Michael Lazar

Is the Jericho Escarpment a Tectonic or a Geomorphological Feature? Active Faulting and Paleoseismic Trenching

The Jericho fault is considered to be the main active fault in the northern Dead Sea–lower Jordan Valley. In previous studies it has been identified by a prominent linear topographic escarpment that is thought to be the surface expression of this fault on land north of the Dead Sea. In this study, the paleoseismic natures of the escarpment and the fault were examined. Seismic activity was investigated in a series of three trenches excavated south of the fault trace on the surface. These trenches show evidence for Late Holocene faulting. A fourth trench excavated 300 m farther to the south exposed continuous, finely laminated marl from the ∼80‐ka Samra Formation at a depth of 2–0.6 m below the surface, with no evidence of faulting. This could suggest that the fault on land is segmented and that the nature of its activity changes from north to south toward the lake. Indeed, the continuation of this fault under the waters of the Dead Sea reveals active faulting along a sharp, segmented, linear bathymetric break, where the steep margin slope on the west meets the flat lake bottom. Evidence of drastic climatic changes and erosion are present in all trenches that were excavated, indicating that the prominent escarpment may in part be an erosional feature, perhaps formed by incision of an ancient Jordan River or along a Holocene lakeshore. A channel fill of a lacustrine nature that followed a period of erosion is interpreted as a high stand of the Dead Sea, which is contemporaneous with the Younger Dryas cooling period.

Two centuries of coastal change at Caesarea, Israel: natural processes vs. human intervention

The coast at Caesarea, Israel, has been inhabited almost continuously for the last 2,400 years, and the archeological sites are today a major international tourist attraction. Because the sites straddle the shoreline, they are subject to constant damage by wave action, and must therefore be frequently restored. In this paper, local shoreline migrations over the last 200 years are investigated with the aim of distinguishing between natural and man-made coastal changes. In order to assess these changes accurately, geomorphological and sedimentological data were examined based on detailed beach profile measurements, bathymetric surveys, and grain-size analyses. In addition, series of old aerial photographs, as well as historical topographic maps and nautical charts were consulted. The results show that shoreline changes can be grouped into two main time periods. During the first period from 1862 to 1949 before the expansion of modern settlements, the position of the shoreline changed irregularly by up to 30 m. In the second period from 1949 onward, numerous coastal structures have been erected, and various coastal modifications have been carried out. The evaluation of the data suggests that human interventions have had relatively little effect on the overall position of the shoreline, as displacements ranged only from 5 to 18 m. Thus, coastal changes at Caesarea are predominantly due to natural wave action reflected in the heterogeneous geomorphological and sedimentological characteristics of the shore. This contradicts the common assumption that human activities are always mainly responsible for large-scale shoreline modifications in the region. It is concluded that, in order to implement meaningful mitigating countermeasures, coastal archeological sites need to be individually assessed with respect to the dominant factors causing local coastal change.

Pockmark asymmetry and seafloor currents in the Santos Basin offshore Brazil

Pockmarks form by gas/fluid expulsion into the ocean and are preserved under conditions of negligible sedimentation. Ideally, they are circular at the seafloor and symmetrical in profile. Elliptical pockmarks are more enigmatic. They are associated with seafloor currents while asymmetry is connected to sedimentation patterns. This study examines these associations through morphological analysis of new multibeam data collected across the Santos continental slope offshore Brazil in 2011 (353–865 mbsl). Of 984 pockmarks, 78% are both elliptical and asymmetric. Geometric criteria divide the pockmarks into three depth ranges that correlate with a transition between two currents: the Brazil Current transfers Tropical Water and South Atlantic Central Water southwestwards while the Intermediate Western Boundary Current transfers Antarctic Intermediate Water northeastwards. It is suggested that the velocity of seafloor currents and their persistence dictate pockmark ellipticity, orientation and profile asymmetry. Fast currents (>20 cm/s) are capable of maintaining pockmark flank steepness close to the angle of repose. These morphological expressions present direct evidence for an edge effect of the South Atlantic Subtropical Gyre and, in general, provide a correlation between pockmark geometry and seafloor currents that can be applied at other locations worldwide.

