First Record of Hantkenina from Saudi Arabia and its Paleoclimatic Significance across the Bartonian–Priabonian Transition

The middle to late Eocene represents a critical interval of global climatic transition following the Middle Eocene Climatic Optimum, yet its expression across the Arabian Plate remains poorly constrained due to limited deep-marine records and long-standing assumptions of regional stratigraphic hiatuses. Here, we present the first comprehensive documentation of the planktonic foraminiferal genus Hantkenina from Saudi Arabia, based on integrated micropaleontological and geochemical analyses of the Rashrashiyah Formation in the Sirhan–Turayf Basin, northwestern Saudi Arabia. Seven species (Hantkenina dumblei, H. australis, H. longispina, H. compressa, H. primitiva, H. alabamensis, and H. nanggulanensis) are identified and calibrated to planktonic foraminiferal biozones E13–E14 and calcareous nannoplankton zones NP17–NP18, confirming the presence of both Bartonian and Priabonian marine sediments and challenging previous interpretations of a middle–late Eocene depositional hiatus in the region. There is a clear bimodal pattern to the stratigraphic distribution of Hantkenina, with occurrences concentrated in the upper and lower portions of the succession and a period of diminished abundance or disappearance in between. Stable oxygen and carbon isotope analyses (δ18O and δ13C) derived from benthic foraminifera (Uvigerina) reveal alternating intervals of warming and cooling, with reconstructed bottom-water temperatures ranging from approximately 23°C to 30°C. The presence of Hantkenina is closely linked to milder intervals, highlighting the genus's noticeable sensitivity to temperature and confirming its significance as a dependable indicator in paleoclimatic and paleoecological studies. An unconformity at the top of the Rashrashiyah Formation indicates the erosion of the uppermost Eocene and Oligocene sediments, attributed to the combined influence of global eustatic sea-level fall during the Eocene–Oligocene transition and regional tectonic uplift associated with Red Sea rifting. These findings refine the Eocene stratigraphic framework of the Arabian Plate and highlight the valuable application of planktonic foraminifera in reconstructing paleoclimate conditions and marine ecosystem responses during major climate transitions.