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. (b) The southwestern vergent thrusting and related folding in the NW-Caucasus belt (in Robinson et al., 1996). upthrusted onto the Shatsky Ridge and SW-vergent Indolo-Kuban and the Tuapse troughs, respectively, deformation prevailed in the entire NW-Caucasus belt, north and south of the NW-Caucasus belt (Tugolesov et as shown in a general cross-section (Fig. 2b). The al., 1985). Many observations and studies allowed boundary fault zones of the ancient Flysch Basin and assuming that an important compression occurred in of the present-day fold-and-thrust belt are the Akhtyr the Great Caucasus in Late Eocene times. Herein, we fault to the north and the Primorsky and East Black Sea propose to develop some of them. First, the regional Faults to the south. During the Oligocene and early angular unconformity of the bottom of the Maykop Miocene times, thick sediments of the Maykop group group on deformed underlying units is observed on the were deposited with angular unconformity in the field (Milanovsky and Khain, 1963; Yakovlev, 1997; .Sitt .Agle etnpyis37(02 1–31 (2002) 357 Tectonophysics / Angelier J. Saintot, A.

Fig. 3. (a) Map of major structures in the NW-Caucasus belt as revealed by Landsat Thematic Mapper images; (b) tectonic slices in the Paleocene cuesta due to southwestern movement along thrust planes (location in (a)). From Saintot, 2000. 5 6 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31

Banks, personal communication; our study) and on et al., 1998b). All stratigraphic units are involved in seismic lines (Tugolesov et al., 1985; Robinson et al., south-vergent thrusting onto the Shatsky Ridge with 1996; Banks, personal communication and Fig. 2b) the southward propagation of the deformation front north and south of the Great Caucasus area. Second, an (Fig. 2b). Without taking into account evidences for important increase of tectonic subsidence occurred in early phases of collisional evolution of the Great the Indolo-Kuban basin as shown by burial history Caucasus in Late Eocene times (see paragraph above), modelling (back-stripping analyses of wells and some authors still assume that the western part of the numerical modelling of lithospheric deformation; basin was not inverted before this Miocene orogenic Nikishin et al., 1998a; Ershov et al., 1999; Mikhailov phase (Dotduyev, 1987; Shcherba, 1987, 1989, 1993; et al., 1999). From these two first points, the referred Zonenshain et al., 1990; Kopp, 1991; Kopp and authors assumed that the Indolo-Kuban and Tuapse Shcherba, 1998). troughs developed as flexural basins in response to lithospheric compression during Late Eocene times. Third, Lozar and Polino (1997) have carried on a study 3. Major structures as identified by remote sensing based on nannofossils assemblage in Maykopian sedi- analyses ments of the Kuban basin and in Upper Cretaceous rocks of the northern slope of the Great Caucasus (close We used Landsat Thematic Mapper images (satellite to Kamennomostsky, for location, see Fig. 3). They Landsat 5, paths and rows: 174-29 and 175-29, Earth have dated the bottom of the Maykopian group as Late surface coverage 185 Â 170 km) to identify major Eocene to Early Oligocene in age. The important points structures of the NW-Caucasus belt (Saintot, 2000). of their study are that the lower part of the Maykopian Classical processing was used in our analysis, involv- unit contains reworked assemblage (80% of the total ing dynamical stretching, directional filtering and assemblage) of Upper Cretaceous (identical to those three-channel combination (to obtain false coloured they found in Upper Cretaceous rocks of the Great images, classically using bands 4, 5 and 7, with a 30-m Caucasus chain) and Paleogene nannofossils and that ground resolution), in order to carry out our structural the delicate structures of these nannofossils are very analysis and to enhance the main lineament trends. well preserved (intact spines for example). Therefore, Initially, we identified the structures of the NW- they argue that the source of sediments was not the Caucasus belt: WNW–ESE and NW–SE directed northern Scythian platform (as previously referred in thrusts. Our structural map is given in Fig. 3a (see the literature) but a southern source area located on the also Fig. 2a for the previous mapping and location). present Great Caucasus where Upper Cretaceous and The stratigraphic units that compose the NW- Paleogene sediments were eroded. Also, the type of not Flysch Zone of Great Caucasus are identified accord- reworked nannofossils present at the bottom of the ing to their characteristic spectral signature; corre- Maykopian group could reflect restricted environmen- sponding ages are given according to the available tal conditions. This allows them to determine that clear geological maps (Geological map of Caucasus, 1964, environmental changes occurred at Late Eocene–Oli- scale 1:200000; Geological map of Western Cauca- gocene times, with a cooler climate or above all, due to sus, 1956, scale 1:500000). Distinct stratigraphic the isolation of the Paratethys domain (by uplift and units characterise four WNW–ESE trending zones. emersion of orogenic zone in the whole Caucasian– In the broad sense, these units compose a major Black Sea region). anticlinorium (Figs. 2 and 3a). Jurassic rocks form From Sarmatian times (Middle Miocene) until the the core of this anticlinorium, while Cretaceous units present, the NW-Caucasus has been affected by a new constitute the northern limb. The contact between compressive deformation (Beloussov, 1940; Sharda- these two units is well observed due to the high nov and Peklo, 1959; Milanovsky and Khain, 1963; contrast between textures on images. Maastrichtian Beliaevsky et al., 1961; Razvetaev, 1989; Kopp and and younger formations crop out as series of typical Shcherba, 1998; Shcherba, 1987, 1989, 1993; Kopp, cuestas, clearly expressed in the morphology of the 1989, 1991, 1996; Giorgobiani and Zakaraya, 1989; northern flank of the belt. The Cretaceous and Danian Zonenshain et al., 1990; Milanovsky, 1991; Nikishin flysch units compose most of the coastal zone to the A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 7 south. The contact between the coastal zone and the rocks. This zone is characterised by ramp anticlines at anticlinorium core is visible in the satellite images the rear of thrust planes, confirming the SW vergence and corresponds to the major thrust zones: the Bezeps of mass displacements (Fig. 3b). We consider that and the Yujni thrusts (Fig. 3a; see also Fig. 2a). The these south-vergent thrust planes are the surface internal structures of these zones are complicated by expression of branches of the Akhtyr Fault, the major numerous WNW–ESE trending faults that we inter- boundary fault between the Indolo-Kuban Basin and pret as south-vergent thrusts (Fig. 3a). the NW-Caucasus belt (Fig. 2). Just south of Goryatchi Klutch town, we can One of the major lineaments that we observe in the observe a system of SW-vergent thrusts producing Landsat TM images is the NW–SE trending Pchekha- tectonic slices in the scarp (cuesta) of the Paleocene Adler fault (Fig. 3a). This large fault complex forms a

Fig. 4. Some points to illustrate the method of fault slip inversion. (a) Illustration of the inversion method based on the Wallace (1951) and Bott (1959)’s principle: ‘‘the stria s is parallel to the shear stress H ’’; the INVD method (Angelier, 1990) minimises the difference m between the real striae s and the calculated shear stress s and also, the angle a. (b, c, d) Examples of polyphase tectonism. (b) The whole set is divided into two subsets, consistent with two different stress regimes. (c) Reactivated fault as shown by superposed sets of striae. (d) Back-tilted stress tensor. 8

Table 1 Characteristics of stress states used to reconstruct stress regimes as illustrated in Figs. 5–7, 10, 11, 14–16

