U-series and oxygen isotope chronology of the mid-Pleistocene Lake Amora (Dead Sea basin)
Introduction
The Quaternary climate is characterized by cyclic shifts between different combinations of cold, warm, humid and dry conditions at various sites and time scales. These changes are recorded in many geological archives such as ice cores, deep-sea sediments, coral reefs, speleothems and lacustrine sedimentary sequences.
The paleo-climatic exploration of these archives, requires the establishment of reliable and precise chronologies, which beyond the radiocarbon time scale (∼50 ka) are usually obtained by U-series methods (e.g., Broecker, 1963, Edwards et al., 1987, Ludwig et al., 1992, Winograd et al., 1992, Stein et al., 1993, Kaufman et al., 1998) or luminescence-based techniques (e.g., Stokes, 1999, Lian and Roberts, 2006). The best targets for U-series dating are probably corals (Edwards et al., 2003) and speleothems (e.g., Wang et al., 2001, Bar-Matthews et al., 2003, Richards and Dorale, 2003) although even there, contamination by detrital material and diagentic effects should be considered (Thompson et al., 2003, Villemant and Feuillet, 2003, Lazar et al., 2004). In the case of lacustrine carbonates, U–Th dating is hampered by the need to correct for both detrital additions of U and Th and for the presence of initial (hydrogenous) Th (Kaufman, 1971, Kaufman, 1993, Lin et al., 1996, Israelson et al., 1997, Kaufman et al., 1992, Haase-Schramm et al., 2004, Stein and Goldstein, 2006). Contrary to the 230Th–234U and 231Pa–235U methods, which are only applicable for sediments younger than ∼500 and 200 ka, respectively, the 234U–238U disequilibrium method can be used to extend the datable range up to 1 Ma (Cherdyntsev, 1971, Ludwig et al., 1992, Richards and Dorale, 2003), although it depends on a good knowledge of the initial 234U/238U activity ratio. Additional chronological constraints can be obtained from the reconstruction of changes in the stable isotopes, chemical ratios or paleontological marine records, and correlating them to the well-known changes in Earth’s orbital parameters. In the case of continental records (e.g., Winograd et al., 1992, Tzedakis et al., 2003) such a correlation is not as straightforward because the sea–land climate connection is not always understood or is not strong. Studying the nature of this connection is a pre-requisite for the correlation of continental and marine records (e.g., Kolodny et al., 2005).
In this study we set out to establish a chronological framework for the mid to late Pleistocene Amora Formation (Fm), deposited in the lacustrine environment of the Dead Sea basin (DSB) (Fig. 1, Fig. 2). Together with its successors (Lake Lisan and the Dead Sea), this sequence of sediments comprises one of the longest records of its kind.
Most investigations of lacustrine records have focused on late Pleistocene and Holocene time scales (i.e., 50 ka). There are only a few examples of lacustrine sequences extending several hundreds of thousands of years back in time such as the Burmester core in the Bonneville basin, Utah (Eardley et al., 1973, Oviatt et al., 1999) and Lake Baikal (Prokopenko et al., 2006). These records, however, were obtained from drill cores that provide limited information on field relations and spatial variability. In the case of Lake Amora, a unique tectonic setting (see below) resulted in the uplift and surface exposure of the sedimentary record over a wide area, enabling a better impression of the sequence, high accessibility and relatively easy sampling.
The study of the limnological history of the DSB lakes is important because they are “amplifier lakes”, i.e., their water level responds sharply to climatic changes (Street-Perrott and Harrison, 1985), therefore reflecting changes in regional climatic–hydrologic conditions that can be correlated to global changes (Bartov et al., 2003, Haase-Schramm et al., 2004). Lake level fluctuations are identified through changes in the sedimentary and chemical composition of the sediments (Neev and Emery, 1967, Begin et al., 1974, Katz et al., 1977, Stein et al., 1997) and their mode of sedimentation (Machlus et al., 2000, Bartov et al., 2002, Bartov et al., 2003). The Dead Sea Group (Sedom, Amora, Lisan and Ze’elim Formations; Fig. 1) was so far dated by radiocarbon (Schramm et al., 2000, Ken-Tor et al., 2001, Migowski et al., 2004, Migowski et al., 2006) and the 230Th–234U method (Kaufman, 1971, Kaufman et al., 1992, Schramm et al., 2000, Haase-Schramm et al., 2004, Waldmann et al., 2007). The lake’s chronology is presently available for the past ∼130 ka, with a few ages reaching ∼300 ka. Beyond that time, the DSB lacustrine bodies have not been directly dated. Based on stratigraphic considerations, Zak (1967) suggested that the Sedom lagoon existed between the late Pliocene and early Pleistocene, and that the age of the Amora Fm. is between ∼1 Ma and ∼100 ka.
