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

Abstract 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 14 C 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.