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For the South Caspian Oil and Gas Bearing Province, the conclusion is made that the Pliocene productivity is predominant in the western part of the province and that the oil and gas prospects in the Mesozoic for the eastern onshore part are a priority. A retrospective analytical review of geological and geophysical data and published materials on the Mesozoic of SouthWest Turkmenistan has been accomplished, it revealed the low efficiency of the performed seismic and drilling works during exploration and evaluation of relatively complex Mesozoic targets. Massive resumption of seismic surveys and appraisal drilling of modern level in the priority areas and targets involving leading Russian companies is proposed. For some areas, a new improved estimation of potential gas resources is provided. The example of modern, highly efficient supplementary exploration of a small Pliocene gas and oil field, West Cheleken, is presented which turned this field into a major one in term of reserves. A first version of this review has been published in Russian (Melikhov et al., 2021). The review is dedicated to the memory of the outstanding Turkmenistan petroleum geologist M.A. Ashirmamedov.

International audience; The Late Jurassic was a period of major global carbon cycle perturbations with episodes of anoxia leading to regional accumulation of organic matter in sediments worldwide. The Tubegatan section (SW Gissar Mountains, Uzbekistan) located in the Northern Tethys, shows atypical organic-rich limestone and marl deposits (up to 6% of total organic carbon) marked by pronounced excursions of δ13Ccarb (amplitude of ca. 12‰) and δ13Corg (amplitude of ca. 4‰) recorded during the Middle Oxfordian (Transversarium Zone). A transdisciplinary approach including sedimentology, palynofacies study, mineralogy, organic and inorganic geochemistry was carried out to elucidate the origin of these organic-rich deposits. Higher TOC and lowest δ13Ccarb values are measured in nodular limestones characterized by thinly laminated facies consisting in alternances of infra-millimeter-thick organic and carbonate laminae. The presence of organic-carbonate peloids and of possible remnants of exopolymeric substances associated with clay indicate that these structures are probably mineralized benthic microbial mats (i.e., stromatolites). Rock-Eval pyrolysis coupled to palynofacies analyses point to a dominant likely altered marine organic matter of probable algal/microbial origin, with subordinate continental phytoclasts inputs in the upper part of the organic-rich interval. Trace elements (U/Th, V/Cr and Mo/Al ratios) indicate two anoxic episodes coinciding with the highest TOC, punctuated by dysoxic periodes. Such O2-depleted conditions have allowed the preservation and probably the development of anaerobic microbial communities in the microbial mats. In these latter, the precipitation of carbonates likely formed during sulfate reduction and anaerobic oxidation of methane, which would explain the abundance of pyrite and the very low δ13Ccarb values.The progressive decrease then disappearance of kaolinite from the base of the organic-rich interval, is interpreted as a progressive aridification of the Amu Darya Basin during the Transversarium Zone, culminating with the progradation of a large-scale gypsum sabkha overlying the organic deposits in the Upper Jurassic. Overall, the organic-rich deposits could record the onset of the disconnection of the Amu Darya Basin from the open sea to the south, induced by compression and subsequent uplifts in the Afghan and Central Iranian blocks. The elevated evaporation, coupled with the presence of hydrological barriers (possibly coral reefs) could have led to the formation of local anoxic environments. Similar organic microbial accumulations are recorded throughout the Tethys (e.g., Arabian Plate, Western Europe) and from other oceans (e.g., Central Atlantic, Pacific) during the Late Jurassic, suggesting common controlling factors. The relatively shallow anoxia model proposed in this study contrasts with the well-known organic carbon-rich pelagic models proposed for the Jurassic (Toarcian, Kimmeridgian) and Cretaceous OAEs.

The intricate basins (Kura and Rioni) located between the Greater and the Lesser Caucasus are the site of several hydrocarbon fields. In eastern Georgia, the Samgori field in the western end of the vast Kura basin extends into Azerbaijan. It is the largest hydrocarbon discovery in Georgia, with a cumulative production of more than 250MbO. In western Georgia in the western and southern Rioni, only small size fields have been discovered (East Chaladidi, Supsa or Shromisubani, a few MbOE produced).The ingredients of the petroleum system belong to the Tertiary : source rocks from the Maikop formation, siliciclastics and volcanoclastics reservoirs, shaly intervals as cap rocks, and Neogene structures linked to the structuration of the Greater and Lesser Caucasus fold belts.The Mesozoic series in the Kura basin constitute a speculative hydrocarbon target to be explored in the future although at greater depth below the Tertiary folds. In the Kartli sub-basin at the western end of the Kura basin, there is only scattered and often over-matured Mesozoic series to look for source, reservoir and cap rocks analogs.In the Rioni basin, less mature Mesozoic series crop out, offering a possible evaluation of all the geologic elements and processes essential to an hydrocarbon accumulation. A preliminary investigation of the Mesozoic series revealed several organic rich horizons, reservoirs and cap rocks in the pre Cretaceous series. This leads to propose a schematic pre-Cretaceous paleogeography constituting the base for defining possible petroleum systems. Preliminary organic geochemical analyses of organic-rich horizons lead to identify several layers having fair to moderate hydrocarbon potential for oil and gas. Based on this preliminary result, information derived from bibliography and published seismic lines, and 1D modeling with Petromod software lead to propose new potential plays in the Rioni basin.This speculative study requires new biostratigraphic studies to confirm the ages of the various identified organic rich horizons, some of them being possibly new to refine the modelings. More detailed fieldwork should focus on reservoir quality and distribution. Eventually, analysis of reprocessed seismic data will permit to confirm new petroleum thematics.

