Haifa

High Resolution seismic characterization of shallow gas bearing sediments, North Western Sea of Galilee, Israel

Elhanaty Y., Makovsky Y.

The Dr. Moses Strauss Department of Marine Geosciences, Leon H. Charney School of marine sciences, University of Haifa, Haifa 31905, Israel

Abstract

The majority of the Sea of Galilee lake bottom is impenetrable to Very High Resolution seismic reflection profiling due to the presence of free gas in the bottom sediments. This study is a preliminary feasibility study aimed at a first order characterization of the undisturbed nature of impenetrable sediments using non-invasive methods. On May 2008, a single channel (approximately zero-offset) seismic survey was carried out at the Sea of Galilee by the Israel Oceanographic and Limnological Research Institute. Profiles were acquired at ~1 m shot interval, using a 1 to 2.5 KHz sparker source. The sparker pulses were also recorded by a stationary hydrophone located 5 m below the water surface along one of the profiles, at the boundary between penetrable and impenetrable bottom. This hydrophone yielded an unusually high resolution wide-angle reflection-refraction dataset.

Most of the length of our single-channel profiles imaged impenetrable bottom. Penetrable bottom was mapped mostly in an anomalously wide (~1 km) stretch opposite the outlet of the Tzalmon drainage. Based on the seismic character of sub-bottom reflections observed in this area, and sediment cores extracted just north of our survey area, we suggest that the lake bottom comprises of finely layered silty-clay sediment. This layer is underlain by a boulders and gravel sequence, which is elevated within the penetrable area. The latter is suggested by us to be the paleo-fan of the Tzalmon drainage. We suggest that penetrability in this area is prompted by advection by groundwater or bottom flow. Convolutional modeling of the average zero offset impenetrable bottom reflection wavelet requires three successive reflectivity pulses relating to each other by the ratio 0.2:-0.45:0.3. This result implies the existence of a distinct low impedance bubble bearing ‘layer’ a short distance below the lake bottom. Travel time modeling of our wide angle data constrained a ~1% reduction in water velocity above the impenetrable bottom; a seismic P-wave velocity of 1501 m/sec at the lake bottom and 1505 m/sec deeper in the sediment. Parallel and continuous trends of the sub-seafloor refractions observed on our wide angle data at large offsets imply that there is no significant lithological difference of the top silty-clay sediment layer between the penetrable and impenetrable areas.

Combining our results with the parameters measured in sediment cores (porosity of 0.74 and mineral density of 2550 kg/m3 ) and formulae for the reflection coefficients densities and seismic velocities of saturated and bubble bearing sediments we constrained the bubbles bearing 'layer' thickness of 22 cm, seismic velocity of 735 m/sec, and gas content fraction of ~0.026%. Above this layer are 15 cm of loose sediments with the porosity of 0.87. We also calculated the reflection coefficients of the top, middle, and bottom interfaces of 0.098, -0.27, and 0.34 respectively.


Investigation of shallow gas and fluid migration within the Pleistocene-Holocene sedimentary section of the Levant basin using 3D seismic data

George S. (1), Ben Gai Y. (2), Makovsky Y. (1)

· Leon H.Charney School of marine sciences. Haifa University, Mt. Carmel, Haifa 31905, Israel

