LATE CRETACEOUS TECTONIC AND SEDIMENTARY EVOLUTION OF THE BANDAR ABBAS AREA, FARS REGION, SOUTHERN IRAN
1 IFP, 1and 4, avenue de Bois-Préau, F-92852 Rueil-Malmaison Cedex, France; and Université de Provence (Aix-Marseille 1), Carbonate Systems and Reservoir Geology Laboratory EA 4229, Case 67, 3 place Victor Hugo, F-13331 Marseille Cédex 3, France.
Current address: NIOC Exploraton Directorate, Tehran, Iran.
*corresponding author, email: a.piryaei@niocexp.ir
2 VU University Amsterdam, Faculty of Earth and Life Sciences, Department of Sedimentology and Marine Geology, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands; and Delft University of Technology, Department of Geotechnology, Delft, Netherlands
3 Université de Provence (Aix-Marseille 1), Carbonate systems and reservoir geology laboratory EA 4229, Case 67, 3 place Victor Hugo, F-13331 Marseille Cédex 3, France.
4 IFP, 1 and 4, avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France; current address: Maersk Oil, Esplanaden 50, 1265 Copenhagen, Denmark.
The Upper Cretaceous succession in the SE Zagros (Bandar Abbas area) is characterized by marked changes in facies and thickness. These changes relate to sediment deposition in a foreland basin along the NE margin of the Arabian plate. The succession was measured at eight outcrop sections in the Khush, Faraghun, Gahkum, Genow and Khamir anticlines. The measured sections illustrate a transition from shallow-water carbonate platform deposits (Cenomanian to Coniacian) to deep-water facies (Santonian to Maastrichtian). Outcrop observations were compared to data from ten off- and onshore wells and to a series of seismic profiles.
Four cross-sections were constructed using well and outcrop data and illustrate facies and thickness variations within the Upper Cretaceous. Based on these regional profiles, the Late Cretaceous depositional history of the Bandar Abbas area was reconstructed and can be divided into two tectono-sedimentary phases suggesting a transition from a passive to an active margin.
Sedimentation during Phase I (late Albian to Coniacian) took place in shallow-water carbonate platform and intrashelf basin settings (Sarvak Formation), and four third-order sequences can be recognised. The uppermost sequence is locally capped by fresh-water, pisolith-bearing carbonate sand and conglomerates with local laterite and palaeosols of the Coniacian Laffan Formation. Shallow-water facies consist mainly of wackestone to packstones with abundant benthic foraminifera. Sediments deposited in intrashelf basins are dominated by oligosteginid-bearing facies. Eustatic variations in sea level, the creation of a foreland basin and salt tectonics most probably controlled patterns of sedimentation during this phase.
During the second tectono-sedimentary phase (Phase II: Santonian to Late Maastrichtian), sediments were dominated by pelagic marls and gravity flow deposits. Lateral thickness variations become more marked to the NE as a result of obduction processes and the creation of the foreland basin.
Allochthonous ophiolitic and radiolarite-bearing units are common in the northern part of the Fars region but are restricted to a few localities in the Bandar Abbas area. Traces of allochthonous materials occur in the SE-most part of the Khush anticline; thrust slices in offshore seismic profiles may link to the Hawasina nappes of Oman. At the top of the Phase II succession, pelagic facies locally interfinger with Omphalocyclus and Loftusia-bearing facies (Tarbur Formation) and evaporites (Sachun Formation). These deposits are overlain by slumped and dolomitized shallow-water carbonates of the Paleocene – Eocene Jahrum Formation.
The sedimentary sequence in the Bandar Abbas area illustrates a far-field response to Late Cretaceous obduction processes and foreland basin development, as well as to halokinetic activity. Rapid variations in thickness and facies document the evolution of depositional processes in the foreland basin.
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