Revision of the foraminiferal biozonation scheme in Upper Cretaceous carbonates

Appraisal of intra reservoir barriers in the Permo-Triassic successions of the Central Persian Gulf, Offshore Iran
July 15, 2018
MAPSA 19th anniversary
July 21, 2018

Revision of the foraminiferal biozonation scheme in Upper Cretaceous carbonates

Abstract
Cretaceous carbonate successions of the Bangestan Group, such as the Sarvak and Ilam formations, are among the most prolific hydrocarbon
reserves of the Middle East. However, relatively little is known about their detailed palaeontology and biostratigraphy. Moreover, due to itho-
logical similarity of these carbonate formations recognition of  their boundaries in subsurface studies is problematic. To investigate these units, biostratigraphic analyses were carried out on nearly 1100 mofcores, including core plug samples and thin sections prepared from five giant and supergiant oilfields in the northern and southern Dezful Embayment, SWIran. Accordingly, 59 species of foraminifera  (assigned to
43 genera) as well as  11 species of non-foraminifera (10 genera) were recognized. As a result,  three  biozones were identified, which in
stratigraphic order are:  Nezzazata -Alveolinids Assemblage Zone; Moncharmontia apenninica – Nezzazatinella – Dicyclina Assemblage Zone;
and  Rotalia skourensis -algae Assemblage  Zone. These are compared with the Wynd’s (1965)  biozonation scheme, previously introduced in
the Zagros area, and a revised scheme is  presented.Accordingly, a Cenomanian–Turonian age and a Coniacian–Campanian age are envisaged for the Upper Sarvak and Ilam formations, respectively. In our new biostratigraphic scheme, the Sarvak–Ilam formations boundary is considered to be located above the Monchar-  montia apenninica – Nezzazatinella – Dicyclina Assemblage Zone (equivalent of Valvulammin a- Dicyclina Assemblage Zone of Wynd, 1965), that is Turonian in age.
This zone is bounded by two palaeoexposure surfaces, which correspond approximately to the C–T boundary transitional interval and apost-Turonian, which can be possibly assigned  to the  Coniacian. Significant sedimentological features of these  disconformities include bauxitic–lateritic horizons, karstified profiles and solution-collapsed  breccias.Geochemical signatures of thesen meteorically altered surfaces are also considered to  calibrate biofacies  and biozones. Finally, we compared our new
biozonation scheme with  other studies in neighboring areas of SW Iran and the Middle East. ©  2014 Elsevier Masson SAS.
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