Lisan Formation Research Articles

Sea-rain-lake relation in the Last Glacial East Mediterranean revealed by δ 18O-δ 13C in Lake Lisan aragonites

We investigated the Sea-Rain-Lake relation during the Last Glacial–Holocene in the East Mediterranean region by comparing the δ 18O and δ 13C records of authigenic aragonite deposited in Lake Lisan, the Dead Sea, Mediterranean foraminifera, and speleothems. The Lisan Formation data display long- and short-term variations of δ 18O, representing steady-state conditions of the lake (e.g., 5.6‰ ± 0.5‰ and 4.5‰ ± 1‰ in the Upper and Lower Members of the Lisan Formation, respectively), and short-term excursions reflecting large floods and droughts. The long-term (steady-state) δ 18O values of the Lisan aragonites show similarity to the corresponding time-equivalent records of the Eastern Mediterranean foraminifera and Judea Mountain speleothems: The Last Glacial deposits are in all of them 2‰–3‰ heavier than the Holocene ones. We interpret this similarity as reflecting the significance of the source effect on the long-term behavior of isotopic reservoirs: Speleothem δ 18O is strongly influenced by the marine reservoir that contributes its vapor to rain formation; the lake δ 18O is dominated by the composition of the inflowing water. Short-term variations in the isotopic composition of rainfall are dominated by the amount effect and the temperature and those of the Lake’s upper water mass by the lake’s water balance. δ 13C values are more variable than δ 18O in the same Lisan sequences (e.g., δ 13C in the Lower Member is 1.0‰ ± 1.7‰, whereas δ 18O is 4.6‰ ± 0.7‰) and are 1‰ to 1.5‰ higher in the Upper Member than in the Lower and Middle Members of the Lisan Formation. These variations reflect significant increase in primary productivity of the lake and algal bloom activity. It appears that the hypersaline-saline lakes were not as “dead” as the Dead Sea is and that algal activity had an important impact upon the geochemistry of Lake Lisan. The δ 18O data combined with independent geochemical and limnologic information (e.g., level fluctuations) indicate that Lisan time was characterized by high precipitation–high lake stands–high atmospheric humidity, whereas the Holocene Dead Sea shows the opposite behavior. This paleoclimatic reconstruction is consistent with independent evidence for significantly wetter conditions in the East Mediterranean region during the Last Glacial period.

U-Th dating of Lake Lisan (late Pleistocene dead sea) aragonite and implications for glacial east Mediterranean climate change

U-series dating can be an effective means to obtain accurate and precise ages on Quaternary carbonates. However, most samples require a correction for U and Th in admixed detritus. This complication is often addressed through generation of U-Th isochrons, requiring analyses of several coeval samples. In addition, presence of water-derived (hydrogenous) Th in the carbonate can cause inaccuracies in isochron ages. This study reports a high-resolution U-series chronology of sediments deposited by Lake Lisan, the last glacial precursor of the Dead Sea. The strategy employed combines multiple measurements from a few stratigraphic heights and fewer analyses from many heights in a single described and measured section. The resulting chronology is based on ages at 22 heights in a ∼40-m-thick section covering the interval of ∼70–14 calendar ka BP. The effects of admixed detritus are evaluated using trace elements. Nearly pure aragonite samples, indicated by very low abundances of insoluble elements such as Nb and Zr, were found to contain hydrogenous Th, which causes the uncorrected U- 230Th age of a modern sample to be ∼2.5 ka. Nevertheless, accurate ages have been obtained by correcting for the detrital and aqueous interferences. The resulting ages are in stratigraphic order, and their accuracy is evidenced by consistency of Lisan Formation U-series and 14C ages with the coral-based calendar-radiocarbon age calibration. The U-Th ages provide a context to unravel the limnological history of Lake Lisan. Boundaries between the Lower, Middle, and Upper stratigraphic units correspond to the MIS 4/3 and 3/2 transitions, respectively. During MIS 2 and 4 the lake generally showed a stable two-layer configuration and a positive fresh-water balance, reflected by deposition of laminated aragonite-detritus. Dry intervals during MIS 2 and 4 are indicated by thick gypsum layers and an inferred depositional hiatus, which are temporally associated with Heinrich events H1 at ∼17 ka and H6 at ∼65 ka, respectively. During MIS 3 the lake level was unstable with intermittent dry periods indicated by abundant clastic layers and a significant hiatus between ∼43–49 ka. Clastic layers are associated with Dansgaard-Oeschger events during MIS 3, and indicate lake level declines during abrupt Northern Hemisphere warmings. Overall, the climate of the Eastern Mediterranean region shows a strong linkage to the Northern Hemisphere climate, with increasing lake size and stability during cold periods, and fluctuations and dessication during warmings and Heinrich events.

