Lower Jurassic and Cretaceous rocks in the Pol-e-Zoghal area of central Alborz have well thickness and vast expansion. The Jurassic rocks have been limited to Shemshak Group deposits which have been covered with a sequence of conglomerates, sandstone and Lower Cretaceous shale (Aptian) with a disconformity. The Dalichai and Lar formations do not exist in studied section.
Absence of these formations could be the result of emergence of the studied region from water at the end of Early Jurassic, created due to the movements of Middle Cimmerian (Batonian) Orogeny. As a result, the Jurassic-Cretaceous boundary in this section is unconformity.
Further advance of the see has occurred during Aptian period when warm climate prevailed in the region and benthic organisms, particularly Orbitolinidae family including Dictyoconus arabicus, Iraqia simplex and Orbitolina discoidea lived in the warm and shallow sea of the period. During Aptian period many volcanic activities have also occurred. Of course, there is a weak possibility that the non-formation of Neocomian and Barremian have been associated with Late Cimmerian incident.
At the end of Aptian period, the region was affected by volcanic activities followed by the subhercinian (Austrian) orogenic movements, it emerged out of water and sea environment was transformed into landmass. As the result of the latter event, the younger nonconformity strata were placed on the Aptian rocks.
Further advance of the sea has occurred during the Coniacian-Santonian period when the sea had been a favorable environment for the planktonic organisms. Of course, non-presence of Albian, Cenomanian and Turonian sediments in different sections can be attributed to the global movements of subhercynian (Austrian).
In the studied section, Coniacian-Santonian and Campanian sea has had a vast expansion and had a great depth, too. Transition from Coniacian-Santonian to Campanian has been observed with a small change in lithology. Campanian and Maastrichtian Sea had been expanded throughout the northern slopes of central Alborz and particularly in Southern Chaloos (Pol-e-Zoghal section) and has had a great depth.
Transition from Campanian to Maastrichtian in the studied region had not been accompanied by a significant incident and is observed with a small change in lithology. In Pol-e-Zoghal section, the Late Masstrichtian sea sediments have been covered by alluviums of contemporary era.
Thus, the effects of Laramid orogeny phase are not clearly visible in this region. In the present research four biozones including the Dictyoconus arabicus-Iraqia simplex Assemblage Zone, Dicarinella primitive-Dicarinella concavata Assemblage Zone, Globotruncana elevate-Globotruncana calcarata Assemblage Zone and Gansserina gansseri-Abathomphalus mayaroensis Assemblage Zone were introduced.