Diagenetic evolution of Early Eocene Chorgali Formation in the Upper Indus Basin of Pakistan: outcrop, petrographic and geochemical signatures

期刊论文
发表日期：

2025年2月28日

查看全文

Muhammad Ibrar,
Mumtaz Muhammad Shah,
Maqsood Ur Rahman,
Imran Ahmad

摘要

The study investigates the Early Eocene Chorgali Formation in the Khair-e-Murat Range of the Upper Indus Basin of Pakistan. The Chorgali Formation has previously been vastly studied for depositional settings and biostratigraphy but have not been evaluated for detailed diagenetic evaluation. Therefore, the present study is carried out to understand the detailed paragenetic sequence of the Chorgali Formation at its type locality in the Khair-e-Murat Range. Outcrop investigations were performed, and samples were collected for laboratory analyses. The collected samples were further studied for detailed petrography and stable isotope geochemistry (δ¹³C and δ¹⁸O). Field, petrographic and geochemical observations were integrated and a paragenetic sequence of diagenesis was developed. The paragenetic sequence of the Chorgali Formation shows the multiple stages i.e., cementation, micritization, compaction, dissolution, dolomitization, pyritization and dedolomitization. The dolomitization in the study section is from mimetic (preserved original depositional fabrics) to non-mimetic fabric (replaced the original depositional fabrics). The stable δ¹³C and δ¹⁸O isotope values of the dolomite matrix vary from δ¹³C (–38.87 to 0.04 V-PDB‰) and δ¹⁸O (–10.12 to –3.95 V-PDB‰) respectively. The isotope values of different calcite types of cement range δ¹³C (–35.88 to –4.76 V-PDB‰) and δ¹⁸O (–13.66 to –3.42 V-PDB‰), respectively. The isotopic values of studied samples of δ¹³C and δ¹⁸O range from (δ¹³C –9.98 to δ¹⁸O-7.84 V-PDB‰). The values are highly depleted, suggesting the meteoric origin of dolomitization. The diagenetic events range from shallow burial eogenetic to deep burial telogenetic diagenesis. The paragenetic sequence of these diagenetic events with help of filed, petrographic and isotopic signature offers insights into the pre- and post-depositional history of the studied sequence and the regional basin evaluation. Additionally, it enhances the understanding of how various diagenetic processes have altered porosity and permeability.