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Alibag Formation
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Alibag Fm base reconstruction

Alibag Fm

Period: 
Paleogene

Age Interval: 
Late Oligocene


Province: 
W.India Mumbai Offshore

Type Locality and Naming

Well B – 38 – 1, (depth interval 1257 – 1333 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 B – 30 – 1 (depth interval 1992 -2270 m); Well D – 4 – 1 (depth interval 2956 – 3415 m)

Synonyms: The Panvel Fm of Zutshi et al. (1993) is considered as junior synonym of the Alibag Fm.

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


Lithology and Thickness

Marl. In the type section, the formation consists of predominantly of shale with a few thin limestone bands. The shale is occasionally pyritic and fossiliferous. The limestone is fossiliferous and micritic.

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


Lithology Pattern: 
Pelagic marl


Relationships and Distribution

Lower contact

Depending on location, the dominantly shaly facies of the Alibag Fm unconformably overlies the Heera Fm or Mukta Fm.

Upper contact

Depends on location. Unconformably overlain by the massive limestone of the Ratnagiri Fm. Over most of Panna-Bassein Block, the limestone of the Bombay Fm overlies the Alibag Fm. In the outer shelf, claystone of the Mahim Fm overlies it.

Regional extent

Most of the deeper regions of the Mumbai offshore region.


GeoJSON

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Fossils

The formation is characterized by Miogypsinoides complanata and Spiroclypeus.


Age 

Late Oligocene. NDRDGH.gov Mumbai stratigraphic chart indicates spans Chattian; but a end-Oligocene disconformity is suggested.

Age Span: 

    Beginning stage: 
Chattian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
27.29

    Ending stage: 
Chattian

    Fraction up in the ending stage: 
0.8

    Ending date (Ma):  
23.89

Depositional setting

Deposited in shallow, inner shelf environment.


Depositional pattern:  


Additional Information


Compiler:  

D.S.N Raju