Dead Sea Depression Research Articles

Unveiling the Transition From Paleolake Lisan to Dead Sea Through the Analysis of Lake Paleoshorelines and Radiometric Dating of Fossil Stromatolites

AbstractTo date, the most complete paleolake‐level reconstructions for the late Pleistocene water bodies that once occupied the Dead Sea depression have been based on the combination of dating of lake sediments and terrestrial materials. However, despite these major accomplishments, there is still limited spatial control regarding the water levels, suggesting some degree of uncertainty concerning the magnitude and rate of lake‐level changes. Here, we re‐examine the late Pleistocene lake‐level changes in the Dead Sea during the transition from paleolake Lisan to the present‐day Dead Sea. We rely on systematic dating of fossil stromatolites including 84 radiocarbon and 15 U‐series ages, stable‐isotope measurements, paleobiology, high‐resolution topography, and numerical modeling to assess lake‐level changes. Our results indicate that the highstand of paleolake Lisan was of shorter duration and the transition between Lake Lisan and the Dead Sea occurred at least 5 Kyrs earlier than previously indicated. By refining the timeline and accuracy of lake‐level positions during the transition paleolake Lisan—Dead Sea, our study offers new insights into the regional and local paleo‐climatic conditions during the last glacial period in this region.

Quaternary tectonic activity in NW Jordan: Insights for a new model of transpression–transtension along the southern Dead Sea Transform Fault

The Dead Sea Transform Fault (DSTF) constitutes the transform plate boundary between the African and Arabian plates. The southern part of this fault has been traditionally divided into two main segments, the Wadi Araba Fault (WAF) and the Jordan Valley Fault (JVF), connected through the Dead Sea continental pull-apart basin. Active tectonic studies in NW Jordan have traditionally focused on these DSTF structures and have neglected other prominent structures in the region, such as the Amman Hallabat Structure (AHS) and Shueib Structure (SHS) fault systems, which have been considered inactive since the Cretaceous. However, some recent studies have suggested a possible local reactivation of the southern parts of these structures. In this work, we carried out a detailed geological study of the NE Dead Sea Basin to analyze the Quaternary activity of the AHS and SHS based on field observations and structural analyses. Our findings have revealed that the AHS and SHS structures present clear Quaternary activity and accommodate a small part of the deformation of the southern DSTF. In the Quaternary, the southwestern part of the AHS has acted as the northernmost continuation of the WAF, whereas the SHS has acted as a transfer fault associated with NW–SE normal faults with low to moderate throws (meters to decameters) that connect this structure to the JVF. These NW–SE normal faults constitute the northeastern border of the Dead Sea depression (Jericho Valley). They produce a topographic front and separate the sediments of the Jordan Valley in the hanging wall from the Mesozoic sedimentary sequence located in the footwall.

Late Neogene rift valley fill sediments preserved in caves of the Dead Sea Fault Escarpment (Israel): palaeogeographic and morphotectonic implications

Evaporitic-lagoonal marl and dolomite laminar fill sediments are preserved in relict dry caves of the Dead Sea Fault Escarpment (Israel) which has been tectonically active since the Late Neogene. The hosting caves are located within Turonian massive carbonate bedrock and at higher altitudes than previously documented fill sediments of the Dead Sea depression. Based on the relative altitudes of the cave sediments, the ‘reversed stratigraphy’ of the Dead Sea depression fill sediments, possible partial correlation of the cave sediments with other fill sedimentary units of the depression, and sedimentary, geochemical and mineralogical characteristics, it is concluded that: (i) the cave sediments are among the oldest of the depression fill; and (ii) the deposition of the cave sediments took place in hypersaline dolomite-precipitating water bodies of Late Neogene age, during the initial morphotectonic stages of the depression formation. Variable and relatively low Sr/Ca and δ34S ratios of the cave sediments (assuming precipitation from sea water) suggest variable fresh water input into the depositional brine. The present altitudes of the cave sediments reflect Late Neogene levels of water bodies in the depression, modified by vertical post-Late Neogene tectonic movements within the still active fault escarpment. According to these altitudes, a 50 to 250 m uplift of the western margins of the depression since the Late Miocene to Early Pliocene is inferred.

