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Pirzal Perched syncline

In the Kohgiluyeh and Boyer Ahmad province in the southwest of Iran, along the road of Dehdasht to Sarfariab city, when pass through the pirzal gorge, we enter to the plain between the two mountains “Siah” and “Mondon”. The two mountains, Siah and Mondon, are anticlines that extend along the northwest to the south-east. In the plain between the two anticlines, there is a beautiful perched syncline.

Syncline is a geologic feature like a “V” fold in layered sedimentary ground, which often occurs when the layers tend to go horizontally, but twisted by the tectonic forces. In analogy, an “anticline” is the convex opposite form, where the sedimentary layers form a dome, and a “monocline” is flat.

A “perched syncline”, or “perched synclinal”, differenciates itself by the fact it stands elevated from the surrounding terrain. Contrary to the monoclines, they form very characteristic mountains, looking like fortresses surrounded by walls.

In fact, a perched syncline is formed when the central layers of syncline (younger) have more resistance than the outer layers (older) against erosion. In this case, the outer stones are eroded and the strong rocks remains in the center. These strong rocks remain in the form of a ship stands elevated from the surrounding terrain and form a perched syncline.

In center of Pirzal perched syncline, thick to medium bedded limestone (Asmari formation – Oligomiocene in age) and on the sides, alternation of Marl and thin bedded limestone (Pabdeh formation – Eocene to Oligocene) have been outcropped. Over the time, marls have been eroded, and strong limestones remain in the center.

This beautiful photo was taken by M.S.Zangeneh looking northward.

Keywords: Iran , Kohgiluyeh , Zagros , Anticline , Syncline , Perched syncline , dehdasht , sarfaryab , geology , geotourism , asmari formation , pabdeh formation , mondon anticline , kuh e siah anticline , pirzal gorge , zamingasht

Asmari formation

The Oligocene–Miocene Asmari Formation of the Zagros Basin is a thick sequence of shallow water carbonate. Asmari formation is the youngest and most important reservoir rock of the zagros Basin in the south-west of Iran.

The Asmari formation has been divided into two members: one is the Sandstone Member of Ahwaz in the south-west of the Khuzestan area and the other one is the Evaporate Member of Kalhor in the Lorestan Province. This formation is divided into three units: the lower Asmari with an Oligocene age, the Middle Asmari with an Aquitanian age, and Upper Asmari with a Burdigalian age. However, these divisions do not exist everywhere.

Also, in some parts of Iran, the lower boundary of Asmari formation is in contact with the Pabdeh Shale formation which is of Paleocene-Oligocene age, but in central Lorestan this formation is overlying the Late Eocene Shahbazan formation and in internal Fars it show a paraconformable contact with the Jahrum formation (Eocene).

The Asmari formation is covered by anhydrites of the Gachsaran formation which is of Early Miocene age, and in internal Fars the upper boundary of Asmari formation is in contact with the Early Miocene Razak formation.

The photo shows the Asmari limestone formation (As) and Gachsaran formation (Gs) Along the shore of Karun 4 Lake Dam near Lordegan city in Chahar mahal va bakhtiyari Province.

Keywords: Asmari formation , Bakhtiyari formation , Gachsaran formation , Geotourism , Iran , Iran Geology , Iran Geotourism , Pabdeh formation , Zagros Mountain , zamingasht