Revision in nomenclature and classification of the Neogene marl deposits: A case study from south and southeast of Tehran

Marl is a type of mixed carbonate–silicate sediment and contains clay and carbonate minerals deposited in different environments. The terms marl and marlstone are still imprecisely used in geology. I n this study, to revise the nomenclature and sedimentary classification of marl deposits, 99 samples were taken from different terrestrial and marine marl formations. The texture and percentage of carbonate and salt contents in the marls were measured. According to Folk's classification, the majority of the samples are in the range of sandy silt, sandy mud, silt, muddy sand, and silty sand. Based on the electric conductivity parameter (EC), all samples have a high content of salt and are classified in saline and very saline classes. The results based on the classification method of Haldar and Tisljar also confirm that most of the samples are in the category of "calcite clayey siltstone", clayey calcite siltstone, and “calcite-silt clay” and a few examples are "calcite – silt clay” and clayey- silt limestone, except for one sample of the Kond Formation, which is within the marl field. The main samples are not classified by the Pettijohn method and samples are mostly silty, and muddy and the name chalk-salt siltstone and mudstone were found to be more suitable for the terrestrial marl deposits under investigation in this research.