- Email: [email protected]
Palaeogeographic environment during the desiccation of the Black Sea
Palaeogeography, Palaeoclimatology, Palaeoecology, 43 (1983): 195--204
195
Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
PALAEOGEOGRAPHIC ENVIRONMENT DURING THE DESICCATION OF THE BLACK SEA
EMILIA KOJUMDGIEVA
Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria) (Received September 16, 1982; revised version accepted April 14, 1983)
ABSTRACT Kojumdgieva, E., 1983. Palaeogeographic environment during the desiccation of the Black Sea. Palaeogeogr., Palaeoclimatol., Palaeoecol., 43: 195--204. During the latest Chersonian (about 10.3 m.y. ago) tectonic movements took place leading to an elevation of the Crimean--Caucasian chain and to an isolation of the ForeCaucasian part of the Black Sea Basin. This part of the basin had been draining the rivers of the Russian Platform and after the isolation it became desalinized, while the main part of the Black Sea Basin was almost desiccated and evaporites, mainly dolomites, formed in it due to the predominant calcium--magnesium--carbonate composition of the Chersonian Sea waters. These dolomites are found in the drillings of DSDP Leg 42B and are confirmed geophysically. The tectonic movements during the latest Chersonian led to the formation of a series of grabens along which the Mediterranean Sea invaded the north Aegean area and a little later (during the Early Maeotian) the Black Sea. INTRODUCTION
The first direct data on the desiccation of the Black Sea during the Late Miocene were supplied by the DSDP Leg 42 drillings in 1975 (Hsti, 1978). This desiccation is discussed by Hsfi and Giovanioli (1979). The proposed explanation through change of the drainage is convincing but is not traced in detail since only the Black Sea and the Mediterranean are directly compared with almost no consideration of other areas. The present paper is an attempt to review this problem in the light of the palaeogeographic environment in East Europe at that time. The discussion is based on a large part of the extensive literature on the Miocene in the Paratethys, but only the most important general publications or those treating the problem directly are cited. PALAEOGEOGRAPHIC ENVIRONMENT IN THE PARATETHYS B E F O R E THE DESICCATION OF THE BLACK SEA (SARMATIAN)
About 14--15 m.y. ago, the chain of basins denoted as the Paratethys was completely isolated from the ocean. That m o m e n t marks the beginning of 0031-0182/83/$03.00
© 1983 Elsevier Science Publishers B.V.
196
the Sarmatian Regional Stage (a sketch of the Paratethys Regional Stages for this interval is shown in Fig.l). The vast, though isolated Early Sarmatian (Volhynian) basin extended from Vienna to the Aral Sea (Fig.2). The inflow of fresh water exceeded evaporation which (due to lack of drainage) led to a rise of the sea level, to eustatic transgression and decrease in the salinity of the basin until equilibrium was reached. The salinity of the basin is determined as 16--18%o (discussion in Ilina et al., 1976). This situation existed until the Middle Sarmatian (Bessarabian) -- about 12.5 m.y. ago, when the elevation o f the Carpathians isolated the Pannonian Basin from the other parts of the Paratethys. The isolated Pannonian Basin turned into an almost fresh-water lake and its sediments are considered as the Pannonian Regional Stage (Fig.l). In the other part of the Paratethys the basin likewise decreased in area, but a new equilibrium was soon reached and its area remained almost the same nearly up to the end of the Late Sarmatian (Chersonlan; about ii m.y. Agel PANNONIAN in MY
8.7 10.3,
FORE-CARPA-I EUXINIAN
Basin P
THIAN Basin N T I
0
PANNONIAN
I A Basin N
I M A EOT CO~ ~ c
H
~ E
I A N
r~Z I ~ ~r~ ~i~ R S 0 N
I
A N
hI
z <
t12,5. v 13.8
0
L
H
Y
N
I
A
N
cr < c/)
Fig.1. Correlation of the Paratethys regional stages and substages.
Fig.2. Palaeogeographic map of the Paratethys during the Early Sarmatian (Volhynian) (near 13 Ma).
197
ago, and it changed only as a result of local factors or relatively small variations of the water level. The map in Fig.3 shows the environment during the Middle Chersonian, corresponding to theMactra bulgarica Zone (Kojumdgieva, 1980) or to the upper part of the Katerlesian horizon (Ilina et al., 1976). This is the period closely preceding the desiccation of the Black Sea. The salinity of the Late Bessarabian and Chersonian basins is difficult to determine. The most detailed studies are available for the Boristhen Bay in the southern Ukraine (Belokrys, 1976, 1977). They prove that the prolonged isolated existence of the brackish basin led to important changes in the water composition. The concentration of many components, particularly of carbonates (mostly magnesium carbonate) was so high that at the end of the Bessarabian and during the Chersonian a vast chemical sedimentation of calcite and dolomite t o o k place. In the other parts of the basin the chemical evolution was similar but not so well expressed. This change in the chemical composition of the waters affected the fauna. It gradually became poorer in species and thus, toward the Chersonian, only several endemic Mactra remained from the molluscs, from the ostracods several endemic euxinocytheres survived, and foraminifers disappeared completely (Ilina et al., 1976; Stancheva, 1976; Kojumdgieva, 1980). According to palynological data and particularly those from the Ukraine (Shchekina, 1979), the climate during the Late Bessarabian and Chersonian was rather dry in close proximity to the basin. The equilibrium between inflow and evaporation was maintained mainly at the expense of the rivers flowing from the north, i.e. from another climatic zone (Volga, Don, Dnepr). The Danube was not yet in existence. Part of the waters which comprise the present river flowed into a strongly desalinized Pannonian Basin and the other part drained into the Fore-Carpathian Basin.
J--FF~
aberrant brackish-water salinity basin lacustrine basin
Fig.3. Palaeogeographic map of the Paratethys during the Middle Chersonian (near 11 Ma).
