Interpreting Interglacial Stratigraphy in Bermuda With New Amino Acid Data

Abstract:

Situated in the North Atlantic Ocean, the islands of Bermuda expose a complex sequence of glacial and interglacial carbonates. The interglacial deposits in particular are not continuous and not easily correlated between exposures, resulting in uncertainty and some disagreement regarding their age. We aim to compile available age dates and evaluate them in context with new information, with the goal of developing an updated framework for further work.

Here we present new Amino Acid Racemization (AAR) dates from previously undated localities, including multiple undescribed deposits on islands within the Great Sound of Bermuda. We analyzed fossil material from 11 localities, 10 of which were previously undated via quantitative methods. Fossil bivalve genera Lucina and Glycymeris were measured at nearly every locality, along with Arca at two localities.

We find that A/I ratios ranging from 0.476 to 0.617 at Verril Island, Bird Island, and Long Island (Great Sound sites) are consistent with published data from Last Interglacial (MIS 5e) deposits of the Rocky Bay Formation. This interpretation is consistent with depositional and diagenetic characteristics of these deposits. We also interpret deposits near Fort Scaur as equivalent to the Belmont formation (likely MIS 7), and we find evidence that a unique depositional sequence near Stokes’ Point is much older than all other studied localities. Across localities we found that differences between Lucina and Glycymeris A/I ratios are significant, with stratigraphic resolution at some localities obscured by species-specific differences. In addition, our compilation of previously published U series data suggests a general consensus with our AAR interpretations; at Fort Saint Catherine in particular we find good agreement between published data and new results, all indicating an MIS 5a age. The review and new data presented here should provide a foundation for new sedimentology and paleoclimatology work on the Bermuda Platform.