Stromatolites in caves of the Dead Sea Fault Escarpment: implications to latest Pleistocene lake levels and tectonic subsidence

A varied assemblage of algal stromatolites was encountered in caves along the northern section of the Dead Sea Fault Escarpment. The caves are situated at the lower part of the escarpment at altitudes −310 to −188 m relative to mean sea level (m.s.l.), i.e. ca 110–230 m above the present Dead Sea level. The cave stromatolites are mainly composed of aragonite yielding U–Th ages of ∼75–17 ka. The altitude, mineralogy and ages, as well as comparison with previously documented stromatolite outcrops in the area, ascribe the cave stromatolites to the aragonite-precipitating hypersaline Lake Lisan—the Late Pleistocene predecessor of the Dead Sea. The stromatolites are used as a lake level gauge, based on the algae being reliant upon the light of the upper water layer. Preservation of the original structure and aragonite mineralogy of the stromatolites, suggests a closed system regarding the radioactive elements, enabling reliable U–Th dating. A curve of Lake Lisan levels is constructed based on the stromatolite ages and cave elevations. The following points are noted: (1) Lake levels of −247 m relative to m.s.l., are recorded at ∼75–72.5 ka; (2) relatively high lake levels above −220 m relative to m.s.l., are achieved at ∼41.5 ka, and are still recorded at ∼17 ka; (3) the peak level is −188 m relative to m.s.l., at ∼35.5–29.5 ka. These results indicate lake stands up to 80 m higher than previously accepted, for large parts of the Lake Lisan time span. This difference is explained by tectonic subsidence of up to 2.2 m/ka within the Dead Sea depression since the latest Pleistocene. This subsidence rate is in the same order of magnitude with previously calculated subsidence rates for the Dead Sea depression [Begin, Z.B., Zilberman, E., 1997. Main Stages and Rate of the Relief Development in Israel. Geological Survey of Israel report, Jerusalem]. Unlike previous Lake Lisan level estimations, the new curve is measured at the relatively stable shoulders of the Dead Sea depression.

The origin of thermal waters from the eastern flank of the Dead Sea Rift Valley (western Jordan)

ABSTRACTThermal waters emerging along the eastern flank of the northernmost part of the Dead Sea Rift Valley close to the Yarmuk river are dilute, Ca–SO4–(HCO3) and Na–Cl water types with measured temperatures of 35–60 °C and estimated teperatures, according to silica solubility, of 60–110 °C. They are fed only by present‐day recharged meteoric waters (Wadi Hasa, Al Himma and North Shuna thermal baths) and by meteoric waters contaminated with saline waters (El Ma'in thermal Bath). Although they have been known for a long time, there is still dispute about their origins and the source of heat. On the basis of new chemical and isotopic analyses, the saline waters could represent residual pockets of groundwater in equilibrium with those filling the Dead Sea depression before the last retreat of Lake Lisan at 17–15 kyr bp or with the ancient seawaters of the Sedom Lagoon in the early Pleistocene, in both cases unaffected by significant evaporation processes but chemically and isotopically modified by water/rock interaction.

The Cave of the Letters Sediments—Indication of an Early Phase of the Dead Sea Depression?

Abstract The highest aquatic sediments along the shoulders of the Dead Sea depression have been found in the Cave of the Letters, Nahal Hever, Israel. The cave has acted as a sediment trap, preserving autogenic dolomite and detritic deposits. The dolomitic sediment may correlate with late Miocene dolomites within the rift valley. The morphostratigraphic setting of the sediment implies deposition within an early topographic low that existed in the Dead Sea region since ∼10 to 7 Ma.

