The Hormuz Formation, Hormuz Series, Hormuz Evaporites or Hormuz Group is a sequence of

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

s that were deposited during the

Ediacaran The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...

(Late

Neoproterozoic The Neoproterozoic Era is the last of the three geologic eras of the Proterozoic geologic eon, eon, spanning from 1 billion to 538.8 million years ago, and is the last era of the Precambrian "supereon". It is preceded by the Mesoproterozoic era an ...

) to

Early Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovic ...

, a period previously referred to as the Infra-Cambrian. Most exposures of this sequence are in the form of emergent salt diapirs within

anticline In structural geology, an anticline is a type of Fold (geology), fold that is an arch-like shape and has its oldest Bed (geology), beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex curve, c ...

s of the

Zagros fold and thrust belt The Zagros fold and thrust belt (Zagros FTB) is an approximately long zone of deformed crustal rocks, formed in the foreland of the collision between the Arabian plate and the Eurasian plate. It is host to one of the world's largest petroleum ...

. As a result of their involvement in post-depositional

salt tectonics upright=1.7 Salt tectonics, or halokinesis, or halotectonics, is concerned with the geometries and processes associated with the presence of significant thicknesses of evaporites containing rock salt within a stratigraphic sequence of rocks. This ...

, the internal stratigraphy of the sequence is relatively poorly understood. They are the lateral equivalent of the evaporite-bearing Ara Group in the South Oman Basin.

Distribution

The Hormuz Formation is known from a wide area of the

Zagros Mountains The Zagros Mountains are a mountain range in Iran, northern Iraq, and southeastern Turkey. The mountain range has a total length of . The Zagros range begins in northwestern Iran and roughly follows Iran's western border while covering much of s ...

and around and beneath the

Persian Gulf The Persian Gulf, sometimes called the Arabian Gulf, is a Mediterranean seas, mediterranean sea in West Asia. The body of water is an extension of the Arabian Sea and the larger Indian Ocean located between Iran and the Arabian Peninsula.Un ...

. Two main depositional basins have been recognised, the North Gulf and South Gulf Basins, separated by the Qatar Arch. The basins were formed as a result of

extensional tectonics Extensional tectonics is concerned with the structures formed by, and the Tectonics, tectonic processes associated with, the stretching of a planetary body's Crust (geology), crust or lithosphere. Deformation styles The types of structure and the ...

towards the end of the

Pan-African Orogeny The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Oro ...

. The main structure formed during this period were NW-SE trending dextral (right lateral)

strike-slip faults In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

and NE-SW trending extensional faults.

Stratigraphy

Most occurrences of the Hormuz Formation are highly disturbed tectonically. However, a broad stratigraphy has been recognised.

Effect on Zagros structure

Halite layers within the Hormuz sequence form the most important decollement level within the Zagros fold and thrust belt. The presence and thickness of the halites has had a major influence on the geometry of the thrust belt and such variations has been used to explain lateral changes in structural style along the belt.

References

{{Reflist Geology of Iran Geology of Iraq Geology of Saudi Arabia Geologic formations of Iran