Stress event Places Latitude/ Stratigraphic Lithology No. R ND r1 r2 r3 Ua%RUP Q longitude age Dir. Plung. Dir. Plung. Dir. Plung. in degrees Strike-slip regime Gelendjik 44.53/38.15 Upper Camp. Flysch 85 *R 7 137 09 228 05 344 80 0.7 11 26 3 with E–W to Novorossiisk 44.82/37.93 Con.-Sant. Flysch 95 *S 12 292 22 091 66 199 08 0.4 14 36 3 NW–SE r1 Anapa 45.02/37.47 Low. Paleoc. Flysch 99 *S 6 122 22 289 67 031 05 0.9 09 28 1 (Fig. 5) Tuapse 44.15/39.18 Con.-Sant. Flysch 110 *S 11 158 05 048 76 249 13 0.2 11 35 3 Tuapse 44.14/39.05 Camp.-Maas. Flysch 113 *S 12 347 01 228 87 077 02 0.3 12 27 3 Tuapse 44.15/39.02 Low. Paleoc. Flysch 114 *S 7 091 13 308 74 183 09 0.6 09 25 3

Tuapse 44.17/39.00 Low. Paleoc. Flysch 116 *S 11 285 02 021 76 194 14 0.4 10 30 1–31 3 (2002) 357 Tectonophysics / Angelier J. Saintot, A. Tuapse 44.18/38.92 Upper Cret. Flysch 118 *R 8 287 00 017 07 195 83 0.3 17 40 2 Arkhipo-Ossip. 44.33/38.70 Upper Maas. Flysch 124 *S 8 155 21 287 60 056 20 0.3 12 41 2 Kamennom. 44.28/40.21 Upper Jura. Limestones 142 S 16 327 09 093 75 235 12 0.3 7 31 3 Kamennom. 44.19/40.02 Lower Jura. Marls 143 S 11 123 07 287 82 032 02 0.4 19 50 2 Tuapse 44.12/39.05 Paleocene Flysch 151 *R 17 134 04 225 12 023 78 0.4 10 29 3 Tuapse 44.12/39.05 Paleocene Flysch 151 *S 13 317 06 213 69 049 20 0.1 12 30 2 Lazarevskoe 43.97/39.26 Upper Cret. Flysch 155 *S 6 100 1 296 89 190 00 0.5 5 11 1 Extensional regime Novorossiisk 44.82/37.93 Con.-Sant. Flysch 95 *N 5 033 78 153 06 244 10 0.4 07 15 1 with NE–SW Tuapse 44.17/39.22 Upper Camp. Flysch 109 *N 9 123 75 356 09 264 12 0.5 08 22 3 to E–W r3 Tuapse 44.15/39.18 Coniac.-Sant. Flysch 110 *N 8 016 77 187 13 278 02 0.6 12 24 2 (Fig. 6) Tuapse 44.16/39.02 Upper Maas. Flysch 115 *N 11 163 57 340 33 071 02 0.8 07 22 3 Tuapse 44.17/39.00 Lower Paleoc. Flysch 116 *N 7 195 80 288 00 018 10 0.8 08 22 1 Kamennom. 44.28/40.21 Upper Jura. Limestones 142 N 16 278 85 171 1 081 4 0.3 11 22 3 Kamennom. 44.19/40.02 Lower Jura. Marls 143 N 24 292 86 154 03 064 03 0.5 11 28 3 Tuapse 44.12/39.05 Lower Paleoc. Flysch 151 *N 12 250 79 358 03 089 11 0.4 13 32 3 Lazarevskoe 43.98/39.20 Upper Cret. Flysch 156-6 *N 4 188 77 314 08 045 10 0.6 10 24 1 Extensional regime Novorossiisk 44.67/37.56 Lower Paleoc. Flysch 14 *N 7 067 70 291 14 198 13 0.4 07 33 1 with NW–SE r3 Novorossiisk 44.67/37.56 Lower Paleoc. Flysch 14 *S 10 249 06 350 63 156 26 0.3 06 25 3 (Fig. 7) Novorossiisk 44.75/37.75 Upper Cret. Flysch 16 *N 23 218 80 039 10 309 00 0.3 07 21 3 Anapa 44.87/37.33 Upper Maas. Flysch 97 *N 5 288 87 029 01 119 03 0.6 15 46 1 Kamennom. 44.28/40.21 Upper Jura. Limestones 142 N 7 108 80 245 07 336 07 0.4 5 11 2 Shaumyan 44.43/39.45 Paleocene Flysch 145 *S 13 067 02 159 54 335 36 0.3 11 36 3 Kamennom. 44.23/40.17 Upper Jura. Limestones 150 N 6 227 41 029 48 129 09 0.7 11 37 1 Strike-slip regime Novorossiisk 44.72/37.60 Maas. Flysch 15 *S 7 195 07 343 82 104 04 0.4 03 12 2 with NE–SW r1 Novorossiisk 44.83/37.07 Con.-Sant. Flysch 96 *S 5 033 09 271 73 125 14 0.6 12 37 1 (Fig. 10a) Tuapse 44.17/39.22 Upper Camp. Flysch 109 *S 12 017 04 230 85 107 03 0.4 10 26 3 Tuapse 44.15/39.02 Lower Paleoc. Flysch 114 *S 4 015 07 266 70 107 19 0.2 03 22 1 Tuapse 44.17/39.00 Lower Paleoc. Flysch 116 *S 5 016 17 186 72 285 03 0.6 02 13 1 Shaumyan 44.43/39.45 Paleocene Flysch 145 *S 33 008 00 100 84 278 06 0.5 05 17 3 Tuapse 44.12/39.05 Paleoc.-Eoc. Flysch 151 *S 6 203 01 300 85 113 05 0.3 5 27 1 Tuapse 44.05/39.13 Maas. Flysch 153 *S 17 190 12 087 46 291 41 0.2 09 25 3 Tuapse 44.03/39.14 Maas. Flysch 154# *S 23 219 03 081 86 309 03 0.4 06 – 3 Lazarevskoe 43.98/39.20 Upper Cret. Flysch 156-4 *S 4 018 01 142 88 288 02 0.5 02 9 1 Compressional Novorossiisk 44.70/37.86 Upper Cret. Flysch 13 *R 13 214 10 122 10 348 76 0.5 16 38 3 regime with Novorossiisk 44.67/37.56 Lower Paleoc. Flysch 14 *R 34 038 03 308 06 152 83 0.5 10 37 3 NE–SW r1 Novorossiisk 44.75/37.75 Upper Cret. Flysch 16 *R 7 028 21 294 11 178 66 0.7 05 32 1 (Fig. 10b) Gelendjik 44.53/38.15 Upper Flysch 85 *R 5 214 10 305 02 044 79 0.6 02 10 1 Gelendjik 44.57/38.10 Upper Camp. Flysch 102 *R 16 047 05 315 22 149 68 0.4 37 51 2 Goryatchi K. 44.55/38.98 Valanginian Flysch 105 *R 15 209 06 300 05 069 82 0.4 12 31 3 Tuapse 44.14/39.14 Con.-Sant. Flysch 111 *R 19 224 02 134 05 334 84 0.6 10 25 3 Tuapse 44.12/39.05 Lower Paleoc. Flysch 112 *R 7 063 13 329 14 194 70 0.5 23 4 2 Kamennom. 44.19/39.90 Upper Jura. Limestones 147 *R 22 223 05 314 11 108 78 0.2 14 49 3 Tuapse 44.02/39.18 Upper Cret. Flysch 152 *R 4 207 13 300 11 067 73 0.6 10 23 1–31 1 (2002) 357 Tectonophysics / Angelier J. Saintot, A. Tuapse 44.05/39.13 Maas. Flysch 153 *R 10 202 11 298 31 095 57 0.3 12 30 3 Lazarevskoe 43.98/39.20 Cretaceous Flysch 156-3 *R 8 045 04 315 03 192 85 0.5 21 29 2 Arkhipo-Ossip. 44.43/38.35 Maas.Danian Flysch 158 *R 5 194 12 288 17 070 68 0.4 11 28 1 Compressional Gelendjik 44.55/38.17 Coniac.-Sant. Flysch 91 R 12 202 26 295 06 036 63 0.8 08 22 2 regime with Gelendjik 44.54/38.15 Con.-Sant Flysch 92 R 10 206 05 116 00 023 85 0.7 07 15 3 NE–SW r1 Tuapse 44.12/39.05 Lower Paleoc. Flysch 112 R 35 217 03 127 11 323 79 0.6 15 33 3 (Fig. 11a) Djubga 44.27/38.82 Upper Maas. Flysch 121 R 15 002 18 093 02 189 72 0.8 10 24 2 Kamennom. 44.28/40.21 Upper Jura. Limestones 142 R 6 032 02 301 12 132 78 0.5 5 20 2 Kamennom. 44.19/40.02 Lower Jura. Marls 143 R 4 222 04 127 52 316 37 0.1 06 38 1 Tuapse 44.12/39.05 Paleoc-Eoc. Flysch 151 R 5 215 00 305 04 121 86 0.6 06 20 1 Tuapse 44.02/39.18 Upper Cret. Flysch 152 R 17 213 02 303 00 041 88 0.3 10 28 3 Tuapse 44.03/39.14 Maas. Flysch 154 R 10 228 03 318 09 117 80 0.4 14 28 3 Tuapse 44.03/39.14 Maas. Flysch 154 R 13 199 08 292 24 092 65 0.2 09 32 3 Lazarevskoe 43.98/39.20 Upper Cret. Flysch 156-4 R 6 197 02 228 03 069 86 0.4 07 16 2 Lazarevskoe 43.98/39.20 Upper Cret. Flysch 156-5 R 7 057 08 148 07 276 79 0.6 05 13 3 Lazarevskoe 43.98/39.20 Upper Cret. Flysch 156-6 R 6 052 13 143 03 247 77 0.6 11 23 2 Arkhipo-Ossip. 44.38/38.35 Maas.Danian Flysch 157 R 4 212 07 302 00 032 83 0.5 01 16 1 Strike-slip Arkhipo-Ossip. 44.38/38.53 Coniac.-Sant. Flysch 86 S 5 024 07 118 33 283 56 0.1 10 29 1 regime with Arkhipo-Ossip. 44.38/38.53 Coniac.-Sant. Flysch 86 N 10 272 82 006 01 097 08 0.4 06 12 2 NE–SW r1 Arkhipo-Ossip. 44.47/38.40 Coniac.-Sant. Flysch 87 S 5 194 11 307 64 099 23 0.6 15 32 1 (Fig. 11b) Goryatchi K. 44.61/39.08 Lower Paleoc. Flysch 103 S 10 199 10 335 77 108 09 0.4 15 34 2 Tuapse 44.15/39.18 Coniac.-Sant. Flysch 110 S 27 190 07 334 81 100 05 0.2 12 34 3 Lazarevskoe 43.98/39.20 Lower Cret. Flysch 156-2 S 8 184 20 337 68 91 09 0.4 16 35 3 Lazarevskoe 43.98/39.20 Cretaceous Flysch 156-5 S 5 197 11 327 73 105 13 0.5 03 16 1 Extensional Gelendjik 44.53/38.15 Camp. Upper Flysch 85 N 4 252 83 147 02 057 07 0.5 02 17 1 regime with Novorossiisk 44.83/37.07 Coniac.-Sant. Flysch 96 N 10 257 84 148 02 058 06 0.4 12 33 3 NNE–SSW r3 Shaumyan 44.30/39.30 Upper Camp. Flysch 107 N 4 278 70 130 17 037 10 0.8 10 34 1 (Fig. 14) Shaumyan 44.28/39.28 Upper Cret. Flysch 108 N 8 058 64 297 14 201 22 0.4 15 45 2 Tuapse 44.15/39.02 Lower Paleoc. Flysch 114 N 5 229 63 136 02 045 27 0.4 05 22 1 Tuapse 44.19/38.89 Upper Maas. Flysch 119 N 12 250 69 114 16 019 14 0.6 11 34 3

