Alexandra M M Robert
email: alexandra.robert@get.obs-mip.fr

Jean Letouzey

Mohammad A Kavoosi

Sharham Sherkati

Carla Müller

Jaume Vergés

Abdollah Aghababaei

Structural evolution of the Kopeh Dagh fold-and-thrust belt (NE Iran) and interactions with the South Caspian Sea Basin and Amu Darya Basin

Keywords: Kopet Dagh, Amu Darya Basin, South Caspian Sea Basin, Inverted Rift System, Structural Geology, Seismic Sections

published or not. The documents may come

Introduction

Iran extended deformed zone is surrounded by the epivariscan Turan Platform to the NE, which is part of stable Eurasia and by the Arabian Plate to the SW (Figure 1a). The Iranian geology is dominated by the long-standing convergence history between Eurasia and Gondwanan-derived terranes as indicated by numerous ophiolitic belts, fold-and-thrusts belts and resistant blocks that remain within the deformation zone. Two major compressional events, as a consequence of oceanic closures are described in Iran: (1) the Cimmerian orogeny, which is related to the closure of the Paleotethys Ocean and (2) the Alpine orogeny as a result of the closure of the Neotethys Ocean. In northeastern Iran, the Paleotethys Ocean separated the Eurasian Plate from Central Iranian blocks whereas the Neotethys Ocean opened on the southern margin of the Central Iranian blocks during the Permian (Muttoni et al., 2009) (Figure 1a). Besides, several ophiolitic domains (Nain Baft, Sabzevar, Sistan) cross-cut Central Iran and are interpreted as remnants of small oceanic domains that opened as small back-arc basins during the Early Cretaceous for the Sistan Ocean, and during the Late Cretaceous for the Sabzevar and Nain Baft domains [START_REF] Agard | Zagros orogeny: a subduction-1183 dominated process[END_REF]. The start of the subduction of these small oceanic domains is considered to be Turonian-Maastrichtian (Saccani et al., 2010) and active subduction of the Sistan Ocean up to the end of the Late Cretaceous has been recently evidenced (Bröcker et al., 2013). These small domains were closed during Paleocene to Eocene times [START_REF] Agard | Zagros orogeny: a subduction-1183 dominated process[END_REF].

In northeastern Iran, the Paleotethys suture zone corresponds to the boundary between the Kopet Dagh fold-and-thrust belt to the NE, and the eastern prolongation of the Alborz range to the SW (Figure 1a). Remnants of the Paleotethys Ocean are located within the Binalud Mountains where the Cimmerian event is characterized by a collisional type event during the Late Triassic/Early Jurassic [START_REF] Sheikholeslami | Structurale analysis and tectonic evolution of the eastern Binalud Mountains, NE Iran[END_REF].

Following this collision, the Kopet Dagh Basin was deposited on the southern margin of the Eurasian Plate from the Jurassic to the Tertiary (Brunet et al., 2003). This basin was inverted during the Tertiary, because of the NE oriented convergence study of the pelagic facies that have been correlated with pre-164 cise lithological descriptions including more than 150 datings 165 is presented, which allows us to propose a new stratigraphic 166 chart for the Kopet Dagh and the surroundings basins (Fig- 167 ure 3). Our biostratigraphy is based on investigation of cal-168 careous nannofossils. Age determination of the Mesozoic was 169 performed from publications of [START_REF] Thierstein | Mesozoic calcareous nannoplankton biostratigraphy of marine sediments[END_REF] and Perch-170 Nielsen (1985) and we used the zonation given by Martini 171 (1971) for the Cenozoic. Our results have been synthesized in 172 the stratigraphic chart (Figure 3) and are also presented in Table 173 1 that indicates location of the main dated samples and names 174 of the nannofossils.

175

In this section, we will describe the detailed stratigraphy of the 176 Kopet Dagh region, from the oldest outcropping rocks to the 177 Tertiary continental sediments. [START_REF] Zanchetta | The record of the Late Palaeozoic active margin of the Palaeotethys in NE Iran: Constraints on the Cimmerian orogeny[END_REF]. The Aitamir Formation is a mudstone that grades upwards 336 to a lower glauconitic sandstone unit with cross-stratifications, 337 hummocky cross-stratifications and ripple marks, to a unit 338 of mudstone intercalated with sandstone beds (Sharafi et al., and marly shales [START_REF] Allameh | Study of os-1193 tracodes in Abderaz Formation in Kopet-Dagh Basin[END_REF]. Its thickness ranges [START_REF] Shahidi | Evolution tectonique du Nord de l'Iran (Alborz et Kopet Dagh) depuis le Mésozoïque[END_REF] The transition between the Upper Campanian and the Pale-384 ocene is characterized by an increase of fine grained sandstones.

385

The Paleocene Pestehleigh Formation is predominantly repre-386 sented by red continental series with sand and siltstones with 387 some conglomeratic levels at its base. It is followed by flu-388 viodeltaic and continental red sandstones and siltstones. Some Eurasia margin [START_REF] Zanchetta | The record of the Late Palaeozoic active margin of the Palaeotethys in NE Iran: Constraints on the Cimmerian orogeny[END_REF]. 453 Allen et al., 2003). This collision led to crustal shorten-454 ing and right-lateral transpression which is still continu-455 ing as indicated by seismic activity [START_REF] Thomas | Sedimentary record of Late Paleozoic to recent tectonism in Central Asia-analysis of subsurface data from the Turan and South Kazakh domains[END_REF]456 Golonka, 2004) and active faulting (Hollingsworth et al., 457 2006(Hollingsworth et al., 457 , 2008(Hollingsworth et al., 457 , 2010;;Shabanian et al., 2009aShabanian et al., ,b, 2012)). Nev-458 ertheless, the margin inversion is not well dated, because and Triassic rocks [START_REF] Ulmishek | Petroleum geology and resources of the Amu-Darya Basin, Turkmenistan, Uzbekistan, Afghanistan, and Iran[END_REF].

506

The thick sedimentary sequence is deformed as large-scale (Amurskiy, 1971;Maggi et al., 2000). Similar 526 striking Paleozoic structures are observed both within the Agh-527 darband Erosional window [START_REF] Zanchi | The Eo-Cimmerian (Late? Triassic) orogeny 1417 in North Iran[END_REF][START_REF] Zanchetta | The record of the Late Palaeozoic active margin of the Palaeotethys in NE Iran: Constraints on the Cimmerian orogeny[END_REF] The eastern cross-section is a 140 km long N-S geological 543 cross-section extending from the Aghdarband erosional win-544 dow to the wide anticline of the Khangiran gas field (Figure 545 6, see location on Figure 5). This cross-section was built using our own field observations (Figure 7) and seismic lines including 3D seismic data and borehole data (Figures 8, 9 and 10).

The Gonbadli and Khangiran gas fields are located in the Iranian part of the Amu Darya Basin and they extend to the Turkmen gas fields. This cross-section will be described from the South to the North.

To the South of the Aghdarband erosional window

The southern boundary of the cross-section corresponds to the prolongation of the Fariman Complex, interpreted as remnants of an intra-arc or incipient back-arc basin [START_REF] Zanchetta | The record of the Late Palaeozoic active margin of the Palaeotethys in NE Iran: Constraints on the Cimmerian orogeny[END_REF]. The Middle Jurassic Kashafrud Formation with evidences of syn-rift normal faulting outcrops to the North of this ophiolitic complex. The occurrence of graben inversion and few short-cuts within the Middle Jurassic Kashafrud Formation are highlighted in this part of the cross-section. Towards the North, within the Kol Malek syncline, Mesozoic sediments are thinner compared to the sediments belonging to the Amu Darya Basin and they are conformably overlain by Cenozoic sediments. The Kol Malek syncline is pinched and its northern flank is overthrust by rocks belonging to the Darreh Anjir ophiolitic complex.

The Aghdarband erosional window

The basement of the South Amu Darya Basin is observed within the Aghdarband erosional window. This basement consists of sedimentary, metamorphic and igneous rocks with ages ranging from Devonian to Triassic and mostly corresponds to preserved fragments of a continental arc (Baud and Stampfli, 1989;Poursoltani et al., 2007). The erosional window corresponds to faulted and folded strata that are preserved below double verging thrusts (Figure 7) and we interpret it as a paleo-horst structure.

To the South of the window, the Darreh Anjir complex, consisting of gabbros and low metamorphosed basalts, cherts and marbles [START_REF] Zanchetta | The record of the Late Palaeozoic active margin of the Palaeotethys in NE Iran: Constraints on the Cimmerian orogeny[END_REF] is thrusted on top of the northern flank of the Kol Malek syncline. The southern boundary of the complex is given by a south verging thrust which stacks the mostly mafic rocks of the Darreh Anjir complex on the Upper Triassic Miankuhi Formation. This mafic rocks of the Darreh Anjir complex overthrust to the North the volcanic complex, which is overthrust to the South by the thick succession of Upper Permian-Lower Triassic molassic-type sediments (Figure 7) [START_REF] Zanchetta | The record of the Late Palaeozoic active margin of the Palaeotethys in NE Iran: Constraints on the Cimmerian orogeny[END_REF]. Previous interpretations suggest that the Darreh Anjir complex corresponds to Paleotethys remnants (Ruttner, 1991;[START_REF] Alavi | The triassic and asso-1189 ciated rocks of the Agh-Darband areas in central and northeastern Iran as 1190 remnant of the southern Turanian active continental margin[END_REF]. However, a recent study suggests that this complex including both intrusive and lavas flows is, thus, remnants of a magmatic arc and related basins developed on the southern Eurasia margin, to the NE of the Paleotethys suture zone [START_REF] Zanchetta | The record of the Late Palaeozoic active margin of the Palaeotethys in NE Iran: Constraints on the Cimmerian orogeny[END_REF]. The Paleozoic and Lower Mesozoic sediments deformed within the Aghdarband window derived from the erosion of the Variscan orogen (Ruttner, 1991). The faults that are affecting these sediments are laterally embedded by the Middle Jurassic Kashafrud Formation, which suggests a Cimmerian age for these faults. as well as an important thickening of the Lower Cretaceous series that is related to a higher initial thickness and to the occurrence of thrusting within this formation. In contrast, there is a lack of most of the Upper Cretaceous in the last syncline (Rud Atkak syncline) that has a core made of Paleocene sediments. At the western end of the section, some seismic lines illustrate that the folds of the Kopet Dagh are plunging laterally below the Gorgan plain sediments (Figure 1). Along the section, an important angular unconformity between the folded Aitamir Formation and the Oligocene-Neogene conglomerates is observed. We have already observed the folded Eocene sediments that have been eroded before the deposition of a subhorizontal Oligocene-Neogene conglomerate. The seismic sections show buried anticlines and the post-Eocene unconformity, which is affected by some recent thrust faults. A drill was done in this region, but due to numerous thrusts and repetitions, it did not reach the Lower Cretaceous Tirgan carbonates. Formation) could be a potential source rock but this formation 915 was deposited within the narrow Aghdarband back-arc basin 916 [START_REF] Zanchetta | The record of the Late Palaeozoic active margin of the Palaeotethys in NE Iran: Constraints on the Cimmerian orogeny[END_REF] and it is hard to infer its present exten-917 sion. the Late Cretaceous, that are not associated with an angular unconformity (Figure 18d). The Paleocene series present important facies variations from red continental series to carbonates across the belt whereas the Eocene Khangiran Formation marks the last marine episode recorded in the Amu Darya Basin and it does not present important thickness or facies variations. Some authors report evidences for a Late Cretaceous-Paleocene compression event in northern Iran (Barrier and Vrielynck, 2008) but this event is not well described at the moment.

