Cretaceous Sedimentation Patterns in the Zagros of Southwest Iran: A Geomodel
V. Vedrenne1, D. Baghbani2, F. Gaumet1, D. Granjeon1, F. Keyvani2,
S. Lopez1, D. Morsalnejad2, F. Van Buchem1, B. Vincent1, and M. Yavari2
1 Institut Français du Pétrole, Rueil-Malmaison, France
2 Exploration Department, NIOC
An integrated biostratigraphic, chemostratigraphic and sequence stratigraphic study of the Cretaceous mixed carbonate/siliciclastic System in the Zagros of SW Iran (Lurestan, Khuzestan, Fars and Offshore) has resulted in a 3rd order sequence time framework with a resolution of 2 to 3 My. This time framework allowed to unravel the complex Cretaceous history which is characterised by the alternation of carbonate platforms and intrashelf basins, periods of siliciclastic influx, shifting depocenters, and major basin re-organisation. This sedimentation pattern is represented in a three-dimensional geomodel, constructed with detailed palaeogeographical and isopach maps, and infilled with a stratigraphic forward modeling program (DIONISOS).
Extensive sedimentological work on the excellent outcrops of the Cretaceous rocks in the Zagros Mountains in SW Iran, in combination with biostratigraphic work on ammonites, pelagic foraminifera and Orbitolinids, and C and O isotope curves, have led to the definition of 15 3rd order sequence boundaries and corresponding flooding surfacesin an area of 30.000 km2. This high resolution time framework allowed to reevaluate the stratigraphic relationships between the major rock units which vary in thickness from several thousand meters in Lurestan to several hundred meters in Fars.
A general subdivision of the Cretaceous succession in 4 stages is proposed, each of them characterised by a specific 1) ecosystem of carbonate producing organisms, 2) architecture of the carbonate systems, 3) tectonic context, and 4) palaeogeography. In order to test the coherency of our interpretations a 3 dimensional geomodel has been constructed, and different infill scenarios have been tested with stratigraphic forward modeling software.