198
As seen from this brief review, towards the end of the Chersonian the basins of the Paratethys were in equilibrium for a rather long time (1.5-2 m.y.). Before any discussion of the possible causes for the change, the environment during the latest Chersonian should be reconstructed as accurately as possible. THE PALAEOGEOGRAPHIC ENVIRONMENT IN THE PARATETHYS DURING THE DESICCATION OF THE BLACK SEA (LATEST CHERSONIAN)
In order to obtain a clear idea first, the changes on the Paratethys only should be reviewed. For this reason regional stages only should be used, leaving the correlation with the Tethys for a later section. The reconstruction is shown in Fig.4. The Pannonian Basin is n o t influenced b y the events from the end of the Chersonian, so that even the accurate position of the time of desiccation is controversial (before, during or after Pannonian C). In the southern part of the Fore-Carpathian Basin (in front of the south Carpathians), a complete regression of the sea is established in the latest Chersonian. In places small, almost desalinized basins were preserved. In the depression in front of the Carpathian curve the sedimentation of coarse molasse sediments was still in progress. It began in the Late Bessarabian and continued also during the Maeotian. However, in the latest Chersonian this deep depression was isolated and nearly desalinized (Pana, 1964, Andreescu, 1972). This interval is considered b y Andreescu (1981) as the Congeria neumayri Zone, b u t it is included in the Maeotian. The situation in the Fore- and Back-Carpathian area proves that in the latest Chersonian no tectonic m o v e m e n t t o o k place in this area and the observed changes are a consequence o f the lowering level of the Black Sea only. The rather deep Fore-Carpathian depression drained the rivers from the
limits of basins in Middle Chersonian
,,~
(Mactra bulgaricaZone ]
lacustrine sediments in l.atest Chersonian
I ~'?~ ~
381 Fig.4. Palaeogeographic map of the Paratethys during the latest Chersonian (near 10.3 Ma).
199 area which led to its desalinization. It is possible that the excess water from the depression flowed into the Black Sea Basin through a river approximately coinciding with the present lowermost course of the Danube. Two parts may be distinguished in the area of the Black Sea -- a southwestern and a northeastern one. The southwestern part covers the Boristhen Bay and the main part of the Black Sea and was affected in the latest Chersonian by a rapid regression in the coastal and shelf parts. The situation in the area of DSDP Leg 42B Site 381 on the continental slope is probably similar. Here, even the existence of landslides of Eocene materials is supposed (Shumenko and Ushakova, 1980). The only direct data from the bottom o f the basin result from Site 380 (Fig.5), where even the latest Chersonian corresponds to a lithologic Subunit IVd -- 20 m (864--884 m) of hemogenic, bedded dolomites. As indicated by Hsii (1978; Hsii and Giovanioli, 1979) they were formed under shallow, subaerial conditions. This bed is traced by seismic surveys (Letouzey et al.,
o5~v L i t h e o-'~_c [ogy ~-
Traverse(in Hsu,1978) Salinity Stratigraphical climate cold ~ warm (inter pre interpretahon steppe-index ration ) Kojumdgieva I00 BO 60 40 20 0 10%~ 20 30 P1979 ) 2
TC -
Neoeuxinion
KaranqatiQn
100-
200
-~Usun~
Ie £----If Ig
Paleo -
~---~---
euxinlan
c @
300
&O0
Tchaudian
500-
o~
Gurian •
~-_~-
700-
.18
Kuyalnikian
600 -
( Egrissian }
TVa
Kimmerian
iVb~__~2~ ~
Pontian
o E
-33 52
800' I V c ~ 900-
' I V d ~
"
)
Maeotian (~
j
Upper
Middle
10001075
Bessa
u° _o
"6 E
103
~, ~ i 13 0
Fig.5. Column of DSDP Site 880 (after Hsii, 1978; stratigraphic interpretation after Kojumdgieva, 1979).
200 1978; Neprochnov and Ross, 1978) which show that it is developed over the whole of the western and parts of the eastern areas of the basin. It shows that these areas of the Black Sea Basin were almost entirely dry towards the latest Chersonian and evaporites were deposited in them. The specific composition of the evaporites (dolomites and other carbonates instead of sulfides and chlorides) is a consequence of the specific composition of the Sarmatian Sea waters. In the northeastern part of the basin, in the area of the Fore-Caucasus, two fresh-water basins formed: one (Azov Basin) in the western part -- the Sea of Azov, the Cuban depression and the Taman peninsula (Zhizhchenko et al., 1968; Ilina et al., 1976) and another one (North Caspian Basin) in the eastern part -- in Dagestan and the northern part of the Caspian Sea (Zhizhchenko et al., 1968). The large rivers which drained the northern, humid regions of the Russian platform (mainly pre-Don and pre-Volga) flowed into these basins. In the latter fresh-water sediments were deposited, referred to the uppermost, Mitridatian horizon of the Chersonian (Ilina et al., 1976). In the upper part of these sediments interbeds of volcanic ash are established (Zhizhchenko et al., 1968). These interbeds are probably related to the continental volcanoes in Georgia, conventionally referred to the Maeotian. Their absolute age is 10.0--10.6 Ma (Gabunia and Rubinstein, 1977). The isolation of these basins (in particular the Azov Basin) was a result of tectonic movements and elevation of the Crimean--Caucasian chain. Such movements of post-Chersonian--pre-Maeotian age are best observed in the western continuation of this chain, west of the Crimea, on the b o t t o m of the Odessa Bay (Morgunov et al., 1975), where at that time several horst-anticlines were formed. This palaeogeographic situation existed for an u n k n o w n b u t relatively short time. The marine {more precisely the marine--brackish) Early Maeotian transgression embraced the Black Sea (Euxinian) Basin approximately within the boundaries of the Middle Chersonian basin before the desiccation (Figs.3 and 6). The connection with the Fore-Carpathian Basin was also restored, b u t not with the Pannonian Basin. In the DSDP Leg 42B boreholes this marine transgression corresponds to lithologic Unit IVc, whose diatomaceous flora, according to the most recent and more accurate determinations of Jous~ and Mukhina (1980), also contains some typical Maeotian endemic species. The flora and fauna of this unit witness a marine transgression of lower salinity (Hsfi, 1978). During the Early Maeotian the humidity was higher as compared to the Chersonian (Shchekina, 1979; also the steppeindex curve -- Fig.5). CORRELATIONS AND LINKS BETWEEN THE BLACK SEA AND THE AEGEAN BASINS BEFORE 10 MA The correlation at the boundary between the Sarmatian (Chersonian) and Maeotian regional stages in the Paratethys with the Tethys is based on
201
marine
sediments
fluvio - lacustrine sediments
Fig.6. Palaeogeographic map of southeastern Europe during the Early Maeotian (9--10 Ma).