Quantification of depositional changes and paleo-seismic activities from laminated sediments using outcrop data

Measurements of laminations from marine and limnic sediments are commonly a time-consuming procedure. However, the resulting quantitative proxies are of importance for the interpretation of both, climate changes and paleo-seismic activities. Digital image analysis accelerates the generation and interpretation of large data sets from laminated sediments based on contrasting grey values of dark and light laminae. Statistical transformation and correlation of the grey value signals reflect high frequency cycles due to changing mean laminae thicknesses, and thus provide data monitoring climate change. Perturbations (e.g., slumping structures, seismites, and tsunamites) of the commonly continuous laminae record seismic activities and obtain proxies for paleo-earthquake frequency. Using outcrop data from (i) the Pleistocene Lisan Formation of Jordan (Dead Sea Basin) and (ii) the Carboniferous–Permian Copacabana Formation of Bolivia (Lake Titicaca), we present a two-step approach to gain high-resolution time series based on field data for both purposes from unconsolidated and lithified outcrops. Step 1 concerns the construction of a continuous digital phototransect and step 2 covers the creation of a grey density curve based on digital photos along a line transect using image analysis. The applied automated image analysis technique provides a continuous digital record of the studied sections and, therefore, serves as useful tool for the evaluation of further proxy data. Analysing the obtained grey signal of the light and dark laminae of varves using phototransects, we discuss the potential and limitations of the proposed technique.

Late Pleistocene paleomagnetic secular variation from the Sea of Galilee, Israel

Stable magnetization of laminated lacustrine Lisan Formation show typical paleomagnetic secular variation and a possible geomagnetic field excursion. 14C ages from the top and assumed 0.9 mm/yr deposition rate constrain the recorded section between 29–28 ka and 22–23 ka. Samples were recovered from two trenches at the southwestern shore of the Sea of Galilee, a graben within the Dead Sea Transform system. The angle between the two site mean directions is 21°, but retilting the beds to horizontal reduces it to 7°, indicating pre‐folding, probably depositional magnetization. Aberrations of field directions at one locality, where VGPs deviate >40° from the geographic north, and low NRM intensities between 29–28 ka and 25–24 ka, are contemporaneous with the Mono Lake Excursion. If the correlation is correct, the new data support the hypothesis that the excursion was global, justifying its utilization as a chronological datum.

Radial clastic dykes formed by a salt diapir in the Dead Sea Rift, Israel

ABSTRACT Fanning structures radiating from a central perturbation are known in various geological environments, where different processes have produced similar geometry. The present contribution describes and analyses fanning clastic dykes in the Dead Sea Rift, a new example of diapir‐related deformation. The dykes are opening‐mode fractures exposed in lacustrine varved marl of the Lisan Formation, deposited 70–15 ka. They are arranged mainly in a radial and tangential geometry. The radial traces converge at the ‘Black Hill’ structural dome. The geometry of the fractures is consistent with stresses exerted by the rise of a salt diapir located underneath the Black Hill. The estimated extension of the radial fractures is in good agreement with the present topographic elevation of the hill. The absence of fractures in the overlying Holocene alluvium probably indicates that either the rise of the Black Hill salt diapir paused or is associated now with a different style of deformation.

Geochemistry of the Lisan and Damya Formations in Jordan, and implications for palaeoclimate

Geochemical, mineralogical and sedimentological investigations, carried out on the lacustrine Lisan and Damya Formations of the Jordan Rift Valley, reveal three major and several minor transgressive depositional cycles, all terminating with massive gypsum precipitation. The highest level of Lake Lisan is reported in the literature at 130 m below mean sea level (b.s.l.). From 70–45 calibrated ka BP, the Lisan Formation is characterised by a high gypsum/aragonite ratio and a low lithogenic content, implying a regression of an initially high water level caused by reduced water input. In the following interval (ca. 45–36 cal. ka BP), two low water stands are marked by higher salt concentrations. After recovery and a period of higher water level, the Lake Lisan era ends with a strong regression at around 16 cal. ka BP. This date coincides with the period when Lake Van, Eastern Turkey also fell dry, thus marking a strong drought signal in the entire Near East. The overlying Damya Formation, containing more lithogenics records lake level fluctuations at around 300 m b.s.l. The existence of a north–south precipitation gradient, as present today, is indicated by increasing Sr/Ca ratios in aragonite and a decreasing lithogenic content in a N–S direction. Secondary gypsum formed diagenetically, and aragonite and low Mg-calcite was transformed into high Mg/Fe-calcite.

Geological and geotechnical characteristics of Karameh dam site, north of the Dead Sea, Jordan

This paper describes a feasibility stage geotechnical evaluation carried out at the Karameh dam site. The 45 m high, 2,150 m long dam will be built across the Wadi Mallaha on Quaternary lacustrine deposits and store fresh water from the King Abdullah Canal. A confined highly saline aquifer was identified at a depth of 25 m, the saline groundwater migrating naturally through the Lisan Formation. Stability analysis of the foundation indicates that the slopes are just stable under dry conditions and may become unstable under wet conditions. The most important problem is the presence of the active main Jordan Valley Fault crossing both the dam body and reservoir.

Sources of salinity in ground water from Jericho area, Jordan Valley.

One of the major problems in the lower Jordan Valley is the increasing salinization (i.e., chloride content) of local ground water. The high levels of salinity limit the utilization of ground water for both domestic and agriculture applications. This joint collaborative study evaluates the sources and mechanisms for salinization in the Jericho area. We employ diagnostic geochemical fingerprinting methods to trace the potential sources of the salinity in (1) the deep confined subaquifer system (K2) of Lower Cenomanian age; (2) the upper subaquifer system (K1) of Upper Cenomanian and Turonian ages; and (3) the shallow aquifer system (Q) of Plio-Pleistocene ages. The chemical composition of the saline ground water from the two Cenomanian subaquifers (K1 and K2) point to a single saline source with Na/Cl approximately 0.5 and Br/Cl approximately 7 x 10(-3). This composition is similar to that of thermal hypersaline spring that are found along the western shore of the Dead Sea (e.g., En Gedi thermal spring). We suggest that the increasing salinity in both K1 and K2 subaquifers is derived from mixing with deep-seated brines that flow through the Rift fault system. The salinization rate depends on the discharge volume of the fresh meteoric water in the Cenomanian Aquifer. In contrast, the chemical composition of ground water from the Plio-Pleistocene Aquifer shows a wide range of Cl- (100-2000 mg/L), Na/Cl (0.4-1.0), Br/Cl (2-6 x 10(-3)), and SO4/Cl (0.01-0.4) ratios. These variations, together with the high SO4(2-), K+, and NO3- concentrations, suggest that the salinity in the shallow aquifer is derived from the combination of (1) upconing of deep brines as reflected by low Na/Cl and high Br/Cl ratios; (2) leaching of salts from the Lisan Formation within the Plio-Pleistocene Aquifer, as suggested by the high SO4(2-) concentrations; and (3) anthropogenic contamination of agriculture return flow and sewage effluents with distinctive high K+ (80 mg/L) and NO3- (80 mg/l) contents and low Br/Cl ratios (2 x 10(-3)). Our data demonstrates that the chemical composition of salinized ground water can be used to delineate the sources of salinity and hence to establish the conceptual model for explaining salinization processes.

