Carbonate deposition in accretionary prism settings: Early miocene coral limestones and corals of the Makran mountain range in Southern Iran

Abstract

The regional mapping of the Makran mountain range on behalf of the Geological Survey of Iran represents a unique coverage: the entire area of the mountain range was compiled in a unified programme. During this mapping, Miocene limestones containing rich coral and foraminiferal faunas were recorded over a strike length of several hundred kilometres, as minor developments within thick neritic clastic sequences which in turn overlie great thicknesses of Eocene-Miocene flysch. These limestones include rigid bioconstructional frame-works, loosely compacted coralline assemblages and foraminiferal calcarenites: they includein situ recfal deposits and material redeposited quite close to their original site of deposition. Most are Burdigalian, as shown by the benthonic foraminifera, but some are Aquitanian. The geotectonic setting was an accretionary prism in a zone of plate convergence. The limestones and enclosing clastic sediments comprise an intensely folded, reverse-faulted and locally dislocated sequence, the duplex structure being the result of a major Late Miocene-Pliocene episode of regional deformation. This concentration of the intense tectonic deformation in a late major episode requires a different model for this zone of plate convergence to the model widely applied to such zones. The possible controls on limestone deposition are discussed-tectonic uplift and shallowing of the sea, climatic warming and eustatic factors. Depositional features of reefal formations in the late Jurassic of the Caucasus, the Pliocene-Recent of Halmahera, and the early Miocene of SE France are discussed in comparison with the Makran model.