Abstract:
The Sirban Member of the Abbottabad Group at Mirpur Section, Abbottabad
District is selected for research study. Research is based on petrographic analysis
comprising of microfacies and geochemical study. The Sirban Member exposed in the
study area having a thickness of 240 to 485 m, with lower part sandy, followed by thick
sequence of dolomite imbricated with sandstone, shale, limestone, quartzitic sandstone and
chert. During the field the features observed in the study area including chert bands, calcite
veins, fractures, stylolites, dissolution, butcher-chop weathering. The petrographic study of
the Sirban member reveals different phases of matrix and cement dolomite and diagenetic
events have also been identified, including chertification, mechanical compaction,
brecciation, stylolization, quartz influx, several stages of fracturing and dolomitization. The
paragenetic sequence is developed for Sirban Member revealing the history. In the dolomite
D1 the oxygen isotopic signatures of the Sirban member ranges from -2.97 to -3.22‰ VPDB while carbon signatures varies +2.42 to +1.83‰ V-PDB. Whereas, dolomite D2 in
Sirban member shows oxygen and carbon values ranges from -4.12% to -3.57% V-PDB
and +1.11% to +2.05% V-PDB respectivelly. Similarly the dolomite D3 in Sirban member
shows oxygen values that varies from −6.49 to −7.07‰ V-PDB and carbon signatures
+2.14 to +1.66‰ V-PDB . This means that these values lies in cambrian marine signature
and show dolomatization has occured through the same fluids.Atomic Absorption shows
values of different element like Iron (Fe), Manganese (Mn), Strontium (Sr) and Sodium
(Na) in three types of dolomite.Based on field study petrography elemental geochemistry
and stable isotopic signature it may be possible that the dolomite is formed by evaporation
and subsequent reflux dolomitization.
