Detailed Investigation of Dolomites in the Middle Jurassic Samana Suk Formation (SMSF), Kahi Section, Nizampur Basin, NW Himalayas, Pakistan
A. Kamal1, M. M. Shah1, H.U. Rahim1,2,*, T. Zafar3, R. Khalil4, M. Shahzeb1, M. S. Ahmed5, M. Sami6,7
1Department of Earth Sciences, Quaid-i-Azam University, Islamabad 45320, Pakistan
2Earth Sciences Division, Pakistan Museum of Natural History, Islamabad 44000, Pakistan
3Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China
4Faculty of Earth Sciences, King Abdulaziz University, Jeddah 21589, Saudi Arabia
5Geology and Geophysics Department, College of Science, King Saud University, Riyadh 11451, Saudi Arabia
6Geosciences Department, College of Sciences, United Arab Emirates University, 15551, Al-Ain, United Arab Emirates
7Geology Department, Faculty of Sciences, Minia University, Al-Minia, 61519, Egypt
Ключевые слова: Dolomites, Samana Suk Formation (SMSF), Middle Jurassic, Petrography, Stable Isotopes
Аннотация
Diagenetically modified carbonate rocks are more common in the rock record. Among these modifications, multiphase dolomitization is the most common process. The Middle Jurassic carbonates of the SMSF are extensively altered by the dolomitization process in the Kahi Section, Nizampur Basin. The primary objective of this study is to investigate this multiphase dolomitization and to elucidate its possible mechanism.
Field investigation show both host limestone (oolitic, fossiliferous and massive) and dolomites. Dolomite bodies are of both bedding parallel and cross cutting the bedding planes. Different types of dolomites were recognized on the basis of color contrast as dark grey colour replacive dolomite, light grey dolomite, brownish dolomite and yellowish dolomite. Beside replacive phase voids and fracture filling cementing saddle dolomite, and cementing calcites are also recognized in the field. Petrographic studies show the complex diagenetic history of Samana Suk Formation from near surface diagenesis including micritization, neomorphism and several varieties of dolomites. These varieties are: RD1 is very fine to fine grained dolomite, RD2 is medium to coarse grained and anhedral to subhedral dolomite, RD3 is coarse to very coarse grained and planner euhedral zoned dolomite and RD4 is coarse grained euhedral to subhedral ferroan dolomite. In addition, cementing saddle dolomite SD have large crystal, curved faces with sweeping extinction. cementing calcite phases are CC1 is granular mosaic, CC2 is twin CC3 is fracture filling and CC4 is ferroan calcite. The stable isotope values of limestone (δ18O: -7.13‰ to -0.73‰ V-PDB and δ13C: -0.05‰ to 1.32‰ V-PDB) showing depletion in from the Jurassic marine signature. The multiphase dolomites RD1-RD4, SD values (δ18O: -8.65‰ to -3.16‰ and δ13C: -3.56‰ to +2.09‰) indicate multiphase dolomitization. The C1-C3 values (δ18O: -11.07‰ to -8.97‰ and δ13C: -2.14‰ to +0.76‰) indicate highly depleted values of δ18O showing its source from the hydrothermal origin. From field, petrography and geochemistry data it is deduced that possible source of the Mg for hydrothermal dolomites is through activation of faults and fractures during active tectonic regime in the area and can be related to activation and reactivation of Kahi Thrust system.
DOI: 10.15372/GiG2024127 |