(continued on next page) 9 10

Table 1 (continued )

Stress event Places Latitude/ Stratigraphic Lithology No. R ND r1 r2 r3 Ua%RUP Q longitude age Dir. Plung. Dir. Plung. Dir. Plung. in degrees Extensional Djubga 44.25/38.85 Upper Maas. Flysch 120 N 11 143 75 287 12 018 08 0.4 06 27 3 regime with Djubga 44.33/38.70 Upper Maas. Flysch 124 N 7 087 54 326 20 225 28 0.3 18 51 1 NNE–SSW r3

(Fig. 14) 1–31 (2002) 357 Tectonophysics / Angelier J. Saintot, A. Transpressional Arkhipo-Ossip. 44.47/38.40 Coniac.-Sant. Flysch 87 R 9 288 14 019 02 115 76 0.1 11 30 3 compressional Arkhipo-Ossip. 44.46/38.38 Upper Cret. Flysch 88 R 17 089 16 182 11 305 71 0.2 10 28 3 regime with Arkhipo-Ossip. 44.52/38.32 Upper Camp. Flysch 89 S 30 108 02 217 82 018 07 0.2 17 37 3 E–W r1 Gelendjik 44.54/38.15 Coniac.-Sant. Flysch 92 S 9 132 04 280 85 042 03 0.4 11 41 2 (Fig. 15a and b) Gelendjik 44.55/38.13 Coniac.-Sant. Flysch 93 R 21 280 08 186 23 027 66 0.7 16 34 3 Gelendjik 44.57/38.10 Upper Camp. Flysch 102 S 12 290 07 138 82 020 04 0.6 12 34 3 Tuapse 44.15/39.02 Lower Paleoc. Flysch 114 S 4 081 18 210 63 344 19 0.5 05 27 1 Tuapse 44.17/38.97 Lower Paleoc. Flysch 117 S 7 081 20 220 64 346 16 0.2 06 23 3 Tuapse 44.12/39.05 Paleocene Flysch 151 S 10 293 13 099 77 203 03 0.4 10 35 3 Tuapse 44.03/39.14 Maas. Flysch 154 R 5 094 03 184 01 298 87 0.3 14 40 1 Lazarevskoe 43.97/39.26 Upper Cret. Flysch 155 S 15 287 05 152 83 017 05 0.4 12 29 3 Compressional Gelendjik 44.53/38.15 Upper Camp. Flysch 85 S 8 338 04 181 85 069 02 0.7 08 29 3 regime with Arkhipo-Ossip. 44.52/38.32 Upper Camp. Flysch 89 R 13 140 00 050 11 231 79 0.5 10 22 2 NNW–SSE r1 Gelendjik 44.54/38.15 Coniac.-Sant. Flysch 92 R 10 165 07 256 09 036 78 0.2 10 24 3 (Fig. 16) Novorossiisk 44.83/37.07 Coniac.-Sant. Flysch 96 R 7 158 02 248 06 051 84 0.3 10 24 3 Tuapse 44.16/39.02 Upper Maas. Flysch 115 S 7 130 06 230 59 036 30 0.4 07 38 3 Tuapse 44.17/39.00 Lower Paleoc. Flysch 116 S 7 158 24 358 65 252 07 0.7 12 30 2 Djubga 44.25/38.85 Upper Maas. Flysch 120 R 14 143 11 052 06 294 78 0.7 12 29 2 Djubga 44.28/38.79 Upper Camp. Flysch 122 S 7 321 07 219 59 056 30 0.2 12 39 1 Djubga 44.30/38.77 Upper Cret. Flysch 123 S 16 159 02 344 88 249 00 0.2 10 30 3 Tuapse 44.02/39.18 Upper Cret. Flysch 152 S 5 170 06 064 69 262 20 0.6 03 15 1 No., reference number of the site; R, stress regime; S, strike-slip faulting; R, reverse faulting; N, normal faulting (with *, back rotated stress tensor). ND, number of fault slip data. Dir. and Plung., trends and plunges of stress axes in degrees. The used method to calculate stress tensor is INVD; for fault population of site 154#-line 39 in the table—R4DT method; methods as referred to in Angelier (1990); U ratio of stress magnitude differences, U=(r2 À r3)/(r1 À r3). a, average angle between observed slip and computed shear, in degrees (acceptable with a <25j). RUP, criterion of quality for the ‘‘INVD’’ method, ranging from 0% (calculated shear stress parallel to actual striae with the same sense and maximum shear stress) to 200% (calculated shear stress maximum, parallel to actual striae but opposite in sense), acceptable results with RUP < 75%. Q as quality of stress tensor: 3, high quality, 2, medium quality, 1, poor quality. A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 11 major boundary between the western Flysch Zone and (Angelier, 1984, 1989, 1990, 1994). Fig. 4 simply the central tectonic zone of the Great Caucasus summarises the main aspects of this approach, which (Milanovsky and Khain, 1963). Its trace allows char- is based primarily on solving the inverse problem acterisation of the fault as a steep plane. Remote according to the Wallace–Bott’s principle (Wallace, sensing analyses also allowed identification of a 1951; Bott, 1959; Fig. 4a). The amounts of data, the fracture network composed mainly of NE–SW and average misfits, and the overall quality of the deter- NNE–SSW trending linear fractures (Fig. 3a). Hydro- minations are listed in Table 1. Because the high and graphic network captures and topographic trends in medium quality stress tensors and stress trends the satellite images reveal this fracture network. Some deduced by stylolites or tension gashes are in suffi- fractures appear as long lineaments and correspond to cient number to reconstruct stress fields accurately, we the main fault zones already identified as deep ancient also took into account 31 stress tensors of lower geological structures (Giorgobiani and Zakaraya, quality. 1989; see the Gelendjik Fault, the Karbadansky Fault A common problem in paleostress determinations, and the Pchada Fault as examples in Fig. 2a). Thrust present in the NW-Caucasus, deals with the inhomo- and fold development seemed not to be influenced by geneous character of the data sets. Fault slip data sets these main structures, except in the Gelendjik region are commonly inhomogeneous because of rotations or where the Semigorsky thrust shows a typical bend particular block behaviour that can be detected based above the Kabardinsky Fault. NE–SW and NNE– on structural analysis; more importantly, this lack of SSW fractures of lesser dimension could be inter- mechanical homogeneity often results from polyphase preted as related to thrust formation, formed parallel brittle tectonism. In such cases, the separation into to the thrusting and accommodating mass displace- homogeneous subsets, which fit with different stress ment above the thrust planes. states and possibly correspond to distinct tectonic In summary, not only did the analysis of the remote events, must be carried out as summarised in Fig. sensing data contribute to the identification of the 4b. To establish the chronology between the brittle major structural grain of the belt (compare Figs. 2a events, we used various criteria, including consider- and 3), within the previously recognised fold-and- ation of the stratigraphic ages of affected rocks, the thrust structure (Fig. 2a and b), but also it allowed crosscutting relationships between various brittle geometric characterisation of major brittle structures structures, and the successive striae observed on fault and fracture networks of the NW-Caucasus belt. The surfaces (Fig. 4c). Furthermore, in folded areas, and SW-vergent thrust planes were well known, but the assuming that one of the principal stress axes was remote sensing analysis revealed the importance of vertical when faulting