· ILDC Energy Ltd. 2,Arie Shenkar St., Tel Aviv 61500, Israel

Abstract

The presence of gas in shallow sediment is of interest because their occurrence may indicate underlying fluid flow, which may point towards deeper reservoirs and the possible presence of gas hydrates. Moreover gas in unlithified sediments may pose hazards to hydrocarbon exploration. My work focuses on the analysis of Southern Israel 3D seismic cube, acquired in 2000 by WesternGeco and processed through an amplitude preserving workflow. We identify three free gas shows within the 1 to 3 km thick post-Messinian sediments based on high-amplitude (bright spot) reflections, seismic phase reversal, and acoustic masking. These shows are found within the shallow (<1500msec) layers, in proximity to Top Messinian and possibly also in proximity to faulting related features. In addition, high resolution picking of the sea floor bathymetry, revealed an abundance of pockmark formations at the western and southern perimeter of Palmachim Disturbance. In particular, our preliminary investigation of the data revealed a formation of a distorted layer at 1500ms, following the seafloor. The characteristics of this reflection suggest that it is associated with free gas, and may represent the current or past presence of gas hydrates. My work will focus on confirming by geophysical means the presence of free gas in the sediments, delineating possible fluid migration pathways through the predominantly clay rich sedimentary section, and examining possible indications of gas hydrates presence.


A New Look at the Tectonic Evolution of the Palmahim Disturbance

Marig Y. (1), Feinstein S. (1), Ben-Gai Y. (2), Makovsky Y. (3)

1. The Geological and Enviromental Sciences Department, Ben-Gurion University of the Negev, Be'er Sheva 84105, Israel

2. ILDC Energy Ltd. 2,Arie Shenkar St., Tel Aviv 61500, Israel

3. Leon H.Charney School of marine sciences. Haifa University, Mt. Carmel, Haifa 31905, Israel

Abstract

The Palmahim Disturbance is a huge scar on the Eastern Levant margins, facing Israel Shore line. The slump footprints are well recognized on top of the bathymetric map and in spite of its great significance in risk assessment related to marine and even continental infrastructures, the origin of the disturbance is still not fully understood.

The two main accepted models for the disturbance origin are based on relatively low resolution seismic data from the 70’s of the last century. According to one of them the disturbance is a consequence of a sediment overburden above evaporitic section that yielded under the load, while the other suggest that the disturbance reflects deep rooted tectonic strain. Seismic data from the 80’s and 90’s of the last century provide a better imaging of the disturbance, and allow proposal of additional model. This model describes the evolution of the Palmahim Disturbanceas integration between sediment overburden and salt dissolving. Still, the seismic data was not sufficient to deal with the complexi geology of the Palmahim Disturbance.

Time sections in the western end of the Palmahim Disturbance reveal a unique structural anomaly, and appears to suggest that the whole section was under great strain. This study focused on imaging in the depth domain of two crossing seismic sections, in order to study the disturbance and its context in the regional geologic evolution. Depth domain imaging suggests that part of the anomalies that appear in the time images sections are attributed to processing artifacts, caused by intra salt morphology anomalies. Our results appear to disprove the possibility that the Palmahim Disturbance was developed by tetonic mechanism. The depth images obtained reveal that the base Mavqi’im Formation is continuous and complete and its topography matches the topography of its surrounding area. In addition, older structures that appear deep in the sections are continuous with no evident of significant tectonism that penetrate the base of the Mavqi'im evaporites in the region. We suggest the existence of a Late Eocene structural step that was active at least till Early Miocene, and is located to the west of other equivalent steps and a Pre-Mesinian channel cutting through the step that appears to have an influence on the evolution of the Palmahim Disturbance.

The mavqi’im formation evaporites are almost completely missing in the western edge of the Palmahim Disturbance, and are replaced with a sedimentary ‘Turtle Structure’. The strain of the western part of the Palmahim Disturbance is characterized with reverse faults opposite to the disturbance direction. We suggest that this ‘Turtle Structure’ includes sediments that were deposited in the Pre-Messinian channel, creating a rigid obstacle in the way of the disturbance.


Pervasive intra-Messinian channels maintain the late Miocene northwestward sediment transportation

Kedem A., Makovsky Y.

