Interplay of Palaeoclimate, Sea-Level, and Basin Configuration in Mixed Clastics-Carbonate Deposits in Zubair Formation, Southern Iraq

Summary The study investigates the depositional controls on the Zubair Formation in southern Iraq, focusing on the interplay of palaeoclimate, sea-level fluctuations, and basin configuration. The Zubair Formation, a Barremian-age unit, was deposited on a stable continental margin with minimal tectonic influence. It exhibits a transition from carbonate-rich lower intervals to clastic-dominated middle sections, followed by a return to shallow marine carbonate deposition. Eight wells were analyzed using borehole images, core data, petrophysical logs, and mud logs. The study identified a fluvial-dominated delta system in the middle Zubair, characterized by high sand content and a well-developed river mouth bar, suggesting a high-discharge, proximal river system. Correlations with eustatic sea-level curves indicate that depositional cyclicity was largely controlled by global sea-level changes. Findings suggest that increased clastic input was driven by wetter conditions on the Arabian Plate, while carbonate deposition coincided with periods of reduced detrital influx. The stable shelf setting and sea-level changes played a critical role in shaping the stratigraphy. The study enhances understanding of sequence stratigraphy and depositional processes in mixed carbonate-clastic systems, offering insights into reservoir distribution and hydrocarbon potential in the region.