radiometric, palaeomagnetic and faunistic (nannoplankton, molluscs and vertebrates) data. The radiometric age of 10.0--10.6 Ma for this boundary was mentioned earlier. The base of the Maeotian (limestones with Membranipora) near the Sea of Azov coincides with the uppermost normal episode in the reversal palaeomagnetic epoch, considered b y Pevzner and Chikovani (1978) as Epoch 8; but according to the correction of Andreescu (1981) this is Epoch 10. This episode is 10.3 m.y. old. Andreescu suggested a similar age for the boundary between the fresh-water Congeria neumayri Zone and the marine Maeotian Dosinia maeotica Zone. The Chersonian/Maeotian boundary coincides with that between the Vallesian and Turolian mammal fauna (Gabunia, 1979; Gabunia and Rubinstein, 1977), with an age of about 10 m.y. In the Maeotian, nannoplankton of Zone NN 10 is found (Semenenko and Ljulieva, 1979), whose age is 9--10 m.y. Sediments of the Miocene marine transgression in the Aegean basin are known from outcrops near Athens, Seres, Fere, the Dardanelles (Stevanovic, 1963; Gramman and Kockel, 1969; Papp and Steininger, 1979; Taner, 1979) and in the Thessaloniki Bay and near Thasos Island (Lalechos and Savoyat, 1979). The outcrops are shallow-water sediments with molluscs, some of them being c o m m o n in the Maeotian. In the clays of Thessaloniki Bay and within interbeds in evaporites near Thasos, Late Miocene planktonic foraminifers occur. In spite of the assumption that the evaporites are of Messinian age (Lalechos and Savoyat, 1979), they may be a little older (Tortonian). The data on the age of the tectonic movements in the Aegean area are still insufficient. Most systematic data are available for Struma (Strimon) Valley and particularly for the Sandanski graben (Kojumdgieva et al., 1982). There, multiple subsidence along faults is established: in the Middle Miocene, a little before the Vallesian/Turolian boundary, between the Maeotian and the
202
Pontian and towards the end of the Pliocene. The faulting which ocurred a little before the change in Vallesian and Turolian mammal fauna, i.e. according to the regional correlation a little before the Chersonian/Maeotian boundary (in the latest Chersonian), is most intensive both in respect of amplitude and the area affected. In higher (Maeotian) parts of the same cycle, there is evidence for marine influence (Palamarev, 1982), which is a consequence of the marine ingression in the area of Seres (Gramman and Kockel, 1969). A BRIEF REVIEW OF THE EVENTS On the basis of the above data, the sequence of events can be reconstructed as follows. In the latest Chersonian (about 10.5--10.3 m.y. ago) intensive faulting and block movements started in the Aegean and Black Sea areas. In the Aegean area this led to the formation of a set of grabens, part of them being invaded by waters of the Mediterranean Sea. Due to differences in the rate and scale of subsidence, local delay o f this marine transgression and formation of evaporites is evident. In the Black Sea area the block movements led to a temporary separation of the basin into t w o parts. One o f them (the Fore-Caucasus) drained the main rivers which flowed into the former Black Sea Basin (pre-Don and preVolga) and was entirely desalinized. The other part (the Black Sea itself) was in deficiency of fresh water and dried up almost completely, leaving a layer of evaporites (mainly dolomites due to the dominant calcium--magnesium-carbonate composition of the Chersonian sea waters). This deeply desiccated depression could not have existed for a long time. Soon it was covered (simultaneously or almost simultaneously) by the marine waters of the Aegean Basin and by the fresh waters of the Fore-Caucasian basins. A new, Maeotian Black Sea (Euxinian} basin was formed, whose salinity was initially stabilized at about 20%o (Ilina et al., 1976), and later gradually decreased. In the Carpathian area there is no evidence of tectonic events during the Chersonian and the Maeotian. The Pannonian Basin was isolated from the Fore-Carpathian and the fluctuations of its level are mostly eustatic. The changes in the Fore-Carpathian Basin are not independent but are related to the changes in the Black Sea Basin. The desiccation of the latter led to an isolation, shrinking and desalinization of the Fore-Carpathian Basin, while the restoration of the links between these t w o basins to a new, marine-brackish Maeotian transgression also in the Fore-Carpathian Basin, could then have taken place. The Danube did n o t play any part in the desiccation of the Black Sea during the latest Chersonian since it did not exist at that time. The waters which form the present-day river were drained at that time into two independent basins -- the Pannonian and the Fore-Carpathian basins. As late as the end o f the Early Pleistocene, when the last remnants of these basins disappeared, the Danube came into existence and it started to play an important role in the Black Sea Basin from the Middle Pleistocene onwards (Hsfi, 1978).
