High occurrence of Orbulina suturalis and “ Praeorbulina-like specimens” in sediments of the northern Arabian Sea during the Last Glacial Maximum

This study focuses on the exceptionally high occurrence of Orbulina suturalis and morphotypes very close to Praeorbulina in Late Glacial sediments from the Northern Arabian Sea. The genus Praeorbulina has been described by Blow (1956) as an ancestor of Orbulina universa. Our study is based on the analysis of three sediment cores retrieved in the Gulf of Oman (KS01, MD04-2849, and MD04-2861), covering the Late Pleistocene (last 30 ka CAL-BP). Planktonic foraminiferal assemblages were investigated and revealed that this remarkable abundance of Orbulina suturalis, and numerous specimens morphologically close to Praeorbulina, occurs during a short time interval roughly representing the Last Glacial Maximum. One AMS 14C date was obtained on a monospecific sample of Praeorbulina-like specimens, giving an age of 19 CAL-ka BP, which confirms the Late Glacial age and unreworked character of this population. In this paper, we discuss the morphological similarities relating the observed Praeorbulina-like specimens to the genera Orbulina and Praeorbulina. We will also discuss the period of occurrence of these specimens and the potential environmental changes that may have caused their atypical morphology. ► Exceptional high occurrence of Orbulina suturalis and specimens close to Praeorbulina were found in Late Glacial sediments of the Arabian Sea. ► 14C date obtained on Praeorbulina-like specimens confirms the unreworked character of this population. ► Praeorbulina-like specimens are discussed at the light of the Praeorbulina/Orbulina lineage. ► Praeorbulina-like specimen is a potential stratigraphical marker of the LGM in the northern Arabian Sea.