The Dr. Moses Strauss Department of Marine Geosciences, Leon H. Charney School of Marine Sciences (CSMS), University of Haifa, Haifa 31905, Israel

Abstract

A great debate is focused on the mechanisms of the Messinian accumulation of thick (~2 km) evaporites sequences, observed in seismic data below much of the Mediterranean deep basin areas. The seismic data show the evaporitic section in the Levant basin as alternating reflective and non-reflective sequences, suggested to represent clastic and evaporitic deposition respectively. Moreover, Messinian deposition of clastic evapirites, transported across great distances from marginal basins, was recently suggested to be an important factor of this accumulation. However, no evidence supporting the existence of an intra-Messinian large scale transport system was presented to date. In this work we map for the first time intra-Messinian channels within the deep part of the Levant basin, and examine their distribution. Our new mapping is based on interpretation of the Pelagic (newly released for academic research), Gal-C and Southern Israel 3D seismic blocks, augmented by several TGS 2D profiles. The Pelagic block images the Messinian depocenter, where the sequence is thickest and the lower internal reflective units (1st to 3rd) seem least deformed. Thus, its internal structure is relatively readily interpreted. The structural maps of the 1st and 3rd intra-Messinian sequences (counted upwards above Base Messinian) show two channels crossing the southern part of the Pelagic block in a northwesterly direction. Another channel crosses only the 1st intra-Messinian sequence at the center of the Pelagic block. Integration of the relief and the seismic amplitude of the mapped horizons, reveal a suggested channel depositional lobe near the western edge of this block. In the other 3D blocks the intra-Messinian seismic reflectors are significantly more deformed, and the channels do not stand out in the intra-Messinian relief. However, changes in the characteristic amplitudes and frequencies suggest the presence of lateral unconformities in the 1st and 3rd intra-Messinian sequences, highlighting northwestward trending channel-shaped bodies. Taken together the different channel segments observed by us are consistent with a major channel system, transporting sediments from the margins to a distance >100 km within the deep basin. This system is reminiscent, though not identical, to the major channel previously mapped within the N horizon, the base of the Messinain evaporates sequence, flowing from the El-Arish/Afiq canyons. We concluded that the northwestwards sediment transportation of the late Miocene was maintained during the Messinian.

 

Identifying and mapping the tracks of recent submarine mass slide events on the continental slope of Israel: a basis for future infrastructure risk assessment.

Gadol O. (1), Bar-Am G. (2), Tibor G. (3), Makovsky Y. (1)

1. The Dr. Moses Strauss Department of Marine Geosciences, Leon H.Charney School of marine sciences. Haifa University, Mt. Carmel, Haifa 31905, Israel

2. Modiin Energy, 3 Azriele Center, Triangle Tower 41st Floor, Tel-Aviv 6702301, Israel.

3. Israel Oceanographic & Limnological Researche Ltd., Tel-Shikmona, P.O.Box 8030, Haifa 31080, Israel

Abstract

Mass sliding events pose a geohazard to marine infrastructures and have been described as the cause of catastrophic tsunami events. The bathymetry of the continental slope offshore Israel is etched by a complex array of mass transport escarpments. Some of these escarpments are the superimposition result of different mass transport features that vary both in the spatial and temporal scales. Our manual interpretation which was implemented on a 50 m resolution DEM (acquired by the Bathymetric Survey of Israel and Israel Oceanographic and Limnological Research) emphasized the complexity of the scars present on the continental slope. Two main morphometric approaches were combined to investigate the dynamics of the events that shape the mass transport escarpments, by delineating the bathymetric marks left by each one of them. Slope gradient and curvature maps were created and classified into categories: break of slope, convex change of slope, concave change of slope and sloping surface. These classes create vectors that follow the main escarpments present on the seafloor and map features that are characteristic for mass transport deposits such as troughs, ridges and blocks. The second approach utilizes the spectral decomposition of the bathymetric data sets. Through the implementation of two-dimensional discrete Fourier analyses the original DEM is transformed into the frequency domain and is subdivided into its main spectral components. These components, which represent different degrees of surface roughness were later redraped on the original DEM. When combined, the two methods create a distinction of features such as headscarps, lateral margins, ridges and troughs as well as a delineation of lobes and sediment flow pathways within mass transport complexes. At this preliminary stage these methods were applied on two different bathymetric data sets (originating from seafloor picking of 3D commercial seismic surveys) that comprise of mass transport escarpments. The first dataset is a 12.5 m resolution DEM of the base of the slope in southern Israel (Southern Israel seismic block). Spectral decomposition enhanced the delineation of an mass transport complex toe region comprised of a set of deposition lobes surrounded by a smoother bathymetric envelope. The later is suggested to be the result of settling of suspended debris at the end of a sliding event. Also delineated are contourites (100 -300 m wide) stretching from surface irregularities, but are overprinted by the slide deposits. The second dataset is a 25 m resolution DEM from the lower slope of central Israel (Yam Hadera seismic block). The combined morphometric analysis delineated several superimposed landslide features. Some of these landslide scars were overprinted by a smoothening erosive flow originating from upslope diverging channels. These preliminary results demonstrate the potential of our morphometric approach for deciphering between the cumulative effects of mass transport processes.