Summary of the western Kopet Dagh cross-section

Notwithstanding, exhumation of the blue schist facies rocks within the Zagros belt and the exhumation of high-pressure rocks in the Sistan are broadly coincident with the obduction process of the Neotethyan lithosphere onto Arabia [START_REF] Agard | Zagros orogeny: a subduction-1183 dominated process[END_REF]Bröcker et al., 2013). [START_REF] Agard | Zagros orogeny: a subduction-1183 dominated process[END_REF] propose that these exhumation phases could be the result of a regional-scale modification of plate-slab coupling in the Neotethys subduction zone during Late Cretaceous time. Further investigations in northern Iran are needed to better describe these compressive events. in Venezuela Andes (Colletta et al., 1997;Duerto et al., 2006, e.g.), in the frontal part of Longmen Shan range (Robert et al., 2010, e.g.) or in the Zagros [START_REF] Sherkati | Detachment folding in the central and eastern zagros fold-belt (iran): salt mobility, multiple detachments and late basement control[END_REF](Sherkati et al., , 2006, e.g.), e.g.).

Late Eocene

Towards the West, the structures are dominated by the resistance contrast between the rigid block formed by the basement of the South Caspian Sea Basin and the weaker western part of the Kopet Dagh range that has been previously deformed by the Cimmerian orogeny. Indeed, this deformation contrast results in the indentation of the rigid South Caspian Sea region during the Alpine compression (Allen et al., 2003). The deformation style is characterized by the double vergence of deep-seated thrusts faults (Figure 8) and important disharmonies within the Mesozoic levels. Fish-tail type structures with décollement lev- Basin and its surrounding domains (Axen et al., 2001;Allen 1082[START_REF] Allen | Late Cenozoic reorganization of the 1197 Arabia-Eurasia collision and the comparison of short-term and long-term 1198 deformation rates. Tectonics 23. 1199 geochemical constraints on the origin of the nehbandan ophiolitic complex (eastern Iran): Implication for the evolution of the Sistan Ocean[END_REF]Copley and Jackson, 2006;[START_REF] Abbassi | Crustal velocity structure in the southern edge of the 1177 Central Alborz (Iran)[END_REF] 1083 Shabanian et al., 2009a) (Figure 19c). Moreover, conversion 1084 from mainly thrusting to oblique-slip and strike-slip faulting 1085 zoic (∼4-5 Ma) as a consequence of the major tectonic reor-1087 ganization in NE Iran (Shabanian et al., 2009a,b). Ritz et al. (Hollingsworth et al., 2006;Hollingworth, 2007;Hollingsworth et al., 2008Hollingsworth et al., , 2010;;Shabanian et al., 2009aShabanian et al., ,b, 2012)). Blue arrows represent GPS velocities relative to Eurasia fixed; the error ellipses indicate formal errors within 95 percent confidence interval [START_REF] Tavakoli | Present-day deformation and kinematics of the active faults observed by GPS in the Zagros and East of Iran[END_REF] Figure 3: New stratigraphic chart of the Kopet Dagh belt and of two main adjacent Amu Darya and South Caspian Sea basins. This stratigraphic study has been constructed from our 159 biostratigraphic datings, sedimentary observations and a wide compilation of published data. Major tectonic events are been indicated on this stratigraphic chart and can be correlated with the main regional observed hiatus. Figure 13: The western regional cross-section (see location in Figure 5) highlights the upper basement décollement level forming double-verging structures that cross-cut the Middle Jurassic rift system. This cross-section also shows two folded unconformities: at the base of the Lower Cretaceous and at the base of the post-Eocene sediments.

  Devonian to Upper Triassic: before the deposition of the 179 Kopet Dagh Basin 180 The oldest rocks outcropping in the Kopet Dagh fold-and-181 thrust belt are Devonian to Lower Carboniferous (Ruttner, 182 1991; Lyberis et al., 1998) and they are mostly outcropping 183 within the Aghdarband erosional window and within the 184 Fariman and Darreh Anjir complexes, in the eastern part of 185 the belt (Ruttner, 1991). Most of the sediments in the Agh-186 darband erosional window are Triassic in age and are strongly 187 deformed as a consequence of the closure of the Paleotethys 188 Ocean during the Cimmerian orogeny. Several unconformities 189 between the different series are observed. The Darreh Anjir 190 and the Fariman complexes have firstly been interpreted as 191 ophiolitic remnants of the Paleotethys ocean but they were 192 recently re-interpreted as remnants of a magmatic arc and 193 related basins developed at the southern Eurasia margin, on 194 top of the north-directed Paleotethys subduction zone long 195 before the collision of Iran with Eurasia

  series are constituted at their base by 198 dark grey thinly bedded volcanoclastics, shales and turbiditic 199 sandstones. These series are overlain by dark green volcan-200 oclastic sediments, with some limestone layers. The Lower 201 Carboniferous is characterized by white limestones of about 202 200 m thickness with the occurrence of some diabase dykes. 203 A massive Permian sedimentary succession, including sand-204 stones, limestones and basaltic to andesitic lava flows has been 205 described in the Fariman Complex (see location on the figure 6) 206 (Zanchetta et al., 2013). The ?Upper Permian to Lower Triassic 207 molassic type rocks are composed of some red quartzitic sand-208 stones and siltstones, with intercalated conglomerates that in-209 clude pebbles of quartz, pink colored granites, radiolarites and 210 Carboniferous to Late Permian limestones. These series present 211 a thickness up to 500 m. 212 Four members are distinguished in the Triassic series of the 213 Aghdarband erosional windows by Ruttner (1991): the three 214 lowermost units that comprise an important volcanic compo-215 nent were deposited before the Middle Cimmerian orogeny, 216 whereas the fourth unit indicates deltaic conditions of deposi-217 tion and results from the erosion of the relief formed during the 218 Cimmerian orogeny. In this study, we are not differentiating the 219 different stages of the Cimmerian orogeny. The first member (Lower Triassic) is characterized by a re-221 dish sandstones and conglomerates at its base (Qara Gheithan 222 Formation) that are overlain by limestones layers (Sefid Kuh 223 Formation and Nazarkardeh Formation). The second member 224 (Middle Triassic, base of the Sina Formation) is constitute at its 225 base by a conglomerate overlain by volcanoclastic sandstone and tuffaceous shales in the upper part. It was dated thanks 227 to two fossil horizons with abundant crinoids and ammonites 228 and assigned to Landinian to Lower Carnian in age. The third 229 member (Middle Triassic) is made of tuffaceous sandstones and 230 some shales (top of the Sina Formation). Finally, the last mem-231 ber (Upper Triassic) presents an unconformity at its base and 232 starts with some sandstones without volcanic components and 233 rich in coal layers on top of which there is some shale (Rutenvironments of the Chaman Bid Formation are on the slope 273 of a carbonate platform and in the adjacent basin (Majadifard, 274 2003). In contrast, towards the East, the Kashafrud Formation 275 is directly overlain by the Upper Jurassic Mozduran Formation 276 (Taheri et al., 2009), which is the main gas reservoir in the 277 Kopet Dagh range (Figure 4). The Mozduran Formation is a 278 well-bedded limestone and its facies varies towards the East to 279 siliciclastic sediments. The thickness of the Mozduran Forma-280 tion varies from 200 m, to 800 m in the Khangiran gas field 281 and up to over 1400 m in the central part of the belt (Afshar-282 Harb, 1979). The sharp and sudden lateral lithological and 283 thickness variations of the Mozduran Formation are interpreted 284 as related to the presence of paleohighs within the basin after 285 the Middle Jurassic rifting in the Kopet Dagh Basin (Kavoosi 286 et al., 2009b). The Mozduran Formation is overlain by Creta-287 ceous sediments, which are divided into 10 different formations 288 (Shurijeh, Zard, Tirgan, Sarchashmeh, Sanganeh, Aitamir, Ab-289 deraz, Abtalkh, Neyzar and Kalat) and associated with a thick-290 ness up to 4000 m thick in the western part of the basin (Afshar-291 Harb, 1979). Emami et al. (2004) suggested that the Cimmerian 292 tectonic phase resulted in widespread Late Jurassic-Early Cre-293 taceous regression, leading to deposition of the Lower Creta-294 ceous continental siliciclastics and evaporites of the Shurijeh Shurijeh Formation consists of red-299 bedded siliciclastic sediments (reservoir rocks) overlain by 300 limestones. The upper part of the Lower Cretaceous Shurijeh 301 Formation consists of gypsum/anhydrite deposits that were de-302 posited under arid conditions as a consequence of the major re-303 gression of the sea that occurred in the Jurassic/Cretaceous tran-304 sition (Moussavi-Harami and Brenner, 1990; Moussavi-Harami 305 et al., 2009). These evaporite levels make the seal for the basal 306 Shurijeh Formation (secondary reservoir for gas in the Kopet 307 Dagh range) and the Mozduran formations. The thickness of 308 the Shurijeh Formation ranges from 100 m above the paleohigh 309 to about 1000 m thick (Afshar-Harb, 1979). Towards the NW, 310 the Shurijeh Formation thickness decreases until being com-311 pletely replaced by the Zard Formation, which mainly consists 312 of marine marls, calcareous shale with some sandstone beds 313 (Afshar-Harb, 1979). Our biostratigraphic results with the re-314 sults from Jamali et al. (2011) indicate a Late Tithonian to Hau-315 terivian age for this formation.

  the continental Shurijeh Formation is fol-319 lowed by shallow marine sedimentation characterized by the 320 deposition of the marls and orbitolinids rich limestone Tirgan 321 Formation with a thickness up to 600 m. The age of these for-322 mations is Barremian and the nannofossils are often strongly 323 recrystallized and fragmented. The Sarchashmeh Formation 324 (about 150-250m thick) conformably overly the calcareous Tir-325 gan Formation and consists of two members: the lowest uni-326 form grey marl unit and the upper layer that consists of an alter-327 nance of shale and limestone.

