Classification of the dolomites of Cretaceous Kawagarh Formation in Hazara Basin North-west Himalayas Pakistan: Evidence from field investigation, petrographic analysis and isotopic studies

Dolomitization is a hot issue due to the fact that dolomitized successions host hydrocarbon reservoirs. Hence understanding the dolomitization process is very vital to anticipate the probable presence of dolomite bodies in the subsurface. Multi-phase dolomitization process can be best understood by investigating partially dolomitized carbonate sequences. Field observations, petrographic studies and geochemical analysis were used to understand the possible mechanism of dolomitization which reveals four replacive matrix dolomite phases (Dol-I, Dol-II, Dol-III and Dol-IV), veins and vug filling Saddle dolomite cement (SD) in partially dolomitized late Cretaceous Kawagarh formation Southern Hazara basin, North-West Himalayas, North Pakistan. Calcitization phases are also found associated with dolomite bodies including white calcite (WC) and twin calcite (TC). Brecciation, cataclastic deformation and stylolitization are other diagenetic modifications. Geochemical examination assisted in differentiating these various dolomite. Extensive range of depleted δ 18 O values (– 11.87 to – 4.23‰ V-PDB) of dolomites phases support multiphase dolomitization at numerous temperatures. Haro Thrust, along which the late Cretaceous Kawagarh formation is thrusted over Paleocene/Eocene rock units, has provide pathways to Mg-rich fluids from the underlying basinal sediments to form fault-related dolomites. In conclusion, burial hydrothermal dolomitization followed by fault related model may be the possible model that explains the mechanism for such type of dolomitization.