Rasoul Sorkhabi¹, Akihiko Okui², Mohammad R. Kamali³, Bahauddin Hamdi⁴

(1) Japan National Oil Corporation, Technology Research Center, Chiba, Japan
(2) Japan National Oil Corporation, Chiba, Japan
(3) Research Institute of Petroleum Industry, National Iranian Oil Company, Tehran, Iran
(4) Geological Survey of Iran, Tehran, Iran

ABSTRACT: Deep Iran: Tectonostratigraphy, paleogeography and source rock potential of Paleozoic shale beds in Iran

The Paleozoic shale beds in Iran have often been neglected for exploration even though similar rocks in Oman and north Africa are major sources rocks for oil and gas. Worldwide, the organic-rich Paleozoic rocks account for almost a quarter of effective source rocks. We first synthesize the available data on Paleozoic shale beds in Iran in terms of their stratigraphic distribution and correlation, paleobasin tectonics and paleogeography, and secondly make an assessment of their source rock potential. The Cambrian-Carboniferous succession in Iran developed on a Paleozoic Tethyan passive margin along north Gondwana, and was affected by extensional tectonics, epeirogenic movements and eustatic changes. We concentrate on southwest Iran (Zagros), central Iran, and north Iran (Alborz), and particularly discuss the following shale horizons: Upper Shale of Soltanieh formation (Tommotian, Alborz); Barut shale in the whole Iran (Lower Cambrian), Ilbyk shale of Mila Group (Upper Cambrian, Zagros), the graptolite-bearing shale deposits of Zardkuh (Zagros), Shirghesht-Zarand (Central Iran) and Lashkarak (Albroz) Formations (Ordovician); Gahkum and Sarchahan shale (Zagros, Lower Silurian); Niur shale (Central Iran, Upper Silurian), Shishtu and Sardar shale deposits (Central Iran, Carboniferous), and Mobarak shale (Lower Carboniferous, Alborz). The available data of total organic carbon (TOC) indicate that the dark-colored Gahkum shale (TOC=1-4.3% with kerogen type II) in southern Iran and the Mobarak shale (TOC >3.1% with kerogen types II and III) in northern Iran are suitable source rocks for petroleum. Indeed, some of Iran*fs gigantic Permian-Triassic reservoirs may have filled from the Paleozoic source rocks.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado