Impact of tectonic and volcanism on the Neogene evolution of isolated carbonate platforms (SW Indian Ocean)
Résumé
Understanding the impact of tectonic activity and volcanism on long-term (i.e. millions years) evolution of
shallow-water carbonate platforms represents a major issue for both industrial and academic perspectives. The
southern central Mozambique Channel is characterized by a 100 km-long volcanic ridge hosting two guyots
(the Hall and Jaguar banks) and a modern atoll (Bassas da India) fringed by a large terrace. Dredge sampling, geo-
physical acquisitions and submarines videos carried out during recent oceanographic cruises revealed that sub-
marine
fl
at-top seamounts correspond to karsti
fi
ed and drowned shallow-water carbonate platforms largely
covered by volcanic material and structured by a dense network of normal faults. Microfacies and well-
constrained stratigraphic data indicate that these carbonate platforms developed in shallow-water tropical envi-
ronments during Miocene times and were characterized by biological assemblages dominated by corals, larger
benthic foraminifera, red and green algae. The drowning of these isolated carbonate platforms is revealed by
the deposition of outer shelf sediments during the Early Pliocene and seems closely linked to (1) volcanic activity
typi
fi
ed by the establishment of wide lava
fl
ow complexes, and (2) to extensional tectonic deformation associat-
ed with high-offset normal faults dividing the
fl
at-top seamounts into distinctive structural blocks. Explosive vol-
canic activity also affected platform carbonates and was responsible for the formation of crater(s) and the
deposition of tuff layers including carbonate fragments. Shallow-water carbonate sedimentation resumed during
Late Neogene time with the colonization of topographic highs inherited from tectonic deformation and volcanic
accretion. Latest carbonate developments ultimately led to the formation of the Bassas da India modern atoll. The
geological history of isolated carbonate platforms from the southern Mozambique Channel represents a new case
illustrating the major impact of tectonic and volcanic activity on the long-term evolution of shallow-water car-
bonate platforms