Geomechanical characterization of marine sediments: an updated tool for studying submarine slides on the continental slope of Israel

Bar-Zvi L., Makovsky Y.

The Dr. Moses Strauss Department of Marine Geosciences, Leon H. Charney School of Marine Sciences (CSMS), University of Haifa, Haifa, Israel, 31905

Abstract

The abundance of recent kilometers-scale scars on the continental slope of Israel, and evidence of repeated local tsunami events, raise concern of the potential risks posed by submarine slides. Direct measurements of the slope sediments geomechanical properties profiles is important for understanding and modelling the sliding potential and processes. Yet, geomechanical studies of marine sediments, sampled from the Israeli continental slope, have been essentially abandoned for the last 20 years. In the framework of a new Ministery of Sciences and Technology funded campaign we intend to core sediments from the head scars of assumed most recent submarine slides, where their original detachment surface is presumably exposed. The cored sediments will be geomechanically characterized and compared to sediments of the adjacent undisturbed slope, to constrain the effects of sliding on the sediment strength profiles and stress history. These in turn are expected to yield new understanding on the mechanics and time of the last sliding event. Sediment sampling will combine the usage of a 6 m long piston core, newly built by the Institute of Oceanographic and Limnological Research (IOLR), and near surface sediments collecetd in a box-corer. Coring locations are being picked based on high precision (~5 m resolution) commercial seafloor bathymetry, and coring will be precisely positioned to ensure the sampling of the exposed scars. Using this new corer we already collected a 5.2 m long core from a depth of 303 m on the continental slope offshore Haifa bay. The cores are cut at 1 m segments and sealed, then transported to the laboratory with minimal mechanical disturbance. Thus their mechanical properties should reflect correctly the original seafloor conditions. Geomechanical testing will utilize an array of testing instruments, addapted and built by us. This array includes a special device for cutting a core pipe wall without mechanical damage to the sediment, consolidation tests, measurements of moisture content , density and maximum undrained shear stress (MUSS) tests. The MUSS is measured both by the conventional 'Vane Shear Test', as well as by using a 'T-Bar', and their results will be compared. The T-bar is a full flow penetrometer that provides quick, continuous and accurate measurements of the MUSS. To date we calibrated our testing procedures using earlier samples of slope sediments.


The current and past potential of Natural Methane Hydrates occurrence in the southeastern Levant

Tayber Z., Makovsky Y.

The Dr. Moses Strauss Department of Marine Geosciences, Leon H. Charney School of Marine Sciences (CSMS), University of Haifa, Haifa, Israel, 31905

