EXTREME INTERGLACIALS DURING THE EARLY PLEISTOCENE AND THE PLIOCENE RECORDED IN SHALLOW-WATER CARBONATES: MAYAGUANA ISLAND, SE BAHAMAS

⁸⁷Sr/⁸⁶Sr-dated reefal, lagoonal and beach sediments exposed along the north shore of Mayaguana Island (SE Bahamas) provide new estimates of the elevation of high sea stands during the Early Pleistocene and the Pliocene that document episodes of major ice collapses during these time periods.

Newly investigated exposures along the northern coast of Mayaguana revealed (1) a complex, ca. 12 m-thick succession of reefal, lagoonal and beach sediments separated by paleosols and/or erosional surfaces that record sea-level highstands at, respectively, >+5, >+8 and +10 m above modern sea level (msl), and (2) an abraded, partly dolomitized coralgal-reef terrace reaching up to +3 m above msl.

Whole-rock ⁸⁷Sr/⁸⁶Sr ratios measured from the complex succession range from 0.709123 at the base to 0.709142 at the top. These deposits were thus formed during the Early Pleistocene, likely between 1.2 and 1.0 Ma BP, and can therefore be correlated with the super-interglacials MIS 37, 31 and 25, respectively. ⁸⁷Sr/⁸⁶Sr ratios measured from the dolomitized reef range between 0.709048 and 0.709081. Considering that dolomitization occurred shortly after deposition, the age of this extensive coralgal terrace can be constrained between 4.5 and 2.2 Ma BP, thus corresponding to the Early Pliocene (Zanclean).

Based on the elevation of the fossil reefs dating from the last interglacial (MIS 5e) and the occurrence of Late and Early Miocene shallow-marine deposits close to modern sea level, Mayaguana Island can be considered as subsiding at a very slow rate (2-3 m/Ma). The elevation values obtained for these Early Pleistocene and Early Pliocene highstands (all around +10 m) are thus potential candidates to calibrate Late Cenozoic eustatic sea-level curves derived from deep-sea oxygen-isotope records, and will also help to better constrain the boundaries of ice-sheet models. To our knowledge, it is the first time that the super-interglacials of the Early Pleistocene are recorded in shallow-water carbonates.