occurred (an hypothesis that the NE–SW to NNE–SSW trending major vertical can be checked by taking into account the geometrical and transverse faults. relationships between the bedding and the recon- structed principal stress axes), we could often estab- lish the chronology of stress tensors relative to a 4. Paleostress fields and major structure known folding event (Fig. 4d). This chronological development relationship between faulting and folding was of particular importance in the NW-Caucasus, because The brittle tectonic analyses allowed us to recon- brittle episodes may have occurred before, during or struct various paleostress fields that have successively after the main Late Eocene folding event (as well affected the NW-Caucasus area. Using the brittle dated during our field studies and analyses), and thus structures identified by the remote sensing analyses, can be better constrained in time within the history of it is possible to infer how the major faults acted under the belt. the reconstructed paleostress fields. At the scale of the whole belt, no paleomagnetic The first step in the paleostress analyses involved data were available and we are unable to assume that data collection in the field and the computation of no block rotations occurred. We estimated that such local stress tensors using the fault slip data sets. The rotations were minor, because within a single stress inverse methods are described elsewhere in detail field, the reconstructed stress trends appear to be 12 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 consistent in the whole area. Had rotations occurred, Paleocene rocks (sites 14 and 145). This extension these trends would have shown large variations for a is recognised at eight sites and well recorded in given event. Kamennomostsky region (sites 142, 148, 149 and 150). The related stress states indicate a change in 4.1. Tectonic evolution of the NW-Caucasus Flysch extensional trend from E–W to NW–SE. At site 142, Basin from Late Cretaceous to Late Eocene (near Kamennomostsky), the chronological relation- ship between NE–SW and NW–SE extensions is 4.1.1. Pre-Late Eocene paleostress fields clearly determined by observations of systematic In this subsection, we refer to 38 stress states which crosscutting relationships between two sets of tension correspond to brittle tectonism that predate the tilting gashes (Fig. 8). The first set of tension gashes, filled of the bedding planes that is related to the major Late with pink calcite, developed under a NE–SW directed Eocene folding and thrusting. These states form three extension whereas the second set, filled with white paleostress fields with contrasting types (strike-slip calcite and pyrite, developed under NW–SE exten- and normal) and directions. sion (Fig. 8). These two sets of tension gashes are First, a strike-slip regime with r1 trending E–W to consistent with the two populations of normal faults NW–SE was inferred (Fig. 5 and Table 1). It affected collected in this site (Fig. 8). Lower Paleocene rocks. This is the oldest event Thus, the extension, which predated folding and recognised with certainty in our analysis in the west- thrusting of Late Eocene times in the NW-Caucasus, ern Great Caucasus (Saintot et al., 1998). A total of 16 is characterised by three trends of r3:NE–SW,E–W stress states reliably compose the stress field and 12 of and NW–SE. One may interpret these three trends as them are of good quality. The brittle tectonism of this the expression of independent extensional events. event is not exclusively strike-slip in type: within this However, because there is no independent geological event, strike-slip stress tensors and compressional evidence to support this hypothesis, we believe that it stress tensors were recorded in rocks such as at site is more reasonable to interpret them as part of a single 151 (Fig. 5). No chronological evidence was found to major extensional period, characterised on the whole distinguish reverse and strike-slip faults. Therefore, by a low average ratio between principal stress differ- because these two types of stress tensors are consis- ences, U=(r2 À r3)/(r1 À r3), resulting in easy tent with a single stress field and hence can be switches between, or rotations of, the extensional interpreted as the simple result of local permutations trends (see discussion about U in Angelier, 1989). between the r1 and r2 stress axes (a common phe- On the other hand, according to the previous nomenon in brittle tectonics), it would not be justified paleostress analyses, carried on by Se´brier et al. to separate the strike-slip and reverse modes as dis- (1997) in the northern part of the Great Caucasus east tinct events. of Kamennomostsky (Fig. 6), the NE–SW to E–W Following this strike-slip stress regime, an exten- extension also corresponds to a Campanian event as sional event occurred with r3 directed NE–SW to E– revealed by syn-sedimentary structures. This is cer- W. It was observed at 14 sites (Fig. 6, Table 1). Six of tainly not the case in our study area for most of the these paleostress tensors are of good quality. Despite stress states related to this event, because the corre- the general consistency, the reconstructed extensional sponding brittle structures (fault and tension gashes) stress states at nine sites showed that the extension affected rock formations up to the Lower Paleocene in also was E–W directed (Fig. 6). Paleocene rocks were age. However, the stress tensors determined in the affected by this tensional event (sites 116 and 151). Jurassic rocks at sites 142 and 143 (Fig. 6) could well The chronology between strike-slip and extensional correspond to a Campanian event. According to this regimes (Figs. 5 and 6) could for example be estab- interpretation and based on the chronology as estab- lished based on observation of the offset of a strike- lished at site 143, the strike-slip stress tensors recon- slip fault surface related to the first event by a normal structed at these two sites (Fig. 5) should belong to the fault related to the second one at site 143. earlier event. This conclusion would be of importance The paleostress field presented in Fig. 7 shows for the history of the belt but the data to support it are another, NW–SE, extensional trend that affected too scarce for full confirmation. Furthermore, the A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 13

