the bed of the structure. The scour of the bench (“plug”) could have the form of regressive ero sion in the direction opposite to the flow in the strait and started from the end of the bench, where it had the maximal steepness. The active erosion of the bench ceased after the development of an equilibrium pro file, though, because of the permanent variations in the levels of the Caspian Sea and the Azov–Black Sea water body, this process seems to have never stopped. The end of the incision stage coincides with the time of active filling of the incision first by marine Caspian deposits, and, after the strait is closed, by terrestrial– aquatic and subaerial formations. The distinction from other similar structures is the existence of narrow, deep, inherited incisions, which determined the regime of discharge of Caspian trans gression water. Those features of the bench are caused by the geological structure of ZundaTogla elevation, composed of erosionresistant dense carbonate rocks of Neogene.
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a ink b a l Ba h c y an
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0.5 km 1.0 km 1.5 km 2.0 km 2.5 km 3.0 km 3.5 km 4.0 km Fig. 6. Geomorphological scheme of the ManychBalabinka Bench. (1) Depression sides, (2) depression bed, (3) lower parts of the bed, (4) water bodies, (5) hypsometric profile.
The Sal’skii Bench, as well as the ZundaTogla, is confined to a structural, though less tectonically active elevation. Because of this, its role as a bench (the deformation of reference horizons and the presence of deep incisions filled with deposits) can be seen in long existed straits—the bakinskii and early khazarskii— while it was not reliably identified in the epoch of shorttime (3–5 thousand years) discharge of khva lynskie waters. The ManychBalabinka bench is also determined by neotectonic elevations. Anomalous benches are absent in this bench everywhere, except for the early khazarskii strait, and the existence of the bench is most
reliably established by geomorphological data and the presence of a deep scour in the foot of khvalynian deposits. Overall, the role of the Sal’skii and ManychBalab inskii benches is less significant than that of the ZundaTogla. It is worth mentioning that no apprecia ble changes in the lithofacial composition of sedi ments, associated with their position, were established in all hydrological benches in the Manych [11]. This suggests the similar, relatively calm hydrological regime in strait arms. The identified faunistic changes in strait waters [10, 11] are mostly due to changes in water salinity under the effect of the inflow of numer WATER RESOURCES
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ous rivers from depression sides, rather than to the presence of geomorphological obstacles. The formation, existence, and the key role of Manych benches in the hydrology of the straits is the joint effect of many factors, primarily, the character and the neotectonic activity of geological structures, the geomorphological structure of strait beds, and the features of the regime of Caspian transgressions, which discharged water through Manych straits into the Pontian.
7. Leont’ev, N.V. and Chepalyga, A.A., Sal’skii Bench of Khvalynian Basin of the Caspian, in Aktual’nye prob lemy paleogeografii i stratigrafii pleistotsena (Urgent Problems of Paleogeography and Stratigraphy of Pleis tocene), Moscow: Rossel’khozakademiya, 2010, pp. 45–46.
ACKNOWLEDGMENTS This study was supported by the Russian Founda tion for Basic Research, project nos. 100500251 and 110500093.
8. Lisitsyn, K.I., Geological Guide for Manych, in Putevoditel’ ekskursii 2i Mezhdunar. assotsiatsii po izucheniyu chetvertichnogo perioda Evropy (Guide for a Trip of the 2nd Intern. Association for Studying the Quaternary Period in Europe), Mocow: Gos. nauch. tekhn. Izd., 1932.
REFERENCES 1. Badyukova, E.N., Some Issues in the Development History of Manych in Late Pleistocene–Holocene, in Chelovechestvo i beregovaya zona Mirovogo okeana v 21 veke (Humankind and the Coastal Zone of the World Ocean), Moscow: Geos, 2001, pp. 326–333. 2. Bogachev, V.V., Manych Basin Steppes, Izv. Geologiya, 1903, vol. 22, no. 2, pp. 73–162. 3. Geologiya SSSR (Geology of the USSR), Moscow: Nedra, 1970, vol. XLVI. 4. Goretskii, G.I., On Paleogeography of the Azov Area and Western Manych Area in UzunlaroGirkanskii and Burtasskie Centuries, Vopr. Geografii, 1953, no. 33, pp. 190–221. 5. Danilevskii, N.Ya., An Abstract of a Letter on a Visit to Manych, Zap. Rus. Geogr. Obshch., 1869, vol. 2, pp. 139–180.
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6. Kvasov, D.D., Pozdnechetvertichnaya istoriya krupnykh ozer i vnutrennikh morei Vostochnoi Evropy (Late Qua ternary History of Large Lakes and Inland Seas in East Europe), Leningrad: Nauka, 1975.
9. Menabde, I.V. and Svitoch, A.A., On the Character of Connection of Caspian and Black Seas in Late Pleis tocene, in Kaspiiskoe more, voprosy geologii i geomor fologii (The Caspian Sea: The Issues of Geology and Geomorphology), Moscow: Nauka, 1990, pp. 34–41. 10. Popov, G.I., Pleistotsen ChernomorskoKaspiiskikh pro livov (Pleistocene of Black Sea–Caspian Sea Straits), Moscow: Nauka, 1983. 11. Svitoch, A.A., Yanina, T.A., Novikova, N.G., et al., Pleistotsen Manycha (voprosy stroeniya i razvitiya) (Pleistocene of Manych: The Issues of Structure and Development), Moscow: Rossel’khozakademiya, 2010. 12. Sudarikov, Yu.A., Zakonomernosti razmeshcheniya nefti i gaza epigertsinskikh platform yuga SSSR (Regularities of Oil and Gas Distribution in EpiHercynian Plat forms in Southern USSR), Moscow: Nedra, 1964, vol. II.
