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This study was carried out to the southern part of the Derenjal mountains, some ten kilometers north of Shirgesht village in East-Central Iran. Stratigraphy of Derenjal, Shirgesht and Niur localities indicate some Lower Palaeozoic rock units in these areas. Among the above-mentioned rock units, the uppermost part of Derenjal Formation, Shirgesht Formation and Niur Formation were studied from palynological point of view. For this purpose the upper part of the Derenjal, Shirgesht and Niur formations were systematically measured and sampled.
Based on appearance and disappearance of the identified palynomorph taxa, six acritarch biozones were established. Biozone-I appears in the uppermost part of the Derenjal Formation and lowermost Shirgesht Formation, and suggests the uppermost Cambrian to lowermost Tremadocian age.Biozones II through V occur in the Shirgesht Formation, representing the Tremadocian to Llanvirnian age. Biozone VI appears in the Niur Formation and suggests an early Silurian age for this Formation.
Therefore, there is a major "hiatus" within the Lower Palaeozoic sequence in the studied area. This appears between the Shirgesht and Niur formations and includes the upper Ordovician strata. This hiatus possibly corresponds to the Caledonian Orogeny.
In this study a palynological zonation has been established and compared with those of the other parts of the world. The comparison reveals that East-Central Iran has been a part of the Mediterranean acritarch province during the Early/Middle Ordovician age.