Abstract

This research aims to investigate the effect of environmental changes on the occurrence of natural methane hydrates (NMH), utilizing the Southeastern Mediterranean Sea (SEMS) as a natural laboratory. The isolation of the SEMS from the global ocean system by the shallow straits of Sicily and Gibraltar, and its relatively small water capacity, dictate an enhanced sensitivity of hydrates stability to regional environmental changes. Our initial modeling of the pressure-temperature conditions in the SEMS predict the existence of methane hydrates stability zone (MHSZ) in the seafloor sediments at water depths 1.2 km with its thickness in the range of 1 up to 600 m. Taken together with observations of free gas in the SEMS seafloor sediments within this range of water depths our results strongly suggest the presence of NMH. Yet, no observation of NMH was reported to date in this area. In this study we first intend to map the MHSZ in the SEMS by integrating into our model information on the actual temperature pressure and sediments properties, as constrained by recent commercial drilling. We then intend to compare our modeled results with seismic and well-logs data recently acquired in the Levant basin, and with known active gas seepage locations. This comparison is intended to examine our hypothesis that methane hydrates are actually present in the SEMS under current environmental conditions, and calibrate our model for actual evidence and constraints of their presence. Then we intend to back project our model to paleo oceanographic conditions that prevailed in the recent geologic past, examine the predicted evolution of methane hydrates in the basin through changing conditions. Understanding the magnitude of the change in MHSZ will have profound implications on comprehension of geologic features and process in the SEMS, such as the emplacement of mass transport deposits and evolution of seafloor gas release structures, and even to understanding the workings of climatic processes (like global warming).


Deformation domains in the outer continental shelf of central Israel

Safadi M. (1), Bar-Am G. (2), Politi M. (3) and Makovsky Y. (1)

1. The Dr. Moses Strauss Department of Marine Geosciences, Leon H. Charney School of marine sciences, University of Haifa, Haifa 31905, Israel.

2. Modiin Energy, 3 Azriele Center, Triangle Tower 41st Floor, Tel-Aviv 6702301, Israel.

3. Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel.

Abstract

Recent and potentially active faulting systems in the post-Messinian section along the edge of the continental shelf of Israel are commonly attributed to the effect of the basinward retreat of the Messinian evaporites. However, a newly available depth migrated 3D seismic survey, covering the Gabriela exploration license at the outer continental shelf of central Israel, reveals that only a few of the faults actually sole at the Messinian evaporites. This study is focused on detailed interpretation of this survey, aided by coherence and structural attributes, to characterize the kinematics of deformation and faulting within the post-Messinian sedimentary sequence. This sequence was divided by us to 3D ‘domains’ of deformation, defined as 3D volumes of sediments with coherent deformational patterns. We mapped the bounding surfaces of each domain and characterized its deformational interaction with the surrounding, as well as its internal deformation patterns. The Top-Messinian (M) surface, at the base of the sedimentary sequence investigated by us, is the top of a widely arched and deformed layer. A ~30 km long fault system is running along the arch axis, and a 1 to 3 km wide northwest-southeast trending channel is truncating the M at the center of the survey. To the northwest of this channel the M is characterized by northeast-southwest trending parallel faults (1 to 4 km long), while at the southernmost extent of the survey the M is dissected by normal faults of the Palmaheem Disturbance. A stratified package up to 250 m thick is overlaying the M in a continuous unbroken manner, with the exception of the Palmahim Disturbance bounding faults. This package clearly detaches the M from faulting systems truncating the post-Messinian section. The overlaying sedimentary package comprises of a dense puzzle of deformation domains, encompassing minor to large mass transport deposits (MTDs) and a complex network of fault systems. The latter are mostly blind faults, reaching sometimes to the current seafloor. In particular, two major domains of deformation near the base of the post-Messin ian sediments are identified by us as large scale MTDs. The first, stretching over an area of ~130 square km within our survey, is characterized as the head-scarp region of a slide. A crown of faults emanates upwards, truncates and deforms significantly later units. The other MTD, stretching over an area of ~150 square km within our survey, is characterized as the terminal parts of a complex slide that incorporates large (~1 km scale) displaced and rotated blocks. Overlaying units appear to be sagged and faulted above this MTD. We suggest that long term post-slumping compaction and deformation, taking place at least in the major MTDs, controls most of the recent to active deformation at the edge of the continental shelf of central Israel.

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