Neill West Coast Fm
Type Locality and Naming
Named after Neill Island. The name was first proposed by Srinvasan and Azmi (1976a) for the limestones exposed on the western part of Neill Island, as the ‘Limestone Member’ of Neill West Coast Formation (Pandey et al., 1993).
[Original Publication: Srinivasan, M.S. and Azmi, R.J. (1976b). New developments in the Late Cenozoic Lithostratigraphy of Andaman-Nicobar Islands, Bay of Bengal. Proc VI Indian Colloq. Micopal and Strat., pp. 302-327.].
Reference well: Well AN-63-C-1
[Figure 1 = Map of Neill Island showing the stratotype locality (after Sharma and Srinivasan, 2007).]
[Figure 2 = Andaman stratotypes]
Synonyms: The Western Coast Limestone and Neill Island Limestone of Singh and Vimal (1974, 1976b) correspond to Neill West Coast Formation. The Malacca Limestone Fm of Car Nicobaar Island (Srinivasan and Sharma, 1973) and Chowra Limestone Fm of Chowra Island (Srinivasan and Srivastava, 1972b) correspond in age to a part of Neill West Coast Formation.
Lithology and Thickness
Siltstone and Limestone: The formation consists of two units 1) a lower Silty Mudstone member and 2) an upper Limestone member. The Silty Mudstone Member consists of dark grey silt and has a limited areal extent, occurring in a few small outcrops. This Member disconformably underlies the Limestone Member, which is rich in foraminifera comprised of fine to medium, compact to porous, buff, foraminiferal-algal biocalcarenite with moderately sorted, broken fragments of corals, algae and polycrystalline quartz grains. Thickness is 194 m in the reference section.
[Figure 3: Type section of Neill West Coast Fm and Taipian and Shompenian regional stages (modified after Sharma and Srinivasan, 2007)]
[Figure 4: Exposures of Neil West Coast Fm at low tide (after Sharma and Srinivasan, 2007)]
[Figure 5: Silty mudstone Member unconformably underlying Limestone Member of the Neil West Coast Fm near Natural Bridge at Neill Island (after Sharma and Srinivasan, 2007)]
[Figure 6: Generalized Subsurface Stratigraphy of Andaman-Nicobar Basin (from dghindia.gov.in)]
Relationships and Distribution
Lower contact
Disconformity: Lower boundary of the formation has a disconformable relation with the underlying Long Fm.
Upper contact
Conformable: Upper boundary is conformable overlain by Sub-recent to Recent shell Limestone and coral rags.
Regional extent
[Figure 7: General Stratigraphic Correlation of Burma, Andaman and North Sumatra (from dghindia.gov.in)]
[Figure 8: Detailed geological map of Andaman area (modified after Bandopadhyay 2012) showing locations mentioned in numbers in B. Ghosh et al., 2017, Geo.Soc.London.Memoirs, 47, 95-110)]
GeoJSON
Fossils
Foraminifera of Globorotalia tosaensis Zone to Globorotalia truncatulinoides Zone were recorded by Srinivasan and Azmi (1976a, b).
Age
Depositional setting
It is interpreted as Outer Shelf to upper bathyal
Additional Information