The sulfur system in anoxic subsurface brines and its implication in brine evolutionary pathways: the Ca-chloride brines in the Dead Sea area

Abstract Important elements in the evolutionary history of saline groundwater might be overlooked when they involve both sulfate removal through reduction and input of sulfate via dissolution. These two simultaneous and apparently contrasting processes can result in a negligible net effect on the sulfate concentration. Isotopic composition of sulfur in sulfate and sulfide can be applied to identify the bacterial sulfate reduction (BSR) though the extent of the process is difficult to quantify. Saturation with respect to gypsum may suggest that gypsum dissolution also occurs. However, a more definite identification of these processes and their quantification can be achieved through the use of ammonium concentration in the anoxic brines. This approach assumes that the ammonium is derived only from the oxidation of organic matter through BSR and it requires that the C:N ratio in the oxidized organic matter be known. A minimum estimate for the sulfate reduction can be obtained when the Redfield C:N ratio (106:16) is assumed. Several calculation methods are presented to identify the extent of sulfate reduction prior to, concomitant with, or following gypsum dissolution that are based on combining sulfur isotopic compositions, Rayleigh distillation equation, and calculated gypsum saturation indices. The required assumptions are presented and their validation is discussed. The subsurface hypersaline Ca-chloride brines in the vicinity of the Dead Sea are taken as a case study. Here sulfur isotope compositions of sulfate and sulfide, and high ammonium concentrations indicate BSR occurs in the subsurface. The sulfur isotopic composition of the sulfate makes it possible to distinguish between two major groups of brine and their recent evolutionary histories: (1) the Qedem–Shalem thermal brines (δ 34 S SO4 =21–24‰) which emerge as springs along the shores and are slightly undersaturated with respect to gypsum; (2) DSIF–Tappuah brines (δ 34 S SO4 =30–60‰) which are found in shallow boreholes and are saturated to oversaturated with respect to gypsum. Calculations based on their ammonium content suggest that both groups of brine require apparent unreasonably high oversaturations with respect to gypsum prior to the onset of the reduction. This implies that the groundwater systems were open with respect to sulfate, and that the sulfate reservoir was replenished continuously or intermittently during the BSR. The DSIF–Tappuah brines continue to dissolve gypsum during their BSR. The dissolving sulfate is derived from relatively isotopically enriched gypsums (δ 34 S SO4 >20‰), such as found in the Lisan Formation. These brines approach the steady-state isotopic composition (δ 34 S ss ) dictated by the combination of the δ 34 S of the dissolving gypsum and the fractionation factor accompanying BSR. The sulfur isotopic composition of the Qedem–Shalem brines implies that most of their ammonium content is derived from an earlier phase of BSR and that the last phase of BSR takes place during the brines’ rapid ascent to the surface. Prior to this stage they evolved through either: (1) dissolution of gypsum with δ 34 S SO4 ≤20‰ which occurred after the main BSR in the subsurface; (2) a previous phase in which the brines were part of a lake and later percolated to the subsurface. As such, their isotopic composition and ammonium content were determined by the combined effect of freshwater sulfate input to the lake and BSR in the stratified lake.

Geologic hazards of an embankment dam constructed across a major, active plate boundary fault