  348 between 200 and 400 m to the East of the Kopet Dagh and 349 decreases towards the western part of the belt (Afshar-Harb, 350 1979). From our biostratigraphy study, a Late Santonian age 351 was determined for the Abderaz Formation but the nannofos-352 sils are often strongly recrystallized and broken within the marl 353 intercalations. 354 The Abtalkh Formation (Campanian) is well developed in the 355 eastern Kopet Dagh and has an almost uniform lithology con-356 sisting of calcareous shales with some lumachelle rich lime-357 stone beds near the top and with locally some small rudist-patch 358 reefs. It presents a constant thickness of 700-800 m (Afshar-359 Harb, 1979). In the western part of the belt, the Abtalkh For-360 mation is not developed and the Abderaz Formation is directly 361 overlain by the Kalat Formation. In contrast, to the East of the 362 belt, the upper part of the Abtalkh Formation is characterized 363 by a progressive transition to the Neyzar Formation which is 364 mostly composed of glauconite and clays with some sandstone 365 in the upper levels indicating a shallow marine condition of sed-366 imentation. The transition between the Neyzar Formation to the 367 Kalat transition is progressive

389

  marine incursions have been observed and dated within zone 390 NP2 in the lowermost part and within zone NP5 upwards in the 391 section. The uppermost Paleocene (zone NP9) was determined 392 in the Chehel Kaman Formation that consists of white carbon-393 ates. The transition to the Lower Eocene is characterized by the 394 occurrence of some layers of marls. The Eocene (zones NP12-395 NP19) is represented by alternating limestones and marls and it 396 becomes sandier within the upper part.

  maps, the youngest sediments represented are 399 indicated as Neogene in age. However, there is no published 400 study about precise dating of these continental series or nei-401 ther about the deformation affecting these series. In this arti-402 cle, we decided to name this formation as Oligocene-Neogene 403 sediments. Most outcrops of the Oligocene-Neogene conglom-404 erates and sandstones are represented as strongly discordant. 405 Deposition of these sediments is associated with the late reacti-406 vation of the fold belt.

  is a stratigraphic gap between the Lower Carbonif-411 erous and the thick Permo-Triassic molassic type series 412 that are in tectonic contact. This contact might be related 413 to the Late Paleozoic active margin activity at the southern 414

415 2 .

 2 Some authors argue about several tectonic phases in the 416 Cimmerian orogeny (Eo-cimmerian and Middle Cimme-417 rian orogenies), but because this article is focused on the 418 post-Cimmerian history, we will not distinguish these dif-419 ferent phases and, instead, use the term of Cimmerian 420 orogeny. 421 3. The major unconformity observed within the range cor-422 responds to the base of the Kashafrud Formation (Mid-423 dle Jurassic) which corresponds to the first deposited sed-424 iments after the Cimmerian orogeny. Then, this unconfor-425 mity corresponds to a post-orogenic unconformity but also 426 to a rift-onset unconformity.

  rifting episode occurred in the Kopet Dagh region dur-428 ing the Middle Jurassic. At this time, the southern part 429 of the Amu Darya Basin was probably linked with the 430 South Caspian Sea Basin (Brunet et al., 2003). The abrupt 431 facies and thickness changes of the Kopet Dagh Basin

  432 fill are inferred to mark activation of several major ex-433 tensional faults during deposition of the Middle Jurassic 434 Kashafrud Formation (Lyberis and Manby, 1999; Thomas 435 et al., 1999).

436 5 .

 5 During the Cretaceous and the Paleogene, several hiatus are interpreted as periods of uplift and erosion and the 438 role of tectonics during these periods could be questioned. 439 These emergent periods are indicated as local uplifts in 440 our stratigraphic chart (Figure 3). These hiatus have pre-441 viously been interpreted a consequence of distal responses 442 to collisional events (Berberian, 1983; Lyberis and Manby, 443 1999). There is no evidence of post-Middle Jurassic rifting 444 as previously suggested by Lyberis and Manby (1999).

445 6 .

 6 Finally, the late reactivation of the belt is not well dated, 446 but occurred after the deposition of the marls of the Eocene 447 Khangiran Formation. The occurrence of continental sed-448 imentation is related to the structural inversion that oc-449 curred after the Eocene as a consequence of the relative 450 motion between the Iran Plate and the Eurasian Plate. This 451 inversion resulted in widespread folding and thrusting of 452 Jurassic to Tertiary sediments (Lyberis and Manby, 1999;

459

  of the lack of information of the precise timing of deposi-460 tion of the post-Eocene sediments that are not widely out-461 cropping in the range. 462 Our new stratigraphic results have been integrated in a detailed 463 structural study of the belt focused on 4 main regional cross-464 sections. The next section presents the detailed and widespread 465 structural study that we carried out across the Kopet Dagh 466 range.

467 4 .

 4 Geological cross-sections and structure of the Kopet 468 Dagh range 469 This part describes the main structures of the Kopet Dagh 470 based on the simplified geological map (Figure 5) and on 4 471 regional cross-sections across the belt (Figures 6, 11, 13 and 472 15). These cross-sections result from numerous field surveys 473 and our structural interpretation locally supported by 2D and 474 3D seismic lines (see location of the presented seismic lines 475 in Figure 5). Our field work was limited to the Iranian part 476 of the range, which explains that the coverage of our data for 477 the frontal part of the belt are restricted to seismic data (parts 478 that connect with the South Caspian Sea region to the West and 479 within the Amu Darya Basin to the NE). In the eastern part, 480 the structural style of the front of the range has been defined 481 using borehole data plus 2D and 3D seismic sections. Towards 482 the South Caspian Sea Basin, folded structures are buried by the 483 thick Oligocene to Quaternary sediments and numerous seismic 484 lines are available in this transitional zone, above the Gorgan 485 Plain. Two of our cross-sections (Figures 6 and 11) illustrate 486 the links between the Kopet Dagh and the Amu Darya Basin, 487 whereas the 2 others (Figures 13 and 15) are focused on the 488 links between the Kopet Dagh and the South Caspian Sea Basin. 489 Pre-Cimmerian sediments outcrop in the Aghdarband ero-490 sional window and in some locations in the inner part of the 491 belt. They have not yet been described in Afghanistan or in 492 Turkmenistan. Then, there is only little and local information 493 about the tectonic history before the Cimmerian orogeny within 494 the Kopet Dagh. Furthermore, folds axes within the Upper De-495 vonian to Lower Carboniferous strata are co-axial with the folds 496 axes observed within Triassic rocks which causes difficulties 497 to unravel tectonic effects resulting from the Variscan orogeny 498 than the one resulting from the Cimmerian orogeny. In this ar-499 ticle, we will focus on the post-Cimmerian structural evolution 500 of the fold-and-thrust belt. Following the Cimmerian orogeny, 501 an extensional regime affected the southern Amu Darya Basin 502 during the Middle Jurassic. From the Middle Jurassic to the 503 Tertiary, over 7 km of sedimentary rocks were accumulated 504 (Afshar-Harb, 1979) and they unconformably overlay Paleozoic

  505

  507 folds. The main crests of the Kopet Dagh range correspond to 508 the fold axial regions of large anticlines mostly developed in the 509 Lower Cretaceous limestones (Tirgan Formation). In contrast, 510 most of the valleys are located in the core of synclines occupied 511 by less competent rocks. There is few Tertiary sediments out-512 cropping in the range, some of them are folded and outcrop in 513 the center of large synclines, whereas some Oligocene-Neogene 514 conglomerates are clearly discordant (Figure 5). 515 In the eastern part of the belt, the observed deformation is char-516 acterized by oblique Middle Jurassic graben inversion with ev-517 idences of forced-folding and few short-cuts, and as well by 518 larger scale structures involving basement. The large-scale 519 structures present long axis those are parallel to the Main Kopet 520 Dagh Fault. From seismic sections, several décollement levels 521 within the Mesozoic sequence explain numerous disharmonies, 522 fish-tail structures in the core of the folds or triangle zones (Fig-523 ures 8 and 12). The orientation of the Main Kopet Dagh Fault 524 is interpreted as associated with the reactivation of old Paleo-525 zoic structures

  528 2013) and to the northeastern part of the Amu Darya Basin. In-529 deed, the Variscan orogeny shaped structural features trending 530 roughly WNW-ESE inside the epi-variscan Turan Platform as 531 the Kyzylkum high, which marks the northeastern border of the 532 Amu Darya Basin. The orientation of the observed structures in 533 the northern and eastern part of the belt is directly related to the 534 Alpine reactivation of these Paleozoic basement structures. In 535 contrast, in the northwestern part, the belt presents an arcuate 536 shape that is parallel to the Paleotethys suture zone (Figure 1b).

537

  In this part, the observed structures are thrust faults involving 538 basement and fault-propagation folds within the sedimentary 539 sequence.

  540 4.1. The eastern cross-section (Aghdarband-Gonbadly sec-541 tion) 542

  To the North, the low metamorphosed molassic succession 601 overthrusts Triassic units that are forming a large south-verging 602 syncline marked in its central part by a narrow anticline. The 603 northern flank of the large syncline is bounded by another 604 double-verging syncline presenting secondary order folds in its 605 core. Its northern boundary is marked by several narrow strips 606 of steeply inclined Triassic rocks that are interpreted as due to 607 a flower structurerelated to a vertical Cimmerian fault striking 608 WNW-ESE with dextral strike-slip component (Zanchi et al., 609 2010). The fold axes observed in Devonian and Carboniferous 610 sediments are coaxial with the ones observed within the Trias-611 sic, which does not allow easily distinguishing the deformation 612 associated with the Cimmerian orogeny from the one due to 613 older orogeny. To the North of the Aghdarband erosional win-614 dow, the Middle Jurassic Kashafrud Formation overlay uncon-615 formably the Devonian strata.

  Figure10) and on the field (Figure4b)).

  4. Summary of the Aghdarband-Gonbadly cross-section 646The Aghdarband-Gonbadly cross-section shows a major 647 basement inversion that affects the southern border of the Amu 648 Darya Basin. A progressive thinning of the Jurassic and Cre-649 taceous series of the basin towards the NE, as well as the oc-650 currence of more pelagic facies to the North and more conti-651 nental facies towards the Aghdarband erosional window, sug-652 gest that the region of the erosional window formed probably 653 a horst during the Middle Jurassic, and a persistent paleorelief 654 during the deposition of the younger series of the basin. Deposition of the Middle Jurassic Kashafrud Formation occurred 656 during active rifting as highlighted by numerous normal offsets 657 shifting the base of this formation. Locally, the rift system has 658 been inverted as suggested by the observation of forced-folding 659 within the Upper series, which is attributed to the Tertiary inver-660 sion of the range. This late tectonic inversion is associated with 661 an important strike-slip component, and with the development 662 of growth strata within the Tertiary sediments. There is little 663 information in the Turkmen part of this cross-section but sev-664 eral gas fields are producing from the clastic series of the Early 665 Cretaceous Shurijeh Formation or from the reefal carbonates 666 of the Late Jurassic Mozduran Formation capped by the Late 667 Jurassic-Early Cretaceous evaporites and salt layers within the 668 Amu Darya Basin.

  Darre Gaz cross-section 670 The 160 km-long DarreGaz cross-section is cutting through 671 the Darre Gaz syncline where the Tertiary series are the thick-672 est observed within the range (Figure 11). This cross-section 673 highlights the front of the Kopet Dagh and it is passing through 674 the area where there are numerous recent strike-slip faults that 675 cross-cut the structures. Along this cross-section, the sedimen-676 tary series are thicker than along the Aghdarband-Gonbadly 677 cross-section and presents uplifted deeper facies. Thicknesses 678 of the formations were estimated according to field observa-679 tions, seismic data and satellite imaging, because of the lack of 680 borehole data. As for the eastern cross-section, the basement 681 is also implied in the deformation and several décollement lev-682 els within the Mesozoic series are observed. This cross-section 683 will be described from the SW to the NE.

