Testing the stratigraphic consistency of Pleistocene microfossil bioevents identified on the Alpha and Lomonosov Ridges, Arctic Ocean

Flor Vermassen, Matt O’Regan, Gabriel West, Thomas M. Cronin & Helen K. Coxall, 2021. Testing the stratigraphic consistency of Pleistocene microfossil bioevents identified on the Alpha and Lomonosov Ridges, Arctic Ocean. Arctic, Antarctic, and Alpine Research: 53,1, 309 – 323. DOI: 10.1080/15230430.2021.1988356

https://www.tandfonline.com/doi/full/10.1080/15230430.2021.1988356

Abstract
Two different biostratigraphic approaches are used to identify Marine Isotope Stage 11 (MIS 11) in Arctic Ocean sediments. On the Lomonosov Ridge, globally calibrated nannofossil bioevents constrain the age of sediments back to MIS 13 (Core LOMROG12-3PC). In the Amerasian Basin the unique occurrence of the planktonic foraminifer Turborotalita egelida is increasingly used as a marker for MIS 11. However, the T. egelida horizon has only been dated using cyclostratigraphy. Here we bridge these approaches through investigation of a new core (AO16-8GC) from the Alpha Ridge, Amerasian Basin. AO16-8GC is easily correlated to LOMROG12-3PC and contains the T. egelida horizon, allowing the first comparison between the biostratigraphy of both regions. Based on the nannofossil biochronology of LOMROG12-3PC, the most convincing lithologic correlation between the Alpha and Lomonosov Ridge cores places the T. egelida horizon between MIS 15 and MIS 17. This potentially older age for the T. egelida biohorizon emphasizes the need for continued caution in interpreting paleoceanographic records predating MIS 6, until further work can reconcile the nanno- and microfossil biostratigraphies that are emerging for middle Pleistocene sediments of the central Arctic Ocean.

Plate 2. SEM images demonstrating wall texture differences between T. egelida and the weakly calcified N. pachyderma morphotype with which it can be confused. (a) to (d) The T. egelida morphotype with corresponding wall texture close-up views showing spine bases, with evidence of broken spines and/or spine holes still visible in some cases, sample AO16-9-PC1-3, 60 to 62 cm. (e) and (f) Weakly calcified N. pachyderma morphotype, having a wall texture with low pustules but no spines or spine bases, sample form the Eastern Fram Strait, ODP Site 986, 15.32 m, MIS 5e (sample provided by A. Zhuravleva/H. Bauch). (a), (c), (d) Scale bar = 100 µm. (b), (d), (f) Scale bar = 10 μm.