Abstract The geological structures associated with the site of the 55 million m 3 Karameh embankment dam constructed in the Jordan Valley and the tectonic effects on dam foundation and reservoir margins were reviewed. The dam crosses the strike-slip fault of the Jordan Valley Rift Zone. Trace evidence of the fault indicates a displacement of 8 to 15 m over a rupture length of some 130 km, which probably took place several centuries ago. Earthquakes with Richter magnitudes as great as 7.8 have occurred along the Jordan Valley Fault. Deterministic studies by Tapponnier (1992) indicated that the dam design should incorporate the possibility of a 7.8 event, a maximum horizontal rupture displacement on the fault of 10 m and a design peak ground acceleration (PGA) of 0.74 g at the site of the dam. These values are consistent with those which would be used in the USA for a similar case. However, the dam was actually designed by a consultant and constructed for a PGA of about a quarter of this value, based on seismic hazard analysis following guidelines of the International Committee on Large Dams (ICOLD) (1989). Moreover, the dam was designed for displacements of 6 m horizontal and 2 m vertically. Liquefiable sand layers were found in the dam foundation. A PGA of 0.50 g will trigger liquefaction of the sand layers in the dam foundation which would be expected to result in a crest settlement of 4.4 m. Slope stability analysis indicated deep failure planes in the foundation zone. The excavation of loose materials from under the dam foundation has not precluded the possibility of liquefaction occurring under the expected earthquake. Field mapping of geological features during the dam foundation excavation and construction revealed that: a) the most likely location of the Jordan Valley fault is in the area where the Wadi Mallaha stream crosses the dam axis, b) zones of en echelon type open fissures have been defined in the laminates sub-parallel to the Jordan Valley Fault Zone, c) at the Wadi Mallaha stream bed a parallel zone of faulting and warping of the Lisan Formation was identified, and d) the alignment is clearly confirmed by the exposure immediately upstream of the core at Ch 1375. The main wrench fault zone crosses the embankment footprint (upstream to downstream approximately) and reaches the surface around Ch 1375. The critical safety elements of the embankment are the core, the downstream fine filter, the chimney drain and the drainage blanket. To resist large earthquake events safely, the following safety measures should be implemented: 1. A freeboard of 7.0 m instead of the 5.0 m constructed. 2. The foundation of the dam should be stabilized against liquefaction. 3. The embankment internal zoning should be designed to accommodate damage resulting from earthquake events with a magnitude of 7.8. 4. The foundation needs relief measures downstream to lower the pore pressure. This paper describes the measures taken during construction as overall defense against future fault movements through a wide plastic core, an extensive upstream blanket, a 5.0-m thick downstream chimney filter and drain zones, a 5-m freeboard and an upstream crack stopper zone which may be critical for normal faults with a lateral extension component. The geological determination of the main wrench fault alignment resulted in the addition of an extra 2-m width to each of the already wide chimney filter and drain zones. In order to reduce potential seepage, local cut-off trenches or slush grouting were used for treatment of any open fissures at the upstream edge of the external blanket and the right bank ridge. The scale and scope of this dam and inherent engineering geological hazards are unprecedented. The design is considered deficient. This paper documents serious safety issues with the dam. The constructed dam presents serious safety risks and represents a case history of a disaster waiting to happen.

On the paleoclimate of Jordan during the last glacial maximum

The uppermost Pleistocene in the Jordan Valley is represented by two closed lakes: the Lisan Lake (and hence the Lisan Formation 63 to 16–15 ka) and the Damya Lake (Damya Formation 16–15 to 12 ka). The Lisan Formation in the central Jordan Valley consists mainly of varved sediments, is capped by a conspicuous white cliff containing abundant gypsum lamina and is overlain by evaporite-free Damya Formation. The white cliff sediments, thus, represent the driest period of the Lidan–Damya times (63–12 ka). This cold, dry period extended from 23–22 to 16–15 ka BP, which corresponds to the Last Glacial Maximum (LGM) world-wide and ended by the demise of Lake Lisan. We believe that the cold, dry climate of the Jordan Valley during the LGM, supported by other workers, records a rather similar paleoclimatic trend with the monsoon-affected North African Sahara, Arabia and SE Asia where cold climatic times are associated with drier, low precipitation, and expansion of desert conditions. Consequently, this might indicate a good possibility of the monsoon rains reaching the interior southern Levant during the warm, wet periods.