203 T h e sharp change in p a l a e o g e o g r a p h i c e n v i r o n m e n t in s o u t h e a s t E u r o p e in t h e latest C h e r s o n i a n p r o b a b l y i n f l u e n c e d t h e e v o l u t i o n and m i g r a t i o n o f the m a m m a l f a u n a and in particular t h e r e p l a c e m e n t o f Vallesian b y T u r o l i a n fauna. This i m p o r t a n t c h a n g e in the A e g e a n and Black Sea area e x e r t little influence o u t s i d e this t e r r i t o r y a n d m a y be t r a c e d m a i n l y b y changes in m a m m a l fauna. REFERENCES Andreescu, I., 1972. Le faciostratotype du Malvensien de la zone de courbure des Carpates orientales. Dari de Seama Sedin., Inst. Geol., Bucuresti, 58(9): 157--176. Andreescu, I., 1981. Middle--Upper Neogene and Early Quaternary chronostratigraphy from the Dacic basin and correlation with neighbouring areas. Ann. G~ol. Pays Hell6n., H.S., 4: 129--138. Belokrys, L. S., 1967. Opresnjalos li yugnooukrainskoe sarmatskoe more? Sov. Geol., 7: 97--110. Belokrys, L. S., 1976. Sarmat yuga SSR. In: Stratigrafia kainozoja Sev. Prichernomorja i Krima, 1. Dnepropetrovsk, 1--21. Gabunia, L. K., 1979. Biostratigraphic correlations between the Neogene land mammal faunas of the East and Central Paratethys. Ann. G4ol. Pays Hell6n., H. S., 411--423. Gabunia, L. K. and Rubinstein, M. M., 1977. On the absolute age of the Hipparion from Saro. Geol. S., Bratislava, 21(1): 7--11 (in Russian with English summary). Gramman, F. and Kockel, F., 1969. Das Neogen im Strimon-Becken (Griechisch-Ostmazedonien). Geol. Jahrb., 87: 445--484. Hsii, K. J., 1978. Stratigraphy of the lacustrine sedimentation in the Black Sea. Initial Reports of the Deep Sea Drilling Project, 42B: 509--524. Hsii, K. J. and Giovanioli, F., 1979. Messinian Event in the Black Sea. Palaeogr., Palaeoclimatol., Palaeoecol., 29: 75--93. Ilina, L. B., Nevesskaya, L. A. and Paramonova, N. P., 1976. Zakonomernosti razvitija molluskov v opresnennih basseinah neogena Evrazii. Nauka, Moscow, 288 pp. Jous6, A. P. and Mukhina, V. V., 1980. Stratigrafija verhnekainozoiskih otlogenii po diatomejam. In: Geologicheskaja istorija Chernogo morja po resultatam glubokovodnogo burenija. Nauka, Moscow, pp. 52--65. Kojumdgieva, E., 1979. Critical notes on the stratigraphy of Black Sea boreholes (Deep Sea Drilling Project, Leg 42B). Geol. Balcanica, 9(3): 107--110. Kojumdgieva, E., 1980. Les communaut6s des Mollusques du Sarmatien et leur importance stratigraphique. In: Proc. XI Congres CBGA, Kiev, Stratigraphy, pp. 72--79. Kojumdgieva, E., Nikolov, I., Nedjalkov, P. and Buzev, A., 1982. Stratigraphy of the Neogene in Sandanski graben. Geol. Balcanica, 12(3): 69--81. Lalechos, N. and Savoyat, E., 1979. La s6dimentation n~og~ne dans le foss6 Nord-Eg~en. In: Proc. VIth Coll. Geol. Aegean Reg., Athens, pp. 591--603. Letouzey, J., Gonnard, R., Montadert, L., Kristchev, K. and Dorkel, A., 1978. Black Sea: geological setting and recent deposit distribution from seismic reflection data. Initial Reports of the Deep Sea Drilling Project, 42: 1077--1084. Morgunov, I. G., Vorobiov, V. P., Kalinin, A. V., Kovalskaja, I. I., Kuprin, P. N. and Pivovarov, V. L., 1975. Strukturnaja poverhnost sarmatskih otlogenii severozapadnoi chasti shelfa Chernogo morja. Kompleksn. Issled. Prirodi Okeana, 5: 149--158. Neprochnov, I. P. and Ross, D. A., 1978. Black Sea: Geophysical framework. Initial Reports of the Deep Sea Drilling Project, 42B: 1043--1055. Palamarev, E., 1982. Die neogene Carpoflora aus dem Melnik-Becken. Paleontol., Stratigr. Lithol., 16:3--44 (in Bulgarian with German summary).
204 Pana, I., 1964. Asupra limitei Sarmatian--Meotian din regiunea euprinsa intre Valea Buzaului si afluentul sau Balaneasa. Anal. Univ. Bucuresti, Ser. Stiint. Nat. (Geol.Geogr.), 13(2): 35--46. Papp, A. and Steininger, F. F., 1979. Paleogeographic implications of Late Miocene deposits in the Aegean region. Ann. G~ol. Pays Hell~n., H. S., 955--959. Pevzner, M. A. and Chikovani, A. A., 1978. Paleomagnitnie issledovanija verhnemiocenovih i nignepliocenovih morskih otlogenii Tamanskogo poluostrova, Izv. Akad. Nauk SSSR, Ser. Geol., 1: 5--15. Semenenko, V. N. and Ljulieva, S. A., 1978. Opit prjamoi korrelacii mio-pliocena Vostochnego Paratetisa i Tetisa. In: Stratigrafia kainozoja Sev. Prichernomorja i Krima, 2. Dnepropetrovsk., pp. 95--105. Shchekina, N. A., 1979. Istoria flori i rastitelnosti yuga Evropeiskoi chasti SSSR v pozdnero miocene-rannem pliocene. Naukova Dumka, Kiev, 197 pp. Shumenko, S. I. and Ushakova, M. G., 1980. Izvestkovie nanofossilii v kernah glubokovodnogo burenija. Nauka, Moscow, pp. 71--73. Stancheva, M., 1976. Zonation of the Sarmatian sediments in northeastern Bulgaria on ostracod fauna. Geol. Balcanica, 6(1): 53--59. Stevanovic, P. M., 1963. Beitrag zur Kenntnis der pontischen Molluskenfauna aus Griechenland und ihre stratigraphische Bedeuting. Bull. Acad. Serbe Sci. Arts, 32, Classe Sci. Math. Nat., N. S., 9 : 7 3 - - 9 3 (in Serbian with German summary). Taner, G., 1979. Die Molluskenfauna der Neogenen Formationen der Halbinsel Gelibolu. Ann. G6ol. Pays Hell~n., H. S., 1189--1194. Zhizhchenko, B. P., Seregenko, V. A. and Churilova, E. V., 1968. Ne0genovaja sistema. Geol. SSSR, IX, Severnii Kavkaz, pp. 388--441.
