Lisan Formation Research Articles

Slide Stacking: A new mechanism to repeat stratigraphic sequences during gravity-driven extension

Gravity-driven sliding of sediments down subaqueous slopes results in mass transport deposits (MTDs) recognised both in outcrop studies and from offshore margins where they may extend for 100's km. While seismic sections may reveal the large-scale geometry of such features, they fail to capture some of the structural and stratigraphic detail necessary for a fuller understanding of the processes involved. Using the late Pleistocene Lisan Formation sediments exposed around the Dead Sea Basin as our case study, we show that interplay between bed-parallel translational slides and associated normal faults may result in stratigraphic repetition through a process we term ‘slide stacking’. This mechanism, where retrogressive slope failure results in slides cutting across earlier normal faults, produces repeated sequences with older over younger stratigraphic relationships more usually attributed to compressional (thrust) deformation. Slide stacking results in a ∼25% attenuation of the upper sequence above the basal shear surface (BSS), which is itself associated with liquefaction and fluidised sediment. The displaced stratigraphy above the BSS is also marked by sedimentary rafts that are broken into blocks by normal faults and become increasingly separated from one another during downslope translation. The hangingwalls of synthetic listric faults form roll-overs that are progressively tightened towards the underlying BSS to create overturned anticlines that apparently verge upslope. The paradoxical situation therefore arises of contractional geometries, such as older over younger stratigraphic repetition across slides, and upslope-verging recumbent anticlines with locally overturned limbs being created during downslope-directed gravity-driven extension. The downslope margin of the slide stack displays earlier normal faults that created scarps where much of the sedimentary buttress, that would otherwise support the toe of the slide, was removed. Consequently, this leads to predominantly superficial and unrestrained downslope slipping, resulting in very localised contractional geometries that do not balance the overall extension, as in classical gravity-failure models. Localised deformation of the sedimentary sequence that unconformably overlies the slide stack indicates that downslope translation continued after the initial rapid slope failure, suggesting that the entire MTD remained inherently unstable. Slide stacking operates at km scales with stratigraphic repetition governed by the throw of earlier normal faults and the amount of downslope translation.

Heinrich Event 2 (ca. 24 ka BP) as a chrono-climatic anchor for the appearance of Epipaleolithic backed bladelets microlith industries in the Southern Levant

The Early Epipaleolithic (EEP) of the Southern Levant, roughly dated to 25-18 ka BP, is characterized by microlithic industries with highly variable synchronic and geographic techno-typological characteristics, the chronology of which remains poorly understood.Here, we present the results from excavations at Idan VII, a well-preserved site amongst a cluster of newly discovered EEP occurrences in the hyper-arid Arava Valley, Israel. The finds are embedded within the Late Pleistocene Lisan Formation lacustrine sediments, an extensively studied paleo-hydroclimatic archive in the Rift Valley. This unique situation enables contextualization of the archaeological finds within the detailed paleo-climatic chronology.The data presented include the stratigraphy (geomorphology and micro-geoarchaeology), relative (related to paleo-lake curve) and absolute (radiocarbon and U–Th) chronology, and archaeological (lithics, faunal and botanical) remains. The results demonstrate that the Idan EEP occurrences are situated within a localized relatively short-lived paleo-wetland area adjacent to Lake Lisan, during or immediately after the extremely cool and locally dry Heinrich Event 2 (H2), ca. 24 ka BP.The results are critically examined with respect to available radiocarbon dates from EEP archaeological sites in the Southern Levant. These, together with the geomorphological evidence, indicate that the Idan VII assemblage, while superficially resembling the so-called ‘Late Kebaran’ industry, actually significantly predates its most pertinent techno-typological analogs, highlighting the necessity of re-evaluating the “Kebaran complex”. Rather, it is coeval with the local, but unrelated ‘Masraqan’ and ‘Nebekian’ industries at the very onset of the EEP, demonstrating the high degree of Last Glacial Maximum hunter-gatherer cultural diversity then present in the Levant.In contextualizing the results within the Northern Hemisphere chrono-climatic framework, we conclude that within the Southern Levant, the H2 provides a solid chrono-climatic anchor for the appearance of fully-fledged backed bladelets microlithic industries, which probably reflects a technological change in composite projectile hunting gear that occurred during the EEP.