  1. Description of the Darre Gaz cross-section 685 In the southwestern part of the cross-section, the folded struc-686 tures present a wavelength of about 12 km and they are cut by 687 several strike-slip faults. We infer that the folding of the se-688 ries could be associated with the inversion of Middle Jurassic 689 half-grabens. The strike-slip faults affect the discordant Tertiary 690 series and are associated with the most recent tectonic phase. 691 The seismic section on Figure 12 highlights an important 692 disharmony between deep and surface structures, with several 693 décollements levels within the thick Cretaceous series. Main 694 décollement levels are located within the Kashafrud Formation, 695 within the evaporitic levels of the Surijeh Formation and within 696 the thick marly Sarchashmeh and Sanganeh formations. Some 697 structures are outcropping laterally, such as the narrow reverse 698 fold affecting the Barremian limestones of the Tirgan Forma-699 tion. Finally, the northeastern part of the cross-section corre-700 sponds to the Zarrineh Kuh anticline. Seismic data (Figure 12) 701 show 2 anticlines: (1) the shallower anticline that affects Cre-702 taceous and Paleocene levels and that is narrower than (2) the 703 deeper one, in which the Jurassic series are affected by larger 704 wavelength forced-folding. There are no seismic data along the 705 section crossing the Zarrineh Kuh anticline but, seismic profiles 706 of its southwestern flank highlight the important disharmony 707 between shallow and deep structures.

  708 4.2.2. Summary of the Darre Gaz cross-section 709 The Darre Gaz cross-section highlights the importance of 710 forced-folding affecting the basement and overlain by shorter 711 wavelength folds detached along several décollement levels. 712 Surrounding seismic sections show that the décollement level of 713 the frontal fold is located within the Lower Cretaceous, proba-714 bly within the evaporitic levels. This cross-section attests of the 715 important partitioning of the recent deformation across the belt: 716 thrusts are located in the frontal part of the range as highlighted 717 by compressional focal mechanisms whereas mostly strike-slip 718 deformation is now affecting the internal parts of the range.

  -long regional cross-section (Figure13) cuts 721 across the western branch of the Kopet Dagh range, from the 722 internal zone until the South Caspian Sea Basin. It is a dog-leg 723 type cross-section based on available outcrops and it presents 724 typical structures and unconformities characterizing this area. 725 At large scale, this section shows the uplift and erosion of the 726 inner part of the Kopet Dagh as a consequence of several pe-727 riods of uplift and/or folding. The southwestern part of this 728 section corresponds to the inner part of the belt, where several 729 basement thrusts are observed and where Paleozoic and Meso-730 zoic formations outcrops at several locations. In this area, the 731 folds of the western part of the Kopet Dagh are oriented SW-NE 732 (Figure 5) and plunge to the SW in the Gorgan Plain below the 733 sediments of the South Caspian Sea Basin.

  1. Description of the western Kopet Dagh cross-section 735 We will describe this cross-section from the internal zone, 736 close to the Late Triassic/Early Jurassic Paleotethys suture zone 737 towards the Gorgan Plain corresponding to the eastern prolon-738 gation of the South Caspian Sea Basin. The large wavelength 739 structures present a SE vergence until Balkor syncline (Figure 740 13). In contrast, the structures that plunge beneath the Gorgan 741 Plain present an opposite NW vergence. 742 The southeastern part of the cross-section corresponds to a large 743 SE-verging anticline (Figure 13) formed by the series from Pa-744 leozoic to Eocene in age. On top of the Paleozoic, Triassic 745 series are outcropping and unconformably overlain by a con-746 glomeratic level corresponding to the base of the Middle Juras-747 sic Kashafrud Formation. The Kashafrud Formation presents a 748 fan geometry and its thickness is locally up to 2500 m in the 749 deeper parts of this rift structure (Figure 14).

750

  The Middle Jurassic Kashafrud Formation overlays lower se-751 ries (Paleozoic or Triassic series) and is unconformably cov-752 ered by the marls of the Upper Jurassic Chaman Bid Forma-753 tion that could locally directly overly the Triassic strata. This 754 erosion on top of the Kashafrud Formation was also observed 755 on some seismic lines in the eastern part of the Kopet Dagh 756 (Kavoosi et al., 2009b). Above a thin marly and clastic level, 757 the Lower Cretaceous Tirgan limestone reaches around 450 m 758 of thickness. On the top of the Tirgan Formation, there are 759 numerous sedimentation lacunas and it is locally covered by 760 the very thin Sarchashmeh Formation or by the Abderaz For-761 mation. The whole Upper Cretaceous series do not reach 400 762 m of thickness and they are overlain by the reddish series of the Paleocene. There is an important thinning of the Mesozoic series and in particularly of the Lower Cretaceous with an important lacuna of deposition from the Aptian to the Turonian that has only been observed in the western Kopet Dagh. Large out-of-sequence thrusts that affect the whole stratigraphic sequence are observed (Figure 14). They are obliquely cutting the previous structures such as the Kashafrud rift, which suggests that they are newly-formed and do not correspond to inversion of the rift faults. The Tirgan Formation is folded and faulted with a short wavelength, which suggests the occurrence of local décollement levels within the underlying Chaman Bid Formation. The series is continuing towards the West (Figure 14) with the occurrence of folds with Kashafrud and Mozduran formations in the core that are cross-cut by the newly-formed S-verging thrusts. To the North, within the northern flank of the Bash Kalateh anticline, the Lower Cretaceous series (1300 m thick) are outcropping, whereas they were absent in the Nabiya syncline. Conglomerates (∼40 m thick) are characterized an erosion level on the top of the Aitamir Formation and they are overlain by the white limestones of the Abderaz Formation that are the only sediments from the Upper Cretaceous. The marine marls of the Eocene directly overlie the Upper Cretaceous. The entire series is concordant and presents a constant dipping whereas the Oligocene-Neogene conglomerate is subhorizontal. Toward the NW, a narrow S-verging anticline with a core made of Upper Jurassic sediments. The Lower Cretaceous series thickens and is unconformably overlain by sediments from the Upper Cretaceous Kalat Formation to the Eocene Khangiran Formation. NW verging large anticlines and synclines are observed,

  This cross-section is characterized by important lateral variations of the formations thicknesses as a consequence of either several unconformity or lateral sediment thickness variations inherited from the deposition of the series. There is a lacuna in the Lower Cretaceous to the East and in the Upper Cretaceous to the West. There are also facies variations and thickening of the Lower Cretaceous toward the West. The unconformity at the base of the Lower Cretaceous (Kalat Formation) is truncated by 819 the post-Eocene unconformity. These several erosional surfaces 820 are associated with stratigraphic lacunas are observed from the 821 Lower Cretaceous to the Eocene, but they are not associated 822 with angular unconformities, in contrast to the major angular 823 unconformity characterizing the base of the post-Eocene series. 824 The entire series until the Late Eocene is folded within double-825 verging structures. Newly-formed thrusts cross-cut the previous 826 structures of the Kashafrud graben.

  Gorgan Plain cross-section: from the Eastern Caspian Sea 828 margin to the Gorgan Plain 829 This part presents the westernmost Kopet Dagh cross-section 830 that is linked with the eastern part of the South Caspian Sea 831 Basin above the Gorgan Plain (Figure 15). The Gorgan Plain 832 is the southern prolongation of a larger delta that outcrops in 833 Turkmenistan, along the Caspian Sea. Numerous wells and dis-834 coveries were made in this region where the fields present an 835 arcuate shape along the coast (Figure 1b) and produce into the 836 Lower and Middle Pliocene clastic series. In this region, the 837 folds are oriented SWS-ENE, but they are masked by the Qua-838 ternary sediments that outcrop in the Gorgan Plain in Iran. Dis-839 covery of gas and condensates was made in one of this buried 840 folded structure, within the Lower Cretaceous carbonates of the 841 Tirgan Formation.

  1. Description of the Gorgan Plain cross-section 843 According to borehole data and similarly to the western 844 Kopet Dagh cross-section, the Gorgan Plain cross-section 845 shows an important angular unconformity between folded and 846 trangressive series that are consequent to the important Tertiary 847 subsidence in the South Caspian Sea Basin. The folds affect-848 ing the Upper Cretaceous series present an asymmetry towards 849 the NW and they prolong the folded structures belonging to the 850 Kopet Dagh range (Figure 15) as attested by borehole data and 851 seismic sections (Figures 16 and 17).

852

  Figure 17 presents a composite seismic section close to the 857

  Late Triassic to Early Jurassic 896 The collision between Central Iran and Eurasian plates (Cim-897 merian orogeny) follows the northward subduction of the Pa-898 leotethys Ocean and occurred during the latest Triassic/Early 899 Jurassic (Zanchetta et al., 2013) (Figure 18a). The trend of 900 the main structures of the northwestern and eastern parts of the 901 Kopet Dagh follows the arcuate shape of the Paleotethys su-902 ture zone, which emphasizes the importance of the structural 903 inheritance in the present-day structure of the belt. Further-904 more, some authors suggest an important oblique component of 905 the convergence from a detailed structural study on transpres-906 sional structures within the Aghdarband window (Zanchi et al., 907 2010). They infer the reactivation of some Paleozoic struc-908 tures as major strike-slip faults during the Cimmerian orogeny. 909 Those linear structures are observed North of the Amu Darya 910 Basin (Mangyshlak and Ustyurt ridges) and within the Kopet 911 Dagh (Main Kopet Dagh Fault) and they have been recently 912 reactivated too (Ulmishek, 2001). From a petroleum point of 913 view, the coal beds of the Upper Triassic sequence (Miankuhi 914