195
Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
PALAEOGEOGRAPHIC ENVIRONMENT DURING THE DESICCATION OF THE BLACK SEA
EMILIA KOJUMDGIEVA
Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria) (Received September 16, 1982; revised version accepted April 14, 1983)
ABSTRACT Kojumdgieva, E., 1983. Palaeogeographic environment during the desiccation of the Black Sea. Palaeogeogr., Palaeoclimatol., Palaeoecol., 43: 195--204. During the latest Chersonian (about 10.3 m.y. ago) tectonic movements took place leading to an elevation of the Crimean--Caucasian chain and to an isolation of the ForeCaucasian part of the Black Sea Basin. This part of the basin had been draining the rivers of the Russian Platform and after the isolation it became desalinized, while the main part of the Black Sea Basin was almost desiccated and evaporites, mainly dolomites, formed in it due to the predominant calcium--magnesium--carbonate composition of the Chersonian Sea waters. These dolomites are found in the drillings of DSDP Leg 42B and are confirmed geophysically. The tectonic movements during the latest Chersonian led to the formation of a series of grabens along which the Mediterranean Sea invaded the north Aegean area and a little later (during the Early Maeotian) the Black Sea. INTRODUCTION
The first direct data on the desiccation of the Black Sea during the Late Miocene were supplied by the DSDP Leg 42 drillings in 1975 (Hsti, 1978). This desiccation is discussed by Hsfi and Giovanioli (1979). The proposed explanation through change of the drainage is convincing but is not traced in detail since only the Black Sea and the Mediterranean are directly compared with almost no consideration of other areas. The present paper is an attempt to review this problem in the light of the palaeogeographic environment in East Europe at that time. The discussion is based on a large part of the extensive literature on the Miocene in the Paratethys, but only the most important general publications or those treating the problem directly are cited. PALAEOGEOGRAPHIC ENVIRONMENT IN THE PARATETHYS B E F O R E THE DESICCATION OF THE BLACK SEA (SARMATIAN)
About 14--15 m.y. ago, the chain of basins denoted as the Paratethys was completely isolated from the ocean. That m o m e n t marks the beginning of 0031-0182/83/$03.00
© 1983 Elsevier Science Publishers B.V.
196
the Sarmatian Regional Stage (a sketch of the Paratethys Regional Stages for this interval is shown in Fig.l). The vast, though isolated Early Sarmatian (Volhynian) basin extended from Vienna to the Aral Sea (Fig.2). The inflow of fresh water exceeded evaporation which (due to lack of drainage) led to a rise of the sea level, to eustatic transgression and decrease in the salinity of the basin until equilibrium was reached. The salinity of the basin is determined as 16--18%o (discussion in Ilina et al., 1976). This situation existed until the Middle Sarmatian (Bessarabian) -- about 12.5 m.y. ago, when the elevation o f the Carpathians isolated the Pannonian Basin from the other parts of the Paratethys. The isolated Pannonian Basin turned into an almost fresh-water lake and its sediments are considered as the Pannonian Regional Stage (Fig.l). In the other part of the Paratethys the basin likewise decreased in area, but a new equilibrium was soon reached and its area remained almost the same nearly up to the end of the Late Sarmatian (Chersonlan; about ii m.y. Agel PANNONIAN in MY
8.7 10.3,
FORE-CARPA-I EUXINIAN
Basin P
THIAN Basin N T I
0
PANNONIAN
I A Basin N
I M A EOT CO~ ~ c
H
~ E
I A N
r~Z I ~ ~r~ ~i~ R S 0 N
I
A N
hI
z <
t12,5. v 13.8
0
L
H
Y
N
I
A
N
cr < c/)
Fig.1. Correlation of the Paratethys regional stages and substages.
Fig.2. Palaeogeographic map of the Paratethys during the Early Sarmatian (Volhynian) (near 13 Ma).
197
ago, and it changed only as a result of local factors or relatively small variations of the water level. The map in Fig.3 shows the environment during the Middle Chersonian, corresponding to theMactra bulgarica Zone (Kojumdgieva, 1980) or to the upper part of the Katerlesian horizon (Ilina et al., 1976). This is the period closely preceding the desiccation of the Black Sea. The salinity of the Late Bessarabian and Chersonian basins is difficult to determine. The most detailed studies are available for the Boristhen Bay in the southern Ukraine (Belokrys, 1976, 1977). They prove that the prolonged isolated existence of the brackish basin led to important changes in the water composition. The concentration of many components, particularly of carbonates (mostly magnesium carbonate) was so high that at the end of the Bessarabian and during the Chersonian a vast chemical sedimentation of calcite and dolomite t o o k place. In the other parts of the basin the chemical evolution was similar but not so well expressed. This change in the chemical composition of the waters affected the fauna. It gradually became poorer in species and thus, toward the Chersonian, only several endemic Mactra remained from the molluscs, from the ostracods several endemic euxinocytheres survived, and foraminifers disappeared completely (Ilina et al., 1976; Stancheva, 1976; Kojumdgieva, 1980). According to palynological data and particularly those from the Ukraine (Shchekina, 1979), the climate during the Late Bessarabian and Chersonian was rather dry in close proximity to the basin. The equilibrium between inflow and evaporation was maintained mainly at the expense of the rivers flowing from the north, i.e. from another climatic zone (Volga, Don, Dnepr). The Danube was not yet in existence. Part of the waters which comprise the present river flowed into a strongly desalinized Pannonian Basin and the other part drained into the Fore-Carpathian Basin.
J--FF~
aberrant brackish-water salinity basin lacustrine basin
Fig.3. Palaeogeographic map of the Paratethys during the Middle Chersonian (near 11 Ma).
