Petrology of Lumshiwal Formation from Gulagah Nala Near Chinali Bridge, Abbottabad-Nathiagali Road, Hazara with Special Reference to Nandpur Gasfield, Punjab Platform
A detailed study of petrology of Lumshiwal Formation of Early Cretaceous age from Gulagah has been carried out for the first time. The objective was to study the petrography, provenance, environment of deposition and diagenesis of the Formation and to compare it broadly with Nandpur gasfield section of Punjab Platform where It is a gas reservoir.
The section of Lumshiwal Formation from Gulagah Nala near Chinali Bridge is medium to thick bedded glauconitic sandstone with intercalations of shale. This Is petrographically divisible Into 8 Internal units. The unit overlying Chlchali Formation is clay and quartz cemented quartz arenite. The other units are mainly quartz, glauconite and carbonate cemented, moderately well to well sorted, sub-mature to mature quartz arenites and shale. The maximum development of glauconite Is In the central part. Since glauconite appears to have originated from clay, the glauconite rich arenites might have originally been wackes. Some horizons are selectively cemented with flint. However intraclasts of quartz grains cemented with flint are also observed towards the top of the Formation.
Accessory tourmaline, zircon, epidote and sphene which may occur either as discrete grains or as Inclusions within quartz grains suggest an ultimate derivation from sialic Igneous metamorphic basement with minor contribution from basic sources. Granitoids were mainly S-type. However, overall mineralogy and texture suggest recycling.
The Lumshlwal Formation Indicates low energy conditions in the sub-tidal zone. The formation of glauconite itself reveals slow rates of sedimentation and mildly reducing conditions. Diagenetic history indicates the formation of glauconite, secondary quartz, feldspar and flint earlier and ferroan calcite and dolomite at a later stage. Development of stylolites in the carbonate parts and suturing of quartz grains occurred during deep burial. The last stage involves the 1Institute of Geology, Quaid-e-Azarn Campus, Punjab University, Lahore. 2 University of Oslo, Norway. 3 Building Research Station, Near Quaid-e-Azarn Campus, Punjab University, Lahore. formation of ferroan dolomite during final uplift with parts converting Into dedolomite