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Bombay Formation
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Bombay Fm base reconstruction

Bombay Fm

Period: 
Neogene

Age Interval: 
Aquitanian to Middle Burdigalian


Province: 
W.India Mumbai Offshore

Type Locality and Naming

Well BH – 1, (depth interval 1287 – 1665 m). [Original Publication: Basu, D.N., Banerjee, A and Tamhane, D.M. 1982. Facies distribution and petroleum geology of Bombay Offshore Basin, India. Journal Petroleum Geology, Volume 5, pp. 57-75.] Reference well: Well BH-55 (depth interval 1403 -1770 m); Well ED – D and 367m thickness in reference section

[Figure: Lithostratigraphy in Mumbai Offshore blocks (from NDRDGH.gov.in; after Jitendra Misra, 2009)]


Lithology and Thickness

Limestone. The formation consists dominantly of limestone interspersed with thin shale beds. The limestones are micrite and biomicrite type. In the type section, the formation is 378 m thick. Towards the southwest and south of Bombay High, it is gradually thicker at the exposure of overlying shale of the Mahim Fm until it finally merges with the limestone of the Bandra Fm. Represented by a thick pile of carbonates hosting huge quantity of oil and gas.

[Figure 1: Formations and their reference sections in Mumbai Offshore Basin (after Pandey and Dave, 1998)]

[Figure 2: Lithology, microfacies, electrolog motif and Miogypsinidae, a few Ostracoda and sequence stratigraphy of well ED-D, Mumbai High compiled by D.S.N Raju and S. Uppal, (modified after Raju et al., 2002)]


Lithology Pattern: 
Shallow-marine marl


Relationships and Distribution

Lower contact

Unconformably overlies the Alibag Fm.

Upper contact

The contact of the Bombay Fm with the deeper-faces (clay-rich) of the overlying Mahim Fm is suggested transgressive? In shallower areas, it is directly overlain by the Bandra Fm.

Regional extent


GeoJSON

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Fossils

The limestone layers of Bombay Formation are very rich in larger foraminifera including Miogypsinidae. The succession of a Miogypsinoides from base to top include Miogypsina (Miogypsina) gunteri, M (M.) tani, M. (Lepidosemicyclina) thecideaeformis, M. (L) talukdari, M. (L) excentrica, M.(L) Bifida, M. (L) droogeri. There are several species of other larger foraminifera, smaller benthic, and ostracodes. Nearly six biochrons based on larger foraminifera are recognized within the Bombay Formation. The shale layers contain rare marginal marine forams.


Age 

Aquitanian to Middle Burdigalian (generally); with maximum upward extent in shallow regions to mid-Langhian.

Age Span: 

    Beginning stage: 
Aquitanian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
23.04

    Ending stage: 
Burdigalian

    Fraction up in the ending stage: 
0.5

    Ending date (Ma):  
18.22

Depositional setting

Several cycles of sedimentation are recognized, nearly nine 4th / 5th order cycles rare recognized within lower to middle Burdigalian itself. The shales were deposited under marginal marine environments, while the limestones were deposited under shallow inner shelf with paleobathymetry up to 20/25 m.


Depositional pattern:  


Additional Information


Compiler:  

D.S.N Raju