198
As seen from this brief review, towards the end of the Chersonian the basins of the Paratethys were in equilibrium for a rather long time (1.5-2 m.y.). Before any discussion of the possible causes for the change, the environment during the latest Chersonian should be reconstructed as accurately as possible. THE PALAEOGEOGRAPHIC ENVIRONMENT IN THE PARATETHYS DURING THE DESICCATION OF THE BLACK SEA (LATEST CHERSONIAN)
In order to obtain a clear idea first, the changes on the Paratethys only should be reviewed. For this reason regional stages only should be used, leaving the correlation with the Tethys for a later section. The reconstruction is shown in Fig.4. The Pannonian Basin is n o t influenced b y the events from the end of the Chersonian, so that even the accurate position of the time of desiccation is controversial (before, during or after Pannonian C). In the southern part of the Fore-Carpathian Basin (in front of the south Carpathians), a complete regression of the sea is established in the latest Chersonian. In places small, almost desalinized basins were preserved. In the depression in front of the Carpathian curve the sedimentation of coarse molasse sediments was still in progress. It began in the Late Bessarabian and continued also during the Maeotian. However, in the latest Chersonian this deep depression was isolated and nearly desalinized (Pana, 1964, Andreescu, 1972). This interval is considered b y Andreescu (1981) as the Congeria neumayri Zone, b u t it is included in the Maeotian. The situation in the Fore- and Back-Carpathian area proves that in the latest Chersonian no tectonic m o v e m e n t t o o k place in this area and the observed changes are a consequence o f the lowering level of the Black Sea only. The rather deep Fore-Carpathian depression drained the rivers from the
limits of basins in Middle Chersonian
,,~
(Mactra bulgaricaZone ]
lacustrine sediments in l.atest Chersonian
I ~'?~ ~
381 Fig.4. Palaeogeographic map of the Paratethys during the latest Chersonian (near 10.3 Ma).
199 area which led to its desalinization. It is possible that the excess water from the depression flowed into the Black Sea Basin through a river approximately coinciding with the present lowermost course of the Danube. Two parts may be distinguished in the area of the Black Sea -- a southwestern and a northeastern one. The southwestern part covers the Boristhen Bay and the main part of the Black Sea and was affected in the latest Chersonian by a rapid regression in the coastal and shelf parts. The situation in the area of DSDP Leg 42B Site 381 on the continental slope is probably similar. Here, even the existence of landslides of Eocene materials is supposed (Shumenko and Ushakova, 1980). The only direct data from the bottom o f the basin result from Site 380 (Fig.5), where even the latest Chersonian corresponds to a lithologic Subunit IVd -- 20 m (864--884 m) of hemogenic, bedded dolomites. As indicated by Hsii (1978; Hsii and Giovanioli, 1979) they were formed under shallow, subaerial conditions. This bed is traced by seismic surveys (Letouzey et al.,
o5~v L i t h e o-'~_c [ogy ~-
Traverse(in Hsu,1978) Salinity Stratigraphical climate cold ~ warm (inter pre interpretahon steppe-index ration ) Kojumdgieva I00 BO 60 40 20 0 10%~ 20 30 P1979 ) 2
TC -
Neoeuxinion
KaranqatiQn
100-
200
-~Usun~
Ie £----If Ig
Paleo -
~---~---
euxinlan
c @
300
&O0
Tchaudian
500-
o~
Gurian •
~-_~-
700-
.18
Kuyalnikian
600 -
( Egrissian }
TVa
Kimmerian
iVb~__~2~ ~
Pontian
o E
-33 52
800' I V c ~ 900-
' I V d ~
"
)
Maeotian (~
j
Upper
Middle
10001075
Bessa
u° _o
"6 E
103
~, ~ i 13 0
Fig.5. Column of DSDP Site 880 (after Hsii, 1978; stratigraphic interpretation after Kojumdgieva, 1979).
200 1978; Neprochnov and Ross, 1978) which show that it is developed over the whole of the western and parts of the eastern areas of the basin. It shows that these areas of the Black Sea Basin were almost entirely dry towards the latest Chersonian and evaporites were deposited in them. The specific composition of the evaporites (dolomites and other carbonates instead of sulfides and chlorides) is a consequence of the specific composition of the Sarmatian Sea waters. In the northeastern part of the basin, in the area of the Fore-Caucasus, two fresh-water basins formed: one (Azov Basin) in the western part -- the Sea of Azov, the Cuban depression and the Taman peninsula (Zhizhchenko et al., 1968; Ilina et al., 1976) and another one (North Caspian Basin) in the eastern part -- in Dagestan and the northern part of the Caspian Sea (Zhizhchenko et al., 1968). The large rivers which drained the northern, humid regions of the Russian platform (mainly pre-Don and pre-Volga) flowed into these basins. In the latter fresh-water sediments were deposited, referred to the uppermost, Mitridatian horizon of the Chersonian (Ilina et al., 1976). In the upper part of these sediments interbeds of volcanic ash are established (Zhizhchenko et al., 1968). These interbeds are probably related to the continental volcanoes in Georgia, conventionally referred to the Maeotian. Their absolute age is 10.0--10.6 Ma (Gabunia and Rubinstein, 1977). The isolation of these basins (in particular the Azov Basin) was a result of tectonic movements and elevation of the Crimean--Caucasian chain. Such movements of post-Chersonian--pre-Maeotian age are best observed in the western continuation of this chain, west of the Crimea, on the b o t t o m of the Odessa Bay (Morgunov et al., 1975), where at that time several horst-anticlines were formed. This palaeogeographic situation existed for an u n k n o w n b u t relatively short time. The marine {more precisely the marine--brackish) Early Maeotian transgression embraced the Black Sea (Euxinian) Basin approximately within the boundaries of the Middle Chersonian basin before the desiccation (Figs.3 and 6). The connection with the Fore-Carpathian Basin was also restored, b u t not with the Pannonian Basin. In the DSDP Leg 42B boreholes this marine transgression corresponds to lithologic Unit IVc, whose diatomaceous flora, according to the most recent and more accurate determinations of Jous~ and Mukhina (1980), also contains some typical Maeotian endemic species. The flora and fauna of this unit witness a marine transgression of lower salinity (Hsfi, 1978). During the Early Maeotian the humidity was higher as compared to the Chersonian (Shchekina, 1979; also the steppeindex curve -- Fig.5). CORRELATIONS AND LINKS BETWEEN THE BLACK SEA AND THE AEGEAN BASINS BEFORE 10 MA The correlation at the boundary between the Sarmatian (Chersonian) and Maeotian regional stages in the Paratethys with the Tethys is based on
201
marine
sediments
fluvio - lacustrine sediments
Fig.6. Palaeogeographic map of southeastern Europe during the Early Maeotian (9--10 Ma).
