MICROFOSSIL EVIDENCE FOR +21 M EUSTATIC SEA LEVEL DURING MARINE ISOTOPE STAGE 11

Geologic evidence for +21 m sea level during Marine Isotope Stage (MIS) 11 is continually building from several global localities. Here we provide microfossil evidence for +21 m sea level during MIS 11 from small, elevated caves in Bermuda (Calonectris, UGQ4, UGQ5, and the Land et al. site discovered in 1987). The sediments containing the microfossils have been repeatedly dated to MIS 11, using both U-series dating and amino acid racemization. Previously, the microfossils from UGQ4, UGQ5, and the Land et al. 1967 site had been interpreted as a tsunamite. However, they were not interpreted in a framework of coastal cave environments and hydrogeology. After statistically comparing a more complete foraminifer assemblage recovered from Calonectris Cave (Pocket A) to other Bermudian coastal environments (reefs, lagoons, mangroves, anchialine caves, littoral caves) using cluster analysis, the foraminifera in Calonectris Cave Pocket A cannot be statistically differentiated from assemblages in modern proximal littoral caves. Protoconchs of the Bermudian endemic stygobite Caecum caverna were also associated with the foraminifera, providing further evidence that these were are fossil coastal cave environments. Sea-level regression following the +21 m highstand first lowered the ancient brackish Ghyben-Herzberg lens (< 0.5 m) to create an anchialine environment, as indicated by rare brackish marsh foraminifera (Polysaccammina, Pseudothurammina) and anchialine gastropods (~95%, >300 individuals), before finally causing vadose conditions suitable for speleothem precipitation during MIS 10. In conclusion, we reiterate the need to resolve the disparity between global marine isotopic records and the physical geologic evidence for sea level during MIS 11.