Evolution of the Glorieuses seamount in the SW Indian Ocean and surrounding deep Somali Basin since the Cretaceous

(IF 3.55; Q1); International audience; Little is known about the geological history of the Glorieuses seamount including basic information about its age and origin related to the regional evolution of the southern tip of the Somali Basin. This study focused on describing and reconstructing the long-term stratigraphic evolution of the Glorieuses seamount (SW Indian Ocean) to identify the mechanisms that have occurred through time to finally shape the emerged modern islands. Distinct terrace levels, currently submerged along the flanks of the seamount and surrounding seamounts, have already been interpreted as resulting from successive carbonate development and back-stepping episodes over the last 62 Myr. New isotopic and biostratigraphic dating on the flanks of the seamount, coupled with sequence stratigraphic interpretation of seismic profiles acquired in the adjacent basin, provide new constraints for the Late Cretaceous and Cenozoic vertical evolution of the seamount topped by carbonate platforms and sedimentation in the surrounding deep basin. Even if starved steep slopes prevent a straightforward source-to-sink continuity between the platform and the basin domains, our findings propose a consistent chronostratigraphic framework for the identified seismic markers and sequences in the deep basin, and discuss a long-term geological model that includes the main driving factors behind deposition (volcanic events, subsidence vs uplift phases, climate and hydro-dynamism changes) and their quantitative impact on the evolution of the isolated carbonate sedimentary system. Our results show that: (i) the Glorieuses volcanic seamount emerged from two successive Late Cretaceous magmatic pulses, firstly during the Turonian, then during the Maastrichtian (ii) at least two potential uplift phases are recognized during the Tertiary (Paleogene and/or the Eocene and Tortonian); (iii) basinal sedimentation recorded an abrupt change probably related to major regional hydro-dynamical changes in Late Eocene times in the Western Indian Ocean; (iv) the export of sediments from the platform towards the basin (numerous gravity flow processes) is strongly enhanced after the Mid Miocene, and is probably linked to the onset of the Asian monsoon winds and bipolar circulation. Finally, the Glorieuses seamount, although located in the vicinity of the Comoros islands, appears to have a much longer history and is geologically more comparable to the nearby Seychelles. This long-term study has enabled us to associate the Glorieuses seamount with the SSE-NNW Madagascar-Seychelles alignment rather than with the Comoro hot spot evolution.