radiometric, palaeomagnetic and faunistic (nannoplankton, molluscs and vertebrates) data. The radiometric age of 10.0--10.6 Ma for this boundary was mentioned earlier. The base of the Maeotian (limestones with Membranipora) near the Sea of Azov coincides with the uppermost normal episode in the reversal palaeomagnetic epoch, considered b y Pevzner and Chikovani (1978) as Epoch 8; but according to the correction of Andreescu (1981) this is Epoch 10. This episode is 10.3 m.y. old. Andreescu suggested a similar age for the boundary between the fresh-water Congeria neumayri Zone and the marine Maeotian Dosinia maeotica Zone. The Chersonian/Maeotian boundary coincides with that between the Vallesian and Turolian mammal fauna (Gabunia, 1979; Gabunia and Rubinstein, 1977), with an age of about 10 m.y. In the Maeotian, nannoplankton of Zone NN 10 is found (Semenenko and Ljulieva, 1979), whose age is 9--10 m.y. Sediments of the Miocene marine transgression in the Aegean basin are known from outcrops near Athens, Seres, Fere, the Dardanelles (Stevanovic, 1963; Gramman and Kockel, 1969; Papp and Steininger, 1979; Taner, 1979) and in the Thessaloniki Bay and near Thasos Island (Lalechos and Savoyat, 1979). The outcrops are shallow-water sediments with molluscs, some of them being c o m m o n in the Maeotian. In the clays of Thessaloniki Bay and within interbeds in evaporites near Thasos, Late Miocene planktonic foraminifers occur. In spite of the assumption that the evaporites are of Messinian age (Lalechos and Savoyat, 1979), they may be a little older (Tortonian). The data on the age of the tectonic movements in the Aegean area are still insufficient. Most systematic data are available for Struma (Strimon) Valley and particularly for the Sandanski graben (Kojumdgieva et al., 1982). There, multiple subsidence along faults is established: in the Middle Miocene, a little before the Vallesian/Turolian boundary, between the Maeotian and the
202
Pontian and towards the end of the Pliocene. The faulting which ocurred a little before the change in Vallesian and Turolian mammal fauna, i.e. according to the regional correlation a little before the Chersonian/Maeotian boundary (in the latest Chersonian), is most intensive both in respect of amplitude and the area affected. In higher (Maeotian) parts of the same cycle, there is evidence for marine influence (Palamarev, 1982), which is a consequence of the marine ingression in the area of Seres (Gramman and Kockel, 1969). A BRIEF REVIEW OF THE EVENTS On the basis of the above data, the sequence of events can be reconstructed as follows. In the latest Chersonian (about 10.5--10.3 m.y. ago) intensive faulting and block movements started in the Aegean and Black Sea areas. In the Aegean area this led to the formation of a set of grabens, part of them being invaded by waters of the Mediterranean Sea. Due to differences in the rate and scale of subsidence, local delay o f this marine transgression and formation of evaporites is evident. In the Black Sea area the block movements led to a temporary separation of the basin into t w o parts. One o f them (the Fore-Caucasus) drained the main rivers which flowed into the former Black Sea Basin (pre-Don and preVolga) and was entirely desalinized. The other part (the Black Sea itself) was in deficiency of fresh water and dried up almost completely, leaving a layer of evaporites (mainly dolomites due to the dominant calcium--magnesium-carbonate composition of the Chersonian sea waters). This deeply desiccated depression could not have existed for a long time. Soon it was covered (simultaneously or almost simultaneously) by the marine waters of the Aegean Basin and by the fresh waters of the Fore-Caucasian basins. A new, Maeotian Black Sea (Euxinian} basin was formed, whose salinity was initially stabilized at about 20%o (Ilina et al., 1976), and later gradually decreased. In the Carpathian area there is no evidence of tectonic events during the Chersonian and the Maeotian. The Pannonian Basin was isolated from the Fore-Carpathian and the fluctuations of its level are mostly eustatic. The changes in the Fore-Carpathian Basin are not independent but are related to the changes in the Black Sea Basin. The desiccation of the latter led to an isolation, shrinking and desalinization of the Fore-Carpathian Basin, while the restoration of the links between these t w o basins to a new, marine-brackish Maeotian transgression also in the Fore-Carpathian Basin, could then have taken place. The Danube did n o t play any part in the desiccation of the Black Sea during the latest Chersonian since it did not exist at that time. The waters which form the present-day river were drained at that time into two independent basins -- the Pannonian and the Fore-Carpathian basins. As late as the end o f the Early Pleistocene, when the last remnants of these basins disappeared, the Danube came into existence and it started to play an important role in the Black Sea Basin from the Middle Pleistocene onwards (Hsfi, 1978).