Fig. 5. Distribution of stress states related to a strike-slip stress field with r1 trending E–W to NW–SE and prior to the Late Eocene phase (from Saintot, 2000). Examples of stereoplots illustrating the stress field (for each site: fault population in the present-day geometry-with calculated stress tensor when homogeneous bedding planes at the site—and calculated stress tensor with primary horizontal bedding planes). Characteristics of used local stress states are shown in Table 1. strike-slip stress tensors could also be interpreted in (1988), or in Paleocene–Eocene times according to terms of local perturbations of the regional extensional Lordkipanidze (1980), Robinson et al. (1996) and stress field, considering that a r1 and r2 stress axis Shreider et al. (1997). The stress events recorded in permutation occurred (the NE–SW orientation of r3 the western Flysch Zone of Great Caucasus, as being maintained). described above, are certainly related to East Black Sea Basin development. In Fig. 9,weproposea 4.1.2. The structural evolution of the western regional tectonic evolution taking into account the Caucasus Flysch Basin under paleostress regimes structure of the Flysch Basin, our paleostress data, and from Late Cretaceous until Eocene times the setting of the East Black Sea Basin. The East Black Sea Basin developed from the Late Fig. 9a presents a map of the activity of the major Cretaceous to the Paleocene according to Finetti et al. structures of the Flysch Basin in Late Cretaceous– 14 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31

Fig. 6. Distribution of stress states related to an extensional stress field with r3 trending NE–SW to E–W (from Saintot, 2000). These extensional stresses occurred prior the Late Eocene folding phase. Examples of stereoplots illustrating the extensional stress fields. Characteristics of used local stress states are shown in Table 1.

Paleocene times, under an E–W to NE–SW exten- sky and Khain, 1963). The major transverse NNE– sional stress field (Fig. 7). The major transverse SSW faults (see Fig. 3a) are thus interpreted as vertical faults trending NE–SW to NNE–SSW can normal-left lateral strike-slip faults under the E–W be interpreted as ancient structures in the western to NE–SW extensional stress trend (Fig. 9a). Just east Caucasus region (Giorgobiani and Zakaraya, 1989). of our study area, in Jurassic as well as in Late At the scale of the Great Caucasus, activity along such Cretaceous times, normal displacements developed structures could have produced the well-known lateral along the NW–SE trending faults under an exten- variations in the oldest sedimentary series (Milanov- sional regime generally directed NE–SW to E–W A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 15

Fig. 7. Distribution of stress states related to an extensional stress field with r3 trending NW–SE (from Saintot, 2000). This stress field occurred prior the Late Eocene folding phase. Examples of stereoplots illustrating the extensional stress field. Characteristics of used local stress states are shown in Table 1.

(Polino et al., 1997; Se´brier et al., 1997), as along the towards a transtensive regime, in the Late Cretaceous. Pchekha-Adler Fault (Fig. 9a). The Akhtyr fault is Note, in this respect, that we assume that the divergent considered to be the southern boundary of the Scy- relative displacements of the micro-blocks involved in thian platform; at that time, it could have been a the Late Cretaceous tectonic setting were oblique normal right-lateral strike-slip fault like the Primorsky relative to the Scythian Platform margin. and East Black Sea faults. These faults comprise the The extensional stress events could correspond to Late Eocene thrust front of the NW-Caucasus belt on the rifting of the East Black Sea Basin (Saintot et al., the Shatsky Ridge, but they could also represent 1998). During the Late Cretaceous, magmatism was earlier structures developed as boundaries between present in the Flysch Basin. It is interpreted as the the Shatsky Ridge and the Flysch Basin (see Fig. 2a result of an important episode of crustal thinning and b for location). The paleostress trends clearly (Lomize, 1969; Chaitsky and Shelkoplyas, 1986; highlight the tectonic transition of the Flysch Basin Koronovsky et al., 1997). The character of the East 16 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31

Fig. 8. Example of field criteria illustrating the chronology between the NE–SW extension and the NW–SE extension. (a) and (b) Chronology between two sets of mineralized tension gashes, observed in Upper Jurassic limestones near Kamennomostsky (site 142). The first set is filled with pink calcite and developed under a NE–SW extension; the second set is filled with white calcite and pyrite and, developed under a NW– SE extension (remark: where the two sets intersect, the youngest tension gashes developed in pre-existing NW–SE directed tension gash planes. Far from this zone, they have a distinct NE–SW orientation). (c) Stereoplots of tension gash sets (on the left) and computed stress tensors (on the right) illustrating the two extensional trends.

Black Sea Basin rift zone is poorly known. According have been inverted. The Pchekha-Adler fault and the to Shreider et al. (1997) and Nikishin et al. (2001),it Flysch Basin marginal faults (Primorsky and East probably trends NW–SE. This trend could be com- Black Sea Faults to the south and Akhtyr Fault to patible with the E–W to NE–SW extension that we the north) were characterised by left-lateral strike-slip determined for the Late Cretaceous–Paleocene in the movements (Fig. 9b). This strike-slip regime (Fig. 5), NW-Caucasus region, which could therefore be that is difficult to correlate with the structural data and related to the East Black Sea Basin opening. tectonic interpretations found in the literature, may Nikishin et al. (2001) mentioned that a compres- reflect the occurrence of transitional stages in the sive phase is recorded in the northern Black Sea paleostress history of this region, during the East region at the Paleocene–Eocene boundary. The Black Sea Basin development and prior to the major strike-slip stress field affecting Paleocene strata (Fig. tertiary compressions in the Caucasus. One may 5) could well fit with this tectonic event. We argue suppose that the basin development has produced that at the Paleocene–Eocene boundary, the western strong perturbations of stress in the surrounding zones Great Caucasus Flysch Basin was affected by an E– as in the western Great Caucasus Flysch Basin; this W to NW–SE transpression (Fig. 9b). Under such a hypothesis, however, is presently not supported by regime, the NNE–SSW initially normal faults could accurate field data or reasonable modelling. Another A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 17

Fig. 9. Structural evolution scheme of NW-Caucasus Flysch Basin from Late Cretaceous to Eocene relative to the East Black Sea Basin development: (a) Late Cretaceous–Paleocene times: E–W to NE–SW extension–transtension relative to the first (?) step of East Black Sea Basin development; (b) Paleocene–Eocene boundary: E–W to NW–SE transpression (with a slowing down in the East Black Sea Basin rift process?); (c) Eocene times: E–W to NW–SE extension–transtension relative to an East Black Sea Basin rift reactivation (?). 18 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 hypothesis takes into account the 90j angular relation- (Lordkipanidze, 1980; Robinson et al., 1996). If East ship between the regional stress axes related to the Black Sea Basin development initially occurred in the rifting on one hand, and to this specific event on the Late Cretaceous times, this Eocene extension could other hand (Fig. 9). This relationship can be regarded imply a post-rift reactivation that we assign to a as a permutation of the stress axes (from an E–W transtensional tectonics with right-lateral movements directed r3 to an E–W directed r1). According to this along the basin marginal faults (Fig. 9c; Saintot et al., observation, the strike-slip stress event may result 1998). from an increase in the confining pressure induced From the Late Cretaceous to the Eocene, according by a decrease in the rifting process intensity, produc- to the obliquity of our reconstructed stress trends ing a transition from opening to transpression. To relative to the geometry of pre-existing structures check this hypothesis, a better knowledge of the basin (Fig. 9), we propose that the western Great Caucasus opening history is needed, because the East Black Sea Flysch Basin was under transpressive or transtensive Basin rifting process would have ceased at this time. regimes of deformation (Angelier et al., 1994; Saintot A completely different explanation would involve the et al., 1998). We also propose that the extensional development of boundary forces caused by the dis- stresses are related to the opening of the East Black placement of the Transcaucasian terranes (located Sea Basin not only in the Late Cretaceous–Paleocene south–east of the studied area) moving toward the times but also in Eocene times. north. This displacement may have induced an E–W directed compression in the area to the NW, and hence 4.2. The Late Eocene compression and the NW- deeply modified the stress regime that prevailed in Caucasus fold-and-thrust belt this area (with important stress trajectory deviations due to pre-existing major fault zones which are Our study has allowed to propose a reconstruction present between the Transcaucasia and our studied of the tectonism of the NW-Caucasus belt during the area). Because of the ongoing East Black Sea Basin main compression in Late Eocene times. Not only is opening, the E–W directed compression was this the best-recorded event in terms of micro-frac- expressed by a strike-slip regime (transpression) turing but also we could recognise a detailed evolu- rather than by a pure compressive regime. To check tion of stresses during the fold-and-thrust belt this third hypothesis, enlarged regional analyses formation. would be necessary. Whatever the real cause of this change, reverse and left-lateral strike-slip movements 4.2.1. Paleostress fields related to the folding and certainly developed under this strike-slip regime at the thrusting of the Late Eocene Paleocene–Eocene boundary, along the basin mar- The rose diagram shown on the lower right corner ginal fault zones of NW-Caucasus (Fig. 9b). of Figs. 10b and 11a presents the orientations of the During the Eocene times, a nearly E–W to NW– entire population of micro-faults measured in the SE extension (Figs. 6 and 7) affected the western field (1801 data). It illustrates two predominant Great Caucasus Flysch Basin. Under this regional directions of micro-fracturing in the NW-Caucasus stress orientation, the NNE–SSW transverse faults belt: WNW–ESE and NW–SE. These directions probably moved as normal faults (Fig. 9c). During the correspond to those of the major structures of the Eocene, the dominant extensional trend was still NW-Caucasus belt: fold axes and thrusts. At the oblique, nearly parallel to the basin margins. The micro-tectonic scale, they also mostly correspond to Eocene extension (Fig. 9c) affected the western the orientations of reverse faults. Considering both Flysch Basin but also the East Black Sea Basin the fault attitudes in relation to the main structural

Fig. 10. Distribution of stress states related (a) to a strike-slip stress field with r1 trending NE–SW to NNE–SSW, and (b) to a NE–SW to NNE–SSW compressional event (from Saintot, 2000). They occurred in Late Eocene tectonic phase but prior the tilting of bedding planes. Characteristics of used local stress states are shown in Table 1. In lower right corner in (b): rose diagram of 1801 micro-fault trends collected in the field. The NW–SE and WNW–ESE main directions correspond to reverse micro-fault populations. These two directions are those of major structures of the studied area (thrusts and folds). A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 19 20 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31

Fig. 11. Distribution of stress states related (a) to a NE–SW to NNE–SSW compressional event and (b) to a strike-slip stress field with r1 trending NE–SW to NNE–SSW (from Saintot, 2000). They occurred in Late Eocene tectonic phase but after the tilting of bedding planes. Characteristics of used local stress states are shown in Table 1 (lower right corner in (a): same as Fig. 10b). A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 21 grain and the fault mechanisms, the paleostress states compressional regimes were related to the develop- inferred from those fault populations reveal the stress ment of major thrusts and associated folds. It is worth fields under which the major folds and thrusts noting that prior to and after these major reverse-type developed and characterised by a NNE–SSW to deformations, the stress fields were strike-slip in type, NE–SW trending r1. This paleostress trend is rec- a transition that can be simply summarised invoking ognised in about 50 local stress states and is certainly permutations between the r2 and r3 stress axes. In the best-recorded tectonic event in the NW-Caucasus detail, a rotation of the stress axes in the horizontal area. In detail, this tectonic event comprises four plane could be involved to explain the occurrence of successive stress regimes. both NNE–SSW and NE–SW trends of r1 in the First, a strike-slip regime with NE–SW to NNE– stress regimes. SSW trending r1 is observed at 11 sites (Fig. 10a). Some field observations clearly outline the evolu- Five calculated stress tensors are of good quality tion of the paleostress fields from Paleocene until the (Table 1). This event affected the NW-Caucasus Late Eocene: extension, strike-slip regime and com- region prior to tilting of bedding planes related to pression (Fig. 12). At sites 109, 151 and 153, the folding. The Paleocene flysch near Khadijensk (site crosscutting relationships and superimposition of suc- 145), near Tuapse (sites 114, 116, 117), as well as the cessive striae in fault planes show that the normal Eocene Flysch near Tuapse (site 151) recorded this faults (developed under extension) were reactivated as stress regime very well. strike-slip faults during the Late Eocene. At site 153, a Second, a NE–SW to NNE–SSW compressional r2/r3 permutation of stress axes is recorded between regime (Fig. 10b) was determined using 14 paleo- the strike-slip compressional regimes of the Late stress states, 10 tensors being of good quality (Table Eocene event (Fig. 12). 1). This stress field also reflects a pre-tilting event and From the structural point of view, this event taken affected Paleocene rocks near Novorossiisk (site 14) as a whole played a prominent role in the develop- and Tuapse (site 112). ment of the NW-Caucasus; the stratigraphic units of Third, 15 stress states form a NE–SW to NNE– the Flysch Basin, including the Eocene units, were SSW compressional stress field, identified as a strongly affected by intense folding and thrusting. post-folding event because the stress axes have Importantly, the younger rocks (from Oligocene to not undergone tilting (Fig. 11a). Eleven local stress Quaternary) that we visited in the northern flank of the tensors grouped in this stress field are of good NW-Caucasus belt definitely did not record this major quality (Table 1). Near Tuapse, this stress regime is tectonic event. This NNE to NE compression is the recorded in Paleocene and Eocene rocks (sites 112 major tectonic regime that affected the NW-Caucasus and 151). belt from Cretaceous times. We have thus assumed Fourth, we reconstructed a strike-slip regime with following Milanovsky and Khain (1963), Gri- NE–SW to NNE–SSW trending r1 at 10 sites (Fig. gor’yants et al. (1967), Milanovsky et al. (1984), 11b). Four calculated stress tensors are of good quality Muratov et al. (1984), Lozar and Polino (1997), (Table 1). This late stress field also occurred after Mikhailov et al. (1999), etc, that it corresponds to tilting of bedding surfaces and hence folding. It is the orogenic phase and to the development of the NW- recognised in Paleocene rocks near Goryatchi Klutch Caucasus fold-and-thrust belt during Late Eocene (site 103), near Anapa (site 98), and near Novorossiisk times (see Section 2). (site 94). Although they differ, especially in terms of chro- 4.2.2. The development of the NW-Caucasus fold-and- nology relative to the occurrence of the major folding, thrust belt under NE–SW to NNE–SSW compressive these stress fields belong to the same major event of paleostress regime during Late Eocene times compressional deformation throughout the collision Fig. 13 summarises the structural evolution of the belt. Furthermore, they allow characterisation in detail NW-Caucasus during the Late Eocene NNE–SSW to of the evolution of the main folding and thrusting of NE–SW compression. This major tectonic event the NW-Caucasus (Saintot et al., 1998), in which r1 corresponds to the closure of the Flysch Basin remained oriented NE–SW to NNE–SSW. The two between the Scythian Plate and the Shatsky Ridge, 22 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31

