Rodrigues Island: carbonate deposition and karst processes as indicators of platform stability

Rodrigues Island is located in the western Indian Ocean ~600 km east of Mauritius, at 19°42′S and 63°24′E, a volcanic island with a small overlay of Quaternary eolian limestones, an area of 108 km2, elongated ENE to WSW, 18 km long and 6.5 km wide, maximum elevation of 396 m. The last volcanic activity was 1.3 ma, and only one lava tube is known. The eolian calcarenites are restricted to a narrow segmented band on the east coast, and two larger patches, Plaine Caverne and Plaine Corail, on the south coast. No subtidal carbonate facies are known, and no flank margin caves are known, indicating that platform subsidence has been in excess of 5 m/100 ka to bring such features from the MIS 5e +6 m sea-level highstand below modern sea level. The eastern eolianite outcrops contain rectangular incisions similar to the bokas found in the Netherlands Antilles, as a large volcanic rock watershed traverses a thin coastal limestone outcrop. The southern calcarenite exposures each contain large epigene cave passages developed by surface catchment from volcanic rocks. The Plaine Corail caves are abandoned by streams today, are segmented and modified by collapse and contain massive calcite speleothems, evidence of an eolianite age of perhaps 1 ma or more. Plaine Caverne contains two long, linear stream caves, mostly intact. Mauritius has flank margin caves, subtidal facies above modern sea level, and abundant lava tubes (volcanic activity as recent as 26 ka), consistent with thermal inflation now long ended on subsiding Rodrigues.