Coincidence or not? Interconnected gas/fluid migration and ocean–atmosphere oscillations in the Levant Basin

A growing number of studies on shallow marine gas/fluid systems from across the globe indicate their abundance throughout geological epochs. However, these episodic events have not been fully integrated into the fundamental concepts of continental margin development, which are thought to be dictated by three elements: tectonics, sedimentation and eustasy. The current study focuses on the passive sector of the Levant Basin on the eastern Mediterranean continental margin where these elements are well constrained, in order to isolate the contribution of gas/fluid systems. Single-channel, multichannel and 3D seismic reflection data are interpreted in terms of variance, chaos, envelope and sweetness attributes. Correlation with the Romi-1 borehole and sequence boundaries constrains interpretation of seismic stratigraphy. Results show a variety of fluid- or gas-related features such as seafloor and subsurface pockmarks, volumes of acoustic blanking, bright spots, conic pinnacle mounds, gas chimneys and high sweetness zones that represent possible secondary reservoirs. It is suggested that gas/fluid migrate upwards along lithological conduits such as falling-stage systems tracts and sequence boundaries during both highstands and lowstands. In all, 13 mid-late Pleistocene sequence boundaries are accompanied by independent evidence of 13 eustatic sea-level drops. Whether this connection is coincidental or not requires further research. These findings fill gaps between previously reported sporadic appearances throughout the Levant Basin and margin and throughout geological time from the Messinian until the present day, and create a unified framework for understanding the system as a whole. Repetitive appearance of these features suggests that their role in the morphodynamics of continental margins is more important than previously thought and thus may constitute one of the key elements of continental margin development.

An extensive pockmark field on the upper Atlantic margin of Southeast Brazil: spatial analysis and its relationship with salt diapirism

We present new evidence for the existence of a large pockmark field on the continental slope of the Santos Basin, offshore southeast Brazil. A recent high-resolution multibeam bathymetric survey revealed 984 pockmarks across a smooth seabed at water depths of 300–700 m. Four patterns of pockmark arrays were identified in the data: linear, network, concentric, and radial. Interpretation of Two-dimensional multi-channel seismic reflection profiles that crosscut the surveyed area shows numerous salt diapirs in various stages of development (e.g. salt domes, walls, and anticlines). Some diapirs were exposed on the seafloor, whereas the tops of others (diapir heads) were situated several hundreds of meters below the surface. Extensional faults typically cap these diapirs and reach shallow depths beneath the seafloor. Our analysis suggests that these pockmark patterns are linked to stages in the development of underlying diapirs and their related faults. The latter may extend above salt walls, take the form of polygonal extensional faults along higher-level salt anticlines, or concentric faults above diapir heads that reach close to the seafloor. Seismic data also revealed buried pockmark fields that had repeatedly developed since the Middle Miocene. The close spatio-temporal connection between pockmark and diapir distribution identified here suggests that the pockmark field extends further across the Campos and Espírito Santo Basins, offshore Brazil. Spatial overlap between the pockmark field topping a large diapir field and a proliferous hydrocarbon basin is believed to have facilitated the escape of fluid/gas from the subsurface to the water column, which was enhanced by halokinesis. This provides a possible control on fossil gas contribution to the marine system over geological time.

Structural styles along the Dead Sea Fault

The Dead Sea fault is a left-lateral transform plate boundary separating the Arabian Plate and the Sinai sub-plate. Motion along the fault is not pure strike-slip and the direction of the plate boundary changes several times resulting in areas of transtension and transpression. This is evident by the variable morphology and structure. The fault is divided into two sections which differ by a reversal in the large-scale asymmetry – the southern section from the Gulf of Elat to south of Lebanon (where the eastern side is usually higher than the western side) and a section continuing northward from Lebanon to the Taurus mountain range in Turkey (where the western side is mostly higher than the eastern one). Along strike variations in topography and structure subdivide the southern Dead Sea fault into five segments. From south to north, these are the Gulf of Elat, Arava, Dead Sea, the Sea of Galilee and the Hula Valley. Deep Asymmetric pull-apart basins, which tend to become shorter and younger in age northwards, formed between left-stepping fault segments of the Dead Sea fault. These basins can be found in topographically lower areas and are separated by structural saddles. Both extensional and compressional features can be found along many of the basins themselves, suggesting that the tectonic regime is more complex than suggested in the simple models.

Mapping exposed and buried river channels using remote sensing techniques with an example from Mubra channel, the Negev, Israel

The Halutza, Agur and Shunra sand dunes are the continuation of the great northern Sinai dunes. Playa sediments from the late Quaternary are found on upper parts of river channels in the area of the dunes of the Northwest Negev and represent disorder in the drainage system caused by wandering of the dunes during other periods. This research examines the ability to use Synthetic Aperture Radar data (SAR), Ground Penetrating Radar (GPR) and other shallow geophysical methods as ground truth in combination with optical and IR data, for detection, identification and mapping of buried channels under sand and exposed channels in the Negev Height, Israel. The buried continuation of Mubra channel, under the Shunra sand dunes towards the west can be seen at a distance of 285 meters from 30:58:42N, 34:36:03E, while it can not be clearly seen in the Landsat TM image in the IR range. The SIR-C image, having several frequencies and polarizations, exhibits meaningful differences in reflectance between Mubra channel and its surroundings. The wavelengths and polarizations that improve the contrast between reflectance from the river channel and the sand are (in descending order): L(HV), L(HH) and C(HH).