Section snippets
The Pleistocene Lake Amora
The history of water bodies in the DSB began with the ingression of the Mediterranean Sea during Pliocene times (the Sedom Lagoon; Zak, 1967). The interaction of the evaporated seawater filling the Sedom lagoon with the carbonate wall-rocks of the Dead Sea rift valley together with sulfate reduction led to the production of a Ca-chloride brine, which played a major role in the subsequent evolution of the lacustrine bodies (Starinsky, 1974). After the disconnection of the Sedom Lagoon from the
Field work and sample preparation
Field samples approximately 20 × 20 × 20 cm in size were collected from the Amora Fm. exposures at AC and PZ2 sites, wrapped in plastic coating to avoid disintegration and transported to the laboratory.
Approximately 5 g of selected laminae (aragonite, detritus, gypsum and anhydrite) were scraped separately and collected. Following grinding and homogenization, the mineralogical composition of selected samples (Table 1) was identified by XRD.
Chemistry
Most samples were processed at the Geological Survey of
230Th–234U ages
The isotopic composition of U and Th was analyzed in 91 samples. In eight more samples only U isotopic compositions were measured (Table 2). Only samples that met the following arbitrarily-determined requirements were considered reliable for single sample age calculation: (1) (230Th/232Th) 10, (2) (238U/232Th) 10, (3) [Th] 0.5 ppm (Fig. 6). Samples that did not pass this test were considered as containing a high-detrital component and therefore not sufficiently clean. 232Th-rich samples display
Conclusions
- 1.
The chronology of the Amora Fm. was established by combining U-series, O wiggle matching, stratigraphic correlations to dated sequences, extrapolated sedimentation rates and complementary paleomagnetic data. This effort extends the chronology of the Dead Sea basin fill, thus establishing one of the longest records of its kind. Each of the chronological tools discussed in this study could not independently suffice for the determination of the chronology of the Amora Fm., and it is only their
Acknowledgments
We thank Y. Enzel (HUJI) and A. Ayalon (GSI) for their critical reading of an earlier version of this work, as well as A. Starinsky (HUJI), I. Gavrieli and M. Bar-Matthews (GSI), and S. Goldstein (LDEO) for fruitful discussions. A. Hofmann (MPI, Mainz) was one of the initiators of this project and provided assistance along the way. E. Shelef, B. Tatarsky, N. Jesselson, U. Shaanan, U. Kodington and S. Reuveni helped in field and lab work. We also thank E. Barkan for performing the oxygen isotope
References (98)
- et al.
Sea-land oxygen isotopic relationships from planktonic foraminifera and speleothems in the Eastern Mediterranean region and their implication for paleorainfall during interglacial intervals
Geochim. Cosmochim. Acta
(2003) - et al.
Lake levels and sequence stratigraphy of Lake Lisan, the late Pleistocene precursor of the Dead Sea
Quat. Res.
(2002) - et al.
Insolation values for the climate of the last 10 million years
Quat. Sci. Rev.
(1991) - et al.
U-series dating of impure carbonates: An isochron technique using total-sample dissolution
Geochim. Cosmochim. Acta
(1991) - et al.
The half-lives of uranium-234 and thorium-230
Chem. Geol.
(2000) - et al.
The climatic and physiographic controls of the eastern Mediterranean over the late Pleistocene climates in the southern Levant and its neighboring deserts
Glob. Planet. Chan.
(2008) - et al.
Changing moisture sources over the last 330,000 years in Northern Oman from fluid inclusion evidence in speleothems
Quat. Res.
(2003) - et al.
Continental oxygen isotopic record of the last 170,000 years in Jerusalem
Quat. Res.
(1999) The stable isotopic composition of Dead Sea waters
Earth Planet. Sci. Lett.
(1984)- et al.
U–Th dating of Lake Lisan (late Pleistocene Dead Sea) aragonite and implications for glacial East Mediterranean climate change
Geochim. Cosmochim. Acta
(2004)
Palynological evidence for the age and rate of sedimentation along the Dead Sea Rift, and structural implications
Tectonophysics
Direct U–Th dating of organic-and carbonate-rich lake sediments from southern Scandinavia
Earth Planet. Sci. Lett.
The geochemical evolution of the Pleistocene Lake Lisan-Dead Sea system
Geochim. Cosmochim. Acta
An evaluation of several methods for determining 230Th/U ages in impure carbonates
Geochim. Cosmochim. Acta
U-series dating of Dead Sea basin carbonates
Geochim. Cosmochim. Acta
U–Th isotope systematics from the Soreq Cave, Israel and climatic correlations
Earth Planet. Sci. Lett.
