Depositional environment reconstruction of the Maragheh Formation, East Azarbaijan, Northwestern Iran

Abstract

The Maragheh Formation is an important deposit, which yields the savanna-type large mammal assemblage known as the “Pikermian Fauna.” Our high-resolution facies analysis of the interval between the Lower Pumice and the White Tuff demonstrated that debris-flow deposits and paleosols are dominant in the studied sequence. Fluvial channel-fill and small pond facies are the subordinate components in this interval. Most of the channel-fill deposits are interpreted as having been accumulated from ephemeral streams. The wide distribution of the Middle Pumice, the fact that it contains grains with older ages than those of the Lower Pumice, and the presence of “traction carpet” deposits allow the interpretation of the pumice interval as having been deposited from a hyperconcentrated flow probably caused by crater-lake destruction around the peak of Mt. Sahand, which supplied older rocks to the flow. The internal architecture of fluvial channel-fill deposits and the structures of paleosols (rhizoliths, cracks and slickensides: probable Vertic Inceptisols) imply a seasonal climate during deposition of the studied interval. This is consistent with previous environmental reconstructions based on mammal fossils (woodland-dominated savannah) as well as the results of phytolith analysis and δ18O data obtained from northern Iran. However, flood deposits covering the paleosols, showing sheet-like geometry, may not have been affected by large trees on the flood plain: the extent of woodland around the study site appears to have been limited.