Seismicity of the Sinai subplate region:kinematicimplications

The seismic activity of the Sinai subplate region on the basis of both historical (2200B.C.–1900 A.D.) and recent (1900–1995) earthquake catalogs have been evaluated.Moderateand large earthquakes occurred mainly at the subplate boundaries, Dead Sea Fault (DSF) systemin the east, Cyprean arc in the north, and Suez rift in the southwest. Along the Dead Sea Fault system the activity concentrated at the southern andcentralsegments. The earthquake distribution appears to have a tendency to cluster in time andspace.The swarms (February, 1983; April, 1990; August, 1993 and November, 1995) in the GulfofAqaba indicate that the southern segment of the Dead Sea Fault system is the mostseismogenicthrough the last two decades. North of the Dead Sea depression the seismic activitytends to haveoccurred with NW trend to extend under the Levantine Sea. Although the northernsegment ofthe Dead Sea Fault system is well defined from geological, geophysical and historicalearthquakeactivity recent seismic activity is practically absent especially north of Latitude 34°N. In the eastern Mediterranean the seismicity is much higher in the area of the Hellenicarcthan in the Cyprean arc. Moreover, the activity occurs in a wide belt suggesting that theplateboundary is a deformation zone instead of a single line. The seismic activity in the Gulf of Suez is scattered and does not have any distincttrend.However, three active zones are delineated. At the mouth of the gulf most of activityisconcentrated where the Sinai triple junction (Africa, Arabia, Sinai) is situated. The centralpartand the northern part of the gulf include the adjacent area as far as the river Nile. Actually,theactivity is markedly decreased from south to north. Although there is no seismological evidence that the Suez rift continues into theeasternMediterranean, the activity in the Gulf of Suez region cannot be ignored. The parameters of magnitude-frequency relation ( a, b) indicate thatthelevel of earthquake activity in the Sinai subplate region is generally moderate. Moreover,theenergy release curve shows a regular trend and reflects occasional high activity. © 1999ElsevierScience Ltd. All rights reserved.

Digital topography and bathymetry of the area of the Dead Sea Depression

The Dead Sea Depression occupies the central part of that segment of the Syrian-African rift extending from the mountains of southern Lebanon to the Arava Valley north of the Gulf of Aqaba on the Red Sea. The lowest continental feature in the world, it encloses the Dead Sea, whose surface now lies at about −409 m. This shrunken sea consists of a shallow southern basin occupied by evaporation pans, and a northern basin, 50 km in length by 13–17 km in width, with a flat floor some −731 m below MSL. The depression is asymmetric, with the mountains to the east being up to 500 m higher. The closed depression has two outlets, one at 60.5 m altitude into the Mediterranean via the Jezreel Valley near Afula, and a second into the Red Sea at about 200 m altitude in the Arava Valley. A digital terrain model (DTM), based upon the local 1:50,000 scale topographic maps and modern bathymetric surveys, gives elevations to decimeter resolution on a grid with 25 m spacing. When visualized as shaded relief or in coloured hypsometric format, the DTM graphically shows the overall morphology and its many features. These include the local tectonics, from the major boundary faults to the associated subsidiary faults and lineaments, and their possible relationships with the incised canyons offshore. Also clearly visible are the volcanic cones on the Golan heights, the coast-paralleling kurkar ridges, and the halokinetic disruptions to the deep offshore topography. The DTM was used to compute a hypsometric curve for the closed depression from −731 m to +60 m. The maximum area and volume of a lake extending to the Afula ‘spillway’ would be 5985 km 2 and 1602 km 3, respectively. Inflection points were observed at −715 m, where the Dead Sea's flat bottom meets its steep flanks, at −385 m where the northern basin meets the flat floor of the southern basin and surrounding plain, at −228 with the step up to the basin of the Sea of Galilee, and at Mediterranean sea level.

Transverse faults at the northern end of the southern basin of the Dead Sea graben

Classical models for pull-apart basins along strike-slip faults predict normal motion along the transverse faults which cross the basin. A detailed geophysical investigation was carried out across the northern end of the southern sub-basin of the Dead Sea depression. The study included analysis of newly obtained 3.5 kHz seismic profiles, and reinterpretation of existing single channel sparker seismic profiles and multichannel seismic profiles. The unique combination of very shallow and deep seismic profiles reveals the recent activity of a transverse fault in the study area and helps trace its direction. The northern end of the southern sub-basin was probably characterized by normal movement during the Miocene-Early Pleistocene. Thereafter, during the Late Pleistocene-present, the mode of its activity changed to strike-slip movement.

