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Bahraich Gr
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Bahraich Gr base reconstruction

Bahraich Gr

Period: 
Paleoproterozoic

Age Interval: 
early PaleoProterozoic (1900 Ma)


Province: 
N.India Ganga Basin

Type Locality and Naming

The name is proposed after district Bahraich in the state of U.P. (Shukla et al., 1993). Holo: Matera-1, Latitude: 27o 43' 22" N, Longitude: 81o36' 51" E. Drilled depth: 3927 m. The top of the group is at 3400 m while the base is not penetrated . The group is penetrated in a number of wells in the basin. This group is correlatable to Delhi Gwalior Gr.


Lithology and Thickness

Sandstone and claystone. This group is composed of epigrade metamorphic rock of diverse composition. The effect of metamorphism is very subtle and as such is not readily recognizable in the wellsite (cuttings). In Matera-1, this section consists of quartzitic sandstone with interbeds of chocolate brown, reddish brown shale. Core No. 8 (3431-3433 m) consists of quartzite showing development of incipient metamorphism and chloritic/sericitic shale with development of initial foliation and parting lineation. Thickness: The base of this group is not penetrated in any of the wells. As such the maximum thickness preserved in the Bahraich depression is of the order of 6.8 km!


Lithology Pattern: 
Clayey sandstone


Relationships and Distribution

Lower contact

Unconformable contact with the underlying Archean Basement

Upper contact

Overlain unconformably by Metera Fm in the type section. In Madhubani depression it is overlain by Madubani Fm. In Gandak and Puranpur depressions it is overlain by Ujhani Fm and further west it is overlain unconformably by the Lower Siwalik Fm

Regional extent


GeoJSON

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Fossils

Unfossiliferous


Age 

The geochronological dating based of Rb/Sr method carried out in the interval 3431-3433 m of Matera-1 gives an absolute age of 1600+ 15 Ma implying mid-Proterozoic (Statherian/Calymmian boundary interval for the dated level). However, this group is correlatable to those forming the Gwalior Gr series and exposed in the southern part of the basin. "Taking the dates into consideration, Absar et al. (2009) bracketed the Gwalior depositional history between 2000 and 1791 Ma." (2020, Episodes, p.148). Those exposed rocks are composed mainly of quartzite banded ferruginous shale, limestone and sandstone. Therefore, to fit Gwalior Gr, then ca. 1850-1950 Ma is used here.

Age Span: 

    Beginning stage: 
Orosirian

    Fraction up in beginning stage: 
0.4

    Beginning date (Ma): 
1,950.00

    Ending stage: 
Orosirian

    Fraction up in the ending stage: 
0.8

    Ending date (Ma):  
1,850.00

Depositional setting

The oldest post-rift cycle is a regressive cycle and represents marginal marine to shallow environments with coarsening upward units. Lagoon and bar complexes are identifiable on the seismic section. The youngest cycle is characterized by continuous to discontinuous depositional environment.


Depositional pattern:  


Additional Information


Compiler:  

Modified from Ravi Misra (Ganga, Punjab and Purnea basins; Chap. 6; ONGC Bull 44, 2009)