Calibration of the 14C time scale to >40 ka by 234U–230Th dating of Lake Lisan sediments (last glacial Dead Sea)

A new comparison of 14C dates with 234U-230Th ages is presented of aragonites from Lake Lisan, the last Glacial Dead Sea, between ∼20–52 cal-ka-BP. The Lisan data are coincident with the coral based 14C-calendar age calibration through the continuous portion of the curve to 23.5 cal-ka-BP, and with the additional ‘checkpoints’ at ∼30 and ∼40 cal-ka-BP. The agreement with the corals provides evidence for the accuracy of the U-Th and 14C ages, and indicates that Lisan aragonites can potentially be used to generate a nearly continuous record of the atmospheric 14C variations through this crucial time interval. The Lisan data are compared with other records older than 25 cal-ka-BP from Lake Suigetsu, Japan, North Atlantic foraminifera, South African cave deposits and tufa from Spain. Over some age intervals the records show broad agreement, over other intervals they diverge. All agree that 14C ages were ∼2.5±0.5 ka younger than calendar ages between 20–32 cal-ka-BP. For ages >32 cal-ka-BP, the Lake Suigetsu data indicate small differences between 14C ages and calendar ages of less than 1.5 ka. The other records broadly agree that 14C ages are too young by ∼3±1 ka from 32–39 cal-ka-BP. At ∼40 cal-ka-BP, the foraminifera show equal 14C and calendar ages, while the corals, Lisan aragonites and the Spanish tufa indicate a large age difference of 4–5 ka. A recent paleomagnetic study of the Lisan Formation indicates that the high calendar-14C age difference at ∼40 cal-ka-BP may be associated with the Laschamp paleomagnetic excursion.

Lithostratigraphy and Depositional History of Part of the Midyan Region, Northwestern Saudi Arabia

ABSTRACT The Midyan region provides a unique opportunity in which to examine exposures of the Upper Cretaceous and Neogene sedimentary succession. Recent investigations have yielded new interpretations of its depositional environments, stratigraphic relationships, and structure. In this paper, all the lithostratigraphic units of the Midyan succession are considered to be informal in advance of an on-going process of formalization. The region is bounded to the north and northeast by mountains of Proterozoic rocks and to the west and south by the Gulf of Aqaba and the Red Sea, respectively. The Wadi Ifal plain occupies most of the eastern half of the region, beneath which is a thick sedimentary succession within the Ifal basin. The oldest sedimentary rocks are the fluviatile Upper Cretaceous Adaffa formation and marine siliciclastics and carbonates of the lower Miocene Tayran group, unconformable on the Proterozoic basement. The Tayran group is unconformably overlain by the deep-marine lower Miocene Burqan formation that, in turn, is overlain by marine mudstones, carbonates, and evaporites of the middle Miocene Maqna group. The poorly exposed middle Miocene Mansiyah and middle to upper Miocene Ghawwas formations consist of marine evaporites and shallow to marginal marine sediments, respectively. The youngest rocks are alluvial sands and gravels of the Pliocene Lisan formation. A complex structural history is due to Red Sea Oligocene-Miocene extension tectonics, and Pliocene-Recent anti-clockwise rotation of the Arabian Plate relative to Africa on the Dead Sea Transform Fault. The Upper Cretaceous succession is a probable pre-rift unit. The Oligocene?-Miocene syn-rift 1 phase of continental extension caused slow subsidence (Tayran group). Syn-rift 2 was an early Miocene phase of rapid subsidence (Burqan formation) whereas syn-rift 3 (early to middle Miocene) was another phase of slow deposition (Maqna group). The middle to late Miocene syn-rift 4 phase coincided with the deposition of the Mansiyah and Ghawwas formations. The Lower Pliocene to Recent succession is related to the drift (post-rift) phase during which about 45 kilometers of sinistral movement occurred on the Dead Sea Fault. The structural control on sedimentation is evident: the Ifal basin was formed by east-west lithospheric extension; pull-apart basins occur along major left-lateral faults on the eastern coast of the Gulf of Aqaba; and basin-bounding faults controlled deposition of the Burqan, Ghawwas, and Lisan formations. Pliocene to Recent earth movements may be responsible for activating salt diapirism in the Ifal basin. Extensive Quaternary faulting and regional uplift caused the uplift of coral reefs to at least 6 to 8 meters above sea level.