Characterising bed-parallel slip during gravity-driven deformation

Despite the recognition that bed-parallel slip (BPS) must operate during gravity-driven deformation of basinal sediments, there is a general paucity of detailed outcrop-based observations to characterise and detect such a process. We therefore present detailed timing relationships between BPS and steeper dip-slip faults that were both created during seismically-triggered downslope-directed movement of sediments. Using the late Pleistocene Lisan Formation that was deposited around the Dead Sea Basin as our case study, we show that ‘sub-seismic’ decametric scale BPS planes may pre-date, post-date, or operate coevally with steeper faults generated as sediments slip downslope towards the depocentre. Older BPS can be recognised by sediment injections and minor folds and fractures, whereas younger BPS displaces marker faults downslope towards the basin. BPS operating coevally with steeper faults results in complex overprinting and development of fault-bound lenses. BPS that forms along single surfaces in the footwall of normal faults becomes separated into two distinct planes in the downthrown hangingwall block, indicating broadly coeval development. Adjacent BPS planes that operate synchronously result in synthetic and antithetic faults that ‘hard-link’ and transfer displacement between BPS planes. Attenuated bedding between segments of BPS that overlap and terminate next to one another suggests that ‘soft-linkage’ also forms between coeval BPS planes. Displacement-length relationships of measured BPS planes plot in the same range as recorded for normal faults, although BPS with larger displacements have relatively ‘short’ lengths, suggesting that complete BPS planes are missing due to limitations of outcrop size. Although the lack of displaced bedding across BPS makes it largely invisible on seismic sections across large-scale gravity-driven systems, it does potentially contribute towards the apparent inbalance between net extension and contraction observed in many sections across mass transport deposits. In addition, the realisation that BPS interacts with dip-slip faults to create repeated and missing sections that are particularly focussed along earlier deformed horizons and turbidites, has implications for palaeoseismic studies that assume broadly continuous stratigraphy.

Criteria to identify sedimentary sills intruded during deformation of lacustrine sequences

Although sedimentary dykes have been widely reported across a range of settings, sedimentary sills have received somewhat less attention, perhaps due to the potential difficulties in identifying largely conformable intrusions within bedded sequences. Most outcrop descriptions of clastic intrusions are based on deep-water marine sequences, with few descriptions of sills in lacustrine settings. The recognition of sills in such settings is, however, important because lacustrine sequences are increasingly used as a record of palaeoseismic activity. The misidentification of sills that contain fragments and clasts of host stratigraphy with seismically-generated turbidites and debris flows, may lead to incorrect interpretations of palaeoseismicity. We use the Late Pleistocene Lisan Formation of the Dead Sea Basin as a case study, where laminated lake sediments preserve intricate relationships with sills. This permits us to not only establish a range of criteria used in the identification of sedimentary sills, but also examine relationships with adjacent seismically-triggered slumps and slides. Key criteria we use to recognise sills include marked changes in their thickness together with bifurcation and bridging geometries. Sills may be internally layered, contain lenses of breccia, together with aligned and folded clasts that may be truncated across upper sill contacts. Critical evidence for the interpretation of sills is also preserved along sharp but irregular upper contacts that erode and truncate bedding in the overlying host sequence. Minor apophyses and ‘wedges’ intrude both upwards and downwards from sills, while isoclinal recumbent ‘peel-back’ folds are created in host sediments by shear generated along the lower contacts of sills. We have undertaken anisotropy of magnetic susceptibility (AMS) analysis and find an oblate fabric that suggests flow and intrusion of sills along the strike of the slope, that may also help with their identification in bedded sequences. Sills form along detachments to both extensional and contractional deformation associated with seismically-generated slumps and mass transport deposits, together with sub-surface fold and thrust systems. High fluid pressures associated with injection of sedimentary sills may facilitate near-surface failure and downslope movement of the sedimentary pile.

