Tobra Fm
Type Locality and Naming
Nilawahan Gr – lowest formation. Holotype section: Near Tobra village, Eastern Salt Range. Hypo: Saiyiduwali section, KR. Author: Hussain, 1967.
Lithology and Thickness
Glacial till. In Eastern Salt Range the formation consists mainly of polymict conglomerate with pebbles and boulders of igneous, metamorphic and sedimentary rocks. Based on polished and scratched boulders, Teichert (1967) interpreted the conglomerate as tillite. In Western Salt Range, it exhibits a distinctly different facies; dark-grey to black diamictic mudstones interspersed with sand-grain size to boulder size clasts; the facies is interpreted as fluvioglacial. In Central Salt Range, the lithology is different from what it is in eastern and western parts; here it is largely comprised of fresh water facies consisting of siltstone and shale with rare occurrence of boulders.
Reference section: Being suggested by Nusrat K. Siddiqui and the lithology is similar to that as in Western Salt Range; in WSR and Khisor Range the formation shows evidence of periodic intensive ice rafting of glacigene material alternation with deposits made by melt water streams.
Thickness: 20-130 m. The formation is 20 m thick at the type locality, maximum thickness of 120-130 m has been observed in Zaluch Nallah in Western Salt Range, whereas it reduces to 67 m in KR reference section.
Relationships and Distribution
Lower contact
Disconformably underlain by Cambrian and Precambrian rocks.
Upper contact
Transitional with overlying Dandot Fm in Eastern Salt Range, and conformably overlain by Warcha Sandstone Fm in Western Salt Range and Khisor Range.
Regional extent
The formation is exposed throughout the Salt Range as well as in Khisor Range. It has been encountered in wells in Potwar, in the Mianwali Re-entrant and the MR as well as the wells drilled on the PP and farther south in east Badin area.
GeoJSON
Fossils
The formation contains ostracods, fresh-water bivalves and floral remains including Glossopteris and Gangamopteris, it has also yielded spores including Punctatisporites cf. gretensis , Leiotriletes spp, Striatopodocarpites sp., Protohaploxypinus sp. etc.
Age
Depositional setting
The Central Salt Range sediments of the formation are largely lacustrine with moderate glacial influence. The Western Salt Range and Khisor Range has been the scene of intensive ice-rafting of glacial material mixed with deposits of melt-water streams, partly in marine or estuarine environment.
Additional Information
EMW: Oil and gas.