Strontium isotopic, chemical, and sedimentological evidence for the evolution of Lake Lisan and the Dead Sea

Precise strontium isotope ratios, combined with chemical analyses and sedimentological information, are used to monitor the water sources and the evolution of the Dead Sea and its late Pleistocene precursor, Lake Lisan (70-18 kyr B.P.). The materials analyzed include bulk aragonite, water-leached soluble salts, and residual aragonite and gypsum from the Lisan Formation in the Perazim Valley (near the SW shore of the Dead Sea). The residual aragonite and the associated soluble salts display systematic fluctuations in 17 Sr 86 Sr ratios between 0.70803 and 0.70806 and from 0.70805 to 0.70807, respectively. In individual soluble salt-residual aragonite pairs, the soluble salt displays a higher 87 Sr 86 Sr ratio. Gypsum samples yield 17 Sr 86 Sr ratios similar to the soluble salts from adjacent layers in the section. This shows that, in individual samples, the source of Sr in aragonite was distinct from that in soluble salts and the gypsum. The sterility of the Lisan sediments, their strictly nonbioturbated fine lamination, and their high content of chloride salts indicate that Lake Lisan was a saline, or even hypersaline water body. In the absence of alternative sources of HCO 3 − and S0 4 2− the abundance of primary aragonite and gypsum in the Lisan column reflects an import of very large volumes of freshwater into the otherwise saline lake, resulting in a density stratification of this water body. The history of the upper water layer and that of the lower brine is reflected in the chemical and strontium isotope composition of the aragonite and in that of the associated soluble salts and in the gypsum samples, respectively. Whereas the bicarbonate and much of the Ca 2+ required for aragonite crystallization were supplied by the freshwater, the complementary Ca 2+ (and Sr 2+) were added by the lower brine. The upper water layer of Lake Lisan acted as a SO 4 2− capacitor during the lake's rise periods. It was removed therefrom, as prominent gypsum beds, upon climatic-induced (drier period) mixing or even complete overturn of the lake. The evolution of Lake Lisan took place between two distinct modes. The first was characterized by an extensive supply of freshwater and resulted in a rise of the lake's level, a (density) layered structure, and precipitation of aragonite. The second mode was marked by a diminishing freshwater input, resulting in mixing or complete overturn of its water, and precipitation of gypsum. These two modes reflect the climatic evolution of the region in the late Pleistocene which fluctuated between drier and wetter periods. The transition to the Holocene is accompanied by the dry up of Lake Lisan and its contraction to the present Dead Sea.

Reevaluation of the lake-sediment chronology in the Dead Sea basin, Israel, based on new [formula omitted] dates

The Dead Sea is surrounded by chemical and detrital sediments that were deposited in its larger precursor lakes, Lake Samra and Lake Lisan. The sedimentary history of these lakes was recon-structed by means of 230Th 234U ages of 30 samples, mostly of argonite laminae, from 8 columnar sections up to 110 km apart. The general validity of the ages was demonstrated by subjecting them to tests of internal isotopic consistency, agreement with stratigraphic order, and concordance with 14C ages. In the south, only the part of the Samra Formation older than 170,000 yr is exposed, while the aragonite-detritus rhythmites found in the central and northern region are generally younger than 120,000 yr. The Lisan Formation started accumulating about 63,000 yr B.P., with the clay and aragonite beds in the south-central area reflecting a rise in water level to at least −280 m. The upper part of the Lisan Formation, the aragonite-rich White Cliff Member, started accumulating about 36,000 yr B.P. The lake probably reached its highest level sometime after this, based on the ages of Lisan sediments preserved in the southernmost reaches of the basin.