Recognising surface versus sub-surface deformation of soft-sediments: Consequences and considerations for palaeoseismic studies

Soft-sediment deformation structures associated with slumps and mass transport deposits (MTDs) are generally considered to form at the surface when unlithified sediment moves downslope under the influence of gravity. Where stratigraphic sequences contain several deformed horizons, the question arises as to whether repeated slope failure at the sediment surface has systematically built-up multiple MTDs in the stratigraphic record in a ‘sequential failure model’. Alternatively, a single failure event may concurrently create surficial and sub-surface deformed ‘intrastratal’ horizons at different stratigraphic levels in a ‘synchronous failure model’. The implications of these differing models are important as sub-surface deformation can be significantly younger than the depositional age of beds it affects thereby weakening age-depth correlations used to estimate the timing of palaeo-earthquakes. In order to investigate the potential for sub-surface deformation, we examine the late Pleistocene Lisan Formation exposed around the Dead Sea Basin that contains numerous MTDs and gravity-driven fold and thrust systems. Surficial deformation is recognised by identifying irregular erosive surfaces above MTDs that are overlain by sedimentary caps deposited out of suspension following the failure event. Such surficial deformation is also characterised by thickened sedimentary successions that create ‘growth’ sequences. Conversely, sub-surface intrastratal deformation is typified by detachment-bound folds and thrusts that are marked by repetitions of stratigraphy across the upper detachment surface, fluidised sediment that intrudes upwards into the overlying sequence, together with abrupt truncations of older faults developed in overburden above the detachment. MTDs created at the surface form relatively competent horizons when subsequently buried as they are internally disrupted and lack ‘layer-cake’ geometries, while repeated seismicity can lead to dewatering and compaction resulting in ‘seismic strengthening’. Later sub-surface deformation may therefore be focussed adjacent to earlier MTDs that influence the mechanical stratigraphy, leading to secondary failures and complications when attempting to ‘balance’ extension and contraction that may be of different ages. Sub-surface deformation is localised along discrete detachments that carry the overlying sequence downslope as relatively intact slides, affecting what appear to be ‘undeformed’ beds between individual MTDs. As sub-surface deformation does not directly correlate with sedimentary caps, the rates of movement on deeper detachments remain unconstrained and may be significantly slower than surficial deformation resulting in downslope creep of the sediment pile.

Zones of inelastic deformation around surface ruptures detected by magnetic fabrics

Characterizing the inelastic strain field around co-seismic faults is a key to understanding earthquake rupture processes. We aim to detect zones of inelastic deformation around surface ruptures, using Anisotropy of Magnetic Susceptibility (AMS) analyses. To characterize the paleo-seismic setting we measured 29 normal faults, which cut the late Pleistocene lacustrine Lisan Formation and were associated with shallow (<~12 km) earthquakes at the margins of the Dead Sea Basin. In order to define the geometry of those zones around a representative fault, 220 specimens were sampled in a 2D grid and analyzed by studying the room temperature AMS axes and parameters using spatial IDW (inverse distance weighting) interpolation on a cross section around the fault plane. To separate the total magnetic susceptibility of the Lisan sediments into diamagnetic, paramagnetic and ferromagnetic susceptibilities, we applied the low temperature AMS (LT-AMS) and Anhysteretic Remanent Magnetization (AARM) methods. The structural measurements demonstrate that the co-seismic faulting in the Dead Sea Basin, triggered mainly by E-W extension. The results show that the paramagnetic phase is dominant in both the aragonite-rich and the detritus-rich layers. The zones of inelastic deformation are distributed asymmetrically about the fault plane, with affinity to the observed displacement profile and in agreement with dynamic propagation models that suggest that the rupture propagated towards the surface. The discontinuous distribution of deformation around the fault plane is the result of both the faults single event propagation style and fault plane asperities. These results demonstrate a novel application of AMS analysis for defining the geometry of the inelastic strain field surrounding co-seismic faults, and improving fault propagation models dealing with the inelastic off-fault response.

