Studies of lithostratigarphic sections of Cambrian rocks exposed in the central and eastern Alborz Mountain and in the Tabas area indicate characters that demand a revision of the upper lower Cambrian (Series 2-series 3 boundary interval) through the lowermost Ordovician lithostratigraphy of nortehern and central Iran. Emended units include the Lalun and the (traditional) Mila Formation, the later now being subdivided into the Fasham Formation (new formerly "White Quartzite", "Top Quartzite", or "Basal Quartzite"), the Deh-Sofian Formation (newly; essentially equivalent to informal members of 1 and 2 of the traditional Mila Formation), the Deh-Molla Formation (newly; essentially equivalent to informal members of 3 and 4 of the traditional Mila Formation). Together with the Ordovician Lashkerak Formation and unnamed formation, these formation constitute the Mila Group. Correlation of these lithostratigraphic units within Iran and intercontinentally are discussed with respect to both biostratigraphy and sequence stratigraphic data. It is obvious that the Lalun Formation records not only (a) sub globally recognizable regressive event towards the ends of the Early Cambrian, but, in association with the Fasham Formation, also provide evidence for the subsequent earliest Middle Cambrian transgression that finally led to the establishment of a carbonate platform that persisted throughout the remainder of the Cambrian period, generating the deposits of the Deh-Sufian and Deh-Molla formations of Mila Group.

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