The Middle and Upper Jurassic peri-Tethyan carbonate platforms host some of the largest hydrocarbon reserves in the world. Over the past decades, extensive research has led to the construction of high-resolution stratigraphic frameworks on the northwestern (e.g., Paris Basin) and southern (e.g., Arabian Platform) Tethyan margins. These studies and others show that although being a period of elevated carbonate production, the Callovian-Oxfordian interval is marked by major changes in carbonate production and platform architecture, stratigraphic gaps and condensed series. These changes have commonly been linked to regional to global climatic and tectonic events associated with the so-called Middle-Late Jurassic Transition (MLJT). The stratigraphy of the northern Tethyan margin (Central Asia) was comparatively less documented. A vast carbonate platform developing on the northern margin of the Amu Darya Basin was recently investigated. A high-resolution stratigraphic framework of the platform was built based on facies analyses, sequence stratigraphy, chemostratigraphy and biostratigraphy. This presentation reviews the key stratigraphic features of the Callovian-Oxfordian carbonate platforms in several areas of the northern, western and southern Tethyan margins. Our comparison shows striking similarities in the stratigraphic records of carbonate platforms which developed at the periphery of the Tethys, several thousands of kilometers apart and reinforce the hypothesis that global-scale events strongly affected the shallow water domain of the Jurassic ocean. The impact of climate, tectonics and major paleoenvironmental events, e.g. the Upper Callovian-Lower Oxfordian cold episode, the sea level fall possibly linked to glacio-eustatism and the tectonic events are finally discussed.

International audience; New investigations are currently underway on the Middle-Upper Jurassic carbonates of the Gissar Mountains in the Amu-Darya Basin. Located in the southwest of the Gissar Mountains (SE Uzbekistan), the Tubiegatan section corresponds to 30-meter-thick limestone, overlain by 10-meter-thick dark limestone and marl interval. These dark, “black shale-type deposits” were also recognized in cores from the subsurface of the Amu-Darya Basin. The organic-rich deposits interval is precisely dated to the Luciaeformis and Schilli Subzones (Transversarium Zone, Middle Oxfordian) by ammonites. A transdisciplinary approach including sedimentology, organic matter characterization (Rock-Eval pyrolysis, palynofacies), bulk and clay mineralogy (XRD), carbon and oxygen isotopes of carbonate and organic fractions and whole rock trace-element geochemistry were used to elucidate the origin of these organic-rich deposits. Carbon-isotope curves were also established to help to correlate this interval with the partly contemporaneous carbonate platform. Both Tmax from Rock Eval analysis and clay mineral assemblages indicate a pronounced burial diagenesis (oil window).Despite this burial, paleoenvironmental and paleoclimatic can still be processed. Rock-Eval pyrolysis analyses performed on 65 samples show that TOC values range from 0 (peloidal grainstone) to 6 % on average for the thinly laminated black limestone. Interestingly, in this dark organic-rich deposits interval, higher TOC were measured in limestone (2% on average), while lower TOC values (0.5% on average) characterized marl and claystone, which is relatively unusual. Rock-Eval parameters (IH, IO) coupled to palynofacies observations (predominant amorphous organic matter) point to a probable marine, algal/microbial origin for the organic matter (Type II), with rare continental inputs mostly located in the upper part. Trace elements, as well as palynofacies and sedimentological observations demonstrate local O2-depleted conditions promoting the preservation of organic matter. Such paleoenvironmental conditions may have supported bacterial mineralization processes related to anaerobic oxidation of methane, which would explain the very low δ13C values (-5‰ to -12‰) measured in laminated facies. From the base of the organic-rich interval, a progressive decrease then disappearance of kaolinite, balanced by illite and illite/smectite mixed-layers (type R1), is observed. This coincides with the development of terrestrial phytoclasts inputs, suggesting a probable aridification in the Amu Darya Basin during the Middle/Late Oxfordian. Overall, the organic-rich deposits of Tubiegatan could record the onset of the disconnection of the Amu-Darya Basin from the open sea in the south, induced by compression and uplifts in the Afghan and Central Iranian blocks.This disconnection, combined with a Tethys-wide aridification could have led to the progressive increase of evaporation and subsequent deposits on the carbonate platform, followed by the massive uppermost Jurassic evaporites (salt, anhydrite) of the Gaurdak Fm.