  918 5.2. Middle Jurassic 919 After the Cimmerian collision (Figure 18b), a rifting phase 920 took place across the studied area with the deposition of the 921 clastic Middle Jurassic Kashafrud Formation. Seismic sections 922 show that the Middle Jurassic Kashafrud Formation was de-923 posited in a rift system, as suggested by the lack or near lack of 924 this formation above pre-Jurassic basement highs in opposition 925 within the hanging wall of the normal faults where this forma-926 tion reaches several thousand meters thick. Furthermore, evi-927 dences of preserved Middle Jurassic normal faulting have been 928 observed at several places in the field. The top of the Middle 929 Jurassic Kashafrud Formation is marked by an important ero-930 sional surface and locally by an angular unconformity with the 931 overlying series. 932 This Middle Jurassic rift system in the Kopet Dagh region has 933 been coeval with the South Caspian Sea rifting event (Brunet 934 et al., 2003; Saintot et al., 2006). From a petroleum point of 935 view, the Kashafrud Formation is considered as one of the main 936 source rocks of the Amu Darya Basin, but forms a bad reservoir, 937 because of early diagenesis (Poursoltani and Gibling, 2011). 938 This rifting phase at Middle Jurassic times has also been ob-939 served along the Black Sea, the Kura and the South Caspian 940 Sea (Brunet et al., 2003, e.g.). This phase is commonly inter-941 preted as a consequence of back-arc developpment due to the 942 subduction of the Neotethys Ocean. According to our observa-943 tions in the Kopet Dagh, we also propose that the collapse of 944 the Cimmerian orogenic system could have play an important 945 role in this rifting phase. 946 5.3. Late Jurassic / Early Cretaceous 947 The Upper-Jurassic to Early Cretaceous series observed in 948 the Kopet Dagh range also belong to the southern part of the 949 Amu Darya Basin (Figure 18c). We infer the occurrence of 950 gentle paleohighs in the eastern part of the Kopet Dagh to ex-951 plain variations in facies and thickness of the series from the 952 Upper Jurassic to the Lower Cretaceous. For example, to the 953 North of the Aghdarband erosional windows, Upper Jurassic 954 Mozduran limestone is reduced to few meters and there are no 955 salt or evaporites above, in contrast to the observations made in 956 the Amu Darya Basin. 957 From a petroleum point of view, the carbonates of the Mozdu-958 ran Formation as well as the clastics of the Shurijeh Formation 959 are the main reservoirs of the Amu Darya Basin. Towards the 960 South, in the Kopet Dagh, there is no salt on top of the Jurassic 961 calcareous and the Upper Jurassic to Lower Cretaceous series 962 are thinner and more clastic.

  and western parts of the Kopet Dagh range, 965 several local erosional levels are observed (Figure 3). For ex-966 ample, a large hiatus from the late Barremian to the Santo-967 nian, as well as important thickness and facies variations are 968 observed on the western cross-section (Figure 13). Further-969 more, the uppermost Cretaceous (Maastrichtian) is correlated 970 with a stratigraphic hiatus, which is generalized in the whole 971 Kopet Dagh region. Furthermore, an angular unconformity has 972 been evidenced at the base of the Upper Cretaceous series in the 973 western Alborz, suggesting the presence of persisting emerged 974 land(Berra et al., 2007). Our results suggest several local tec-975 tonic uplifts in the southern part of the Amu Darya Basin during 976

  / Early Oligocene: onset of the Alpine orogeny The main inversion phase recorder in the Kopet Dagh occured during the Late Eocene, which is when the Neotethys locked and when the far-field deformation developed in both Eurasian and African plates (Frizon de Lamotte et al., 2011). The thick-skinned folding and related uplift of the Kopet Dagh may be related to reactivation of former Paleozoic or Cimmerian fault systems (Figure 19a), which is suggested by the linear front of the Eastern and Central Kopet Dagh. During the main Alpine compressive phase, folding style and structures vary laterally as a function of pre-existing structures, rock behavior and mechanical stratigraphy (Figure 19a). In the southeastern part of the Kopet Dagh, the Paleotethys suture zone and the inherited Paleozoic trend of the Main Kopet Dagh Fault are parallel. These pre-existing structures probably control both the location of the Alpine Kopet Dagh uplift and folding and the basementinvolved tectonic style we observed. Some local inversions of Middle Jurassic graben were also highlighted even though evidences of force folding within the Upper Jurassic to Lower Cretaceous (Barremian) series have been shown too. On top of the Barremian series, several décollements located within the thick Aptian-Albian marls lead to the formation of the triangle zone. Quite similar structures have already been described

1032

  els within Jurassic or Cretaceous shale levels are suggested. In 1033 this part, there is not much evidence of reactivation of the nor-1034 mal faults associated to the Middle Jurassic rifting faults and 1035 numerous short-cuts have been observed. 1036 Marine sediments up to the Late Eocene are folded with the un-1037 derlying formation during the Alpine phase. Eocene sediments 1038 are clipped inside the synclines and are unconformably covered 1039 by post-Eocene series. Within the Kopet Dagh range, most 1040 of the Oligocene-Neogene series are discordant, but growth 1041 strata within the Oligocene-Neogene series were observed in 1042 the southeastern part of the belt. Further datings of these series 1043 are needed, but a Late Eocene-Early Oligocene age for onset 1044 of the Alpine orogeny within the Kopet Dagh belt can be pro-Oligocene to Mid-Pliocene: Important subsidence in the 1047 South Caspian Sea Basin 1048 The rapid subsidence of the South Caspian Sea starts just af-1049 ter the Late Eocene-Early Oligocene compression folding that 1050 is responsible for the main uplift phase within the Kopet Dagh 1051 and the Alborz mountains (Allen et al., 2003; Brunet et al., 1052 2003). Most of the authors agree that the basement of the South 1053 Caspian Sea is an oceanic crust resulting from the opening of 1054 a back-arc basin north of the Neotethyan arc (Brunet et al., 1055 2003). According to Allen et al. (2003), the South Caspian Sea 1056 basement corresponds to a resistant block with almost no inter-1057 nal deformation, playing an indentor role, which could explain 1058 the arcuate shape of the surrounding fold-and-thrusts belts (Al-1059 borz, Kopet Dagh, and Talysh). The important thickness of the 1060 Caspian series is sealing the previously described structures in 1061 the western Kopet Dagh. Progressive onlap of these Oligocene 1062 and Miocene series on top of the unconformity is observed on 1063 seismic sections. The structures with hydrocarbon discoveries 1064 that exist along the western coast of Turkmenistan up to the 1065 Moghan Plain in Iran (Figure 1b) are associated with the deep 1066 shale ridges of the Oligocene Maykop Formation. These arch 1067 structures correspond to a Miocene proto Amu Darya delta in 1068 that region and the development of shale ridge in the delta front 1069 during the Miocene. An increase of the subsidence rate was 1070 observed during the latest Miocene and Pliocene periods and 1071 the Amu Darya River shifted to a northward position. This 1072 new large prograding system towards the South Caspian Sea 1073 Basin is associated with the deposition of the Lower Pliocene 1074 main reservoirs. It cover nearly half of the surface of the South 1075 Caspian Sea Basin with the development of a new delta front 1076 oriented NE-SW in the central part of the basin.

  Mid-Pliocene to Present day: Indentation and onset of the 1078 extrusion in the Kopet Dagh 1079 Major changes of tectonic regime have been highlighted dur-1080 ing the Plio-Quaternary at the scale of the South Caspian Sea 1081

  suggested that a northwestward motion of the South 1089 Caspian Sea Basin compared to Eurasia and/or its clockwise ro-1090 tation could explain this tectonic reorganization. Masson et al. 1091 (2006) proposed a second tectonic force due to the initiation of 1092 the northward subduction of the oceanic basement of the South 1093 Caspian Sea Basin below the Apsheron ridge. 1094 In the Gorgan Plain and along the Turkmen margin of the 1095 Caspian Sea, the discordant series lying on top of the older 1096 series folded by the first Alpine phase are deformed too (Fig-1097 ure 15). This deformation implies a refolding of the uncon-1098 formity by reactivation of the underlying structures. Oblique 1099 inversion of the Kashafrud grabens and strike-slip along the 1100 Main Kopet Dagh Fault, which extends from the South Caspian 1101 Sea to the Afghan border are associated with this late defor-1102 mation phase. En echelon pattern of the folds along this zone 1103 and en echelon fault pattern observed on 3D seismic blocks 1104 demonstrate a dextral shear component during the folding and 1105 inversion/reactivation. The importance of the strike-slip faults 1106 is demonstrated by the present-day seismicity across the range 1107 as well as by geomorphological data.1108 6. Conclusions1109In this paper, we provide a detailed and revised characteri-

Figure 1

 1 Figure 1: a. Topographic map (ETOPO 1 data) of Iran showing the main tectonic units with location of the main volcanic rocks, salt and ophiolites outcrops. Neotethys and Paleotethys sutures zones are indicated. MKF: Main Kopet Dagh Fault; GKF: Great Kavir Fault; GKB: Great Kavir Basin; ABS: Apsheron-Balkhan System b. Topographic map of the Kopet Dagh range from ASTER GDEM data showing the location of the gas and oil fields (red area) from publications (Dikenshteyn et al., 1983; Ulmishek, 2004) and from the Oil and Gas Infrastructure in the Caspian Sea region, March 2001 from the United State Government. The Paleotethys suture zone and major places are indicated on this map. Major gas fields: 1: Dauletabad; 2: Gonbadli; 3: Khangiran; 4: Shaltyk; 5: Bayram-Ali; 6: Achak

  Figure 2: Seismotectonic map of the Kopet Dagh region where the major recent faults are represented according to(Hollingsworth et al., 2006; Hollingworth, 2007; Hollingsworth et al., 2008 Hollingsworth et al., , 2010;; Shabanian et al., 2009a Shabanian et al., ,b, 2012)). Blue arrows represent GPS velocities relative to Eurasia fixed; the error ellipses indicate formal errors within 95 percent confidence interval[START_REF] Tavakoli | Present-day deformation and kinematics of the active faults observed by GPS in the Zagros and East of Iran[END_REF]. The location of the Paleotethys suture zone is indicated. Focal mechanisms are taken from CMT Harvard catalogue for the period 1976-2012. The shaded relief background has been made from ASTER GDEM data. DF: Doruneh Fault; KF: Khazar Fault; MKF: Main Kopet Dagh Fault; NFS: Neyshabur Fault System.

Figure 4

 4 Figure 4: a) Prograding sequence of limestones belonging to the Upper Jurassic Mozduran Formation within the upper part of the upper Jurassic shally Chaman Bid Formation b) Clastic filling between 2 reefs within the Upper Jurassic Mozduran Formation. Similar features have been observed on seismic sections as highlighted in Figure 10.

Figure 5 :

 5 Figure 5: Simplified geological map of the Kopet Dagh area compiled from the geological maps of the Geological Survey of Iran. Locations of the 4 regional cross-sections presented in this article are indicated.

Figure 6 :

 6 Figure6: The Aghdarband-Gonbadly cross-section (see location on Figure5). This cross-section shows structural relationships between the rocks deformed by the Variscan and/or the Cimmerian orogeny that outcrop in the Aghdarband erosional windows and the series deposited in the southwestern part of the Amu Darya Basin affected by the Alpine inversion of the Middle Jurassic extensional structures. Locations of the seismic data presented in this article and borehole data are indicated.

Figure 7 :

 7 Figure 7: Tectonic sketch of the Aghdarband erosional window, modified from previous published cross-sections (Ruttner, 1991; Zanchi et al., 2010). The folded Triassic and older series are preserved below double verging thrusts. The deformed rocks are overlain by the Middle Jurassic Kashafrud Formation characterized by its basal conglomerate (J2). D: Devonian, C: Carboniferous, PT: Permo-Triassic molassic sediments, T: Triassic series excepting the Miankuhi Formation (Tm), J2: Conglomeratic base of the Middle Jurassic Kashafrud Formation and J3: Upper part of the Middle Jurassic Kashafrud Formation.