Re-evaluation of lake-sediment chronology in the Dead Sea basin, Israel, based on new 230Th/U dates
Quat. Res.
Sea-Rain-Lake relation in the last Glacial East Mediterranean revealed by O - C in Lake Lisan aragonites
Geochim. Cosmochim. Acta
The dating of impure carbonates with decay-series isotopes
Nuclear Instrum. Methods Phys. Res.
Diagenetic effects on the distribution of uranium in live and Holocene corals from the Gulf of Aqaba
Geochim. Cosmochim. Acta
Dating the Quaternary: progress in luminescence dating of sediments
Quat. Sci. Rev.
New 230Th/U and C ages from Lake Lahontan carbonates, Nevada, USA, and a discussion of the origin of initial thorium
Geochim. Cosmochim. Acta
Paleoclimatic implicatins of U-series dates for lake sediments and travertine’s in the Arava Rift Valley, Israel
Quat. Res.
Calculation of 230Th/U isochrones, ages, and errors
Geochim. Cosmochim. Acta
U-series isochron dating: A generalized method employing total-sample dissolution
Geochim. Cosmochim. Acta
Reconstructing low levels of Lake Lisan by correlating fan-delta and lacustrine deposits
Quat. Int.
Pluvial conditions in the eastern Sahara following the penultimate deglaciation: implications for changes in atmospheric circulation patterns with global warming
Palaeogeog. Palaeoclim. Palaeoec.
Holocene climate variability and cultural evolution in the Near East from the Dead Sea sedimentary record
Quat. Res.
Recurrence pattern of Holocene earthquakes along the Dead Sea transform revealed by varve-counting and radiocarbon dating of lacustrine sediments
Earth Planet. Sci. Lett.
The Mid-Pleistocene climate transition: onset of 100 ka cycle lags ice volume build-up by 280 ka
Earth Planet. Sci. Lett.
Reinterpretation of the Burmester Core, Bonneville Basin, Utah
Quat. Res.
Orbital forcing of continental climate during the Pleistocene: a complete astronomically tuned climatic record from Lake Baikal, SE Siberia
Quat. Sci. Rev.
Palaeoenvironment of the Acheulian Gesher Benot Ya’aqov Pleistocene lacustrine strata, Northern Israel-lithology, ostracod assemblages and ostracod shell geochemistry
J. Afr. Earth Sci.
A synthetic pollen record of the eastern Mediterranean sapropels of the last 1 Ma: implications for the time-scale and formation of sapropels
Mar. Geol.
Calibration of the C time scale to 40 ka by 234U–230Th dating of Lake Lisan sediments (last glacial Dead Sea)
Earth Planet. Sci. Lett.
Strontium isotopic, chemical, and sedimentological evidence for the evolution of Lake Lisan and the Dead Sea
Geochim. Cosmochim. Acta
Luminescence dating applications in geomorphological research
Geomorphology
Ages of Quaternary pluvial episodes determined by uranium-series and radiocarbon dating of lacustrine deposits of Eastern Sahara
Palaeogeog. Palaeoclim. Palaeoec.
Astronomical calibration of the Matuyama–Brunhes boundary: Consequences for magnetic remanence acquisition in marine carbonates and the Asian loess sequences
Earth Planet. Sci. Lett.
An open-system model for U-series age determinations of fossil corals
Earth Planet. Sci. Lett.
Gypsum as a monitor of the paleo-limnological-hydrological conditions in Lake Lisan and the Dead Sea
Geochim. Cosmochim. Acta.
The sources and evolution of sulfur in the saline Lake Lisan (paleo-Dead Sea)
Earth Planet. Sci. Lett.
Comparison of changes in vegetation in northeast Greece with records of climate variability on orbital and suborbital frequencies over the last 450,000 years
Earth Planet. Sci. Lett.
Paleoclimate and location of the border between Mediterranean climate region and the Saharo-Arabian Desert as revealed by speleothems from the northern Negev Desert, Israel
Earth Planet. Sci. Lett.
Dating open systems by the 238U–234U–230Th method: application to Quaternary reef terraces
Earth Planet. Sci. Lett.
Primary carbonates and Ca-chloride brines as monitors of a paleo-hydrological regime in the Dead Sea basin
Quat. Sci. Rev.
Late Quaternary geological history of the Dead-Sea area, Israel
Quat. Res.
Evolution of the late Pleistocene - Holocene Dead Sea basin from sequence stratigraphy of fan deltas and lake-level reconstruction
J. Sed. Res.
Catastrophic arid episodes in the Eastern Mediterranean linked with the North Atlantic Heinrich events
Geology
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Present address: Lamont-Doherty Earth Observatory, Columbia University, USA.