Distinguishing coeval patterns of contraction and collapse around flow lobes in mass transport deposits

Gravity-driven mass transport deposits (MTDs) form by the downslope-directed movement of sediment associated with slope failure. Simple models suggest that extension forms at the upslope (head) area, contraction is focussed in the downslope toe of the slump, while differential shear associated with strike-slip is restricted to the lateral margins of the slump. Although the head and toe are considered to be dominated by layer-parallel shear (LPS), differential layer-normal shear (LNS) may be generated around the lateral margins of slumps and potentially also within MTDs where flow has been separated into different ‘lobes’. Despite this realisation that LNS must form, there has been little work into the geometries and spatial relationships of resulting structures. Using the late Pleistocene Lisan Formation exposed around the Dead Sea Basin as our case study, we examine detailed (<10 m) relationships of folds and thrusts created during LNS and LPS, as well as investigating the role of broadly coeval extension that may reactivate these structures. We also undertake analysis of anisotropy of magnetic susceptibility (AMS) fabrics to determine flow and shear relationships around folds and detachments created during LNS and LPS. Our study shows that LPS results in gently-curvilinear fold hinges that arc around the transport direction while LNS results in cylindrical fold hinges developed oblique or sub-parallel to transport. Such folds may be recumbent or upright, and associated with lateral ramps marking areas of differential LNS within the MTD. These structures are interpreted to accommodate variations in the amount and direction of downslope-directed movement resulting in LNS around the margins of individual flow ‘lobes’ that are developed over tens of metres. These ‘lobes’ display broadly down-slope transport with locally radial flow that results in along-strike shortening between lobes. Our analysis of AMS fabrics shows that they are controlled by slump folds, but magnetic fabrics do not differentiate how these folds were created in zones of LPS or differential LNS. AMS taken from gouge formed along detachments marked by differential LNS provide a first-order indicator for the transport direction. In addition, AMS fabrics in gouge or fluidised layers directly beneath thrust ramps, reveals prolate fabrics marking a component of strike-parallel flow along the branching intersections of thrust ramps and flats. Extensional faults directly reactivate existing thrusts, or create new extensional faults that are sub-parallel to thrusts or cut across them at steeper angles. Extension is part of the same MTD event as a sedimentary cap that is deposited out of suspension following slope failure, overlies and locally thickens into the hangingwall of extensional faults to create ‘growth’ sequences. Extensional reactivation and ‘collapse’ of original thrusts may help explain why contraction is apparently ‘missing’ from many seismic sections across MTDs.

Folding during soft-sediment deformation

Abstract The detailed analysis of folding in rocks was in part pioneered by John Ramsay, and resulted in a range of techniques and criteria to define folds. Although folding of unlithified or ‘soft’ sediments is typically assumed to produce similar geometries to those in ‘hard rocks’, there has to date been little detailed analysis of such folds. The aim of this paper is therefore to investigate folds developed during soft-sediment deformation (SSD) by applying techniques established for the analysis of tectonic folds during hard-rock deformation (HRD). We use the Late Pleistocene Lisan Formation exposed around the Dead Sea as our case study, as the laminated lake sediments record intricacies of fold detail generated during seismically triggered slumping of mass transport deposits (MTDs) towards the depocentre of the basin. While it is frequently assumed that folds created during SSD are chaotic and form disharmonic structures, we provide analyses that show harmonic fold trains may form during slumping, although larger upright folds cannot be traced for significant distances and are more typically disharmonic. Our analysis also reveals a range of fold styles, with more competent detrital-rich layers displaying buckles (Class 1B), as well as upright Class 1A folds marked by thickened limbs. Class 1A buckle folds are generally considered to be created by flattening that overprints folds with an original Class 1B geometry. As thickened fold limbs are truncated by overlying erosive surfaces, the vertical flattening is considered to have occurred during the slump event. Different fold shapes may partially reflect variable flattening, depending on the original orientation of upright or recumbent folds, together with continued downslope-directed simple-shear deformation that modifies the fold geometry. Analysis of fold wavelength, amplitude and bed thickness allows us to plot strain contour maps, and indicates that beds defining slump folds display viscosity contrasts in the range of 50–250, which are similar to values estimated from folds created during HRD in metamorphic rocks. A range of refold patterns, similar to those established by John Ramsay in metamorphic rocks, are observed within slumps, and are truncated by the overlying sediments, indicating that they formed during a single progressive slump event rather than distinct ‘episodes’ of superimposed deformation. This study confirms that techniques developed for the analysis of folds created during HRD are equally applicable to those formed during SSD, and that resulting folds are generally indistinguishable from one another. Extreme caution should therefore be exercised when interpreting the origin of folds in the rock record where the palaeogeographical and tectonic contexts become increasingly uncertain, thereby leading to potential misidentification of folds created during SSD.

