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

Summary 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. The previously unknown corals from the limestones comprise more than 40 genera and 90 species and represent the largest recorded Miocene coral collection between the Mediterranean and Indonesia. A faunal list is provided and their significance is discussed, especially with respect to the apparent absence of higher energy assemblages. The respective influence of local ecological conditions, regional palaeogeographical setting, and late Cainozoic global change are assessed as causes of this pattern, and the latter favoured. The essential poritid-faviid character of most global coral communities remained relatively static for much of the Cainozoic notwithstanding background taxonomic turnover. Coral assemblages typical of higher energy, especially those dominated byAcropora, then appeared late in the Cainozoic alongside the older assemblages. However, a global increase in wave energy around this time is probably too na?ve an explanation and causes arising from intensification of glacioeustasy should be considered instead. Associated algae, foraminifera and molluscs are briefly discussed. The Makran fossils have especial palaeobio-geographical and palaeogeographical interest as they come from localities close to the areas of Miocene uplift which finally severed the Middle Eastern seaways of Tethys. Together with several previously recorded faunas elsewhere in Iran, their original location lay within an arm of the Miocene Arabian Sea, named here ‘The Proto-Persian Gulf’, at a palaeolatitude of about 25°N. The corals and foraminifera show an almost entirely Indo-Pacific affinity which began to emerge even before the final Zagros closure, indicative of strong biogeographical discontinuity with the early Miocene Mediterranean region.