Varves of the Dead Sea sedimentary record
Graphical abstract
Introduction
Annually laminated lake sediments (i.e. varves) are valuable high-resolution archives of past climate and environmental settings in the terrestrial realm (Brauer, 2004; Ojala et al., 2012; Zolitschka et al., 2015 and references therein). Rhythmically layered silt and clay deposits in proglacial lake environments have been first defined as varves by DeGeer (1912), who originally used them for developing the chronological framework of glacier retreat at the end of the last glaciation in Scandinavia. Later on, varve thickness and other sedimentological, biological and geochemical properties have been introduced as proxies of climate and environmental conditions (e.g., Anderson, 1961; Brauer, 2004; Zolitschka et al., 2015). With the development of additional methodologies, such as micro-facies analyses (Brauer, 2004; Swierczynski et al., 2013) and micro X-ray fluorescence (μXRF) measurements (Brauer et al., 2009; Dulski et al., 2015), seasonal deposition processes can be described and interpreted at unprecedented detail and resolution. Additional development in the application of varves for chronological purposes (e.g., Brauer et al., 2014) allows precise determination of climate change and its effects (e.g., Brauer et al., 2008) on extreme events such as earthquakes (e.g., Migowski et al., 2004), floods (e.g., Ben Dor et al., 2018; Czymzik et al., 2013; Swierczynski et al., 2012) and debris flows (Ahlborn et al., 2018).
The original definition of varves by DeGeer (1912) as clastic silt-clay laminations in proglacial lakes has been extended to describe annually laminated sediments of diverse compositions in various depositional environments. A comprehensive overview of available varve records is provided by the PAGES varve database (http://pastglobalchanges.org; Ojala et al., 2012). In addition to clastic varves, deposition of biogenic, endogenic or mixed varves has been described in lacustrine (Brauer, 2004; Zolitschka et al., 2015) and marine sediments (Schimmelmann et al., 2016), whereas in arid regions varve records exhibit different facies as clastic-organic (Anderson, 1993; Francus et al., 2013), and clastic-carbonate deposits (Dean et al., 2015).
The Dead Sea is the only hyperarid locality where lacustrine evaporitic varves have been reported thus far (Heim et al., 1997; Migowski et al., 2004; Neugebauer et al., 2014, 2015; Palchan et al., 2017; Prasad et al., 2004, 2009). While not all its sedimentary record is laminated, and not all laminated Dead Sea sediments are varves (López-Merino et al., 2016; Neugebauer et al., 2014), several floating varve chronologies have been established and corroborated in the sediments of the Dead Sea using varve counting and radiometric dating (e.g., Migowski et al., 2004; Neugebauer et al., 2015; Prasad et al., 2004).
In this paper, we review the variety of laminated Dead Sea sediments and their mode of accumulation, and illustrate their implications for palaeoclimate reconstructions. We begin with a short introduction, continued with a detailed review of the three main types of laminated lacustrine sedimentary facies of the Dead Sea: alternating aragonite and detritus (‘aad’), laminated detritus (‘ld’), and layered halite (‘lh’). We further apply a novel 2D μXRF scanning technique on exemplary segments of laminated sediments to complement micro-facies descriptions and previously available μXRF line scans. In addition, we critically evaluate the implications of the record on seasonal processes, required to interpret sedimentary sequences as varves, and further emphasize the applications of Dead Sea varves as an independent chronological tool and as proxies of past hydrological, environmental and climatological conditions.
Section snippets
Settings
The hypersaline Dead Sea fills the deepest continental depression on Earth along the Dead Sea transform in the eastern Mediterranean-Levant region (e.g., Niemi et al., 1997), where water scarcity and hydrometeorological hazards are expected to pose a significant challenge as global warming proceeds (e.g., Hoerling et al., 2012; Seager et al., 2014). It has one of the largest catchments in the Levant (ca. 40,000 km2), with high-topography escarpments to its west and east and pronounced stream
The laminated sediments of the Dead Sea
Owing to the morphology of the basin and its watershed, as well as to its unique Ca-Cl brine, and the significant hydroclimatic changes it had experienced during the geological past, the sediments of the Dead Sea comprise an exceptional variety of laminated sedimentary facies. Main lithologies include different types of evaporites, as well as siliciclastic and carbonate-rich detritus, reflecting a varied array of sedimentary processes. These include authigenic precipitation (e.g., Begin et al.,
Annual sedimentation
Because of their varied sedimentary facies, the interpretation of laminations of the Dead Sea sedimentary record as varves requires critical investigation and individual corroboration. This can be achieved by comparing varve counting in laminated sequences and radiometric dating (Migowski et al., 2004; Prasad et al., 2009). However, detailed understanding of the depositional processes responsible for varve accumulation is required in order to confirm an annual sedimentation regime. In some
Conclusions
The sedimentary characteristics of varved intervals in the Dead Sea sedimentary record were reviewed, analysed and discusses with respect to limnological observations. These sediments have a large potential to improve our understanding of the impacts of climate change in the eastern Mediterranean-Levant that is still not fully explored. Key conclusions arise:
- a.
Significant portions of the laminated sedimentary record of the Dead Sea basin were likely deposited seasonally and thus form varves, but
Acknowledgements
Y.B. and I.N. equally contributed to this manuscript. This study is a contribution to the PALEX project “Paleohydrology and Extreme Floods from the Dead Sea ICDP core” (DFG grant BR2208/13-1 and BR2208/13-2). Y. B. and Y. Enzel were funded by the Israel Science Foundation (ISF grant 1436/14). Y.B. is also grateful for a scholarship from the Advanced School of Environmental Studies, the Hebrew University of Jerusalem, and from the Rieger Foundation-Jewish National Fund program for environmental
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