Changes in biogeochemistry recorded in the Lisan formation and the Dead Sea Basin

<p>Terrestrial climate archives provide a rich array of information on regional climate dynamics that often can link to global climate change.  A range of new metal and coupled isotope proxies is helping to unlock the most information from terrestrial archives and this paleoclimate information. The Jordon-Arava valley, tectonically active since the early Neogene, is one of the world’s largest pull-apart basins.  Throughout the Pleistocene to the Holocene, the valley contained a series of lacustrine water bodies.  As the valley is located on the boundary between the African-Arabian deserts and the Mediterranean regional climatic zone, studies of past conditions in these lacustrine bodies allows the reconstruction of changes in the regional hydrological cycle.  Lacustrine sediments, such as those found in the Jordon-Arava valley, record paleoclimatic information similar to that found within marine sedimentary archives and often at much higher resolution, from millennial to even annual timescales. The Lisan Formation is a 40-80m thick Pleistocene marl, which was deposited in Lake Lisan, which existed over the last glacial cycle in the Jordan-Arava Valley. The Lisan Formation contains a significant quantity of annually-precipitated primary aragonite, which has not recrystallised to calcite, allowing for direct U-Th dating, which has led to an exceptional age model for the Lisan Formation.</p><p>Here we discuss the measurement of the sulfur and oxygen isotopic composition of gypsum in the Lisan formation, as well as the generation of sulfur nodules within the formation that are not found in the sediment cores of the Dead Sea. We use this data to explore how sediment diagenesis, relating to changes in biogeochemistry, changes as a function of climate change over the last glacial cycle. We then present the calcium isotopic composition of the gypsum and interbedded aragonite, and show how the aragonite calcium isotopic composition covaries with lake level, and thus offers profound insight into the regional hydrological cycle in the Jordon-Arava Valley.</p>

Resistivity survey investigating salinity hazard and aquifer system in the alluvial fans in central Jordan Valley

In the course of this study geological and geophysical resistivity survey were conducted in the area extended from Deir Alla to Suleikhat (Middle Ghor Area) in Jordan valley. In order to evaluate the potential and characteristic of the groundwater quality and distribution of the aquifer in the alluvial in the area. The aquifer system in the area consists of Ajlun and Belga Group, in addition to the Plateau Gravel Group and the Alluvial Aquifers.The resistivity survey encounter an average thickness of the alluvial fans of about93 meters. The source of salinity in the alluvium aquifers was predicted to be Lisan Formation, which underlies the Whole alluvium in the area.Quantitative interpretation of VES data coupled with field and preexisted electrical conductivity reading work out the following characteristic for water bearing layer in the alluvial fan deposits: The alluvial fans exhibit recurrently lateral variation, even in the same area.The continuity of static water table may be interrupted by mud dominated area. These facts forearm to conclude that the aquifer system in the alluvial fans are lenses to micro-aquifers bodies of saturated gravel and sand dominated layers, with resistivity range between 30-60 ohm.m, with apposite thickness range of 8-42 meters.Calculated Porosity ofsuch aquifers is approximated to be in range of 20-27%. In addition to these layers there is a mud gravel layerswith resistivity ranges from 20 to 30 ohm.m, their thickness are in range of 5-23 meters, and their porosity is approximated to 33%.

Radiocarbon Reservoir Ages as Freshwater-Brine Monitors in Lake Lisan, Dead Sea System

A continuous and high-resolution record of the radiocarbon reservoir age (RA) has been recovered from the primary aragonites that were deposited from the last glacial Lake Lisan. The RA is calculated as the difference between the measured 14C “apparent” age in the aragonite and the atmospheric age at any particular time. The RA shows temporal decreases during the time interval of ≃28 to ≃18 ka cal BP. This behavior is attributed to a continuous addition of low RA-high bicarbonate freshwater into the high RA-Ca-chloride (low bicarbonate) brine solution filling the lake. The mixing of the brine with freshwater drives the precipitation of CaCO3 in the form of aragonite from the lake epilimnion (surface layer). The runoff-brine mixture in Lake Lisan is also reflected by the Sr/Ca ratios that are positively correlated with the RA. Nevertheless, the 14C content in the epilimnion did not drop at the same rate as the atmospheric value but rather remained nearly constant. We suggest that turbulent mixing with the much saltier hypolimnion (lower layer) across the hypolimnion/epilimnion interface at a depth of about 390 m below sea level, buffered the 14C content as well as the Sr and Ca concentrations in the aragonite precipitating solution. The RA-Sr/Ca related limnological model developed here opens the way to determine the reservoir-age-corrected atmospheric ages of Lisan Formation aragonites beyond 28 ka cal BP.

Synopsis

The two large lakes named Samra and Lisan existed in the Dead Sea graben from 350,000 to 120,000B.p. and 60,000 to 12,000B.p. Their sediments tentatively are correlated with the European Riss and Würm glacial epochs. Thick marls are the chief sediments in the deep water north basin. Rocksalt deposition dominated within the troughs of both north and south basins throughout the intervening Riss-Würm Interglacial stage. Lithology of Lisan Formation (Würm) in that basin indicates rapid and extreme fluctuations of level. Eight major climatic cycles are recorded during Würm glaciation when the level fluctuated between -180 m m.s.l. and probably lower than -400 m m.s.l. Rocksalt was deposited within both basins during warm dry phases of the Lisan stage. At the present state of knowledge no specific tectonic or volcanic activities can be tied to these climatic events. The Holocene Period was similar lithologically to that of the Lisan Formation and transition between them was gradual. Primarily the difference between the two was change in relative time span between alternate wet and dry phases. Dry phases of Holocene gradually became longer while wet ones with Dead Sea transgressions became shorter. Tectonic regimes during the first part—the Natufian age to Early Bronze III, 12,000 to 4400 B.P.—seem to have been milder than later ones, end of Early Bronze III to the present. The severe earthquake that destroyed Sodom and Gomorrah in 4350 B.P. was followed by a 300-year long subphase of gradually warming climate that became extremely dry during the latter part of the Intermediate Bronze age. Climatic Wet Phase III began about 3900 B.P. It was the longest, about 800 years, and most intense wet phase of Holocene and it probably was associated with volcanism. No abrupt cultural or demographic changes are known during transition from Epi-Paleolithic or Geometric Kebaran from the last glacial phase of the Pleistocene Period through Natufian to the early part of Holocene Pre-Pottery Neolithic. The reason for this stability is not clear especially because average temperatures of global oceans during the latest Pleistocene glaciation were appreciably lower than those during Early Holocene (Emiliani, 1978).

Reevaluation of the Lake-Sediment Chronology in the Dead Sea Basin, Israel, Based on New 230Th/U 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.

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.

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.