Geopersia 9 (1), 2019, PP. 43-63 DOI: 10.22059/geope.2018.255122.648378 Coastal foraminifera from the Iranian coast of Makran, Oman Sea (Chabahar Bay to Gawater Bay) as an indicator of tsunamis Seyed Hamid Vaziri1*, Eduard G. Reinhart2, Jessica E. Pilarczyk3 1 Department of Geology, North Tehran Branch, Islamic Azad University, P.O. Box 19585–851,Tehran, Iran 2 School of Geography & Earth Sciences, McMaster University, 1280 Main Street W., Hamilton, ON, L8S 4K1, Canada 3 Division of Marine Science, University of Southern Mississippi, Stennis Space Center, 1020 Balch Blvd., MS 3952, USA *Corresponding author, e–mail: h_vaziri@iau–tnb.ac.ir (received: 31/03/2018 ; accepted: 29/09/2018) Abstract Extreme coastal inundation associated with the 2004 Indian Ocean and 1945 Makran tsunamigenic–earthquakes highlight the risk of tsunamis to coastlines of the northern Oman Sea. Foraminifera have been used as indicators of paleotsunamis in the past where allochthonous tests, found in low–energy environments such as in coastal lagoons, ponds, and marshes, indicate marine overwash. In this study, we constrain the modern distributions of foraminifera from coastal Iran so that they may be used to identify and interpret (e.g. assess provenance) paleotsunami deposits in the geologic record. We collected surface sediment samples from sixteen sites within the study area from Chabahar to Gawater Bays on the Makran coast of Iran, selecting locations impacted by the 1945 Makran tsunami. Foraminifera obtained from these locations are dominated by supratidal, intertidal, and subtidal species, with minor abundances of planktic taxa. Samples collected from study locations are characterized by abundances of iron–stained and heavily corroded (e.g. edge rounded and pitted) individuals. Cluster analysis was used to determine three foraminiferal assemblages within the Makran coastal zone: subtidal, intertidal and supratidal. Characterizing modern distributions of foraminifera along the Makran coast of Iran will aid in identifying the provenance of older overwash deposits previously identified in this region. Keywords: Foraminifera, Coastal Sediments, Paleotsunami, Makran, Oman Sea. Introduction storm overwash because they identify Paleotsunami deposits preserved in the geological allochthonous sediments in marginal marine record provide a means of extending the known environments such as coastal lagoons, ponds, and record of events from several hundreds of years to marshes. Studies that employ foraminifera to several thousands of years, capturing both the identify marine overwash are abundant in temperate frequent and infrequent, but higher magnitude, regions (e.g. Hippensteel et al., 2000; Scott et al., events. The majority of studies on paleotsunami 2003; Hawkes & Horton, 2012; Pilarczyk et al., deposits have been conducted in temperate regions, 2012), with few studies in tropical regions with few studies in tropical regions, and even fewer (Sugawara et al., 2009; Sieh et al., 2015; Goff et in arid environments. Although the 2004 Indian al., 2011), and even fewer in arid environments Ocean tsunami and the 1945 Makran tsunami (e.g. Dominey–Howes et al., 2006; Pilarczyk & demonstrate the tsunami risk to the Makran area of Reinhardt, 2012). Tsunami deposits in arid Iran and adjacent coastlines, this area has been the environments are generally poorly preserved due to subject of few published (Mokhtari et al., 2008; high rates of deflation. The accelerated post– Shah–Hosseini et al., 2011; Hamzeh et al., depositional change in arid environments results in 2013;Okal et al., 2015) paleotsunami studies. difficulty in identifying and interpreting overwash Donato et al., (2008, 2009) and Pilarczyk et al., deposits. Foraminifera help in this regard because (2011, 2012) investigated shell layers, grain size their tests preserve well in the geologic record and distributions, and foraminifera, respectively, from their presence indicates a marine origin (Pilarczyk the 1945 Makran tsunami in Sur Lagoon (coast of et al., 2014). Oman). Numerical studies have also been done to Studies that document the modern spatial assess the tsunami risk of the Makran and adjacent distribution of foraminifera can be used as a basis coastlines (Mokhtari et al., 2008; Heidarzadeh et for comparison with overwash sediments to assess al., 2008a, 2009; Okal & Synolakis, 2008; Okal et sediment provenance (Kosciuch et al., 2018; Phat et al., 2015; Jaiswal et al., 2009; Shah–Hosseini et al., 2018). Modern distributions of various al., 2011; Payande et al., 2015). subenvironments found in western India, Oman, Foraminifera are useful indicators of tsunami and Iran, and the Persian Gulf have been extensively 44 Vaziri et al. Geopersia, 9 (1), 2019 docuemented (e.g. Murray, 1965, 