High Resolution Sr Records and Late Pleistocene Sea Level Highstands in a Periplatform Sediment Drift (Inner Sea, Republic of Maldives)

High resolution cyclic records of Sr concentrations in the upper 12-14 m of a muddy periplatform drift in the Maldives Inner Sea (cores M74-4-1120, -1143, and -1144 in about 500 m of water depth) reveal high-frequency sea level oscillations during late Pleistocene highstands. Export variations of bank-top produced fine aragonite to adjacent slopes and basin floor faithfully record bank-top flooding and exposure, and therefore sea level.

Here we present the results of a new analytical method based on Sr concentrations, as a proxy for bank-derived fine aragonite content, measured downcore using a X-ray Fluorescence (XRF) Core Scanner. The three piston cores were analyzed for Sr concentration at 1 cm spaced intervals. Large cations, such as Sr, are preferentially substituted for Ca in orthorhombic aragonite, whereas small cations such as Mg are preferentially substituted for Ca in rhombohedral calcite. Based on a calibration curve in core M74-4-1143, Sr concentrations become a valuable proxy for bank-derived fine aragonite content. This new methodology reveals that observed Sr concentration cyclic downcore variations can be correlated to the marine and ice sheet oxygen isotope records and sea level fluctuations at Milankovitch frequencies in addition to millennial frequencies during interglacial stages.

Downcore variations of Sr concentrations in cores 1144 and 1120 mimic well the Lisiecki and Raymo (LR) (2005) stack benthic O istope record down to the end of Marine Isotope Stage (MIS) 11 and to the beginning of MIS 15, respectively. Planktic O isotope records at 10 to 5 cm spaced intervals are currently being produced in both cores as an assurance that the cyclic downcore variations of Sr concentration are in phase with the LR2005 O isotope stack.

Core 74-4-1144 was scanned for Sr concentration at higher resolution (0.5 cm) for the full MIS 5 interval. Variations of Sr concentrations values at sub-Milankovitch millennial frequencies, since the MIS 5 e/d transition, appear to correlate well with the North GRIP Greenland O isotope ice record and the Red Sea high frequency sea level record. Preliminary interpretation of ultra high resolution Sr analyses during the end of MIS 5, therefore, suggest that sea level fluctuations, between 20 to 60 m below modern sea level, frequently exposed and flooded at millennial time scale the Maldives atoll lagoon floors and were faithfully recorded in the muddy periplatform drift in the Maldives Inner Sea.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California