Abstract
The western Makran coast displays evidence of surface uplift since at least the Late Pleistocene, but it remains uncertain whether this displacement is accommodated by creep on the subduction interface, or in a series of large earthquakes. Here, we address this problem by looking at the short-term (Holocene) history of continental vertical displacements recorded in the geomorphology and sedimentary succession of the Makran beaches. In the region of Chabahar (Southern Iran), we study two bay-beaches through the description, measurement and dating of 13 sedimentary sections with a combination of radiocarbon and Optically Stimulated Luminescence (OSL) dating. Our results show that lagoonal settings dominate the early Holocene of both studied beach sections. A flooding surface associated with the Holocene maximum transgression is followed by a prograding sequence of tidal and beach deposits. Coastal progradation is evidenced in Pozm Bay, where we observe a rapid buildup of the beach ridge succession (3.5 m/years lateral propagation over the last 1950 years). Dating of Beris Beach revealed high rates of uplift, comparable to the rates obtained from the nearby Late Pleistocene marine terraces. A 3150-year-old flooding surface within the sedimentary succession of Chabahar Bay was possibly caused by rapid subsidence during an earthquake. If true, this might indicate that the Western Makran does produce large earthquakes, similar to those that have occurred further east in the Pakistani Makran.
Highlights
The Makran coast, in southeastern in the western segment of the Makran (Iran), sits above oceanic lithosphere of the Arabian plate that is currently subducting northward under Eurasia
Our focus is on three main sites, Beris Beach, Chabahar Bay and Pozm Bay (Figure 3), which we describe separately
Dating using radiocarbon and Optically Stimulated Luminescence (OSL) yield conflicting results, we favor the OSL data because they directly date sediment deposition and are not affected by reworking issues. These results suggest that Chabahar Bay has undergone an abrupt flooding event 3150 years ago. This rapid flooding event is not consistent with (1) the tectonic uplift experienced by the coast, that tends to emerge the sedimentary system, (2) subsidence by sediment compaction, which operate over longer timescales and (3) the form of the eustatic sea-level curve, that is undisturbed since the mid-Holocene transgression (Figure 1)
Summary
The Makran coast, in southeastern Iran, sits above oceanic lithosphere of the Arabian plate that is currently subducting northward under Eurasia. In the western segment of the Makran (Iran), there is no obvious historical evidence for large earthquakes in the last 1000 years [6,7,8,9]. It is currently unclear whether the lack of seismicity reflects a different mechanical behavior at the subduction interface, or if infrequent large earthquakes occurred in the past and should be expected to happen again [10,11,12]. We apply some concepts of coastal evolution to the Makran coast, coupled
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