BIOSTRATIGRAPHY AND REGIONAL ASPECTS OF THE TARBUR FORMATION (MAASTRICHTIAN) IN CENTRAL ZAGROS, SOUTHWEST IRAN

Abstract

The aim of this study is to investigate the biostratigraphy and regional stratigraphy of the Maastrichtian deposits (Tarbur Formation) in the high outreaches of the Zagros Mountains in Chahar Mahal and Bakhtiyari Province, southwest Iran. The thickness of the investigated sequences is about 600 m in Tang-e-Vanak, 156 m inTang-e-Zendan,and 111 m in Kuh-e-Dozdaran sections. Shale and marls of the Gurpi Fm. (Campanian) mark the lower lithostratigraphic limit of the Tarbur Fm. in Kuh-e-Dozdaran section, whereas its upper limit is disconformably distinguished by the dolomitic Jahrom Fm. (Eocene). The Tarbur Fm. in Tang-e-Vanak andTang-e-Zendansections overlies the clastic Amiran Fm. (Maastrichtian) and is truncated with a sharp disconformity by the white dolomites of Shahbazan Fm. (Eocene). Biostratigraphically, the Tarbur Fm. is characterized by a Loftusia-Omphalocyclus assemblage zone, indicating a Maastrichtian age. Within this biozone, three regional subbiozones are proposed. They are: the Loftusia arabica range subzone , the Loftusia persica interval subzone , and the Loftusia baykali interval subzone . Based on the foraminiferal content, the age of the Tarbur Fm. in Kuh-e-Dozdaran section is assigned to the lower-middle parts of the Maastrichtian. Likewise, the Tarbur Fm. in Tang-e-Vanak and theTang-e-Zendansections is Maastrichtian in age, possibly extending locally into the Paleocene. The identification of the biostratigraphic limits of the Tarbur Fm. in the studied areas assists the reconstruction of the sedimentary basin in the Late Cretaceous.