Spatial and temporal reconstruction of the late Quaternary Dead Sea sedimentary facies from geophysical properties

The sedimentary sequences that accumulated within various lakes that occupied the Dead Sea Basin since the Pliocene, contain a detailed record of the climate and tectonic history of the area. Until recently, most of the information about these paleo-lakes was derived from exposures along the marginal terraces of the current Dead Sea (lake), focusing mainly on the last Glacial Lake Lisan and the Holocene-modern Dead Sea. The International Continental Drilling Program (ICDP) recovered a series of cores in the northern Dead Sea Basin, both in the deep depocenter (300 m water depth) and in shallower waters near the current shore. Here, we present downhole logging measurements that were used to provide continuous records of petrophysical properties at depth and to reconstruct lithological profiles. The study highlights how logging data can overcome gaps in drilled-core recovery and be used to examine subsurface geology on a regional scale. Gamma ray, resistivity and velocity wire logs were examined to infer a log-derived lithofacies. The reconstructed profiles presented in this study constitute a first attempt to link deep central settings of the basin with marginal sedimentary sequences. Three main facies were identified in the boreholes including: (Bartov et al., 2002) Finely laminated sequences of mudstones interbedded with siltstones to sandstones; (Bartov et al., 2003) Medium to thick bedded mudstone to sandstone: and (Bartov et al., 2007) Evaporites (e.g. halite and gypsum with some intervals of detrital sediments). The formations that were previously defined along the marginal terraces of the Dead Sea: the Holocene Ze'elim Formation, the last Glacial Lisan Formation, the last interglacial Samra Formation and the early to mid-Pleistocene Amora Formation are identified in the boreholes. A spatial correlation is established providing the stratigraphic architecture of the sedimentary structure beneath the Dead Sea during the late Quaternary. This paper combines geophysical and lithological data and provides the base for subsequent studies on facies interpretation.

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%.

Integrated Paleoseismic Chronology of the Last Glacial Lake Lisan: From Lake Margin Seismites to Deep‐Lake Mass Transport Deposits

AbstractSeismically disturbed sedimentary sequences (seismites) in the last glacial (70–14 ka) Lisan Formation are exposed in the marginal terraces of the Dead Sea and recovered from sedimentary core drilled by the International Continental Scientific Drilling Programs at the depocenter of the lake at water depth of 300 m. The core reveals various types of centimeter‐ to meter‐scale disturbed lake sediments: turbidites, homogenites, slumps, and other deformations, interspersed with undisturbed lamination. The transported sediments comprise a main source of the thickness tripling of the Lisan Formation at the depocenter of the lake compared to the margins. Excluding (mass transport deposits MTDs) from chronology yields a normal, event‐free age‐depth model for core. Moreover, time intervals of units missing at the exposed sections of the lake margin are synchronous with intervals of mass transport deposits (MTDs) at the deepest lake floors. In the deep core, the recurrence interval range of MTD with thickness &gt; 1 cm is ~ 100–300 years, while that of the thick MTD (&gt;50 cm) is ~ 2,500 years, twice the recurrence interval of the seismites at the lake's margins. The ~1,000 year recurrence at the lake's margins lies within the ranges that have been calculated for ~M6.5–7 earthquakes. The significantly higher figure shown by depocenter core suggests activity on various faults and the response of the lake sediments in the entire Dead Sea basin. Overall, an unprecedented chronology of seismic activity was achieved for the late Pleistocene Lisan Formation providing a framework of earthquake activity in the vicinity of the Dead Sea basin during the period of the last high lake stand.

