Home Multi-Country Search About Admin Login
Cenozoic
Mesozoic
Paleozoic
Neoproterozoic
Mesoproterozoic
Paleoproterozoic

Search by
Select Region(s) to search
Hold Ctrl (Windows/Linux) or Command (Mac) to select multiple
Cherra Formation
Click to display on map of the Ancient World at:
Cherra Fm base reconstruction

Cherra Fm

Period: 
Paleogene

Age Interval: 
Early Eocene


Province: 
Bangladesh NW

Type Locality and Naming

Lowest formation of Jaintia Gr as used in NW Bangladesh (coeval with Tura Fm). Medlicott (1869) had recognized the clastic sequence exposed around Cherrapunji which was designated as ‘Cherra band’ of then presumed Cretaceous age. Usage (e.g., USGS-PetroBangla 2001; Banglapedia) of Cherra Fm now seems limited to NW Bangladesh (subsurface, but with particularly in the Khasi and Jaintia hills of the Northern Foreland Shelf), where it seems mainly defined as the sandstones below the Sylhet Fm limestone.

Synonyms: Cherra Sandstone. See the long discussion for the Tura Fm (NE Basin regions). "Standard Vacuum Oil of the USA adopted the well-established name Cherra Formation for the description of the sequence in the Kuchma and Bogra wells. Later, this rock unit was designated Kuchma Sandstone." But many publications, for regional consistency, use Tura Fm, instead of Cherra Fm.


Lithology and Thickness

Sandstone. Predominantly arenaceous sequence.


Lithology Pattern: 
Sandstone


Relationships and Distribution

Lower contact

Unconformable onto either Rajmahal Traps Fm basalts (Aptian) or the post-Trap clastics (Sibganj Trapwash Fm, Bolpur Fm, Ghatal Fm) depending on location and usage of "Cherra Fm".

Upper contact

Conformably overlain by the Sylhet Fm Limestone (although the base of Sylhet Fm usage is diachronous, and the "Megachart" by Dr Raju 2021 suggests that in some basin usage, the "Tura Fm", hence also "Cherra Fm" might correspond to lower-members of the Sylhet elsewhere). That limestone is a reflector in NW Bangladesh and SE Bangladesh.

Regional extent

Subsurface, but with particularly in the Khasi and Jaintia hills of the Northern Foreland Shelf. Similar deposits in the Garo Hills and other Assam basins are known as the Tura Fm. Equivalent to the Jalangi Fm of West Bengal.


GeoJSON

{"type":"Feature","geometry":{"type":"MultiPolygon","coordinates":[[[[89.25,23.94],[90.18,24.9],[90.59,25.17],[89.87,25.3],[89.8,25.59],[88.95,25.6],[89.022,25.26],[88.48,25.22],[87.95,24.64],[89.25,23.94]]]]}}

Fossils


Age 

"The age assignment of the Cherra Formation as well as that of the Tura Fm, both forming the basal succession of the Tertiary in the marginal portion of the shelf was long debated. Apart from lithological similarities, the correlation of the microfloral assemblages shows a close correspondence between the two. Palynological data reveal that the Tura Fm is divisible into 4 cenozones, while 3 palynological cenozones were recognized within the Cherra Formation, although only minor variations in the composition of the microfloral assemblages were seen within the rock sequence. In many publications, both formations were regarded as Paleocene sediments. However, a few authors mentioned that certain palynomorphs in the studied sequences provide some evidence which points towards a Lower Eocene age for the Cherra Formation." (Banglapedia, 2015). A similar point was also later accepted by other authors. USGS-PetroBangla 2001 usage is shown as potentially extending down to base of Paleocene.

Age Span: 

    Beginning stage: 
Ypresian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
56.00

    Ending stage: 
Ypresian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
48.07

Depositional setting


Depositional pattern:  


Additional Information


Compiler:  

Largely copy-pasted from Banglapedia (National Encyclopedia of Bangladesh as compiled by several geologists; http://en.banglapedia.org/index.php/Geological_Group-Formation; 2015); but with J.Ogg attempt to make sense of different usages.