This chapter shows 2D time-migrated seismic profile through the Bitsminda anticline: southern part of the Kura foreland fold and thrust belt (Georgia). In the chapter, fault-related folding theories are used in structural interpretation of S-N trending seismic profile. Identification of stratigraphic units at a depth for seismic profiles is based on outcrop correlations and Bitsminda-1 borehole data. Interpreted seismic reflection profiles show that the Bitsminda anticline is a shallow fault-propagation fold with the front limbs broken by thrust faults. The fold shows a strongly normal dragged hanging wall block, and a less dragged footwall block. Syntectonic (or synorogenic) Middle and Upper Miocene strata are represented by shallow marine, predominantly, terrigenic fine clastics, limestones and marls with rare conglomeratic interbeds and sandstones and thick continental sediments.
We report new observations in the eastern Black Sea-Caucasus region that allow reconstructing the evolution of the Neotethys in the Cretaceous. At that time, the Neotethys oceanic plate was subducting northward below the continental Eurasia plate. Based on the analysis of the obducted ophiolites that crop out throughout Lesser Caucasus and East Anatolides, we show that a spreading center (AESA basin) existed within the Neotethys, between Middle Jurassic and Early Cretaceous. Later, the spreading center was carried into the subduction with the Neotethys plate. We argue that the subduction of the spreading center opened a slab window that allowed asthenospheric material to move upward, in effect thermally and mechanically weakening the otherwise strong Eurasia upper plate. The local weakness zone favored the opening of the Black Sea back-arc basins. Later, in the Late Cretaceous, the AESA basin obducted onto the Taurides–Anatolides–South Armenia Microplate (TASAM), which then collided with Eurasia along a single suture zone (AESA suture).
The article presents an overview of the structural structure of the Rioni Forland Fold-and-thrust Belt. The structures are mainly represented by folds and duplexes associated with south-vergent faults. The synclines are overlaid by Middle Miocene-Pleistocene syntectonic sediments and are represented by piggy-back basins. Faultrelated folds are mainly represented by growing fault-propogation folds. The kinematic evolution of the Rioni Forland Basin in the Late Alpine period is related to the structural wedge (or duplexes) of the Caucasus foundation moving southwards, and its modern structure is represented by a thin-skinned fold-and-thrust belt.
In the broader Caucasus region, multiple extrusive volcanic units are present within the Jurassic, Cretaceous, Eocene and Miocene sedimentary successions. Partial reworking of volcanic material from various provenance areas into Eocene, Oligocene and Miocene reservoir units is commonly observed in the Eastern Black Sea and in the Rioni, Kartli and Kura Basins of onshore Georgia. Reservoir quality has in general been negatively affected by volcanic rock fragments which may have undergone complex diagenetic alteration. However, despite concerns regarding reservoir quality, oil at the Samgori field, the largest field in Georgia (∼200 MM brl recovered), is hosted in altered Middle Eocene volcaniclastic sandstones interbedded with deep‐water turbidites. Previous studies of core material from numerous wells in this field showed that most of the oil is contained in altered, microfractured, laumontite‐rich tuffs which have fracture and cavernous net porosities averaging 12% and average permeability of 15 mD. The laumontite tuffs comprise only up to 20% of a tuffaceous sandstone section and occur as isolated lenses or pods on a sub‐seismic scale (i.e. 5‐10 m thick), causing highly variable oil productivity from one well to another. The petrographic analysis of samples of Middle Eocene volcaniclastic sandstones from outcrops in the central part of the Kartli Basin around Tbilisi broadly confirms the main conclusions of studies completed some 30 years ago which were based on the analysis of subsurface samples. However, the surface samples analysed show that zeolitization events typically did not improve, but actually reduced, reservoir quality due to extensive zeolite cementation. The poor reservoir properties of the plug samples, which are age‐equivalent to the proven subsurface Middle Eocene reservoir interval, highlight fracturing as a key factor controlling the presence of exceptional producers (up to 9000 b/d) in the Samgori field complex. The study therefore underlines the critical role of fracturing of the Middle Eocene volcaniclastic reservoir sequence in the Kartli Basin.
The Rioni foreland basin system is located between the Lesser Caucasus (LC) and the Greater Caucasus (GC) orogens. Deformation of the Rioni double flexural foreland basin was controlled by the action of two opposing orogenic fronts, the LC retro-wedge to the south and the GC pro-wedge to the north (Alania et al., 2022). The Rioni foreland fold-and-thrust belt (RFFTB) is part of the Greater Caucasus pro-wedge.  Here we show the deformation structural style of the RFFTB based on seismic reflection profiles and serial structural cross-sections. On the basis of serial structural cross-sections, 3-D structural models. 2-3D structural models show that the Rioni foreland is a thin-skinned fold-and-thrust belt and the main style of deformation within the RFFTB is represented by a set of fault-propagation folds, duplexes, and triangle zones. The presence of two detachment levels in the RFFTB raises important questions about the deformation sequence. The serial structural cross-sections show that fault-propagation folds above the upper detachment level can develop by piggyback and break-back thrust sequences. The formation of fault-bend fold duplex structures above the lower detachment is related to piggyback thrust sequences. The synclines within the Rioni foreland fold-and-thrust belt are filled by the Middle Miocene-Pleistocene shallow marine and continental syn-tectonic sediments, forming a series of typical thrust-top basins. The evolution of the thrust-top basins was mainly controlled by the kinematics of thrust sequences. Fault-propagation folds and duplex structures formed the main structure of the thrust-top basin. Recent earthquake data indicate that the RFFTB is still tectonically active and earthquake focal mechanisms within the RFFTB are thrust faults (Tsereteli et al., 2016), and active structures are mainly represented by thrust faults, blind thrusts, and blind wedges.  Acknowledgments. This work was funded by the Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377). References Alania, V., et al. (2022). Deformation structural style of the Rioni foreland fold-and-thrust belt, western Greater Caucasus: Insight from the balanced cross-section. Frontiers in Earth Science 10, 10968386. Tsereteli, N., et al. (2016). Active tectonics of central-western Caucasus, Georgia. Tectonophysics 691, 328–344.
'/%3e%3cuse xlink:href='%23b' transform='rotate(90)'/%3e%3c/g%3e%3c/defs%3e%3cpath d='M0 0h300v200H0z' style='fill:%23fff'/%3e%3cpath d='M130 0v80H0v40h130v80h40v-80h130V80H170V0h-40z' style='fill:red'/%3e%3cuse xlink:href='%23c' fill='red' transform='translate(64.45 39.45)'/%3e%3cuse xlink:href='%23c' fill='red' transform='translate(235.55 160.55)'/%3e%3cuse xlink:href='%23c' fill='red' transform='translate(235.55 39.45)'/%3e%3cuse xlink:href='%23c' fill='red' transform='translate(64.45 160.55)'/%3e%3c/svg%3e)
