Introducing the Mid-Kimmerian Tectonic Event in Iran

A closer look at the Alpine tectonic events reveals that the first upheavals occurred in Middle Triassic resulting in significant changes in paleogeographic conditions of Iran. Consequently, these movements transformed the Late Precambrian-Middle Triassic prevailing platformal settings into lagoonal-lacustrine settings. In addition to paleogeographic changes, the Middle Triassic tectonic movements resulted in folding, emplacement of intrusive bodies and metamorphism that are referred to as Early Kimmerian event in the literature. Many geologists are of the opinion that the second Alpine tectonic event has taken place at the Jurassic-Cretaceous boundary and was accompanied by folding (in Central Iran), formation of paraconformities (in Alborz, Kopet Dagh and Zagros), emplacement of intrusive bodies, and metamorphism. This latter event is known as Late Kimmerian tectonic event. Geological investigations on the west of Tabas show that the sedimentological characteristics of the successions occurring between the Early and Late Kimmerian events allow their division into two separate sedimentary cycles (Aghanabati, 1972). The lower cycle is dominated by fossiliferous shale and sandstone with coal intercalations, which points to lagoonal continental environments of deposition, while the upper cycle mostly comprises marl and limestone characterized by marine fossils (e.g. ammonites) of moderate depths. The first cycle has developed during Late Triassic-late Early Jurassic (at places up to early Middle Jurassic), whereas the second spans over Middle Jurassic-late Late Jurassic). The boundary between the two cycles is marked by an event (Aghanabati, 1975) that has caused development of paraconformities, angular unconformities, igneous activity and metamorphism in different parts of Iran, thus proposed as Mid-Kimmerian event.