Revisiting the Biostratigraphic Range and Possible Cause of the First and Last Occurrence of Globigerinoides Ruber (Pink) in the Northern Indian Ocean

The first and last occurrence datums of species are often used as biostratigraphic markers to establish chronology beyond the range of radiocarbon dating. One such datum, the last occurrence of Globigerinoides ruber (pink) from the Indo-Pacific region, has been extensively used as a biostratigraphic marker. However, the first occurrence of G. ruber (pink) in the Indian Ocean and the possible causes thereof are debated. We report the first and last occurrence datums of G. ruber (pink) from the northern Indian Ocean and explore the possible reasons for its first and last occurrence. The first occurrence of G. ruber (pink) in the Bay of Bengal is 399 ka. The last occurrence datums are 128 ka and 123 ka in the Bay of Bengal and Arabian Sea, respectively. The occurrence of G. ruber (pink) in the Indian Ocean is attributed to its invasion through the warmer southeast Atlantic Ocean via the Agulhas Return Current. Based on the synchronous occurrence during Marine Isotopic Stage 11, we propose that the first occurrence of G. ruber (pink) can be used as an additional marker throughout the northern Indian Ocean.