Characterization of Marine Isotope Stage (MIS) 5a aeolianite deposits following the Last Interglacial Highstand (LIG) using remote sensing imagery and field investigations across the Western Atlantic

Abstract:

Increasing chronostratigraphic and amplitude estimates of sea level in the Quaternary is useful for understanding ice volume changes and climate variation between interglacial and glacial phases. Investigation of sea level change following the LIG such as the less studied MIS 5a highstand (~75-84 ky) has direct implications for building on the Western Atlantic regional model of glacio-isostatic adjustment (GIA) following volume changes in the Laurentide Ice Sheet (LIS).

Here we combine mapping using LiDAR-based digital terrain models of San Salvador Island with surface sampling and mapping. Twelve-meter resolution digital elevation data from TanDEM-X of the Bahamas, and information from previous studies of MIS 5a aeolian deposits across the area was combined to create a Bahamas-wide model. Field studies, petrography, and relative age dating (AAR) done on eastern San Salvador Island show consistencies in MIS 5a aeolian sedimentological characteristics (eg. skeletal-dominated, high porosity, minor cementation) as well as stratigraphic observations (eg. caliche capped rhizomorph-rich aeolian grainstones dipping below the modern datum) that make these deposits differentiable from aeolianites associated with LIG oolitic grainstones. MIS 5a aeolianites are also spatially differentiated by average area, dune ridge elevation, and relative position on the island profile from LIG aeolianites and the Holocene well-cemented mixed ooid/skeletal facies.

We interpret presence of paleosols within and capping windward catenary cay stacked deposits of miliolid- and peneroplid-rich skeletal grainstones to be representative of more than one highstand event within MIS 5a. Evidence of truncation surfaces and abundantly rhizomorph-rich protosols observed in San Salvador, Eleuthera, and Mayaguana could suggest multiple highstand deposits in this substage. Exposures on Abaco, Turks and Caicos, Cozumel, and other islands in the Western Atlantic are needed to define the MIS 5a paleogeography. These stratigraphic relationships implicate one or more MIS 5a paleoshorelines 5-8 meters below present-day sea level. When compared regionally across the Western Atlantic, these occurrences support a trend towards decrease in relative sea level further away from the LIS as a result of GIA effects.