Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Permian stratigraphical and paleontological investigations in High Zagros Area

Document Type : Original Research Paper

Authors
Mostafa Zahedi
Mahmoud Rahmati Ilkhchi
Geological Survey of Iran
Abstract
For the preparation of the Shahre- Kord geological quadrangle map, it deemed necessary to investigate in detail two Permian sections during the mapping project. But nevertheless, older rocks constitute the Permian basement complex, including some Lower Paleozoic rock, as well.
     Detrital evaporitic deposits are vastly exposed in the area. They are stratigraphically located between Lalun Formation (Lower Cambrian), and the Mila (Middle to Upper Cambrian) with conformable boundaries. It should be noted that these soft sediments crop out mostly as salt domes and are related to the important faults of the area.
     The Mila Formation comprises the main part of the Lower Paleozoic sediments in the High Zagros area, and it is divided into three (Lower, Middle, and Upper) parts, the lower portion of the upper part, which is mainly shaley with Billingsella fossils contains 45 meters of the Ilbek Formation (Ilbek and Zard Kuh Formations are located over the Mila Formation respectively, and were previously introduced by A. Setudehnia).
   The Ilbek and Zard Kuh Formations contain Nautiloids, Brachiopods and Trilobites of Early Ordovician age. It seems that these two Formations cannot be separated lithologically and stratigraphically. Ordovician phosphatic horizons, in Chaleh Sheh area, are the same as the layers in Zard Kuh Formation. Moreover, the Lower Ordovician sequence in Chaleh Sheh, are perfectly comparable with the Ordovician sediments in Khan Kushteh, near the Ilbek valley of the Zard Kuh region.
      The overlying Ordovician sediments in Chaleh Sheh area, contain plant remains (Sigillaria persica), which for the first time aged as Upper Devonian to Carboniferous.
      We propose the name Chaleh Sheh Formation for these plant- bearing sediments, which are discovered for the first time in Khan Kushteh area. Moreover, the dip change between the Lower Permian Sandstone layers with underlying and overlying sediments is noted, both, in Chaleh Sheh and Khan Kushteh areas.
      The boundary between Faraghun Sandstone Formation and the Dalan Limestone Formation is unconformable in Chaleh Sheh and Khan Kushteh area. The fossils of Dalan Formation belong to Murghabian- Dzhulfian age. The sedimentation continued calmly during this time interval and thus, no unconformable contact is discernible.
      The Triassic rocks overlie the Permian sequence with a paraconformable contact. The absence of characteristic ammonoids, which often occur in some other Permo-Triassic sections in Iran, is considered here as due to the retreat of the sea rather than an ecological factor, as advocated by some others before.
Keywords
Paleontology
Permian
High Zagros
Subjects
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Scientific Quarterly Journal of Geosciences
Volume 4, 15-16
Spring & Summer 1995, Vol. 4,No. 15-16
Summer 1995
Pages 2-13