Petrologic Characteristics of Dolomite of Cretaceous Kawagarh Formation Khanpur Section North West Himalayas Pakistan; Evidence from Field Study, Petrography and Geochemical Studies

Abstract

The dolomite of study area belongs to the Kawagarh Formation and is exposed in the southern Hazara basin, NW Pakistan which is present in Khanpur region that is Kohi Mera village.The study area is northern deformed fold and thrust belt.Alot of local faults are present in study area ,which are Koh-e-mera thrust, Haro thrust, Bamala thrust Pakala thrust and Nathia-gali thrust. With extensive field work in the study rea and petrographic studies helped us recognize and understand the different diagenetic features and their respective effects on the attributes of the reservoir during the diagenesis. There were four types of matrix dolomite for field observation. I) D-I is a dark grey dolomite that is coarse grained crystalline in texture. (ii) D-II is slightly light grey, with a coarse grained crystalline texture. (iii) D-III is light blackish grey colored dolomite, which is fine grained crystalline in texture. iv) D-IV is a pink dolomite that is coarse grained crystalline in texture. Butcher chop weathering and parallel stylolites for bedding and other features observed in the study area. Dolomite 1 (D-I) & D-II, was formed under shallow burial conditions, evidenced by the lighter oxygen isotope values and low temperature values compare to the rest of D-III & DIV formed at comparatively high temperature with depleting oxygen under tectonic driven flow through Haroo Thrust. The studies carried out on the porosity and permeability of the dolomite showed that an increase in porosity was generated as a result of certain diagenetic phases such as dissolution, replacement and recrystallization, as well as diagenetic changes along faults, but was reduced due to the compaction and cementation processes at the late stage. In conclusion, due to percolation of Mg-rich fluids along the Haroo Fault and its splays, dolomitization took place. The potential cause of dolomitization may be the dewatering of basin fluids from the underlying siliciclastic rocks or deep and hot hydrothermal fluids.