Luminescence chronologies for coastal and marine sediments

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BOREAS Luminescence chronologies for coastal and marine sediments 523 Preusser et al. (2005) dated 42 samples from the coastal deposits of the Wahiba Sand Sea in Oman, using a multiple-aliquot additive-dose IRSL method, to derive palaeoenvironmental information for the late Pleistocene and Holocene. In addition to the beach sands discussed above, they collected samples from aeolianites and dune sands. The timing of three pulses of dune formation was identified: the transition from MIS 3 to 2 (34–24 kyr), the high-latitude late-glacial periods (16–13 kyr) and the early Holocene (9–8 kyr). Each of these represents an arid period during which sand supply increased due to exposure of the continental shelf. The aeolian dune formations around the coast were shown not to be synchronous with those further north and inland. This asynchroneity, and the lack of Last Glacial Maximum deposits, was interpreted by Preusser et al. (2005) as the result of deficient accumulation potential rather than reduced aeolian transport. Both the Zander et al. (2007) and Preusser et al. (2005) studies demonstrate the potential for dating coastal deposits in the Middle East to better our understanding of Quaternary climates in a region that is highly sensitive to changes in the Southwest Asian monsoon system. Mediterranean A number of studies have applied luminescence dating procedures to different types of coastal deposits in the Mediterranean over the years. Most of these studies were conducted along the coasts of Italy and Israel, with a limited number in Spain, Portugal and along the Mediterranean coast of North Africa. The studies conducted in Italy were mostly concerned with the dating of uplifted marine shorelines to help reconstruct the Pleistocene sea-level evolution of the Mediterranean Basin, assess local and regional deformation rates and evaluate regional differences in the intensity of tectonic changes. Uplifted marine deposits are found along the Italian coast at elevations ranging substantially in space and time. Balescu et al. (1997) were the first to apply luminescence dating to coastal deposits in Italy, along the Calabrian coast of southern Italy. They used alkali feldspar grains to obtain TL ages for last interglacial, shallow marine deposits at two MIS 5e (Tyrrhenian) reference sites, Ravagnese and Bovetto, where deposits occur at 129 m and 125 m a.m.s.l., respectively. The TL ages of 11613 kyr and 11612 kyr obtained after correcting for anomalous fading, confirmed their MIS 5e association. Average uplift rates of 1 mm/year were calculated for these deposits. In contrast, Federici & Pappalardo (2006) reported a single OSL age for a last interglacial beach deposit at 28 m a.m.s.l. along the Ligurian coast, resulting in an order-of-magnitude smaller, and very gradual, uplift rate of 0.18 mm/year. Along the northwest coast of Sicily, Mauz et al. (1997) reported TL ages consistent with MIS 5e at elevations of between 15 and 118 m a.m.s.l. Antonioli et al. (2006) indicated that this part of Sicily is relatively stable, with little evidence of uplift during the Holocene and uplift rates of 0.08–0.56 mm/year during the late Quaternary. These variable uplift rates along the Italian coast determined on the basis of TL ages (and independent age control) indicate, therefore, that late Quaternary tectonic movements in this region have been significantly different over small distances, resulting in a very complex tectonic history. Two further detailed studies of sedimentary successions along the central west (Tyrrhenian) and southern (Crotone) Italian coasts provided additional information about eustatic sea-level change spanning the period between the last interglacial and the end of the last glacial (Mauz 1999; Mauz & Hassler 2000). Both studies used MAAD TL and IRSL procedures to obtain ages for the different sedimentary units. Although the calculated ages were relatively imprecise due to anomalous fading and substantial measurement uncertainties, both studies indicated that the extent of eustatic sea-level change was smaller in the Mediterranean than in the open oceans, especially during MIS 3, highlighting the lack of information on Mediterranean thermohaline circulation and sea-water exchange between the Atlantic and Mediterranean sea during glacial periods. Improved precision in age control, through the use of SAR OSL applied to these extensive deposits found along the Italian coast, could make a substantial contribution towards improving our understanding of sea-level change in the Mediterranean. The complex interplay between sea-level change, tectonic activity and changing environments along the Atlantic coast near Huelva, southwestern Spain, has also been documented using OSL dating (e.g. Zazo et al. 2005). Further east, on the coast of Israel, three to five narrow linear ridges running parallel to the strandline form the most conspicuous geomorphic features on the coastal plain. These ridges consist of a series of aeolianites (kurkar), palaeosols (hamra) and beachrock, which are believed to indicate changing coastal, continental and marine environmental influences. Luminescence studies have attempted to detail the stratigraphic relations between the kurkar, hamra and beachrock, since this coastal sequence is an important archive of climate change and environment for this region. A large number of IRSL and TL ages have been determined for outcrops along the Carmel and Sharon coastal plains to estimate the formation times of kurkar and hamra (e.g. Engelmann et al. 2001; Frechen et al. 2001, 2002, 2004; Porat et al. 2004). MAAD IRSL and TL ages were calculated for outcrops along both the Carmel (Frechen et al. 2004) and Sharon (Engelmann et al. 2001; Frechen et al. 2001) coasts, with the former representing a much longer temporal sequence since
