Quaternary marine terraces and tectonic uplift rates on the south coast of Iran

Abstract

Abstract A survey of 1500 km of the Iranian coastline, from Bushehr (Persian Gulf) to the Pakistani border, made it possible to visit several sequences of raised marine terraces, some of which (especially on the Makran coast) had already been described by previous workers. As many as 18 marine terraces, up to 220 m in altitude, were identified on Qeshm Island and as many as 19 levels, up to 246 m in altitude, near Chah Bahar. Though in situ coral heads and fossilized marine shell deposits exist in many uplifted areas, only a few samples, mainly from elevations lower than 30m, appeared to be unrecrystallized and thus suitable for radiometric dating. Six uranium-series analyses of aragonitic corals from Haleh, Jazeh and Qeshm Is. gave apparent ages between 100 and 140 ka bp , in some cases demonstrating that previous radiocarbon dates between 20 and 40 ka bp had to be considered minimum ages. This made it possible to estimate that average uplift rates since the last Interglacial period had been about 0.2 mm/year, i.e. one order of magnitude less than most previous estimates. Radiocarbon dates suggest almost uniform emergence of 2–4 m since mid-Holocene times along most of the coastal sectors investigated. This is in agreement with the 2–3 m emergence predicted by glacio-hydro-isostatic models in this area if an uplift rate of about 0.2 mm/year is also taken into account. Near a salt dome on Qeshm Is., however, a much faster uplift rate of about 6 mm/year was documented for the period between 6 and 5 ka bp but only over a limited area.