Figure 8 :

 8 Figure 8: Seismic section showing the triangle structure to the NW of the Aghdarband erosional window (location on the Aghdarband cross-section, Figure 6). This seismic line shows two major North-directed basement thrusts that branch into an inferred detachment within the shales of the Campanian. For calibration, we used field data and information from the borehole represented n the figure. Legend of the horizons: Black = Top Trias; Dark blue = top Kashafrud Formation (Middle Jurassic); Light blue = top Mozduran Formation (Upper Jurassic); Dark green = Top Shurijeh Formation (Neocomian); Green = Top Aitamir Formation (Cenomanian); Light green = Top Kalat Formation (Uppermost Cretaceous); Orange = Top Chehel Kaman Formation (Paleocene).

Figure 9

 9 Figure 9: a) Seismic section from the Gonbadli gas field area (location in Figure 5) showing large-scale basement uplift. The Jurassic structure is shown by opposite set of normal faults, some of which seem to preserve their original normal displacement. b) Zoom on the previous seismic transect with a flattening done at the top Middle Jurassic horizon which highlight of the Kashafrud half graben structures. Legend of the horizons: Purple = Top Trias; Dark blue = top Kashafrud Formation (Middle Jurassic); Light blue = top Mozduran Formation (Upper Jurassic); Dark green = Top Shurijeh Formation (Neocomian); Green = Top Aitamir Formation (Cenomanian); Light green = Top Kalat Formation (Uppermost Cretaceous); Orange = Top Chehel Kaman Formation (Paleocene).

Figure 10 :

 10 Figure 10: Seismic section across the Khangiran gas field extracted from a 3D cube. The Khangiran structure is due to the Tertiary inversion of a Middle Jurassic half graben. The occurrence of growth strata within the Oligocene-Neogene sequences highlights that the graben inversion is associated to the Alpine tectonic phase as a consequence of an inversion tectonics. The black arrow highlights some carbonate build-ups within the Upper Jurassic Mozduran limestones. Legend of the horizons: Purple = Top Trias; Dark blue = top Kashafrud Formation (Middle Jurassic); Light blue = top Mozduran Formation (Upper Jurassic); Dark green = Top Shurijeh Formation (Neocomian); Green = Top Aitamir Formation (Cenomanian); Light green = Top Kalat Formation (Uppermost Cretaceous); Orange = Top Chehel Kaman Formation (Paleocene); Yellow = Intra Oligo-Neogene conglomerates.

Figure 11 :

 11 Figure11: The Darre Gaz regional cross-section (see location in Figure5) shows the inversion of Middle Jurassic front of the belt is characterized by North-verging basement thrusts that mostly branch into a major detachment within the Aptian-Albian series.

Figure 12 :

 12 Figure 12: Seismic section showing typical structures of the Darre Gaz area with a disharmony between deep and surface structures implying several décollement levels within the Cretaceous series. The deeper horizons of this section are not calibrated. Legend of the horizons: Black = Top Trias; Dark blue = top Kashafrud Formation (Middle Jurassic); Light blue = top Mozduran Formation (Upper Jurassic); Dark green = Top Shurijeh Formation (Neocomian); Green = Top Aitamir Formation (Cenomanian); Light green = Top Kalat Formation (Uppermost Cretaceous); Orange = Top Chehel Kaman Formation (Paleocene).

Figure 14 :

 14 Figure 14: Scheme of several fields observations highlighting the structural relationships between the different stratigraphic formations.The important thickness variations of the Middle Jurassic Kashafrud Formation is due to active rifting during deposition. An erosional surface at the base of the Late Jurassic Chaman Bid Formation and several progradations of the Upper Jurassic Mozduran limestones into the marls of the Late Jurassic Chaman Bid Formation are observed. Notice the reduced thickness of Cretaceous and Tertiary series.

Figure 15 :

 15 Figure15: The Gorgan Plain regional cross-section (see location in Figure5) shows the buried folds of the Kopet Dagh beneath the thick post-Eocene sediments belonging to the South Caspian Sea Basin. This cross-section has mainly been constructed from seismic sections.

Figure 16 :

 16 Figure 16: Seismic section below the Gorgan Plain to the Western part of the Kopet Dagh. This section shows the folded structures overlain by a major unconformity with progressive onlap above this unconformity. The pink horizon near the top of the section corresponds to the top of the Mid-Pleistocene strata, the red horizon corresponds to the Late-Eocene and Early Oligocene unconformity, the green horizons correspond to the Late Cretaceous marls and clastic sediments. Within the syncline, it is possible that the Paleogene up to the Upper Eocene were preserved. (a) Folded and faulted structures, the folds are oriented NE-SW parallel to the orientation of the western part of the Kopet Dagh belt (b) The red line corresponds to the folded unconformity at the base of the Oligocene-Neogene strata.

Figure 17 :

 17 Figure 17: Seismic profile of the margin of the Caspian Sea Basin below the Gorgan Plain. Notice the unconformity highlighted in red which is covered by sediments of the South Caspian Sea Basin. A shale ridge structure is marked in red (M?) suggesting that the sediments just on top of the unconformity are probably made of the Oligocene Maykop Formation. The pink horizon corresponds to the near top Mid-Pleistocene, the yellow horizon corresponds to the near top Miocene, the red horizon corresponds to the Late Eocene-Early Oligocene unconformity and the green horizons correspond to the Late Cretaceous.

Figure 18 :

 18 Figure 18: Schematic reconstructions of the geodynamic settings of the region centered on Central Iran during a) the Late Triassic to the Early Jurassic; b) the Middle Jurassic; c) the latest Jurassic to the Early Cretaceous and d) the Late Cretaceous to the Eocene. Reconstructions for the Neotethys and Iran were adapted from Agard et al. (2011); Barrier and Vrielynck (2008).

Figure 19 :

 19 Figure 19: Schematic reconstructions of the geodynamic settings of the region centered on Central Iran during a) the Late Eocene to the Early Oligocene; b) the Oligocene to the Middle Pliocene and c) the Late Pliocene to the presentday. Reconstructions for the Neotethys and Iran were adapted from Agard et al. (2011); Barrier and Vrielynck (2008).

  These thick marls become richer 328 in fine grained sandstone layers in the upper part which corresponds to the Sanganeh Formation. From our biostratigraphic 330 study, a Late Barremian to Aptian age is proposed for the Sar-

	331
	332	chashmeh Formation and the Sanganeh Formation appears to
	333	be Albian in age.
	334	3.6. Upper Cretaceous (Aitamir, Abderaz, Abtalkh and Kalat
	335	formations)

  . The Kalat For-

		382	3.7. Paleogene (Pestehleigh, Chehel Kaman and Khangiran
		383	formations)
	368
	369	mation is a widespread unit in the whole Kopet Dagh region and
	370	consists of a bioclastic limestone and carbonate build-ups with
	371	subordinate sandstone beds observed only in the eastern part of
	372	the region (Afshar-Harb, 1979). This formation has been re-
	373	cently dated as Upper Campanian to Maastrichtian (Shahidi,
	374	2008) and our biostratigraphic results indicate a Campanian
	375	age. The Kalat Formation consists of marls partly rich in gas-
	376	tropods and recifal limestones with rudists or algae, must have
	377	been deposited in a shallow shelf environment with a connec-
	378	tion with the open sea (Afshar-Harb, 1979). The upper part of
	379	the Kalat Formation is marked by an erosional surface that is
	380	associated with the second general hiatus of sedimentation in
	381	the region.

Summary of the Gorgan Plain cross-section

This cross-section shows the relationship between the Kopet 873 Dagh affinity folds uplifted and eroded after the Eocene ma-874 rine transgression. The trend of the buried folds is SSE-NNW, within the Kopet Dagh range occurred during the late Ceno-


Antoine De Rengervé

Souheil Hanoune
email: souheil.hanoune@ensea.fr

Pierre Andry
email: andry@ensea.fr

Mathias Quoy
email: quoy@ensea.fr

Philippe Gaussier
email: gaussier@ensea.fr

Building Specific Contexts for On-line Learning of Dynamical Tasks through Non-verbal Interaction

Trajectories can be encoded as attraction basin resulting from recruited associations between visually based localization and orientations to follow (low level behaviors). Navigation to different places according to some other multimodal information needs a particular learning. We propose a minimal model explaining such a behavior adaptation from non-verbal interaction with a teacher. Specific contexts can be recruited to prevent the behaviors to activate in cases the interaction showed they were inadequate. Still, the model is compatible with the recruitment of new low level behaviors. The tests done in simulation show the capabilities of the architecture, the limitations regarding the generalization and the learning speed. We also discuss the possible evolutions towards more bio-inspired models.

I. INTRODUCTION

Action selection is the choosing of the most appropriate action out of a set of possible candidates. The word "action" can represent notions ranging from high level abstracts ("pour water in a glass") to low level motor commands ("move arm joint with chosen speed"). We are interested in a task related to the second case (Fig. 1). A robot must navigate to different places depending on the transported object. The robot takes an object at the picking place P and goes to the correct dropping places (A or B) to release the objects depending on their sizes. The robot has to select the adequate actions (moving directions i.e. low level actions) according to the current sensory inputs. After the mid 80's, solutions to action selection problem based solely on executing the steps of a given plan to achieve a goal have been progressively abandoned for more reactive behaviors [START_REF] Brooks | A robust layered control system for a mobile robot[END_REF]. Using behavior modules that always directly monitor the environment allows the system to react faster to changes. The organization of these modules can be in parallel [START_REF] Maes | Learning to Coordinate Behaviors[END_REF] or in hierarchy [START_REF] Tyrrell | Computational mechanisms for action selection[END_REF]. It has also been argued that partial activation of reactive modules depending on a carefully designed hierarchy with attentional switching can also provide a robust solution with an easier coordination of modules [START_REF] Bryson | Hierarchy and Sequence vs. Full Parallelism in Action Selection[END_REF]. In [START_REF] Maes | Learning to Coordinate Behaviors[END_REF], the behavior modules are encoded as a condition (a combination of sensory inputs determining when the behavior can activate), an action (what the behavior consists in) and a result (expected sensory inputs after the action is performed). At first, the condition is general and the activation of the behavior is easy. Learning increases the selectivity of the condition to match the fact that the desired result cannot be obtained by the particular action in any situation. The learning is based on the correlation between the occurring of particular sensory inputs and the occurring of the result after the action is executed. Sensory inputs are progressively integrated in the condition of a behavior to better determine when it should be active, improving the coordination between Fig. 1. Left Example of contextual task in navigation. A solution is to encode contexts biasing the selection of actions in the particular situations (locations (circles) + objects status) when there is a choice to make. In place P, the decision is between picking objects, moving left and moving right. In place A and B, the possible actions are dropping held object and moving to picking place. Right Example of typical trajectory learned through interaction as an attraction basin emerging from place-cell/orientation couples (black arrows). the different behaviors. Reinforcement learning is another candidate solution for the action selection problem [START_REF] Sutton | Reinforcement Learning: An Introduction[END_REF]. Relying on neurobiological results, computational models of the Basal Ganglia were developed to explain the action selection by humans. The properties of dopamine neurons indicate that they could implement some kind of reinforcement learning [START_REF] Schultz | A neural substrate of prediction and reward[END_REF]. The Basal Ganglia, organized in parallel loops (potentially coding actions) with mutual inhibition, can perform the competition necessary for the action selection [START_REF] Gurney | A computational model of action selection in the basal ganglia. II. Analysis and simulation of behaviour[END_REF], [START_REF] Girard | Integration of navigation and action selection functionalities in a computational model of cortico-basal-ganglia-thalamo-cortical loops[END_REF]. However, both the reinforcement learning and the correlation learning are quite slow to learn. In order to have a reactive interaction, the behavior should be adapted in a faster way.