Fig. 12. Examples of reconstructed local stress tensors in polyphase sites illustrating the evolution of successive paleostress fields in NW- Caucasus from Paleocene to Late Eocene. Where the stress tensor corresponds to a pre-tilting event, the two presented rose diagrams correspond to fault population in the present-day geometry—with calculated stress tensor when homogeneous bedding planes at the site—and calculated stress tensor with primary horizontal bedding planes.

during which folds and thrusts developed that char- NW–SE trending thrusts are south vergent (Cf. Fig. acterise the main structural grain of the present-day 3b). We suppose that, during the shortening, south- belt. vergent thrust planes propagated from the south dip- SW-vergent thrusts developed under the NNE– ping Akhtyr Fault (Fig. 13a). SSW to NE–SW compressional regime (Giorgobiani The vertical NNE–SSW to NE–SW pre-existing and Zakaraya, 1989; Khain, 1984). Fieldwork carried major faults (as the Pchekha-Adler Fault, the on in the NW-Caucasus belt (Banks, personal com- Gelendjik Fault, Pchada Fault; Cf. Fig. 3a) were munication) shows a south-vergent deformation for not active during the Late Eocene compression as the whole belt. The offshore East Black Sea and they strike parallel to the r1 stress axis trend. The Primorsky faults represent the southwestern front of Pchekha-Adler fault was a right-lateral strike-slip the belt (Finetti et al., 1988; Terekhov and Shimkus, fault (Fig. 13b). 1989; Robinson et al., 1996). The dense network of NNE–SSW to NE–SW The Akhtyr fault is a north-vergent thrust produc- faults of lesser length (Cf. Fig. 3a) could have ing the fan-shape of the belt (Milanovsky and Khain, developed during the Late Eocene event, contempo- 1963; Dotduyev, 1987; Philip et al., 1989; Robinson, raneous of the major thrust and fold development, in 1997). However, the Landsat Thematic Mapper anal- order to accommodate mass displacement and/or the yses shows that the northern visible WNW–ESE to folding deformation above the major thrust planes. A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 23

Fig. 13. The Late Eocene NNE–SSW to NE–SW compression and the development of the NW-Caucasus Fold-and-Thrust belt. (a) Cross- section of folding and thrusting; (b) map of southwest vergent thrusts.

Fracturing at 30j from both sides of the compressive Second, 14 stress states characterise a strike-slip trend could have also developed as a strike-slip compressional regime with WNW–ESE directed r1 conjugate system synchronous with the folding proc- (Fig. 15a and b, Table 1). Nine calculated stress ess. tensors are of good quality. The occurrence of stress states both strike-slip and compressional in type could 4.3. The tectonic evolution of NW-Caucasus Flysch be explained by local permutations between r2 and Basin from Oligocene to Quaternary times r3, r1 keeping the same trend. Third, 10 stress states determine a strike-slip and Major tectonism also took place at a later stage in compressional stress field (Fig. 16, Table 1). Eight the history of the NW-Caucasus fold-and-thrust belt, tensors are of good quality. Grouping stress states clearly post-dating the Late Eocene orogenesis. Three compressional and strike-slip in type is justified by the main events were identified from Oligocene to Qua- occurrence of r2 and r3 stress axis permutations, the ternary times. r1 axis keeping its NNW–SSE orientation. Three considerations led us to interpret the NNW– 4.3.1. Post-Eocene paleostress fields SSE compressive stress field as the latest tectonic Thirty-six stress states post-date tilting of bedding event recorded in the NW-Caucasus: (1) at site 92, planes. They reveal three main paleostress fields that near Gelendjik, the successive stress regimes devel- affected the NW-Caucasus belt after the Late Eocene oped successive striae on the fault planes. Strike-slip NNE–SSW to NE–SW compression. slips developed during the WNW–ESE post-Eocene First, 11 stress states reveal an extensional stress strike-slip compressional regime on the former reverse field with NNE–SSW trending r3 (Fig. 14, Table 1), striae that developed under the NE–SW Late Eocene with four tensors of good quality. compression. The latter striae developed under the 24 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31

Fig. 14. Distribution of stress states related to an extensional stress field with NNE–SSW trending r3 (from Saintot, 2000). This stress field occurred after the Late Eocene folding phase. Examples of stereoplots illustrating the extensional stress field. Characteristics of used local stress states are shown in Table 1.

NNW–SSE compression and clearly crosscut the field could be obtained by a stress axis rotation in the previous reverse and strike-slip ones; (2) the same horizontal plane. The successive stress fields from NNW–SSE compressional stress field was deter- Oligocene to Quaternary thus defined three major mined in the Kertch-Taman peninsulas (location in tectonic stages: NNE–SSW extension, WNW–ESE Fig. 1) as a Plio-Quaternary stress event, still active contraction and NNW–SSE contraction. (Saintot et al., 1999; Saintot and Angelier, 2000); (3) the NNW–SSE trending r1 is also defined by focal 4.3.2. Structural evolution of the NW-Caucasus belt mechanism inversion (Gushtchenko et al., 1993a,b). from Oligocene to Quaternary times No chronology has been established between the The Kuban and Tuapse flexural basins developed NNE–SSW extension and the WNW–ESE strike-slip during the Oligocene times in response to NW-Cau- compressional regime. However, a release of stresses casus mountain building (Milanovsky and Khain, could have occurred just after the NE–SW/NNE– 1963; Beloussov et al., 1988; Lozar and Polino, SSW Late Eocene compressive stress field, producing 1997; Nikishin et al., 1998a,b). The NW-Caucasus an extensional stress field by a r1 and r3 stress axis belt emerged and eroded sediments were deposited in permutation. Another r1 and r2 stress axis permuta- the peripheral Kuban and Tuapse Basins (Milanovsky tion produced the following strike-slip-compressive and Khain, 1963; Lozar and Polino, 1997). Consider- regime with WNW–ESE trending r1. The latest stress ing the southwestern vergence of the NW-Caucasus A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 25

Fig. 15. Distribution of stress states related to (a) strike-slip and (b) compressional stress fields with WNW–ESE trending r1 (from Saintot, 2000). This stress regime occurred after the Late Eocene folding phase. Examples of stereoplots illustrating the stress fields. Characteristics of used local stress states are shown in Table 1. thrust front, the Tuapse Basin was at the location of According to our results, we argue that the post- the expected flexural foreland basin (Fig. 17a), Eocene NNE–SSW extensional stress field is closely whereas the Indolo-Kuban developed at the rear of related to the trough development (Saintot et al., the chain (Fig. 17a). 1998). The NNE–SSW extension trend is perpendic- 26 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31

Fig. 16. Distribution of stress states related to strike-slip and compressional stress field with NNW–SSE trending r1 (from Saintot, 2000). This stress regime occurred after the Late Eocene folding phase. Examples of stereoplots illustrating the stress field. Characteristics of used local stress states are shown in Table 1. ular to the Oligocene–Lower Miocene zones of max- discussion concerning Indolo-Kuban and Kertch- imum subsidence (Fig. 17a and b). In this context, the Taman trough development in Saintot and Angelier, normal faults developed near the surface. They could 2000). As already mentioned, a NW–SE extension is have been formed by the accommodation of flexural recorded at sites 142, 148, 149 and 150 (Fig. 7). The deformation of the surrounding Indolo-Kuban and stress states were grouped in the extension that Tuapse troughs (Saintot et al., 1998; see also the occurred before the Late Eocene folding and thrusting