Implications of the Wadi al-Hammeh sequences for the terminal drying of Lake Lisan, Jordan

The ancestral valley of the Wadi al-Hammeh in northwestern Jordan is backfilled by a 60-m thick body of sediment. A comprehensive series of radiocarbon dates and in-situ archaeological sites ranging in age from Middle Palaeolithic to Epi-Palaeolithic, show that the sedimentary sequence is a lateral, continental equivalent to the Lisan Formation. The geometry and sedimentological character of the sequence indicate that backfilling of the wadi was in response to a gradual rise in lake levels until about 11,100 yr B.P. The clearly defined lithofacies variations and the uniformity of sedimentary sequences implies no significant drop in lake levels occurred between 31,000 and 11,100 yr B.P. The present topography arises from incision of the wadi sequences in response to lowered base levels of sedimentation following the drying of the lake at about 11,000 yr B.P. The presence at the mouth of the wadi of low-energy calcareous silts with Melanopsis shell layers dated between 15,000 and 19,000 yr B.P., at levels some 30–40 m above the highest levels reached by Lake Lisan (−180 m), is attributed to post-Lisan tectonism.

Age and paleoclimatic implications of the Bet Shean travertines

From 41,000 to over 22,000 yr B.P., a massive and areally extensive spring travertine was deposited in the Bet Shean Valley, Israel. This travertine is coeval with the Ami'az Member of the Lisan Formation which represents a high lake stand. The travertine deposition is contemporaneous with a more active hydrologic regime associated with wetter conditions in the arid zones of the southern Levant adjacent to southern Israel. These wetter conditions facilitated formation of a widespread spring tufa and also enhanced the water levels of Lake Lisan.

The stable isotope composition of Dead Sea waters

Dead Sea waters are moderately enriched in 18O; the degree of enrichment constitutes a balance between the dilution by freshwater influx and the isotope fractionation which accompanies evaporative water loss and vapour exchange with the atmospheric moisture. Modelling of the seasonal cycle and long-term trends of δ 18O, in response to the changes in the environmental parameters, shows that the major control is exercised by the salinity of the surface waters, through its effect on the vapour pressure gradient between the lake's surface and the atmosphere; the (steady state) isotopic composition of the more saline brines tends towards less enriched 18O values. This fact can explain the relatively high δ 18O levels encountered in the Lisan formation, which was deposited from Lake Lisan, —the less saline Pleistocene precursor of the Dead Sea.

Evolution of reg soils in Southern Israel and Sinai

Reg soils (mostly Camborthids and Gypsiorthids) cover some 15% of the Negev and Sinai deserts. Analytical data of seven profiles on depositional surfaces of increasing age in the Negev show clear relationships between ages of surfaces and soil profile features, exemplified in the development of the cambic, salic and gypsic horizons.The youngest soil, a Coarse Desert Alluvium soil (Typic Torriorthent) of dry wadi beds, up to a few thousand years old, has little profile differentiation and is generally non-saline or slightly saline. On the higher terraces connected with the Lisan Formation (about 70 000–12 000 years B.P.) clear profile differentiation and the beginning of development of cambic horizons can be discerned, evident in their colour-textural p differences. The soils are already saline and somewhat gypsiferous. Both soils are not yet defined as Regs because of their negligible or restricted profile differentiation.Reg soils on the older and higher geomorphic surfaces in the Arava Rift Valley, several hundred thousand years old, have well-differentiated profiles, with cambic, salic and gypsic horizons. Below their stony desert pavements, typical Reg soils have light coloured vesicular horizons, over mellow, very pale brown loam, frequently with laminar structure, almost completely stone-free layers. The reddish brown loamy to clay loam B horizons are very saline and show intensive salt weathering of gravels. Gypsic and petrogypsic horizons occur at depth. Such Reg soils represent the stable surfaces and soils of deserts and were developed over a long period of desert weathering.

Accuracy of the Radiocarbon Time Scale Beyond 15,000 BP

Ionium dates for the Upper Lisan Formation in the Dead Sea valley average (10 ± 3) percent higher than a set of radiocarbon dates from the same profiles. No analytical explanation can be found so that the discrepancy may be real for the period 15,000 BP to 35,000 BP (conventional radiocarbon years). This would have implications for the chronology of the Upper Pleistocene.