Following a simple trajectory can be encoded as an attraction basin emerging from multiple place-cell/action associations [START_REF] Giovannangeli | Robust mapless outdoor vision-based navigation[END_REF]. A place is encoded by merging "what" is seen with "where" it is seen 1 . A recruited place-cell (PC) responds accordingly to the distance to the encoded place with a maximal response when at the learned spot (see [START_REF] Giovannangeli | Robust mapless outdoor vision-based navigation[END_REF] for details). The actions are direction of movement2 . The robot selects its moving direction depending on its place in the environment (see an example of learned trajectory in Fig. 1). The obtained navigation controller is robust due to the generalization capabilities of the place-cell recognition. New place-cell/action couples are learned from on-line non-verbal interaction [START_REF] Giovannangeli | Interactive teaching for vision-based mobile robots: A sensory-motor approach[END_REF]. When the robot moves too far from the desired trajectory, the robot is shown how to get back to the desired trajectory by forcing its orientation 3 . This corrected orientation is associated to a new learned place-cell completing the encoded attraction basin. In order to learn the task of Fig. 1, the information about the object (e.g. size, but it could be visual, tactile,. . . ) should be included in the condition of the actions i.e. transforming placecells into multimodal categories. Two approaches are possible to build the adequate multimodal categories. Local solutions to action selection can be learned and progressivelly adapted to enable good generalization. For instance, when the behavior of the robot is corrected, multimodal categories can be recruited and associated with the correct actions. The generalization depends on how the different modalities contribute to the context activation. Without any particular a priori, the recruited categories would include all the modalities equally. Thus, the generalization properties should be improved by learning how much each modality should contribute, with a possible pruning of the irrelevant links. The alternate solution is to start from a general category (i.e. taking only a few modalities into account) and progressively increase the selectivity of the category (like with conditions in Maes's model [START_REF] Maes | Learning to Coordinate Behaviors[END_REF]). Selectivity can be adapted on the basis of the feedback provided by the interaction. In the framework of the place-cell/action based controller, we propose that the place-cells be non-specific categories progressively refined by inhibiting them in situations when they predict undesired behaviors according to the interaction from the teacher. Some multimodal contexts are thus recruited to store which place-cells should be inhibited and when. A task may not be solved by only refining the existing PC/action couples. The recruitment of new PC/action couples may occur to enrich the basis of behaviors of the system. We will also show that the whole process can run in parallel with the aforementioned trajectory learning.

In Section II, we present the neural network based architecture recruiting contexts for the inhibition of irrelevant PC/action couples. The evaluation of the actions and the context recruitment are detailed with the conditions to recruit new place-cells. The model is implemented in the neural network simulator Promethe [START_REF] Lagarde | Distributed Real Time Neural Networks In Interactive Complex Systems[END_REF], and tested in a robotic simulation based on Webots (Cyberbotics) (Sec. III). The first experiment studies the behavior of the learning process when the contexts are not needed to learn a trajectory. Then, the model is validated in the task described in Fig. 1. The model manages to learn the task. Even though this learning scheme shows limited generalization properties, we discuss in Sec. IV whether they could be a basis for longer learning that will focus on summarizing the contexts into chunks. Such a fast adaptation of the action selection may be useful to complete and even train a slower learning network extracting the statistics of the task.

II. MODEL FOR SPECIFIC CONTEXT BUILDING BASED ON INTERACTIVE LEARNING

The combination of several PC/action couples is sufficient to shape an attraction basin so that the robot follows a desired trajectory (Fig. 1 and2, [START_REF] Giovannangeli | Robust mapless outdoor vision-based navigation[END_REF]). The action evaluation block in the architecture learns the contexts in which some place-cells should be inhibited. The place-cells are thus biased by the output I of the action evaluation process before the competition between the biased place-cells. The winning biased placecell P C I determines the selected action i.e. the orientation to be followed. Figure 3 corrects the behavior of the robot by opposing to the predicted dynamics i.e. by moving the current orientation away from the current desired orientation. The interaction may even be more like making the robot turn left or right than explicitly giving the exact direction to follow (no explicit supervision). Selected PC/action couples predicting rotations opposite to the executed rotation during the interaction are to be inhibited. Contexts are created to encode which place-cells should be inhibited and when. After this learning, if the behavior happens to be corrected again, the task has probably changed. Therefore, when a new interaction phase starts in an already known context, the previous associations with place-cells to inhibit will be removed to learn the new situation. However, a particular case may be taught by the teacher by alternating between correcting behaviors and evaluating the result. Though, it will be sensed by the robot as separated interaction phases. The aforementioned process is completed by a short term memory of the wrong PC/action couples to ensure the consistency of the teaching. Even if, the contextual associations are reset prematurely, the short term memory keeps the results of recent detections. Finally, repeated corrections in the same context mean the condition refining of existing behaviors fails. Hence, a new PC/action couple is recruited adding a new behavior to solve the task, possibly through condition refining.

A. Wrong action detection

The neural layer D W outputs the result of the detection. The neurons in D W match the existing place-cells. An activity of 1 in D W means that the corresponding place-cell should be inhibited because the associated action is evaluated as wrong. A competition between the different biased place-cells P C I determines the action to be performed (Fig. 2). Currently, only the action predicted by the winning biased place-cell i M = argmax i (P C I i ) can be evaluated. Therefore no wrong action detection can succeed with other PC/action couples (D W i =i M = 0). In the case of the i th M couple, the action is evaluated as wrong if, during the interaction, the robot orientation θ cur moves away from the robot proposed orientation θ d . The teacher's control being primary, he can prevent the robot from following the desired orientation θ d . The sensorimotor error E r is based on the difference between these two orientations 3. Context learning to inhibit PCs associated to wrong actions and learn new place-cells through on-line interactive teaching. Given a correction, the variation of the similarity is used to estimate if the selected action is wrong. A multimodal context is then recruited if none already encodes the situation. Each time a new interaction phase starts, the actions to inhibit are reset and the contextual vigilance increases. The short term memory of wrong actions ensures the consistency of a split interaction. Eventually, if the activity of the winning place-cell after inhibition P C I is under the vigilance V , a new place-cell/action couple will be recruited. This architecture details the content of the action evaluation block shown in Fig. 2.

E r = min(| θ d -θ cur |, (θ max -θ min )-| θ d -θ cur |) with NI Fig.
θ max = 2πand θ min = 0. This particular computation is needed because the orientation space loops on itself (2π rad is the same as 0 rad). The similarity measure S for the i th M PC/action couple uses this error to recognize how much the current orientation is similar to the desired orientation (Eq 1).

S i M = 1 - 2E r (θ max -θ min ) (1)
with H 0 the Heaviside function that verifies H 0 (0) = 0. The coefficient multiplying E r normalizes the dynamics of the similarity measure (values between 0 and 1). Detecting that the i M th PC/action couple is wrong (D W i M = 1) depends on the dynamics of the similarity (∆S B i M ) as well as on its value S i M (Eq 3). An action is estimated as wrong if the evolution of the similarity indicates that the followed orientation moves away from the desired one (Eq 2) and if the similarity is low enough. When a negative variation of the similarity for the i M th action is detected, ∆S B i M is equal to 1. In that case, the similarity measure is compared with a similarity threshold equal to 1 -t E , with t E equivalent to an error threshold.

∆S B i M (t) = H 0 (S i M (t -∆t) -S i M (t)) (2)
D W i M = H 0 (∆S B i M -t E -S i M ) and D W i =i M = 0 (3)

B. Context management

Contexts are recruited when the behavior of the robot is corrected. The input X of the multimodal contexts C is the concatenation of the different discrete binary codes for each sensory modality. The raw place-cell activities P C R give localization information. The obstacle detection U S based on ultrason sensor is categorized into 2 neurons (frontal obstacle present or not). The gripper state GS is encoded by three neurons each one corresponding to an opening width. The input X is normalized and then connected to the context layer C (Eq 4). The context learning (Eq 5) is based on Adaptive Resonance Theory [START_REF] Carpenter | Adaptive resonance theory (ART)[END_REF]. The maximal activity in the context layer C is compared with a vigilance threshold λ C . If the maximum is lower, then a new context (with index r) is recruited so that the weights ω C rl reproduce the input pattern. As the input is normalized, the activity of a context is maximal when the same encoded pattern is presented again.

X N k = X k || X || with X = [P C R ; U S; GS] (4)
     C j = k ω C jk • X N k ∆ω C rk = (X N k -ω C rk ) if λ C > max j (C j ) (5)
with λ C the vigilance threshold equal to 0.99 if there is an active neuron in the wrong action layer W and 0 otherwise. The active context layer C a only contains one active neuron corresponding to the maximally recognized context j M = argmax j (C j ) in C. The activity of the winning context must be over the context threshold t C (Eq 6).

C a j M = H 0 (C j M -t C ) and C a j =j M = 0 (6)
C. Short term memory of wrong PC/action couples During an interactive teaching phase, the PC corresponding to detected wrong actions are memorized in a short term memory. The wrong PC/action layer W depends on the new detected wrong action D W i as well as on the content of the memory of the recent incorrect actions M W (Eq 7). If there is no ongoing interaction, the content of the wrong action layer is inhibited. Otherwise, any active neuron in this layer will trigger the learning of a multimodal context C and the association between this context and the neurons corresponding to the same PC in the inhibition layer I.

W i = H 0 (M W i + D W i -2 • N I) (7)
The short term memory M W is fed by the wrong action layer W . The temporal forgetting γ ensures that the memory is reset within a few seconds. It can also be reset when the index of the winning context in C a changes (C C = 1).

M W i (t) = [M W i (t -∆t) -γ] + + W i -2 • C C (8)
with [x] + = x if 0 < x < 1, 0 if x < 0 and 1 otherwise. A new correction phase starts whenever one neuron in the wrong actions memory becomes active. During the first iteration a new correction phase is detected (N C = 1). The phase ends when all neural activities decay to 0 with the forgetting or when a reset signal is received because the context changed (C C = 1).

D. Learning PCs to inhibit

The inhibition layer I contains the PCs to inhibit. The associations are learned with a Hebbian like rule (Eq 9) and stored on the synaptic weights ω I connecting the active context layer C a with the layer I. When a new correction starts (N C = 1), the previously stored inhibitions are reset. When the teacher is correcting the robot, the wrong PC/actions stored in the short term memory M W transit through the wrong PC/action layer W . The PCs to inhibit are associated with the active context in I. The context/PC associations are also reset when a new place-cell is recruited (α P C = 1).

  

I i = [W i + j ω I ij • C a j ] + ∆w I ij = W i • (C a j • I i -ω I kj ) -(N C + V P C ) • C a j • ω I ij ( 9
) where V P C = 1 when a new place-cell is recruited. The PCs represented in the layer I are inhibited so that the selected orientation is predicted by one of the correct place-cells (see Figure 2).

