50. STRUCTURE AND EVOLUTION OF THE MEDITERRANEAN BASINS Bernard Biju-Duval, Jean Letouzey, and Lucien Montadert, Institut Français du Petrole Rueil-Malmaison, France ABSTRACT In this paper we attempt to reconstruct the general history of the Alpine-Mediterranean realm on the basis of geological cross- sections onland and offshore, general mapping of the basins and the main structural units of the Mediterranean area, and geophysi- cal data. The history of the Alpine-Mediterranean realm is related to the plate movements of Europe and Africa and associated with the opening of the Atlantic. After a first stage with a broad oceanic domain (Tethys), the opening of a proto-eastern Mediterranean and the formation of active margins south of Europe modified the physiography until the stage of continental collision. The western and eastern Mediterranean basins differ. The western basins are very young: Oligocene-Miocene episutural and intracontinental marginal basins, recently rejuvenated (Tyrrhenian Sea) and always part of the Alpine orogenic belt. The eastern basins are remnants of a former much larger Mesozoic basin south of the still active Alpine belt. The Cyprus, Aegean, and Calabrian arcs are described succes- sively. Diagrammatic sections and schematic maps show this Ceno- zoic evolution and a speculative history is presented. INTRODUCTION northern Algeria [Burollet et al., in press]; Israel [Gvirtzman et al., in press]; Turkey, the Aegean Sea, Relatively few seismic reflection data with good etc.). penetration were available in the deep Mediterranean All this information can be used to place the results basins at the time of the completion of DSDP Leg 13. of Leg 42A in a broad geological setting and we In particular, almost no information existed on the attempt here to emphasize the contribution of Leg 42A geological structure below the top of the Messinian to the reconstruction of the structural history of the evaporites defined by Horizon M (Ryan, 1969). The Mediterranean basins (Figure 1). first deep seismic information came with the use of Drilling and seismic reflection, however, give data multichannel seismic reflection which was used in 1970 mainly on the more recent geological history only: to establish the seismic stratigraphy of the deep west- primarily the Cenozoic in the western Mediterranean ern Mediterranean basins (Montadert et al., 1970). and part of the Mesozoic in the eastern Mediterranean. Since that time, data accumulated by several institu- But the recent history of these basins is related to their tions (IFP-CEPM, OGST, CNEXO, etc.) and oil com- earlier history and we must consider the geological panies have produced a better understanding of the events that succeeded one another in the region be- general geological framework of the different Mediter- tween Africa and Eurasia before describing the present ranean basins (Mulder, 1973; Finetti et al., 1973; basins. Mauffret et al., 1973; Biju-Duval et al., 1974; Morelli, Because of the very large number of publications 1975). concerning the Mediterranean area that have appeared These new data enabled new objectives to be pro- in the last 100 years, we cannot give a complete posed for the Glomar Challenger. In particular, the bibliography of all the papers considered in this syn- possibility of exploring the pre-evaporitic series was thesis. Many of them have been cited in previous recognized. These objectives were defined by several papers (Biju-Duval et al., 1974; Biju-Duval, 1974). site surveys conducted in both the Western and Eastern Consequently, we cite here only more recent papers or Mediterranean Sea by IFP-CNEXO with multichannel those useful for providing a general background or seismic reflection. specific data. Moreover, some information from offshore oil drill- ing has recently been published. These data are of prime importance for understanding the geological OUTLINE OF THE GEOLOGICAL HISTORY OF history of the margins and deep basins, and they THE ALPINE-MEDITERRANEAN AREA DURING provide an opportunity to relate land geological data MESOZOIC AND EARLY CENOZOIC TIME and DSDP drilling data (for example, drilling in the Several attempts have previously been made to Gulf of Lion [Cravatte et al., 1974] Gulf of Valencia, reconstruct the Alpine-Mediterranean geological his- 951 B. BIJU-DUVAL, J. LETOUZEY, L. MONTADERT 1 Sedimentary Basins 2 Stable Areas 3 Orogenic Belts 4 Main directions of folding 5 Major overthrusts , fronts of nappes 6 Major faults a) onshore b) offshore Figure 1. Structural map of the Mediterranean Sea. tory following different approaches: (1) from mainly employ the broad plate tectonic framework for the land data (for example, Klemme, 1958; Dercourt, Alpine-Mediterranean area which was briefly presented 1970; Argyriadis, 1975; Enay, 1972; etc.); (2) from the by Biju-Duval et al. (Split Symposium, 1976) and was application of plate tectonics concepts, using a reconsti- discussed in detail later (Biju-Duval et al. 1977). tution of relative movements of Europe and Africa and recognizing the geological consequences in the Alpine- Pre-Mesozoic (Figure 2[1]) Mediterranean