Enhanced Saharan dust input to the Levant during Heinrich stadials

The history of dust transport to the Levant during the last glacial period is reconstructed using the isotope ratios of Pb, Sr, Nd, and Hf in sediments of Lake Lisan, the last glacial Dead Sea. Exposed marginal sections of the Lisan Formation were sampled near Masada, the Perazim Valley and from a core drilled at the deep floor of the modern lake. Bulk samples and size fractions display unique isotopic fingerprints: the finest detritus fraction (<5 μm) displays higher 87Sr/86Sr and lower εNd values (0.710–0.713 and −7.0 to −9.8, respectively) relative to the coarser fractions (5–20 μm and <20 μm; 0.708–0.710 and −3.4 to −8.3) and the bulk detritus samples (0.709–0.711 and −6 to −7.5). Similarly, the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios (18.26-19.02, 15.634-15.68, and 38.25-38.82, respectively) are systematically higher in the finest detritus fraction relative to corresponding coarser fractions and bulk samples.The 87Sr/86Sr and εNd values of the finest fraction correspond with those of atmospheric dust originating from the Sahara Desert, while those of the coarse fractions are similar to loess deposits exposed in the Sinai and Negev Deserts. Pronounced excursions in the Sr-Nd-Pb isotope ratios toward more Sahara-like values coincide with the Heinrich (H) stadials 6, 5 and 1, reflecting significant increases in Saharan dust fluxes during regionally arid intervals, reflected by sharp lake level drops. Moreover, during H6 the dust came from different Saharan sources than during H1 and H5. While the relatively wet glacial climate in the Levant suppressed the transport of dust to the lake watershed, short-term hyper-arid spells during H-stadial intervals were accompanied by enhanced supply of fine Sahara dust to this region.

Identifying soft-sediment deformation in rocks

The correct identification of ‘sedimentary’ folds and fabrics created during gravity-driven deformation of unlithified successions from those ‘tectonic’ structures formed during regional deformation is essential when interpreting geological histories preserved within the rock record. This topic has become increasingly relevant over the past 40 years as improved seismic resolution and coverage have led to the realisation that significant portions of unlithified sediments along the continental margins undergo gravity-driven deformation to create mass transport deposits (MTD's). The late-Pleistocene Lisan Formation, exposed in the Dead Sea Basin, was chosen as a case study because it remains poorly lithified, and structures developed within it are unequivocally related to ‘soft-sediment’ deformation (SSD) created when the succession underwent downslope-directed movement. This work tests various assertions previously used to deduce if structures were formed in unlithified sediments or during ‘hard-rock’ deformation (HRD) associated with subsequent tectonism. Within the Lisan Formation, we describe veins developed along fractures, and cleavage forming axial-planar to folds, that are structures previously assumed to be restricted to HRD. In addition, truncated folds, incorporation of deformed fragile fragments into overlying sediment, and cross-cutting clastic dykes are all indicative of SSD. The key diagnostic feature in establishing SSD is the sedimentary infill of irregular erosive surfaces that truncate underlying structures. Although compaction and diagenesis have not played a significant role in the case study, caution should be exercised when examining structures preserved in the rock record as folds and fabrics originally created by SSD may be considerably enhanced and altered where significant overburden exists.

Coseismic horizontal slip revealed by sheared clastic dikes in the Dead Sea Basin

Despite the hazard caused by near-surface destructive horizontal displacements during earthquakes, field evidence for coseismic slip along horizontal discontinuities is exceptionally rare, mainly due to the lack of adequate exposure and markers. However, within the seismically active Dead Sea Basin, the late Pleistocene Lisan Formation contains vertical clastic dikes that are sheared laterally at maximum depths of 15 m, and thereby provide unique profiles of such horizontal displacement. In order to investigate how coseismic horizontal shearing is distributed near the surface, we document an ∼1-m-thick brittle shear zone, consisting of up to 11 slip surfaces that can be traced for tens of meters in the Lisan Formation. Displacements along individual slip surfaces are up to 0.6 m, and the total displacement across the shear zone is up to 2.0 m. Displacement profiles and gradients indicate that the brittle shear zone formed by simple shear, and deformation was associated with slip partitioning and transfer between primary and secondary slip surfaces. Evidence for concurrent displacement along slip surfaces during a single event indicates that the brittle shear zone was formed during a coseismic event subsequent to 30 ka. We consider the mechanical effect of seismic-wave–related transient stress, which, when added to the initial static effective stress, may result in concurrent horizontal shear failure along detrital-rich layers in the Lisan Formation. The exceptional quality of exposures and markers enables us to document, for the first time, the details of near-surface horizontal shearing, and indicates that displacement along horizontal bedding planes is a viable mechanism to absorb coseismic deformation in well-bedded near-surface strata.