203 T h e sharp change in p a l a e o g e o g r a p h i c e n v i r o n m e n t in s o u t h e a s t E u r o p e in t h e latest C h e r s o n i a n p r o b a b l y i n f l u e n c e d t h e e v o l u t i o n and m i g r a t i o n o f the m a m m a l f a u n a and in particular t h e r e p l a c e m e n t o f Vallesian b y T u r o l i a n fauna. This i m p o r t a n t c h a n g e in the A e g e a n and Black Sea area e x e r t little influence o u t s i d e this t e r r i t o r y a n d m a y be t r a c e d m a i n l y b y changes in m a m m a l fauna. REFERENCES Andreescu, I., 1972. Le faciostratotype du Malvensien de la zone de courbure des Carpates orientales. Dari de Seama Sedin., Inst. Geol., Bucuresti, 58(9): 157--176. Andreescu, I., 1981. Middle--Upper Neogene and Early Quaternary chronostratigraphy from the Dacic basin and correlation with neighbouring areas. Ann. G~ol. Pays Hell6n., H.S., 4: 129--138. Belokrys, L. S., 1967. Opresnjalos li yugnooukrainskoe sarmatskoe more? Sov. Geol., 7: 97--110. Belokrys, L. S., 1976. Sarmat yuga SSR. In: Stratigrafia kainozoja Sev. Prichernomorja i Krima, 1. Dnepropetrovsk, 1--21. Gabunia, L. K., 1979. Biostratigraphic correlations between the Neogene land mammal faunas of the East and Central Paratethys. Ann. G4ol. Pays Hell6n., H. S., 411--423. Gabunia, L. K. and Rubinstein, M. M., 1977. On the absolute age of the Hipparion from Saro. Geol. S., Bratislava, 21(1): 7--11 (in Russian with English summary). Gramman, F. and Kockel, F., 1969. Das Neogen im Strimon-Becken (Griechisch-Ostmazedonien). Geol. Jahrb., 87: 445--484. Hsii, K. J., 1978. Stratigraphy of the lacustrine sedimentation in the Black Sea. Initial Reports of the Deep Sea Drilling Project, 42B: 509--524. Hsii, K. J. and Giovanioli, F., 1979. Messinian Event in the Black Sea. Palaeogr., Palaeoclimatol., Palaeoecol., 29: 75--93. Ilina, L. B., Nevesskaya, L. A. and Paramonova, N. P., 1976. Zakonomernosti razvitija molluskov v opresnennih basseinah neogena Evrazii. Nauka, Moscow, 288 pp. Jous6, A. P. and Mukhina, V. V., 1980. Stratigrafija verhnekainozoiskih otlogenii po diatomejam. In: Geologicheskaja istorija Chernogo morja po resultatam glubokovodnogo burenija. Nauka, Moscow, pp. 52--65. Kojumdgieva, E., 1979. Critical notes on the stratigraphy of Black Sea boreholes (Deep Sea Drilling Project, Leg 42B). Geol. Balcanica, 9(3): 107--110. Kojumdgieva, E., 1980. Les communaut6s des Mollusques du Sarmatien et leur importance stratigraphique. In: Proc. XI Congres CBGA, Kiev, Stratigraphy, pp. 72--79. Kojumdgieva, E., Nikolov, I., Nedjalkov, P. and Buzev, A., 1982. Stratigraphy of the Neogene in Sandanski graben. Geol. Balcanica, 12(3): 69--81. Lalechos, N. and Savoyat, E., 1979. La s6dimentation n~og~ne dans le foss6 Nord-Eg~en. In: Proc. VIth Coll. Geol. Aegean Reg., Athens, pp. 591--603. Letouzey, J., Gonnard, R., Montadert, L., Kristchev, K. and Dorkel, A., 1978. Black Sea: geological setting and recent deposit distribution from seismic reflection data. Initial Reports of the Deep Sea Drilling Project, 42: 1077--1084. Morgunov, I. G., Vorobiov, V. P., Kalinin, A. V., Kovalskaja, I. I., Kuprin, P. N. and Pivovarov, V. L., 1975. Strukturnaja poverhnost sarmatskih otlogenii severozapadnoi chasti shelfa Chernogo morja. Kompleksn. Issled. Prirodi Okeana, 5: 149--158. Neprochnov, I. P. and Ross, D. A., 1978. Black Sea: Geophysical framework. Initial Reports of the Deep Sea Drilling Project, 42B: 1043--1055. Palamarev, E., 1982. Die neogene Carpoflora aus dem Melnik-Becken. Paleontol., Stratigr. Lithol., 16:3--44 (in Bulgarian with German summary).
204 Pana, I., 1964. Asupra limitei Sarmatian--Meotian din regiunea euprinsa intre Valea Buzaului si afluentul sau Balaneasa. Anal. Univ. Bucuresti, Ser. Stiint. Nat. (Geol.Geogr.), 13(2): 35--46. Papp, A. and Steininger, F. F., 1979. Paleogeographic implications of Late Miocene deposits in the Aegean region. Ann. G~ol. Pays Hell~n., H. S., 955--959. Pevzner, M. A. and Chikovani, A. A., 1978. Paleomagnitnie issledovanija verhnemiocenovih i nignepliocenovih morskih otlogenii Tamanskogo poluostrova, Izv. Akad. Nauk SSSR, Ser. Geol., 1: 5--15. Semenenko, V. N. and Ljulieva, S. A., 1978. Opit prjamoi korrelacii mio-pliocena Vostochnego Paratetisa i Tetisa. In: Stratigrafia kainozoja Sev. Prichernomorja i Krima, 2. Dnepropetrovsk., pp. 95--105. Shchekina, N. A., 1979. Istoria flori i rastitelnosti yuga Evropeiskoi chasti SSSR v pozdnero miocene-rannem pliocene. Naukova Dumka, Kiev, 197 pp. Shumenko, S. I. and Ushakova, M. G., 1980. Izvestkovie nanofossilii v kernah glubokovodnogo burenija. Nauka, Moscow, pp. 71--73. Stancheva, M., 1976. Zonation of the Sarmatian sediments in northeastern Bulgaria on ostracod fauna. Geol. Balcanica, 6(1): 53--59. Stevanovic, P. M., 1963. Beitrag zur Kenntnis der pontischen Molluskenfauna aus Griechenland und ihre stratigraphische Bedeuting. Bull. Acad. Serbe Sci. Arts, 32, Classe Sci. Math. Nat., N. S., 9 : 7 3 - - 9 3 (in Serbian with German summary). Taner, G., 1979. Die Molluskenfauna der Neogenen Formationen der Halbinsel Gelibolu. Ann. G6ol. Pays Hell~n., H. S., 1189--1194. Zhizhchenko, B. P., Seregenko, V. A. and Churilova, E. V., 1968. Ne0genovaja sistema. Geol. SSSR, IX, Severnii Kavkaz, pp. 388--441.