Stratigraphy and Chronology of Karst Features on Rodriguez Island, Southwestern Indian Ocean

Abstract

6 Abstract: The remote Indian Ocean island of Rodrigues, while largely of volcanic origin, also contains a large body of eolian calcarenite with over thirty surveyed caves and many other karst features. Little is known, however, regarding the age and stratigraphy of the clastic deposits in the caves and the associated fossils of the highly endemic, now mostly extinct, fauna. On the Plaine Caverne and Plaine Corail of the southwestern part of the island, we obtained sediment cores up to 10 m in length and excavated bones of the extinct fauna from caves in the vicinity. Stratigraphic description and radiocarbon dating revealed that sediments in Canyon Tiyel, a collapsed-cave feature, primarily accumulated during the early and middle Holocene. Sedimentation in the canyon and adjacent caves has slowed in recent millennia, with the result that many bones of fauna that went extinct after human arrival in recent centuries are on or near the surface. The chemistry of the sediments and the alternate wet and dry regime of the cave and canyon surfaces are often not conducive to preservation of bone collagen and plant microfossils. Grotte Fougere, with an apparently unique anchialine pond inside a collapsing cave, however, contains over one meter of highly organic sediment with excellent preservation of plant and animal remains.