Upper-Quaternary Radiolaria from the Piston Core ABP-06, Indian Ocean: Taxonomy and biostratigraphy

After being recovered from the Central Indian Ocean, core ABP-06, Station II, underwent a thorough micropaleontological analysis. Forty well-preserved radiolarian species were discovered and recorded from a total of 40 sediment samples. Each species’ taxonomy and vertical distribution of the core are thoroughly described in the paper. Two radiolarian biozones—the Buccinosphaera invaginata Zone and the Collosphaera tuberosa Zone—have been identified based on the evolutionary boundaries, morphotypic appearances and disappearances, and abundance patterns of important species. These zones help to refine the Neogene-Quaternary stratigraphy in the area and represent important biostratigraphic boundaries within the core. Four reworked species were found in addition to the primary tropical assemblage, indicating sedimentary reworking from the Miocene to Pliocene intervals: Acrosphaera spinosa echinoides , Heliodiscus echiniscus , Spongaster pentas and Spongaster berminghamii. Additionally, the presence of Stylodictya validispina , a recognised cold-water taxon, and Tetrapyle octacantha , an indication of upwelling conditions, shows evidence of paleoceanographic variability, including the effect of cooler bottom waters and episodes of nutrient-rich upwelling. According to the biostratigraphic data of the radiolarian assemblage, the section under study is of Upper Quaternary age, with an estimated range of 0.18–0.5 million years. The Central Indian Ocean radiolarian biozones NR1 and NR2 are biostratigraphically similar to the Globorotalia truncatulinoides (N23) zone of planktonic foraminifera.