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Loralai Formation
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Loralai Fm base reconstruction

Loralai Fm

Period: 
Jurassic

Age Interval: 
Late Triassic, may extend up to Middle Jurassic (Bajocian)


Province: 
Pakistan Indus Basin

Type Locality and Naming

Alozai Gr. – upper formation. Holotype section: Zamari Tangi. Author: Hunting Survey Corporation, 1960. Reference section: None.


Lithology and Thickness

Limestone. The formation consists mainly of well-bedded limestone with shale and marl interbeds in the lower part. The limestone is dark grey to black, weathers brownish grey, thin to thick bedded, hard, argillaceous, fine grained, and sub-lithographic and breaks with conchoidal fracture. Chert lenses are developed along the bedding planes. In the upper part, it contains oolitic, pisolitic and peletal beds at places. The shale is black, grey, splintery, peppery and calcareous. The marl is greenish grey and soft. The formation being resistant than the overlying Sembar Fm, forms prominent ridges in the area.

Thickness: 150-360 m. 250 m in the type section, 360 m in the Mara Tangi and 150 m in Tazi Ketch sections.


Lithology Pattern: 
Oolitic limestone


Relationships and Distribution

Lower contact

Conformably underlain by Spingwar Fm (transitional).

Upper contact

Disconformably overlain by Sembar Fm

Regional extent

The formation is widely exposed along a long strip in the northern Balochistan between Loralai and Zhob Valley (Axial Belt). [This seems to border or be in the Sulaiman Province = southern Indus Basin?]


GeoJSON

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Fossils

Nejdia sp., Protogrammoceras sp., Phymatoceras sp. Rich in radiolarians.


Age 

Late Triassic, may extend up to Middle Jurassic (Bajocian). [NOTE by J.Ogg – the underlying Springwar is cited as " Ammonites indicate Early Jurassic age", therefore difficult to reconcile if this formation extends down to Late Triassic.]

Age Span: 

    Beginning stage: 
Pliensbachian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
192.90

    Ending stage: 
Bajocian

    Fraction up in the ending stage: 
0.5

    Ending date (Ma):  
169.54

Depositional setting

Thin bedded, radiolarian and micritic limestone suggests low energy conditions.


Depositional pattern:  


Additional Information


Compiler:  

Nusrat K. Siddiqui