International audience; The geological evolution of Central Asia commenced with the evolution of a complex Precambrian–Palaeozoic orogen. Cimmerian blocks were then accreted to the southern margin during the Mesozoic, leading to tectonic reactivation of older structures and discrete episodes of basin formation. The Indian and Arabian blocks collided with Asia during the Cenozoic, leading to renewed structural reactivation, intracontinental deformation and basin development. This complex evolution resulted in the present-day setting of an elongated Tien Shan range flanked by large Mesozoic–Cenozoic sedimentary basins with smaller intramontane basins distributed within the range. The aim of this volume is to present multidisciplinary results and reviews from research groups in Europe and Central Asia that focus on the western part of the Tien Shan and some of the large sedimentary basins in that area. These works elucidate the Late Palaeozoic–Cenozoic tectono-sedimentary evolution of the area. Emphasis is placed on the collision of terranes and/or continents and the ensuing fault reactivation; the impact of changes in climate on the sedimentation is also examined.

The Greater Caucasus is Europe's highest mountain belt and results from the inversion of the Greater Caucasus back-arc-type basin due to the collision of Arabia and Eurasia. The orogenic processes that led to the present mountain chain started in the Early Cenozoic, accelerated during the Plio-Pleistocene, and are still active as shown from present GPS studies and earthquake distribution. The Greater Caucasus is a doubly verging fold-and-thrust belt, with a pro- and a retro wedge actively propagating into the foreland sedimentary basin of the Kura to the south and the Terek to the north, respectively. Based on tectonic geomorphology - active and abandoned thrust fronts - the mountain range can be subdivided into several zones with different uplift amounts and rates with very heterogeneous strain partitioning. The central part of the mountain range - defined by the Main Caucasus Thrust to the south and backthrusts to the north - forms a triangular-shape zone showing the highest uplift and fastest rates, and is due to thrusting over a steep tectonic ramp system at depth. The meridional orogenic in front of the Greater Caucasus in Azerbaijan lies at the foothills of the Lesser Caucasus, to the south of the Kura foreland basin.

International audience

International audience; The SW-Gissar range (westernmost part of the Tien Shan) consists of a succession of anticlines andsynclines forming a relief between the Amu Darya and Afghan-Tajik basins. Recent fieldwork has beenperformed to study the development and the architecture of a vast Middle-Upper Jurassic carbonate platform. The studied carbonate series crops out along cliffs overlying Lower to Middle Jurassic continental then marine deposits. Carbonate thickness reaches 500 m in the central and southern Gissar and thins up northwards, near the paleo-border of the Amu Darya Basin. The goal of this study was to build a highresolution stratigraphic framework for these deposits, based on chemo-and lithostratigraphic correlations between seven sections. It was associated with a detailed microfacies analysis in order to establish the spatial and temporal evolution of the palaeoenvironments in this poorly known area. Two major sequences were recognized, (1) Callovian in age, and (2) possibly Oxfordian to Lower Tithonian. The reconstruction of the deposition profile indicates that the Gissar was a gently dipping ramp during the Callovian major sequence. Dark mudstones with entire bivalve and brachiopod shells and oncoids-rich float-to rudstones predominated below and around the storm wavebase. Oobioclastic grainstones were deposited in the permanently agitated shallow water zone, while patch and pinnacle reefs built up distally at the inner-mid ramp transition and in the mid ramp. Small shallow water siliciclastic deltas developed close to the emerged lands located in the north. The Callovian sequence is subdivided into seven fourth-order transgressive-regressive sequences. The transition between the two major sequences is marked by a significant change in the carbonate sedimentary system associated with a positive shift in the bulk carbon isotope values. It could record a major climatic change coeval with the Middle-Late Jurassic Transition. Further, it is hypothesized that a sedimentary hiatus exists, possibly caused by the exposure of the platform. The Upper Jurassic major sequence is mostly composed of peritidal deposits, showing rapid vertical and lateral transitions, depicting a more complex architecture. The series consists in numerous meterthick alternations of pellets/algal pack-to grainstone, ‘microbial oncoid’ floatstone, ooid grainstones and mudstones. These deposits could have accumulated in a vast, mostly aggrading lagoon protected by a barrier reef. Basinwards, close to the Uzbek-Turkmen border, Middle Oxfordian organic-rich algal/microbial carbonates are intercalated within the platform carbonates and could have formed in small stratified and partly isolated intra-shelf depressions. Lastly, a general aridification of the basin could be responsible for the observed increase in gypsum characterizing the upper part of the carbonate platform (Late Oxfordian? to Tithonian?). The numerous oscillations in carbon isotopes evidenced in these evaporite-rich carbonates may be the consequence of high frequency exposure of the platform preceding the deposits of massive evaporite during the Tithonian. This study allows a better understanding of the paleoenvironmental evolution of the northern Tethys during the Middle and Upper Jurassic. Our results will be compared with other Peri-Tethyan Jurassic platforms in order to understand the carbonate platform response to large-scale climatic and tectonic changes occurring at this period.