E. Learning new PC/action couples

The aforementioned process may fail because PC/action couples with sufficiently recognized PCs may not be already encoded. The vigilance threshold V P C controlling the learning of new PC/action couples is thus managed (Eq 10). Each time a new correction occurs in a context (N C = 1), the vigilance V associated with this context increases. Trajectory (gray line) during learning and reproduction of the task (several times consecutively). The colored dots are the learned placecells. The chunks associated with the place-cells are represented around the corresponding dots (circle: the context exists but does not inhibit an action, square: the context does not inhibit the winning PC, star: the context is used). The arrow starting from the dots indicates the orientations that are associated to the place-cells. At the end of the learning, only one chunk still modifies the behavior. The others only inhibit PC that could not win. with i M = argmax i (P C I i ). The activity of the winning action P C I is compared to this vigilance threshold V P C = H 0 (V -P C I i M ) to trigger the recruitment of a new place-cell. When a new place-cell is recruited, the context/PC association for the context in which occurred the recruitment is reset (V P C = 1 in Eq 10). The context/action association in the inhibition layer I is also reset for this context (V P C = 1 in Eq 9). The system can switch between the PC inhibition and learning new PC/action couples.

   V = [ j ω V j C a j ] + ∆ω V j = N C(P C I i M -V ) • C a j -V P C • V • C a j (10)

III. EMERGENT ATTRACTION BASINS AND CONTEXTS

In this section, the model is tested in two different experiments performed with a simulated robot, running with the Promethe simulator under the Webots (Cyberbotics) 3D environment. The robot is composed of a mobile platform with a camera mounted on a pan servomotor (Fig. 4). The walls of the room are covered with pictures to provide textured images for visual processing i.e. the recognition of the placecells. In the first experiment, the robot has to learn a simple trajectory that does not require multimodal contexts. As the new model extends the model from [START_REF] Giovannangeli | Interactive teaching for vision-based mobile robots: A sensory-motor approach[END_REF], the initial test aims at studying whether the recruited contexts are useful and whether the system will rely on these contexts to tackle the task. In Figure 5, the learned place-cell/orientation associations are Trajectory (gray line) during reproduction of the task (several times consecutively). The colored dots are the learned place-cells. The chunks associated with the place-cells are represented around the corresponding dots. The arrows starting from the dots indicate the orientations that are associated to the place-cells. Due to the effect of the chunks, the orientation may not be followed as the PC selecting this orientation is inhibited. displayed with the followed trajectories. During the learning phase, the first time a correction is performed in a given placecell. A context is recruited to encode the sensory configuration. Each time the orientation of the robot is corrected, the active context is associated with the inhibition of the incorrect PC/orientation couples. When a new place-cell is recruited in a context, previous associations between this context and the PCs to inhibit are unlearned. At the end of the learning phase, i.e. when the robot is finally capable of performing rounds without correction, the contexts do not influence the behavior anymore because they do not inhibit the already winning PC/orientation couple (see Fig. 5). The contexts appear as only temporarily used. Only one context still influences the behavior. It corresponds to the situation where the robot detects a wall nearby, and thus should aim at a different direction than the one associated with the winning place-cell.

In the second experiment, we focus on testing the learning of a task that requires selecting the trajectory depending on sensory information not directly related to navigation. The information is the width opening of the gripper i.e. the size of the held object. The environment contains three obstacles at interesting locations (see Fig. 4). The white one is where the robot has to take objects, the two others (red and blue) are where the robot can drop them. The colors of the obstacles are not directly used by the system. The task of the robot is to take objects at the picking place and then, depending on the simulated size of the object, move to one location or the other to place it there. The objects are simulated through the gripper state coding the object size. A correct orientation maintained during a few seconds is a prerequisite to validate the reaching to one of the places. In this experiment, there is no obstacle avoidance behavior so that the robot can face an obstacle without avoiding it. Yet, the forward speed of the robot is decreased when the robot gets closer to an obstacle so that it will not bump into it. The robot is corrected by simply changing its orientation (using a joystick) whenever it moves in the wrong direction. The trajectory followed by the robot during the reproduction of the task is presented in Figure 6. The learning phase is quite long as each new place-cell introduces a new potential context preventing previous generalization from other context and also a new possible PC/orientation that may have to be inhibited when in other contexts. The robot can reproduce the task without any correction after about fifteen rounds of the pick-and-place task using a small object and eleven rounds using a big object. As the robot only needs correction when it makes mistakes, less and less corrections are necessary as the learning process goes on.

At the end of the learning process, the robot performs the task without any correction. The learned contexts enable the robot to exhibit the correct behavior. Depending on the gripper information, the robot follows different trajectories. Even if the learned contexts are very specific and encode particular sensory configurations, the effective attraction basins can be interpreted as depending on the gripper state. The resulting attraction basins are displayed in Figure 7. Because the robot did not start from any location in the environment, the attraction basin is only correct in a limited area. Depending on its starting position, the robot can end up stuck in front of a wall (as there is currently no obstacle avoidance). The robot may also select the wrong dropping place. For instance in Fig. 7b), the dropping place on the left is where the robot should go with a small object. However, the dropping place on the bottomright of the figure is also an attractor where the robot can go depending on its starting position. Without the corresponding learning, the robot has generalized the dropping place on the bottom-right as valid for any size of object. This is due to the fact that the learned PC/orientation couples in the vicinity of this place converge to the dropping place. The interest of the contexts appears when no object is held, by reducing the attraction basin so the robot can move to the picking place. Hence, the robot exhibits the expected contextual behavior that can emerge from the recruited contexts and the learned inhibition of PCs.

IV. DISCUSSION

In this paper we presented a model of action selection based on contexts guiding sensory-motor associations. This approach allows us to extend the place-cell/action model [START_REF] Giovannangeli | Robust mapless outdoor vision-based navigation[END_REF] to solve the action selection problem. In [START_REF] Giovannangeli | Interactive teaching for vision-based mobile robots: A sensory-motor approach[END_REF], the authors showed the influence of the teacher on the learned trajectory by comparing different methods of learning. The authors showed that a compromise between proscriptive and prescriptive learning was more robust and that the choices of the human interacting teacher corresponded to such compromise. We expect the same kind of influence to be at work in the contextual navigation task. The issue will be explicitly addressed in future work, in order to validate that the convergence of the context learning is not (too) dependent on the expertise of the teacher. Besides, in our experiment, we tested the model in a simulated environment, without variations and always in the same situation.

The goal of this paper was to study a minimal model that could explain the fast adaptation of multimodal behaviors during interaction with a teacher. The results showed that the proposed principles are efficient but need to be improved for a real autonomous development. First, the contexts are computed with a threshold that prevent generalization on different placecells. Second, we also used binary values to build the sensory inputs of the contexts. This allowed us to ease the study but a) this constraint should be removed for better generalization. The generalization properties of the existing low level behaviors also determines the quality of overall behavior. There should be a cooperation between the proposed fast learning of contexts and a slower learning solution improving the low level behaviors at the basis of the system.

Many neurobiological studies were dedicated to the action selection process and thus can give hints to improve the capabilities of a robotic system. Different cerebral regions are involved in the action selection process. In particular, the implication of the cortico-baso-thalamo-cortical loop was clearly exposed [START_REF] Prescott | Introduction. modelling natural action selection[END_REF]. The GPR model [START_REF] Gurney | A computational model of action selection in the basal ganglia. II. Analysis and simulation of behaviour[END_REF] is based on a dynamical system approach and the internal connectivity of the BG is unknown. The CBTC model [START_REF] Girard | Integration of navigation and action selection functionalities in a computational model of cortico-basal-ganglia-thalamo-cortical loops[END_REF] tends to improve the exposure of the internal connectivity and introduces a fusion with reinforcement learning mechanisms to improve the GPR model. Those models tend to be very complex. In this paper, we focused on a minimal solution to obtain an action selection behavior, by using a selective inhibition of PC/action couples depending on the recruitment of multimodal contexts. However, this fast on-line learning is to be completed by a slower learning that could encode chunk like categories directly selecting the action to be done. The theory of chunking was first introduced in the 1950s by DeGroot [START_REF] De Groot | Thought and Choice in Chess[END_REF] and Miller [START_REF] Miller | The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information[END_REF]. The main idea is that a chunk collects pieces of information in order to obtain a higher level of information coding. In a previous work [START_REF] Hanoune | An architecture for online chunk learning and planning in complex navigation and manipulation tasks[END_REF], we suggested that a modified version of Schmajuk's and DiCarlo's learning of conditioning [START_REF] Schmajuk | Stimulus configuration, classical conditioning, and hippocampal function[END_REF] could model the cortico-basal loop with associative conditioning in the cerebellum and resulting in the learning of chunks. Our goal is now to combine the fast on-line learning of contexts presented in this paper with the aforementioned slower learning of chunks to improve the action selection capabilities of the robot.

Fig. 2 .

 2 Fig.2. Architecture for place-cell based navigation with the action evaluation part of the architecture (see Fig.3). Sensory and predicted signals are provided to the action evaluation system. It outputs a vigilance signal and an inhibitory signal preventing some place-cells to exhibit their associated orientation. The vigilance signal can trigger the learning of a new place-cell.

Fig. 4 .

 4 Fig. 4. Simulated environment and robot. The robot has to learn to navigate between the different blocks according to the object size signal.

  Fig. 5.Trajectory (gray line) during learning and reproduction of the task (several times consecutively). The colored dots are the learned placecells. The chunks associated with the place-cells are represented around the corresponding dots (circle: the context exists but does not inhibit an action, square: the context does not inhibit the winning PC, star: the context is used). The arrow starting from the dots indicates the orientations that are associated to the place-cells. At the end of the learning, only one chunk still modifies the behavior. The others only inhibit PC that could not win.

  Fig.[START_REF] Schultz | A neural substrate of prediction and reward[END_REF].Trajectory (gray line) during reproduction of the task (several times consecutively). The colored dots are the learned place-cells. The chunks associated with the place-cells are represented around the corresponding dots. The arrows starting from the dots indicate the orientations that are associated to the place-cells. Due to the effect of the chunks, the orientation may not be followed as the PC selecting this orientation is inhibited.

Fig. 7 .

 7 Fig.7. Change in behavior according to the held object. Trajectories (gray) from different starting points when the gripper is holding (a) no object, (b) small object, (c) big object. Contextual attraction basins toward the pickup place P, the dropping place A and the dropping place B can emerge even though the contexts encode specific sensory configurations.

The codes use visual, proprioceptive (camera orientation) and magnetic compass information to build place-cells.

Orientations of movement are given with respect to an absolute reference (North). The orientation of the robot is read from a magnetic compass.

In the experiments of this article, a joystick was used considering that it simulates the action of a leash.

ACKNOWLEDGMENT

This work was supported by the AUTO-EVAL project, the INTERACT french project ANR-09-CORD-014, and the NEUROBOT project ANR-BLAN-SIMI2-LS-100617-13-01.