Introduction to the geography and geomorphology of the Andaman-Nicobar Islands

The geography and the geomorphology of the Andaman–Nicobar accretionary ridge (islands) is extremely varied, recording a complex interaction between tectonics, climate, eustacy and surface uplift and weathering processes. This chapter outlines the principal geographical features of this diverse group of islands

Paleogene tectonic and sedimentation history of the Andaman-Nicobar Accretionary Arc, Northeast Indian Ocean

The Andaman-Nicobar archipelago in the northeastern Indian Ocean is a nonvolcanic outer arc island chain developed by tectonic accretion of sediments and ocean crust along the eastern margin of the subducting Indian lithosphere. The Paleogene stratigraphy of the island chain comprises olistostromes, olistoliths and coarse-grained volcaniclastic turbidite facies, and reefal limestones of late Paleocene- Eocene MithakhariMelange and finer-grained siliciclastic turbidites (Andaman Flysch) of Oligocene age. The lower Paleogene sedimentary rocks were deposited in shallow-water basins formed on the upper trench slope and growing accretionary wedge and contain material sourced from a local volcanic arc and eroded ophiolite. By contrast, the Oligocene continent-derived siliciclastic sediments were originally deposited outside of the accretionary wedge as part of a large submarine fan system. Subsequent deformation and thrusting juxtaposed these different formations as trench rollback progressed and the accretionary wedge expanded westwards

Sediment geochemistry of coastal environments, southern Kerala, India: implication for provenance

Late Quaternary sediments representing the floodplain, estuary and offshore environments of southern Kerala were investigated to infer provenance. The grain size reveals the dominance of sand to silty clay, clay to clayey silt and clayey silt in the floodplain, estuary and offshore sediments, respectively. The chemical index of alteration (CIA) values and A-CN-K plot attributes to high, moderate and low weathering in floodplain, estuary and offshore regions, respectively. The SiO 2 /Al 2 O 3 values lesser than Post-Archean Australian Shale indicate low to moderate maturity for the estuarine and offshore sediments. The geochemical immaturity indicates its derivation from low to moderately weathered source rocks. The major and trace elemental ratios and discriminant function diagrams attribute that the sediments were derived from intermediate to felsic source rocks. The enrichment of Cr and Ni concentration in the sediments compared to the upper continental crust, related to the contribution of orthopyroxenes, weathered from charnockite and garnets from the granulite terrain, respectively