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AAPG Bulletin

Abstract


Volume: 55 (1971)

Issue: 8. (August)

First Page: 1280

Last Page: 1294

Title: Uppermost Permian and Permo-Triassic Transition Beds in Central Iran

Author(s): Hushang Taraz (2)

Abstract:

A continuous marine carbonate sequence (more than 2,650 m or 8,692 ft thick), commencing with the Artinskian transgression and ending with the regression of probably early Middle Triassic age, was discovered by the writer in 1967 in Central Iran near the town of Abadeh, lat. 30°55^primeN, long. 53°15^primeE.

The contacts between the different units of this sequence (referred to as the Abadeh section) are apparently transitional and continuous. Artinskian and Guadalupian fossils, mostly fusulinids, are present in the lower part of this section. In the middle part, 41.3 m (135.7 ft) of gray and red limestone compares closely with the Dzhulfian and the Permo-Triassic transition beds, including the lowermost part of the Lower Triassic beds in the region of the Dzhulfian stratotype section along the Armenian border. The upper part of the sequence represents the lower Triassic Claraia beds, locally known as "calcaires vermicules facies." The uppermost part of the section consists of 780 m (2,558 ft) of dolomite, tentatively assigned to the Lower to Middle Triassic.

For the Upper Permian and Permo-Triassic transition beds of this section, the global subdivision of the uppermost Permian has been used. As the Julfa sections, including the Dzhulfian stratotype section, are the nearest known sections of this age to the Abadeh region, a semi-detailed correlation between the Abadeh section and the Julfa sections has been attempted. This correlation established that the fossil zones in the Julfa region, assigned to the Dzhulfian Permo-Triassic and lowermost Triassic, are also present in the Abadeh section. The main difference is that the Julfa sections contain more shale, whereas the Abadeh section consists of marine limestone; hence the thickness of the Dzhulfian and Permo-Triassic transition beds in the Abadeh region is less than that of the Julfa reg on.

An abrupt change of facies occurs at the contact between the Claraia and Paratirolites beds in the Abadeh region. No trace of any detrital material was observed in this contact which would indicate an erosional and sedimentary gap. The situation at the same horizon in the Julfa region is identical. The similarity between the two regions, 1,100 km (683 mi) apart, suggests that the sharp contact and abrupt change of facies is due to a sudden climatic change, rather than to a regression and a sedimentary gap. This climatic change caused deposition of dolomitic formations in Early to Middle Triassic time in Central Iran and could be the main reason for the extinction of the stenohaline faunas and appearance of the new faunas.

In their global subdivision of the Upper Permian, Glenister and Furnish considered the contact between the Guadalupian and Dzhulfian Stages transitional. Study of the Abadeh section suggests that there is a gap between these two stages, filled by a series of about 334 m (1,096 ft) of limestone, shale, and marlstone called the Abadeh Formation, which is pre Dzhulfian and post-Guadalupian in age.

The writer proposes that this formation be recognized as representing the Abadehian Stage, between the Guadalupian and Dzhulfian Stages. The Abadeh Formation may help in the correlation of the scattered Upper Permian sections throughout the world.

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