Source shifts to periplatform deposits during the early to middle Miocene in response to climatic and oceanographic forcing, Maldives, western Indian Ocean

Periplatform carbonate ooze records a composite signal reflecting both the regional oceanographic state and the development of the adjacent carbonate platform. Deconvolving these signals offers the possibility to obtain a holistic perspective on the factors governing the evolution of the platform, especially when the platform itself is not accessible. Here, we examine a case study from periplatform deposition in Site U1468 on the margins of the Kardiva Platform, Maldives. This site has a well-constrained record with seismic control of the geometric evolution of adjacent carbonate platforms. Here we integrate geochemistry, sedimentology and external constraints to address the relationship between local (platform evolution), regional (nutrient regime) and global (temperature, sea level) effects. The lower to middle Miocene succession at Site U1468 is comprised of a wackestone to packstone sequence that hosts foraminifera and other bioclastic grains, derived from neritic and pelagic sources, as well as biogenic siliceous material such as sponge spicules. The sequence records an increase in neritic supply to the periplatform from the late Burdigalian to the early Serravallian as recorded in Sr/Ca and δ¹³C values. The increase in neritic material coincided with a stepwise intensification of the regional Oxygen Minimum Zone (OMZ) recorded by Mn/Ca ratios. During these trends, short-lived oscillations in local carbonate production and OMZ intensity were superimposed on the larger trend. The expansion of the OMZ was driven by periods of cooling while the increase in neritic production was driven by warming and sea-level rise. These results reinforce existing models of the evolution of the Kardiva Platform with respect to sea level and add to it a refined understanding of the relation to regional nutrient patterns.