The genus Hantkenina in Saudi Arabia: Implications for biostratigraphy and paleoecology across the Bartonian–Priabonian transition

This research provides a first description and biostratigraphic analysis of Hantkenina species in the middle to upper Eocene Rashrashiyah Formation of the Sirhan-Turayf Basin, northwest Saudi Arabia. Seven species—Hantkenina dumblei, H. australis, H. longispina, H. compressa, H. primitiva, H. alabamensis, and H. nanggulanensis—are identified within planktonic foraminiferal biozones E13 to E14, aligning with the NP17 to NP18 calcareous nannoplankton zones. The co-occurrence of H. dumblei, H. australis, and H. longispina in the E13/NP17 Zone suggests a warm marine setting in the lower Rashrashiyah Formation, while their absence in the middle portion indicates a cooling interval, followed by a warming phase in the upper E14/NP18 Zone marked by the appearance of H. compressa, H. primitiva, and H. alabamensis. This stratigraphic transition, alongside stable isotope data (δ¹⁸O and δ¹³C) from benthic foraminifera, reflects complex temperature variations impacting species distribution. An unconformity between the Rashrashiyah and Miocene Sirhan formations points to the absence of upper Eocene and Oligocene deposits, likely due to significant eustatic sea-level fall during the Eocene–Oligocene transition and regional tectonic uplift of the Red Sea rifting and the Syrian Arc. Correlating planktonic foraminifera (E13–E14) with calcareous nannoplankton (NP17–NP18) zones improves the middle to late Eocene stratigraphy, confirming the presence of Bartonian and Priabonian sediments and challenging previous assumptions of an Eocene hiatus in Saudi Arabia. This study not only refines the Eocene stratigraphy of Saudi Arabia but also highlights the role of Hantkenina as a key biostratigraphic marker in global paleoecology reconstructions, strengthening worldwide Eocene correlations.