Facies distribution and depositional environment of Fatha Formation (Middle Miocene) in Heet area, western Iraq

The Fatha Formation, the youngest recognized formation, represents a Middle Miocene age in the study area. The Heet section, which is situated in the northeast part of Al-Anbar city, about 70 kilometres from Al-Ramadi, was sampled carefully for microfacies studies of the Middle Miocene succession of the Fatha Formation. Lithologically, this formation consists of two cyclic alternations of sandstone, siltstone, and claystone interbedded with marl, marly limestone, and gypsum with a thickness ranging from 7.2 to 4.8 meters. The details obtained from the textural and faunal properties have aided in the identification of microfacies zones, which have led to the division of the environment. Seven mixed clastic-carbonate facies types were recognized in the Fatha Formation in the Heet section. These include: Sandy Lime Mudstone, Dolomitized Lime Mudstone, Gastropods Lime Packstone, Bioclastic Lime Packstone, Claystone to Siltstone lithofacies, Marly Limestone lithofacies, and Gypsum lithofacies. These microfacies types can be grouped into four depositional environments: coastal, evaporitic, restricted to shoal environments.