Episodic reef growth in the granitic Seychelles during the Last Interglacial: Implications for polar ice sheet dynamics

We present a detailed taxonomic and lithologic analysis of fossil reefs in the Granitic Seychelles to improve constraints on global mean sea level behavior during the last interglacial sea-level highstand, ~129,000-116,000 years ago. In particular, we have assessed the coralgal reef outcrops for any sedimentalogic evidence of sub-orbital sea level oscillations that may have occurred during this warm, interglacial period. At the outcrop scale, we observe at least three distinct episodes of reef growth punctuated by two discontinuities that typically manifest as coral rubble layers or extensive lateral encrustations of the hydrozoan coral Millepora exaesa. Hiatuses in reef growth at other sites around the world have been interpreted as relative sea level falls and/or environmental disturbances. We have tested the hypothesis that these discontinuities, that we refer to as disturbance horizons, are related to ephemeral drops in sea level that have been inferred at last interglacial reef sites from other sites around the globe. At two sites, there is sedimentological evidence in the form of extensive dissolution and freshwater cements associated with the disturbance horizons that would require subaerial exposure followed by marine inundation. At the remaining sites, evidence is consistent with, but not necessarily indicative of, an ephemeral drop in sea level. To establish if these disturbance horizons are coeval between the outcrops and if they are local or global features, requires high-precision dating of the disturbance horizons along with a critical analysis of sedimentary and chronological evidence from other sites around the globe. If the disturbance horizons observed in the Seychelles represent transient sea-level falls or still stands during the last interglacial, this would imply a dynamic behavior of the polar ice sheets during this past warm period.