Authors(s): Anni Rani Das, Meghali Baruah*, Mrinal Kanti Pathak, Devesh Walia and Shikhar Kumar
Date of Publication: January, 2025
Publication reference: J. Ind. Geophys. Union, 29(1) (2025), 12-25
Abstract:
Early Eocene Umlatdoh Limestone of Sylhet Limestone Group have been studied to understand their framework constituents and diagenetic processes. Additionally, an approach was made to infer the depositional environment of this limestone based on the abundance of biogenic assemblages. Two vertical profile sections were measured and representative rock samples were collected for petrographic study. The limestones of the study area are classified as wackestone, packstone and grainstone, dominated by calcareous green algae (Dasycladalean algae) and large benthic foraminifers. An open lagoonal to proximal middle shelf environment has been envisaged during the deposition of the studied limestone. The diagenetic overprints of these limestones are characterized by several key diagenetic features, including micritization, cementation, compaction, dissolution and neomorphism. These diagenetic processes occurred in marine phreatic, meteoric phreatic, mixed meteoric phreatic, and burial diagenetic environments. Micritization of allochems, cementation by isopachous and granular calcite, neomorphism, and bioclast recrystallization occurred during meteoric-phreatic diagenesis. Meteoric-vadose diagenesis led to extensive dissolution and the infilling of fractures with sparry calcite. During burial diagenesis, blocky calcite cementation appears to have become prominent.
Keywords: Umlatdoh Limestone, Meghalaya, Petrography, Diagenesis, Depositional environment