Late Pleistocene sediment record of the Maldives carbonate platform

A piston core from the Maldives carbonate platform was investigated for carbonate mineralogy, grain-size distributions, calcium carbonate content and organic carbon. The sedimentary record was linked to Late Pleistocene sea-level variations, using an age model based on oxygen isotopes obtained from planktonic foramanifera, nannofossil biostratigraphy and 14C age determinations. The correlation between the sedimentary record and Late Pleistocene sea-level showed that variations in aragonite and mud during the past 150 000 years were clearly related to flooding and sea floor exposure of the main lagoons of the atolls of the Maldives carbonate platform. Platform flooding events were characterized by strongly increased deposition of aragonite and mud within the Inner Sea of the Maldives. Exposure events, in contrast, can be recognized by rapid decreases in the values of both proxy records. The results show that sediments on the Maldives carbonate platform contain a continuous record of Pleistocene sea-level variations. These sediments may, therefore, contribute to a better understanding of regional and even global sea-level changes, and yield new insights into the interplay between ocean currents and carbonate platform morphology.

(Table 1) H2O and CO2 contents in submarine basaltic glasses from Ontong Java Plateau

The Ontong Java Plateau in the western Pacific is anomalous compared to other oceanic large igneous provinces in that it appears to have never formed a large subaerial plateau. Paleoeruption depths (at 122 Ma) estimated from dissolved H2O and CO2 in submarine basaltic glass pillow rims vary from ~1100 m below sea level (mbsl) on the central part of the plateau to 2200-3000 mbsl on the northeastern edge. Our results suggest maximum initial uplift for the plateau of 2500-3600 m above the surrounding seafloor and 1500+/-400 m of postemplacement subsidence since 122 Ma. Our estimates of uplift and subsidence for the plateau are significantly less than predictions from thermal models of oceanic lithosphere, and thus our results are inconsistent with formation of the plateau by a high-temperature mantle plume. Two controversial possibilities to explain the anomalous uplift and subsidence are that the plateau (1) formed as a result of a giant bolide impact, or (2) formed from a mantle plume but has a lower crust of dense garnet granulite and/or eclogite; neither of these possibilities is fully consistent with all available geological, geophysical, and geochemical data. The origin of the largest magmatic event on Earth in the past 200 m.y. thus remains an enigma.