Reconstruction of Paleoenvironment of Ziyarat Formation, based on large benthic foraminifera (Upper Palaeocene - Middle Eocene), Alborz.

The Ziyarat Formation is an Upper Paleocene to Middle Eocene carbonate sequences, located in North of Tochal Village (south-east of Tehran), near Emam Zadeh Abdollah. The Ziyarat Formation with the total thickness of 212.5 m is conformably overlies the Fajan conglomerate and is overlain by greenish tufaceous siltstone of the Karj Formation. The age of Upper Paleocene to Middle Eocene was considered for the Ziyarat Formation at the type section. Carbonate sequences of the Ziyart Formation mainly consist of large benthic foraminifera (e.g., nummulites and discocyclina) along with other skeletal and non-skeletal components. In this formation the water depth during deposition was determined based on the variation and type of different benthic foraminifera, and other components in different facies. Microfacies analysis led to recognition of 11 microfacies that are related to 3 sub-environments such as: inner ramp, middle ramp and outer ramp. Five microfacies such as evaporite, dolomudstone, ooid intraclast packstone to grainstone, miliolidae wackestone and alveolina nummulite packstone were recognized in the inner ramp. Four microfacies such as nummulite packstone, red algae nummulite packstone, discocycline nummulite wackestone and nummulite discocycline wackestone to packstone are belong to middle ramp. And finally, two microfacies such as benthic foraminifera packstone and radiolar sponge spicule wackestone were distinguished in outer ramp sub-environment. In this study, an absence of calciturbidite deposits, reefal facies, gradual facies changes and widespread tidal flat deposits, support that the Ziayart Formation was deposited in a (homocline) carbonate ramp environment. Due to the great diversity and abundance of larger benthic foraminifera, this carbonate ramp is referred to as a "foram-dominated carbonate ramp system".