524 Zenobia Jacobs BOREAS MIS 6, including evidence of the MIS 5e high sea-level in the form of beachrock. The deposits along the Sharon coast date to o65 kyr. These TL and IRSL ages are imprecise (10–20% relative errors), however, and are commonly not in agreement with TL showing significantly more scatter than IRSL. The IRSL ages are also systematically younger; this may be a result of anomalous fading for which no corrections were made, although preliminary tests suggested no fading (e.g. Frechen et al. 2004). The lack of precision prevents reliable calculation of rates of accumulation and separation of some units, making correlation with climate cycles difficult. Along the Sharon coast, Porat et al. (2004) used a SAAD IRSL procedure to obtain ages with improved precision (5–10% relative errors). They found that all units comprising the most western kurkar ridge were deposited during the last 65 kyr, which confirmed the earlier MAAD IRSL and TL age estimates (e.g. Engelmann et al. 2001; Frechen et al. 2002). They also found that the accumulation rates of the kurkar and hamra were very different: 1–7 m/kyr and 0.1 m/kyr, respectively. Both types of deposit have relatively high carbonate contents, so the accumulation rate is the decisive factor in whether or not a deposit will result in the formation of kurkar or hamra. All kurkar units were deposited during MIS 4, but slow deposition of hamra spanning MIS 3, 2 and 1 prevents any correlation to specific climatic events. Frechen et al. (2004) suggested that more climate variations are represented in the terrestrial deposits of the Carmel coast than in those on the Sharon coast. Although neither the kurkar nor hamra formative episodes can be related to the glacial or interglacial periods of the Northern Hemisphere, they do seem to show some agreement with climate-related cycles identified in marine and terrestrial archives of the eastern Mediterranean (Frechen et al. 2004). Northwestern Europe Luminescence dating studies applied to late Holocene sand dunes in northwestern Europe have proliferated in recent times. Holocene dune fields are well developed along these coasts and constitute ‘soft’ coasts that are especially susceptible to the impact of predicted sealevel rise and increased storminess as a result of global warming. Understanding the Holocene evolution of dunes in relation to established patterns of environmental change can, therefore, provide valuable information for effective management of fragile coastal systems, including the protection of many low-lying areas in northwestern Europe. The time of formation of these coastal dunefields has been documented in a number of articles based on SAAD IRSL dating of feldspar grains (e.g. Wilson et al. 2001, 2004; Clarke et al. 2002; Clarke & Rendell 2006) or SAR OSL dating of quartz grains (e.g. Clemmensen et al. 2001a, b; Sommerville et al. 2003; Clemmensen & Murray 2006; Nielsen et al. 2006; Aagaard et al. 2007). It can be deduced from these luminescence chronologies that dune formation was episodic; periods of sand drift and dune formation alternated with periods of stabilization and soil formation. Many of these studies have suggested that dunefield development was initiated by cooler and stormy periods (i.e. increased storminess and storm surges), which may be a result of the southward displacement of polar water and sea ice in the North Atlantic Ocean, creating an increased thermal gradient that caused a number of deep cyclones to pass over northwestern Europe. This hypothesis is based, in part, on the recurrent identification of dune formation during the Little Ice Age (AD 1350–1800) in different parts of northwestern Europe (e.g. Bailey et al. 2001; Clemmensen et al. 2001b; Wilson et al. 2001, 2004; Clarke et al. 2002; Clarke & Rendell 2006). The most recent phase of coastal dune-building in northwest Europe was also identified from luminescence dating, which suggests that it typically ended 100–200 years ago (e.g. Clarke & Rendell 2006; Clemmensen & Murray 2006). The effects of global warming and ongoing relative sea-level change may also be assessed using luminescence dating techniques. Some studies have determined past changes in sea level from the construction and timing of beach ridges (e.g. Orford et al. 2003; Nielsen et al. 2006; Bjrnsen et al. 2007; Roberts & Plater 2007), whereas in other studies estuarine (e.g. Madsen et al. 2005, 2007a), mud-flat (e.g. Madsen et al. 2007b; Mauz & Bungenstock 2007) and salt-marsh (e.g. Madsen et al. 2007a) deposits have been investigated. The latter environments may be more sensitive indicators of ongoing sea-level change, as well as providing a means by which to evaluate sediment stability and budgeting in coastal estuarine and lagoonal settings. However, dating young sediments derived from such depositional environments necessitates careful investigation of the bleaching properties of the grains, the effect of changing burial depth on dose-rate estimates, and the difficulties inherent in determining water content. Madsen et al. (2005) presented a detailed luminescence study in which all these different aspects are described. Madsen et al. (2005, 2007a) also tested the accuracy of their assumptions using independent age estimates derived from 210 Pb and 137 Cs measurements. They demonstrated good agreement of OSL ages with 210 Pb and 137 Cs ages, from which they inferred that the sediments have received sufficient sunlight exposure at deposition. But they also reported that the D e values obtained from the uppermost layers were very scattered, despite largesize aliquots being used to maximize the OSL output. Scatter in D e values for such large aliquots suggests either partial bleaching or significant mixing as a result of
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Luminescence chronologies for coastal and marine sediments

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