Sedimentary and structural controls on seismogenic slumping within mass transport deposits from the Dead Sea Basin

Comparatively little work has been undertaken on how sedimentary environments and facies changes can influence detailed structural development in slump sheets associated with mass transport deposits (MTDs). The nature of downslope deformation at the leading edge of MTDs is currently debated in terms of frontally emergent, frontally confined and open-toed models. An opportunity to study and address these issues occurs within the Dead Sea Basin, where six individual slump sheets (S1–S6) form MTDs in the Late Pleistocene Lisan Formation. All six slumps, which are separated from one another by undeformed beds, are traced towards the NE for up to 1km, and each shows a change in sedimentary facies from detrital-rich in the SW, to more aragonite-rich in the NE. The detrital-rich facies is sourced predominantly from the rift margin 1.5km further SW, while the aragonite-rich facies represents evaporitic precipitation in the hyper saline Lake Lisan. The stacked system of MTDs translates downslope towards the NE and follows a pre-determined sequence controlled by the sedimentary facies. Each individual slump roots downwards into underlying detrital-rich layers and displays a greater detrital content towards the SW, which is marked by increasing folding, while increasing aragonite content towards the NE is associated with more discrete thrusts. The MTDs thin downslope towards the NE, until they pass laterally into undeformed beds at the toe. The amount of contraction also reduces downslope from a maximum of ~50% to <10% at the toe, where upright folds form diffuse ‘open-toed’ systems. We suggest that MTDs are triggered by seismic events, facilitated by detrital-rich horizons, and controlled by palaeoslope orientation. The frequency of individual failures is partially controlled by local environmental influences linked to detrital input and should therefore be used with some caution in more general palaeoseismic studies. We demonstrate that MTDs display ‘open toes’ where distributed contraction results in upright folding and shortening rather than distinct thrusts. Such geometries may account for some of the contraction that is apparently missing when balancing seismic sections across large off shore MTDs.

Clastic dikes in the Dead Sea basin as indicators of local site amplification

Early Holocene seismic activity triggered fluidization and clastic-dike emplacement within Late Pleistocene lacustrine Lisan Formation sediments in the Dead Sea basin (DSB). Hundreds of opening-mode clastic dikes were documented cross-cutting the Lisan Formation in four distinct sites in relatively small ( 6.5). The injection of clastic dikes in distinct and relatively small areas in the Lisan Formation along the DSB may serve as evidence for a unique combination of three factors: (a) clay-rich sediments and high water table as favorable conditions for fluidization on the exposed surface following the Lake Lisan regression; (b) the occurrence of moderate-to-strong earthquakes (M w > 6) in the early Holocene after the deposition of the Lisan Formation; and (c) the local geological structure characterized by edge and basin effects, which can amplify seismic waves. The present study indicates that injection due to fluidization of clay-rich strata during earthquakes was dominant throughout the DSB. We suggest that the clastic dikes can serve as evidence for local amplification conditions following seismic processes that occur close to active faults.

Fold and fabric relationships in temporally and spatially evolving slump systems: A multi-cell flow model

Folds generated in ductile metamorphic terranes and within unlithified sediments affected by slumping are geometrically identical to one another, and distinguishing the origin of such folds in ancient lithified rocks is therefore challenging. Foliation is observed to lie broadly parallel to the axial planes of tectonic folds, whilst it is frequently regarded as absent in slump folds. The presence of foliation is therefore often considered as a reliable criterion for distinguishing tectonic folds from those created during slumping. To test this assertion, we have examined a series of well exposed slump folds within the late Pleistocene Lisan Formation of the Dead Sea Basin. These slumps contain a number of different foliation types, including an axial–planar grain-shape fabric and a crenulation cleavage formed via microfolding of bedding laminae. Folds also contain a spaced disjunctive foliation characterised by extensional displacements across shear fractures. This spaced foliation fans around recumbent fold hinges, with kinematics reversing across the axial plane indicating a flexural shear fold mechanism. Overall, the spaced foliation is penecontemporaneous with each individual slump where it occurs, although in detail it is pre, syn or post the local folds. The identification of foliations within undoubted slump folds indicates that the presence or absence of foliation is not in itself a robust criterion to distinguish tectonic from soft-sediment folds. Extensional shear fractures displaying a range of temporal relationships with slump folds suggests that traditional single-cell flow models, where extension is focussed at the head and contraction in the lower toe of the slump, are a gross simplification. We therefore propose a new multi-cell flow model involving coeval second-order flow cells that interact with neighbouring cells during translation of the slump.

