Tectonophysics 357 (2002) 1–31 www.elsevier.com/locate/tecto Tectonic paleostress fields and structural evolution of the NW-Caucasus fold-and-thrust belt from Late Cretaceous to Quaternary Aline Saintota,*, Jacques Angelierb a Vrije Universiteit, Instituut voor Aardwetenschappen, De Boelelaan 1085, 1081HV Amsterdam, Netherlands b Tectonique, ESA. 7072, Universite´ P. et M. Curie, T 25-26, E1, case 129, 4 Place Jussieu 75252 Paris cedex 05, France Received 26 May 2000; accepted 11 January 2002 Abstract The NW-Caucasus fold-and thrust belt essentially corresponds to the inverted western Flysch Zone of the Great Caucasus Mountains, a deep basin that developed from Late Jurassic to Eocene times between the Scythian Plate to the north and the Transcaucasian terranes to the south (the Shatsky Ridge, SW of the NW-Caucasus zone). The Flysch Basin was strongly affected by compression in Late Eocene times, when the characteristic WNW trending folds and thrusts of the NW-Caucasus belt developed (some authors regard the main compressive deformation as Miocene in age). By means of remote sensing analysis, we elucidate the geometry of major structures in the belt: WNW trending south-vergent thrusts and folds, and major vertical and transverse NNE–SSW to NE–SW deep fault zones. The later structures are interpreted as ancient faults that were active during the development of the Flysch Basin. Paleostress investigations reveal seven main tectonic episodes in the evolution of the NW-Caucasus since Late Cretaceous. Combining structural interpretation, remote sensing analysis and paleostress field reconstruction, we propose a model for the structural evolution of the belt. During the Late Cretaceous–Paleocene, the western Caucasus zone was under transtensional regime with an E–W to NE–SW trending r3 that generated oblique normal movements along NNE–SSW transverse faults and WNW–ESE margins of the Flysch Basin. This tectonism could correspond to rifting related to the formation of the Eastern Black Sea Basin. At the Paleocene–Eocene boundary, a transpressional event with an E–W to NW–SE trending r1 developed and the NNE–SSW to NE–SW trending faults could have been inverted. This event could correspond to an attenuation in the Eastern Black Sea Basin formation or to the incipient accretion of the Transcaucasian terranes. During the Eocene, another E– W to NW–SE oblique extension (-transtensional event) affected the Flysch Basin that could be related to a known rifting phase in the Eastern Black Sea Basin. Strong NNE–SSW to NE–SW compression characterises Late Eocene tectonism. The fold- and-thrust belt developed at this time as a result of the direct collision of the Shatsky Ridge with the Scythian Plate. A NE–SW extension followed the Late Eocene event, related to basin development around the newly formed fold belt. A WNW–ESE oblique contraction affected the belt during the early Miocene as the result of Arabian Plate convergence with the Caucasian system. The latest inferred event is a compressional regime, with NNW–SSE trending r1 that is affecting the NW-Caucasus belt from Sarmatian times until the present. Under this oblique compression, the belt has deformed as in a dextral shear zone and the thrust surfaces have acquired lenticular shapes. This study highlights the occurrence of oblique movements in the NW-Caucasus area prior to and after the dominant Late Eocene compression. From the Late Cretaceous until the Eocene, the structural * Corresponding author. E-mail addresses: [email protected] (A. Saintot), [email protected] (J. Angelier). 0040-1951/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S0040-1951(02)00360-8 2 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 development of the NW-Caucasus was closely related to the evolution of the Eastern Black Sea Basin. From the Late Eocene until Quaternary times, it was rather related to the Arabia–Eurasia plate convergence. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Brittle tectonics; Structures; Paleostress field; NW-Caucasus; Fold-and-thrust belt; Eastern Black Sea 1. Introduction Mesozoic–Cenozoic times along the Crimea–Cauca- sus boundary (Milanovsky and Khain, 1963; Razve- Between the Black Sea domain and the East-Euro- taev, 1977; Muratov et al., 1984; Khain, 1984; pean platform, major deformation occurred during Dotduyev, 1989; Zonenshain et al., 1990; Nikishin et Fig. 1. (a) Location of the studied area. (b) Geodynamics: Late Cenozoic plate kinematics of the Black Sea–Caspian region from Vardapetyan (1980) and Zonenshain et al. (1990). (c) Structural setting from Tugolesov et al. (1985), Finetti et al. (1988) and Shreider et al. (1997). A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 3 al., 1998a,b). This study is focused on the NW-Cauca- structural analysis and reconstruction of stress states sus, the westernmost segment of the Great Caucasus was indispensable. Along with remote sensing analy- belt, adjacent to Crimea (Fig. 1). The timing of tectonic ses, it allowed us to depict the tectonic evolution of events that have