1966a, b, c; Chabahar Bay coastline is mapped in order to Reddy & Rao, 1984; EL–Nakhal, 1990; Nigam & determine which species and taphonomic characters Khare, 1995; Cherif et al., 1997; Lezine et al., (i.e., surface condition of individual foraminifera) 2002; Bahalla et al., 2007; Moghaddasi et al., 2008; will be most useful in detecting and interpreting Ghosh et al., 2009; Pilarczyk et al., 2011). overwash deposition. Historical records mention several tsunamis that have impacted coastlines around the northern Regional setting Arabian Sea (e.g. events at 325 BC, 1483, 1765, The northwestern Makran coast is vulnerable to 1851, etc.; Ambraseys & Melville, 1982; earthquakes and tsunamis as a result of its Heidarzadeh et al., 2008a, 2008b; Heidarzadeh et proximity to the Makran Subduction Zone. The al., 2009), including at least six events that had a coastline stretches a distances of approximately magnitude greater than 8.0. On 28 November 1945, 1000 km between Iran and Pakistan, from the Strait a Mw 8.1 subduction zone earthquake occurred of Hormoz in the west to Karachi, Pakistan in the approximately 300 km west of Karachi, Pakistan, east. This region is part of the accretionary wedge resulting in a tsunami with wave heights ranging of the Makran Subduction Zone, formed by the from 2 to 13 m (Ambresys & Melville, 1982; Byrne subduction of the Arabian Plate under the Eurasian et al., 1992; Pararas–Carayannis, 2006). Tsunami Plate (Byrne et al., 1992; Regard et al., 2005). The run–up heights along the Iranian coast from this Makran coast is marked by a series of prominent event were variable, ranging from 0.5 m in Gordim headlands separated by bays. Further inland, Bay near the town of Konarak to 10 m in Gawater uplifted Plio–Pleistocene marine terraces and Bay near the border with Pakistan (Hamzeh et al., sandstones are undergoing intensive erosion under 2013). Death tolls associated with the 1945 tsunami arid conditions (Reyss et al., 1998). The coastline were low along the Iranian coast due to the low has been prograding since the mid–Holocene, population density that was limited to small fishing owing to both the slight tectonic uplift and marine villages (e.g. Chabahar, Lipar, Beris, and and alluvial sedimentation (Reyss et al., 1998). Pasabandar). The Iranian part of the Makran coast is a In this study, we document the surface subtropical arid region, extending for approximately distribution of foraminifera in coastal sediments 640 km from Bandar Abbas in the Strait of Hormuz along the Iranian coast between Chabahar and to Gawater on the Iranian–Pakistani border. Gawater Bays and assess whether they can be used However, this study focuses on the area between as indicators of tsunami overwash in this region. Chabahar and Gawater Bays (Fig. 1). The modern distribution of foraminifera along the Figure 1. Geomorphology map (modified from Hamzeh et al., 2014) and locations of the study sites from Chabahar to Gawater Bay, on the Iranian Makran coast, Oman Sea. Coastal foraminifera from the Iranian coast of Makran, Oman Sea … 45 The Iranian coast along the Oman Sea (Sistan maximum (Fig. 6). A scanning–electron and Baluchestan Province) can be divided into three microscope (SEM) located at the Canadian Centre main geomorphologic features: coastal platforms for Electron Microscopy at McMaster University (terraces), sand beaches, and mud flats (deltas and was used to take photographs of foraminiferal estuaries) (Hamzeh et al., 2014; Fig. 1). Coastal specimens. platforms are the most frequent landform in the area Partitioning Around Medoid (PAM) cluster and are formed by the aforementioned tectonic analysis (Kaufman & Rousseeuw, 1990) was then uplift of coastal Makran and the effect of waves used to identify biofacies within the modern upon the shoreline. Onshore sandy dunes are environment at Chabahar and Gawater Bays. The common features in the study area. Within the bays, methods of Pilarczyk et al. (2016) and Kosciuch et paleobeaches are seen as sand bands parallel to the al. (2018) were followed, where foraminiferal modern shoreline. Deltas and estuaries are formed counts (iron stained versus unstained foraminifera) by sedimentation of seasonal streams, with were first converted to relative abundances, and mangroves formed in some estuaries, such as at then standardized using z–scores. PAM cluster Bahukalat, and in parts of Chabahar Bay (Fig. 1). In analysis produces silhouette widths that indicate general, the geomorphology of coastal Makran is how appropriately a given sample is clustered. A closely controlled by the coast’s structural pattern, silhouette width of –1 indicates an incorrect weather conditions, and geological facies (Hamzeh classification, whereas a silhouette width of 1 et al., 2013). indicates perfect