Fire and Brimstone: The Microbially Mediated Formation of Elemental Sulfur Nodules from an Isotope and Major Element Study in the Paleo-Dead Sea

We present coupled sulfur and oxygen isotope data from sulfur nodules and surrounding gypsum, as well as iron and manganese concentration data, from the Lisan Formation near the Dead Sea (Israel). The sulfur isotope composition in the nodules ranges between -9 and -11‰, 27 to 29‰ lighter than the surrounding gypsum, while the oxygen isotope composition of the gypsum is constant around 24‰. The constant sulfur isotope composition of the nodule is consistent with formation in an ‘open system’. Iron concentrations in the gypsum increase toward the nodule, while manganese concentrations decrease, suggesting a redox boundary at the nodule-gypsum interface during aqueous phase diagenesis. We propose that sulfur nodules in the Lisan Formation are generated through bacterial sulfate reduction, which terminates at elemental sulfur. We speculate that the sulfate-saturated pore fluids, coupled with the low availability of an electron donor, terminates the trithionate pathway before the final two-electron reduction, producing thionites, which then disproportionate to form abundant elemental sulfur.

Seismogenic slump folds formed by gravity-driven tectonics down a negligible subaqueous slope

Abstract The Late Pleistocene Lisan Formation contains superb examples of soft-sediment deformation generated during gravity-driven slumping and failure down extremely gentle (

Hydrogeochemical investigation of groundwater in Jericho area in the Jordan Valley, West Bank, Palestine

Water resources in the Middle East, particularly in Palestine, are extremely scarce and costly. The Jordan Valley is a fertile productive region, described as the food basket of Palestine. Groundwater originating from the Quaternary Aquifer System forms the main water resource in the Jordan Valley. However, the quality of this groundwater is threatened mainly by the high chloride concentration. The most representative area of the Jordan Valley is Jericho area, which was chosen to be the study area. The study area (65km2) is almost a flat area with a gentle decline towards the east. It is the lowest land on earth with ground levels reaching 400meters below sea level (mbsl) near the Dead Sea shores. The Quaternary Aquifer System in the study area could be divided into an upper alluvial layer with thickness varying from 40 to 150m and a lower low-permeable Lisan layer, which crops out in the eastern part of the study area with thickness over 200m. Hydrogeochemical investigation reveals that the water is generally earth alkaline with higher content of earth alkalis and prevailing chloride. According to Stuyfzand (1986) and Piper’s (1944) classification systems, water type in the Alluvial Aquifer varies from fresh hard CaMgHCO3 or MgCaHCO3 water in the west and northwest to brackish very-hard MgNaCl or NaMgCl in the middle. In the east, the water becomes brackish-salt extremely-hard MgNaCl or NaCl. Groundwater quality is deteriorating (increase in salinity) spatially towards the east and vertically with increasing depth (when nearing the Lisan Formation). As an indication of groundwater salinity, total dissolved solids show some variability with time over the last 21years (1983–2004). In short-time scale, there are high seasonal and yearly fluctuations with regard to salinity, specifically in Cl− and SO42- contents. Spring water from the Upper Cenomanian Aquifer (CaHCO3) represents the fresh end member, while Rift Valley Brines (RVB-CaNaCl) and Dead Sea Brines (DSB-MgNaCl) represent the saline end members. Existing water types are mixtures of the 3 end members. There is a consistency in results and analysis of geological, hydrogeological, hydrochemical and geophysical data. There are three probable sources of increase in groundwater salinity: mixing with saline end members (RVB/DSB); dissolution of minerals of the Lisan Formation (calcite, dolomite, gypsum and halite); and to some extent, agricultural effluent pollution.