Diagenetic history of Cretaceous sandstones of the Neyzar Formation, Kopet-Dagh Basin, NE Iran: a case study of albitization

The Cretaceous Neyzar Formation, more than 300 m thick, was studied from 21 sandstone thin sections using the polarizing microscope, scanning electron, and hot-cathode cathodoluminescence microscopy to determine the petrography and diagenetic processes. Most samples are arkose, lithic arkose, and rarely subarkose and feldspathic litharenite, derived from tectonic elements of recycled orogens, dissected arcs, and passive margins. Petrographic and BSE results indicate that diagenesis was dominated by carbonate cementation (calcite, ankerite, and dolomite), compaction, fracturing, and albitization. BSE and HC-CL images show that, in places, albite partially replaced detrital K-feldspar and was a significant diagenetic process for the formation. Saline pore waters probably accumulated sodium for albitization during the transition from smectite to illite and chlorite, and sodium may also have originated from the dissolution of detrital albite. According to the suite of diagenetic processes observed, the temperature at the base of the Neyzar Formation may not have exceeded 100°C. © 2021, Saudi Society for Geosciences.