area (Dewey et al, 1973); or (3) by a Many geologists and geophysicists agree that before combination of both approaches (Bosellini et al., 1973; the Mesozoic a very large Tethyan Ocean existed in the Trumpy, 1975; Laubscher and Bernouilli, in press). east which was connected with the Pacific Ocean. This In this paper we do not try to present a detailed concept of a very large ocean, however, cannot be reconstruction, but to schematically present our view accepted as definitive. Argyriadis (1975) cast doubt on of the structural history of the area at different periods: it by arguing that no marginal- or oceanic-type Per- pre-Mesozoic, Triassic, upper Liasic, Upper Jurassic, mian deposits have been found. Also, the concepts of Upper Cretaceous, upper Eocene. We use these specu- plate kinematics, on the basis of Atlantic magnetic lations as a starting point for the discussion of the anomalies, do not allow for a precise fit before anom- western Mediterranean Basin, whose history began in aly 32 (Santonian). Before that time a small difference the Oligocene, and as a general framework for the in the Atlantic fit would introduce very great differ- older eastern Mediterranean Basin. In this paper, we ences in reconstructions of the eastern part of the 952 STRUCTURE AND EVOLUTION OF THE MEDITERRANEAN BASINS gravity slidings 8 Volcanism 9 Major recent deltas 10 Mediterranean Ridge - Central Black Sea High 11 Tyrrhenian abyssal plain 12 Bathymetry Figure I. (Continued). future Mediterranean area. Thus, the existence of this Menderes) the metamorphic series have been so af- large Tethys is still speculative, and consequently its fected by later orogenies that their true nature, age, western extent is also questionable. and structural position are currently being studied. For Note that all the Paleozoic massifs surrounding the example, recently metamorphosed platform deposits of western Mediterranean (Iberian Meseta, Pelvoux, Mer- Mesozoic age have been discovered around the Men- cantour, Corsica, Sardinia, Kabylia, Menorca, etc.) deres (5 th Symposium on the Geology of Aegean were involved in the Hercynian Orogeny. The southern Regions, 1975). Thus the pre-Triassic Tethys was boundary of the Hercynian fold belt was probably located between the Hercynian fold belt to the north located near the present Saharan flexure (Figure 211]). and the Arabic-African-Anatolian-Apulian plate in the There are only a few indications of flexures, possibly South. To the West, the Mesozoic features are located related to margins of upper Carboniferous to Permian inside the Hercynian fold belt. age, in the northwestern Sahara region. The Permian Djeffara flexure is an intracratonic feature. In the eastern Mediterranean, it now appears that the Paleo- Triassic-Lias Period (Figure 2[2]) zoic in Taurus (Turkey) is a northern extension of the In the Triassic a clear contrast in depositional Arabic-African series. It was not involved in the environment existed between the west and the east. Hercynian Orogeny. In Yugoslavia, Greece, western During the entire time the western area was receiving Turkey (Serbo-Macedonian, Pelagonian, Cyclades, shallow-water marine deposits or continental deposits 953 B. BIJU-DUVAL, J. LETOUZEY, L. MONTADERT / / iI 1 PRETRIASIC > 200 M.A. (Size of the Tethys depending 4 LOWER CRETACEOUS 125 M.A. Opening of the Atlantic on the southern Atlantic fit) L a 2 LIASIC 180 M.A. Opening of Western Tethys 5 UPPER CRETACEOUS 70 M.A. initiation of Eastern Mediterranean Continental collision north of Arabia 3 UPPER JURASSIC 150 M.A. First obduction of ophioiitβs 6 EOCENE 45 M.A. Continental collision Figure 2. Tentative plate evolution in the Tethys-Alpine-Mediterranean area. 954 STRUCTURE AND EVOLUTION OF THE MEDITERRANEAN BASINS with well-characterized brackish intercalations ("Ger- Characterization of the continental margins created manic facies"). After the Werfenian episode when at that time is nevertheless still difficult because of the continental or brackish influences predominated, a succession of several tectonic phases. Studies in pro- marine transgression occurred which probably came gress by Bernoulli, Marcoux, Bourbon, Lemoine, and from the east (Tethys) and resulted in deposition of Blanchet are resolving this problem. carbonate platform sediments. More restricted condi- tions with large evaporitic deposits prevailed during Late Jurassic (Figure 2[3]) the upper Triassic (Keuper). In the eastern area, In the east, the Late Jurassic was a time of intense toward the edges of the Tethys, the presence of marine tectonic activity (Paleo-Dinarides, Dercourt, 1970; "Alpine facies" indicate the proximity of an open sea Aubouin et al., 1970), with obduction of the ophiolites during that time. On these edges (Lombardy, Di- which were later reworked into the flysch. It is still narides, Hellenides), platform carbonate facies merge uncertain whether they are chunks of a true ocean floor into deep water facies, particularly in the upper Trias- or of a marginal basin. sic deposits (Bernoulli et al., 1974; Bosellini et al., We do not know if the oceanic area that had 1973).