Fig. 17. (a) and (b) Extension at Oligocene–Lower Miocene times and flexural development of the Indolo-Kuban and Tuapse troughs around the neo-formed NW-Caucasus fold-and-thrust belt: (a) location of troughs on structural map (Fig. 1c) and (b) cross-section (location as grey line in (a)). (c) and (d) Tectonic phase in Lower Miocene times: WNW–ESE contraction: (c) major structures of the NW-Caucasus belt under a WNW–ESE transpression and (d) on the origin of a WNW–ESE transpressive regime in the NW-Caucasus area (background scheme after Zonenshain et al., 1990). (e) From Sarmatian times, the last NNW–SSE compressive event in the NW-Caucasus belt. The NW-Caucasus was as a right-lateral shear zone and the consequent movements produced a lenticular shape of pre-existing thrust planes. The NNE–SSW to NE–SW fault zones could be left-lateral strike-slip faults under the stress field. A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 27 28 A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 event. However, at these sites, (1) no chronology was (Middle Miocene), due to the indentation of the established between the NE–SW Late Eocene com- Arabian plate on the Caucasian syntax (Beloussov, pression and the NW–SE extension, and (2) the tilting 1940; Shardanov and Peklo, 1959; Milanovsky and of bedding planes is not sufficient to recognise pre- or Khain, 1963; Beliaevsky et al., 1961; Razvetaev, post-tilting stress events. Thus, according to the loca- 1989; Kopp and Shcherba, 1998; Shcherba, 1987, tion of these sites at the southeastern tip of the Indolo- 1989, 1993; Kopp, 1989, 1991, 1996; Giorgobiani Kuban trough, the well-recorded NW–SE extension and Zakaraya, 1989; Zonenshain et al., 1990; Mila- (Fig. 7) might also be related to the development of novsky, 1991; Nikishin et al., 1998b). the Indolo-Kuban trough (Fig. 17a). The NE–SW Under the NNW–SSE compression, the WNW– normal faulting may occur at the brittle level to ESE orientated Primorsky and East Black Sea thrusts accommodate the flexural deformation of the Indolo- were reactivated and the belt propagated toward the Kuban Basin during strong rates of subsidence at the south (Fig. 17e). The Krasnaya Poliana Fault (Fig. Oligocene–Lower Miocene times (Saintot et al., 17e) is one of the main Sarmatian thrusts between the 1998). Flysch Zone deformed in Late Eocene times and the The WNW–ESE transpressional paleostress field Oligocene–Miocene Adler depression (Fig. 17e). All (Fig. 15) could correspond to the so-called Save tec- the stratigraphic units up to Quaternary are involved tonic phase that affected the NW-Caucasus area at the in this deformation (Terekhov et al., 1973; Terekhov, beginning of Miocene times (Shardanov and Peklo, 1979; Khain, 1984; Finetti et al., 1988; Giorgobiani 1959; Kopp and Shcherba, 1998). Under this stress and Zakaraya, 1989; Terekhov and Shimkus, 1989; field, the NE–SW to NNE–SSW transverse fault Robinson et al., 1996; Shreider et al., 1997). How- zones could have reworked as right-lateral strike-slip ever, more important were the right-lateral move- faults and the major thrust planes could have been ments that could occur along these faults as well as reactivated as left-lateral strike-slip faults (Fig. 17c). along the Akhtyr Fault (Razvetaev, 1989; Kopp, The origin of the WNW–ESE maximal stress trend is 1989, 1991). The NW-Caucasus belt is a right-lateral difficult to determine. From the Early Miocene, the shear zone and a lenticular shape of thrust planes collisional stage affected the whole Black Sea–Cauca- developed (Fig. 17e). sus region (Zonenshain et al., 1990) and during Early From the Sarmatian, the NNE–SSW to NE–SW Miocene, before 20 my, the direction of convergence of transverse fault zones are left-lateral strike-slip in the Arabian Plate with respect to the (fixed) Eurasia character whereas the Pchekha-Adler Fault is a was NW–SE (Fig. 17d; Savostin et al., 1986; Zonen- right-lateral fault (Fig. 17e; Razvetaev, 1989; Giorgo- shain et al., 1990). In this geodynamic context, the biani and Zakaraya, 1989; Kopp, 1991; Polino et al., Great Caucasus central zone could have been lifted up, 1997; Se´brier et al., 1997). producing a strong lateral contraction, restricted to the lateral zones like the NW-Caucasus belt (Fig. 17d).Itis also possible that displacement along the main thrust 5. Conclusion front that occurred from the Pontides to the Lesser Caucasus was oblique with an important right-lateral Paleostress studies and structural mapping using component. Accordingly, to accommodate the dis- Landsat TM images allow to propose a reconstruc- placement along the main thrust zone, left-lateral tion of a consistent scheme of tectonic development strike-slip movements could have developed along for the NW-Caucasus Flysch Zone. The western part the main WNW–ESE trending fault zones of the Black of the Great Caucasus was affected by transtensive Sea and NW-Caucasus region (Fig. 17d). The Central and transpressive tectonic events from Late Creta- Great Caucasus uplift plus the right-lateral movement ceous times. This analysis support previous studies along the main thrust zone could thus explain the (Se´brier et al., 1997) revealing oblique convergence record of a WNW–ESE directed transpressional and/or divergence trends relative to the Scythian regime in the NW-Caucasus belt. Plate margin. The last NNW–SSE compressive stress field However, considering the stratigraphic ages of reflects the collisional setting from Sarmatian times studied NW-Caucasus formations, the paleostress A. Saintot, J. Angelier / Tectonophysics 357 (2002) 1–31 29 fields that characterise older events (as Cimmerian The tectonic evolution of the NW-Caucasus from tectonic phases) have not been determined. The Late Cretaceous to Eocene (1 to 3 above) is probably NNE–SSW to NE–SW transverse fault zones that related to the East Black Sea Basin tectonism. From we observed on the Landsat TM data could have been the Late Eocene folding and thrusting to the Quater- formed during Cimmerian or even Hercynian defor- nary (4 to 7 above), the NW-Caucasus tectonic mation phases. evolution can be interpreted in terms of the general Summarising, seven major tectonic regimes are collision of the Arabian Plate with Eurasia in the recorded in the NW-Caucasus area, as follows, from Caucasian syntax area; starting from the Miocene, it oldest to youngest. Some remarks are added concern- mainly reflects the indentation of the Arabian Plate. ing the development of major structures. (1) Transtensional event in the Flysch Basin, with an E–W average trend of r3 and first (?) rifting phase of Eastern Black Basin in the Late Cretaceous times. Acknowledgements Normal and right-lateral movements along the mar- gins of the basins. This study was supported by the Peri-Tethys (2) Transpressive stress field with E–W to NW– program (fieldwork), the French Embassy in Moscow and the French M.E.S.R. (thesis grants). First of all, SE r1 at the Paleocene/Eocene boundary, related to the Eastern Black Sea tectonism (possibly while the we have to thank A. Ilyin without whom no fieldtrips rifting process was slowing down). Right-lateral would have been carried on in the NW-Caucasus belt. movements along the basin margins; inversion of We also thank both reviewers and especially, Dr. M. the NNE–SSW to NE–SW trending fault zones in Se´brier for his fruitful comments. Many thanks to Dr the Flysch Basin. R. Stephenson to have improved the English (3) Eocene transtensional event in the Flysch Basin phrasing. with an E–W average trend of r3 (possibly with rift reactivation in the Eastern Black Basin). 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