Astrochronology of the late Oligocene-middle Miocene in the Maldives, central Indian Ocean

Abstract

Substantial work based on biostratigraphy has been done to constrain the chronology of the late Oligocene-middle Miocene in the Maldives (Indian Ocean), but a high-resolution temporal framework for the sedimentary record of this region remains elusive. This hampers a fuller understanding of the evolution of the carbonate platform, which is the second largest modern isolated carbonate platform. Moreover, the sedimentary record of the Maldives platform has the potential to provide insights on the onset of the ‘modern-like’ South Asian Monsoon (SAM) system. Here we present a detailed astrochronology for International Ocean Discovery Program (IODP) Site U1468 through the late Oligocene-middle Miocene in the Maldives. Our cyclostratigraphy of the site is integrated with existing biostratigraphy and statistical evaluation, providing a robust ∼12-Myr absolute astronomical time scale (ATS). Using this time scale, we assign numerical ages of 12.229 ± 0.46 Ma and 11.561 ± 0.46 Ma for the core depths of 450 mbsf and 430 mbsf, respectively. These depths, constrained by biostratigraphy, have previously been suggested to mark the onset of the SAM in the Maldives. Our ATS provides time constraints on the evolution of the platform sequence stratigraphy, and we find evidence of a ∼1.2-Myr obliquity amplitude modulation (AM) control on sea level changes and sequence development. In addition, our results indicate that the deposition of organic-rich sediments towards the base of the record in this area was driven by obliquity cycles and the combined effect of glacio-eustasy and hydrographic changes.