affected the area is poorly constrained. the belt, including determination of the structural The main orogenic phase is considered to be Late expression of tectonic events. Combining remote Eocene by Milanovsky and Khain (1963), Grigor’yants sensing analyses and paleostress results thus allows et al. (1967), Milanovsky et al. (1984), Muratov et al. us to propose a new scheme for the Late Cretaceous (1984) and others, whereas it is Miocene according to and Cenozoic structural evolution of the NW-Cauca- Dotduyev (1987), Shcherba (1987, 1989, 1993), sus fold-and-thrust belt. Zonenshain et al. (1990), Kopp (1991), Kopp and Shcherba (1998), etc. Another issue that is still matter of debate is the age of the opening of the East Black Sea 2. Geological setting of NW-Caucasus Basin, close to the NW-Caucasus belt: Late Cretaceous and Paleocene according to Finetti et al. (1988), Eocene The NW-Caucasus belt is classically described as a according to Lordkipanidze (1980), and Late Paleo- wide anticlinorium. Lower and Middle Jurassic rocks cene–Eocene according to Robinson et al. (1996) and are present in its core, whereas Late Jurassic to Eocene Shreider et al. (1997). Flysch formations lie on its flanks and Maastrichtian to We aim at better constraining the Late Cretaceous Quaternary deposits form successive cuestas on its and Cenozoic tectonic evolution in the NW-Caucasus northern limb (Fig. 2a). The Triassic and Jurassic area by combining structural analysis with the paleo- history of the area is not well constrained and still a stress reconstruction method (Saintot, 2000). In the matter of debate. The extent and age of Cimmerian NW-Caucasus, brittle deformation has been well orogenic phases, in Late Triassic or Early Jurassic, recorded in the competent beds of the widespread Middle Jurassic and Late Jurassic times, as well as the Flysch formation, which is Cretaceous to early Cen- successive rifting events, are not known. Nevertheless, ozoic in age. The overlying and underlying series an angular unconformity is reported at the bottom of have also been observed in places. The inversion of Upper Jurassic (due to the intra-Callovian Cimmerian more than 2000 brittle structural data, collected at 58 orogenic phase; Nikishin et al., 1998a,b). Most of the sites in the NW-Caucasus, has allowed reconstruction NW-Caucasus (Fig. 2a) corresponds to the western part of 124 local stress states. A majority of sites revealed of the so-called Flysch Zone of the Great Caucasus. polyphase tectonics. Fault slip data, 1800, were used This ancient basin was evolving from the Late Jurassic to calculate 72 stress tensors of good quality. We show up to the Late Eocene, between the Scythian Plate and that several stress regimes prevailed at different tec- the Shatsky Ridge. This basin was filled by 6–8 km of tonic stages in the late history of the WNW–ESE flysch-type sediments (Milanovsky and Khain, 1963; trending western Caucasus Mountain belt. Lordkipanidze, 1980; Koronovsky, 1984; Gamkre- The determination of paleostress regimes is of lidze, 1986; Beloussov et al., 1988; Adamia and particular interest if their relation to the general Lordkipanidze, 1989; Zonenshain et al., 1990). structure of the mountain belt is identified. In order According to the many authors, the closure of the to determine the relation between major structures and Flysch Basin and the orogeny of the Great Caucasus paleo-tectonic regimes, we undertook a systematic belt occurred in the Late Eocene times (Shardanov and study based on remote sensing mapping. In addition Peklo, 1959; Beliaevsky et al., 1961; Milanovsky and to the compilation of available geological maps and Khain, 1963, Grigor’yants et al., 1967; Milanovsky et numerous papers on the geology of the NW-Caucasus, al., 1984; Muratov et al., 1984; Giorgobiani and Zakar- we had access to the structural pattern through a aya, 1989; Robinson et al., 1996; Lozar and Polino, detailed analysis of the Landsat Thematic Mapper 1997; Robinson, 1997; Nikishin et al., 1998a,b, 2001, imagery. Although the remote sensing analysis pro- Mikhailov et al., 1999). The resulting dominant struc- vided valuable structural information, it could not tural grain is trending WNW–ESE, expressed by many suffice to thoroughly explain the tectonic evolution major thrust planes and folds (Fig. 2a). The strati- of the area. Field study in terms of both conventional graphic units of the ancient Flysch Basin were 4 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 Fig. 2. (a) Structural map of NW-Caucasus (in Giorgobiani and Zakaraya, 1989) with location of the profile (b). Ak, Akhtyr Fault; Bz, Bezeps Thrust; D, Djiguinsky Fault (or Anapa Fault); Dj, Djankhot Fault; G, Gelendjik Fault; K, Kabardinsky Fault; KP, Krasnaya Poliana Fault; M, Moldavansky Fault; Mo, Monastirsky Fault; NM, Novo-Mikhaı¨lovka Thrust; P, Pchada Fault; Pc, Pchich Thrust; PA, Pchekha-Adler Fault; S, Semigorsky Thrust; Sm, Semisamsky Thrust; T, Tougoups Fault; Ta, Tamakhinsky Fault; To, Tuapse Fault; VA, Verne-Abinsky Fault; Y, Yujni Thrust.