BIOSTRATIGRAPHY OF THE ILAM FORMATION IN HALEGAN WELL, SOUTHERN IRAN

Halegan oil well is selected in order to study the biostratigraphy of Cenomanian to lower Companian sediments in the southern Zagros mountain, southern Iran. The sediments are consisted of limestone sequences of upper parts of the Sarvak and lower parts of the Ghorpi Formations, that overlay disconformably top of the Sarvak Formation and paraconformably underlay the Ghorpi Formation. Based on microscopic studies, six planktonic genus and eleven planktonic species along with eight benthonic genus and seven benthonic species and eight samples of non-foraminifera were distinguished. Based on studies by Martinez (2009), among distinguished benthic foraminifers, four genus and five species of rotallid like-form are reported for the first time from the Halegan well in this study. Based on distinguished benthic foraminifers, middle to upper Cenomanian age for the Sarvak Formation, Cantonian age for Ilam Formation with interfingering of the Ghorpi Formation marls and early Companian age for lower part of the Ghorpi Formation are prposed. Based on foraminifers stratigraphic distribution and comparison with biozones of Martinez (2009), four biozones are introduced for Cenomanian and Cantonian sediments. Based on distinguished zones, Cantonian sediments are divided into lower, middle and upper parts for the first time in this study. The introduced foraminifers show that there are no Tronian and Coniacian sediments in the studied area.

Boix, C., Villalonga, R., Caus, E., and Hottinger, L., 2009. Late Cretaceous rotaliids (Foraminiferida) from the Western Tethys. Neues Jahrbuch für Geologie und Paläontologie 253, 197-227.