Pronin N.A.

Atyrau branch KMG Engineering LLP Republic of Kazakhstan 060097Atyrau region, Atyrau city, Nursaya microdistrict, ave. Elorda, Building 10: n_pronin@bk.ru

DOI: 10.35714/ggistrat20250100014

Summary. The study of sea-level fluctuations in the southeastern Caspian Basin during the Jurassic-Cretaceous transition provides critical insights into the region’s paleogeographic evolution and hydrocarbon potential. By analyzing detailed core samples from key oil and gas fields, researchers identified distinct lithological sequences, including sandstones, shales, limestones, and evaporites, reflecting dynamic depositional environments – from shallow marine shelves to sabkha-like evaporitic basins and fluvio-deltaic systems. These variations were driven by a combination of large-scale global factors, such as the breakup of Pangaea, intensified mid-ocean ridge activity, and climatic shifts (e.g., greenhouse conditions in the Cretaceous), as well as regional influences like subsidence, halokinesis (salt dome movement), and episodic influxes of clastic material from nearby uplifted areas. Sequence stratigraphy revealed high-resolution transgressive-regressive cycles, highlighting stark differences between the Jurassic and Cretaceous periods. The Jurassic was characterized by non-marine, lacustrine, and alluvial plain conditions, with occasional short-lived marine incursions, while the Cretaceous experienced a prolonged marine transgression, leading to widespread carbonate platform development. However, localized regressive episodes suggest intermittent basin restriction, possibly due to tectonic barriers or eustatic sea-level drops, complicating paleoenvironmental reconstructions. The study underscores the critical interplay between global eustasy and regional tectonics when modeling ancient sea-level changes. Such integrated models improve the accuracy of paleogeographic reconstructions and enhance the prediction of reservoir quality and seal rock distribution. These findings are particularly valuable for hydrocarbon exploration, as they help pinpoint stratigraphic traps and optimize drilling targets in the Tengiz-Kashagan region. Further research incorporating biostratigraphic zonation and isotopic dating could refine chronostratigraphic frameworks, reducing uncertainties in resource assessments for analogous basins.

Keywords: The Caspian Basin, Jurassic-Cretaceous period, global ocean fluctuations, transgressions-regressions, sedimentation, paleogeography, collectors

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