Tectonic control of the petroleum system characteristics in the South Caspian Basin

The South Caspian Basin (SCB) is known as prolific petroleum province. The proven petroleum system is related with Oligocene-Miocene (Maikopian) marine type source rocks and Pliocene fluvial-deltaic sands, as a reservoir. Rich oil and gas fields are known in the northern and central part of the basin. At the same time in the south-western part of the basin a number of dry holes were drilled in early 2000’s. Overall the main reason of the failure was related with lack of charge.

Simultaneously, there is a distinct difference in structural shapes in two zones. The anticlines of the southern-south-western part of the basins have smaller wavelengths comparing with the anticlinal structures of the central South Caspian. This observation led to the question whether the difference in hydrocarbon behavior was related to the geodynamic nature.

South Caspian is genetically classified as a back-arc basin, whose evolution is closely linked to the subduction of the Neotethys oceanic lithosphere beneath the Eurasian continental margin during the Early Jurassic. Basin opening persisted until the early Late Cretaceous, followed by the progressive closure of the Neotethys Ocean. The subsequent collision of the Arabian Plate with the Eurasian Plate in the Late Cretaceous initiated a regional compressional tectonic regime, resulting in further subsidence and structural reorganization of the basin.

Tectonically, the basin can be subdivided into two distinct domains: an arc-distal zone, characterized by relatively wide and gently deformed structures, and an arc-proximal zone, marked by narrow, asymmetric, and intensely folded structural geometries. Variations in the thickness, burial depth, and rheological properties of the Maikop detachment layer exert primary control on this structural differentiation. In the central, deeply buried parts of the basin, increased gas saturation within the Maikop sequence reduces effective viscosity, facilitating detachment-controlled deformation.

From north to south, the detachment layer thins by more than a factor of two and becomes progressively shallower. This systematic variation governs the width and geometry of anticlinal structures: thin and shallow detachments favor the development of narrow and asymmetric folds, whereas thick and deeply buried detachments promote broader and more laterally extensive structures. Overall, arc-distal areas are characterized by a thick sedimentary cover and relatively low tectonic stress, while arc-proximal zones exhibit higher stress regimes and more intense deformation. Thus, the thickness and depth of the source interval in the southern portion of the basin lead to the lack of charge in that area.