Biostratigraphy of the Gurpi Formation in Zagros Basin, Iran

Introdaction: The Gurpi Formation is developed in the central of the Zagros fold in Khuzestan, Lorestan and Fars provinces of southwestern Iran, defined az theZagros basin, The Gurpi refers to Gurpi Mountain in the Kuzestan province.type section gurpi,which is N of the Lali oil wells and N-E of Masjed – Soleiman city,comprises 320m argillaceous limestone and gry-to-blueshale marl(James and Wynd,1965)Although the boundary the Gurpi Formation and the underlying Ilam Formation is reported to be gradual,the altered facies found at this boundrary could be a sign of a low disconformity or even unconformity.In some place,the Ilam Formation does not exist and tne Gurpi Formation lie abave the Sarvak Formation.The upper boundry of the Gurpi Formation is more noticeable and there are different overlying formations.In Khozstan province,the Gurpi Formation is overlain by purplr shale of pabdeh Formation with signs of unconformity.The Gurpi Formation is not always concurrent. Biostratigraphy and lithological characteries of the Gurpi Formation were studied by James and Wynd (1965), Taheri (1998), KameliAzao (2002), Zarei (2005), Hematinasab (2008), Madavian (2009), Tavalaian (2011). This research study aims at describing the biostratigraphy of Gurpi Formation.In this study five stratigraphic section is investigate for its Planktonc Foraminiforal content. Method and Matrials: This study involves five stratigraphic sections from the Gurpi Formation that were measured the ticknes and determind of Litostratigrapic limit as well as recognizd of detail litostrstigray the Gurpi Formation.More than 525 thine sections were examined. Some samples from the underlying Pabdeh Formation were also analysed for comparison. then recognizd Genus and species of Planktonic foraminifera and biozones mentioned wells have been introduced. In order to the biozonation of Gurpi Formation, stratigraphic distribution of well- known foraminifora is recognizd and then biozones are established through stratigraphic column. Discussion of Results & In order to study biostratigraphy Gurpi Formation, in Wells numbers 45,21, 43, 123, 41of Marun Oil Field sections, 525 thin sections were studied. The thickness of Gurpi Formation in this Wells is 181, 186, 194, 197, 222 meters and its main lithology includes Marl, Limy Marl, Limestone and Shale. In all of the wells Lower boundary of Gurpi Formation is transition with Ilam Formation, and its upper boundary with Pabdeh Formation is unconformite accompanied by lack of stratigraphy in the length of Paleocene. In this study, alonge with recognition of 54 species belonging to 18 Genus of Planktonic foraminifera, 8 biozones mentioned wells have been introduced as follows. 1) Dicarinella asymetrica zone (Upper Santonian), 2) Globotruncanita elevata zone (Lower Campanian), 3Globotrnucana ventricosa zone (Middle Campanian), 4) Radotruncana calcarata zone (Upper Campanian), 5) Globltruncanella havanensis zone (Upper Campanian), 6) Globotruncana aegyptica zone (Uppermost Campanian), 7) Gansserina gansseri zone (Upper Companian- Lower Massrtistian), 8) Contusotruncana contusa zone (Middle to Upper Massrtistian) Based on the assemblage of foraminifer and determinate biozones, the age of Gurpi Formation in The examined wells are determined of Late Santonian to Late Maastrichtian. In this study, Gurpi Formation in of Marun Oil Field with Section samples in the region Lali (Khuzestan) has been compared and. show that the sedimentation of Gurpi Formation has been starte in Wells at Latest Santonian time, wile in the type section start at the Early Companian time.