Chhidru Fm
Type Locality and Naming
Zaluch Gr - highest formation. Holotype section: Chhidru Nallah, Western Salt Range. Author: C. O. Dunbar, 1933. Reference section: None.
Synonym: Chidru Fm (spelling)
Lithology and Thickness
Sandstone. It consists of dark to grey sandy shale at the base, overlain by calcareous sandstone and sandy limestone. The top is formed by a characteristic white sandstone layer as much as 5 m thick, sandstone shows ripple marks and is hard at places due to increase in calcium content. In the softer part of this unit, the terrigenous material makes up as much as 85% of the rock.
Thickness: 64-85 m. 64 m in the type section.
Relationships and Distribution
Lower contact
Conformably underlain by Wargal Limestone Fm (transitional).
Upper contact
Overlain by Kathwai Member of Mianwali Fm of Triassic age across a paraconformity.
Regional extent
The formation is exposed in Central and Western Salt Range, as well as in SuR and Khisor Range. In Eastern Salt Range the formation has been truncated by the base Paleocene unconformity.
GeoJSON
Fossils
Brachiopods: Aulosteges, Callispirina sp., Chonetella sp., Cleiothyridina cf., C. capillata, Derbiya cf., etc. Ammonoids: Stacheoceras antiquum, Cyclolobus oldhami, Episageceras wynne, Xenodiscus carbonarius etc. The genus Cyclolobus is restricted to this formation, which has been reported from levels of 18 to 48 m below its top. Episageceras was found below the middle of the formation.
Age
Depositional setting
The abundance of terrigenous clastic material in the formation indicates a near shore environment and/or uplift of the source area. The white sandstone forming the top of the formation was subjected to subaerial erosion.
Additional Information