Lithostratigraphic revision of the middle Cambrian (Series 3) and upper Cambrian (Furongian) in northern and central Iran

Abstract

Studies of stratigraphic sections of Cambrian rocks exposed in the central and eastern Alborz Mountains and in the Tabas area indicate characters that demand a revision of the upper Lower Cambrian (Series 2-Series 3 boundary interval) through lowermost Ordovician lithostratigraphy of northern and central Iran. Emended units include the Lalun and the (traditional) Mila Formation, the latter now being subdivided into the Fasham Formation (new; formerly White Quartzite, Top Quartzite, or Basal Quartzite), the Deh-Sufiyan Formation (new; essentially equivalent to the informal members 1 and 2 of the traditional Mila Formation), the Deh-Molla Formation (new; essentially equivalent to the informal members 3 and 4 of the traditional Mila Formation). Together with the lower Ordovician Lashkerak Formation and an unnamed formation, these formations constitute the Mila Group. Correlation of these lithostratigraphic units within Iran and intercontinentally are discussed with respect to both biostratigraphic and sequence stratigraphic data. It is obvious that the Lalun Formation records not only a (sub)globally recognisable regressive event towards the end of the Early Cambrian, but, in association with the Fasham Formation, also provides 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-Sufiyan and Deh-Molla formations of the Mila Group.