Microearthquake activity in the Dead Sea region

Small earthquakes in the Dead Sea depression, part of the Jordan valley-Dead Sea rift, were recorded and analysed. With 117 identified events of 0.5 ≤ ML ≤ 4.2, the microseismicity, recorded by a local portable network during a period of about 20 months, shows a normal rate of seismicity for the region with b values around 0.8. The recorded seismicity is mainly confined to the basin and its boundaries. In the southern part of the Dead Sea basin we found a tendency to clustering, which is clearly demonstrated in very similar seismograms of several events recorded at the same station. Two clusters on the eastern fault are separated by an area with no seismicity for at least 5 yr. Relative location of events in one of the clusters exhibits a clear north-south lineament. Two active north-south left-lateral strike-slip faults along the east and west boundaries of the southern section of the Dead Sea basin are distinguished and confirmed by using composite focal mechanism solutions. In four, out of more than 60 events, we found normal faulting, where one has a ML = 4.1. For 34 events with 1.6 ≤ ML ≤ 4.2 we found seismic moment estimates, M0, of 1.2 × 1019 ≤ M0 ≤ 2.3 × 1022 dyne cm and Brune stress drop estimates, Δσ, between 0.6 and 92 bars. For earthquakes of M0 smaller than about 5 × 1021 dyne cm, we found only small variations in corner frequency, f0, resulting in decreasing Δσ with decreasing M0. This breakdown of the scaling relation for small earthquakes suggests an fmax slightly lower than 10 Hz for the Dead Sea region. The fmax is confirmed by available accelerometer data.

Structural features in the Dead Sea-Jordan rift zone, interpreted from a combined magnetic-gravity study

The results of a combined analysis of aeromagnetic and gravity data covering the rift and adjacent areas show two different deep structural models: (a) Across the northern and central portions of the rift zone the crustal thickness and the character of the upper mantle remain unchanged. On the other hand, the lithology of the upper crust varies laterally so that the mafic composition of the rock type probably increases from east to west. (b) The southern portion of the rift may be underlain by an anomalous, low-density upper mantle. Local negative gravity anomalies within the rift zone delineate deep depressions, separated by structural highs. The Dead Sea depression is interpreted to be filled by 7.5 km of young, low-density sediments. Local magnetic anomalies which cover the northern portion only are interpreted as basalt flows. This approach enables delineation of fault patterns which support the classic view of sinistral strike slip movement along a complicated fault system.

Asymmetry and basin migration in the dead sea rift

The Dead Sea depression sensu stricto, forms the deepest continental part of the Dead Sea rift, a transfer which separates the Levanthine and Arabian plates. It is occupied by three distinct sedimentary bodies, deposited in basins whose depocenters are displaced northward with time. They are: the continental red beds of the Hazeva Formation (Miocene), the Bira-Lido-Gesher marls and the exceptionally thick rocksalt of the Sedom Formation (Pliocene—Early Pleistocene), and the successive Amora, Lisan and Dead Sea evaporites and clastics (Early Pleistocene—Recent). Lengthwise and crosswise asymmetries of these sedimentary basins and their respective depocenters are due to: leftlateral shear combined with anticlockwise rotation of the Arabian (eastern) plate; steeper faulting of the crustal eastern margin than of the western sedimentary margin, and modification of depositional pattern by twice filling up of basins, by Hazeva red beds during Late Miocene pause of shear and by Sedom rocksalt during Pliocene marine ingression.

The genesis of the asphalt in the Dead Sea area

The hydrocarbon occurrences of asphalts, heavy oils and oil shales in the Dead Sea area and the possible genetic relation between them have been studied. The similarity in organochemical characteristics, i.e., the elemental composition of asphaltenes, the distribution pattern of the saturated hydrocarbons and the predominance of V (over Ni)-porphyrins in both the oils and the asphalts indicate a close relation between them. On the other hand, dissimilarities in the same organochemical characteristics in both the asphalts and the oil shale exclude the hypotheses that asphalt was generated and expelled from the oil shales or that the shales were contaminated by oils. Water washing and biodegradation are considered to be the processes through which preferential depletion of hydrocarbons occurred, altering the oils to asphalts. The burial of the degraded asphalt to a relatively great depth resulted in a secondary generation of small amounts of light saturated hydrocarbons in these asphalts. The oils, which are thought to be the precursors of the asphalts, have either been flushed into the Dead Sea depression from the surrounding elevated areas or have seeped upwards from deep local accumulations in the graben.