Classifying marine faults for hazard assessment offshore Israel: a new approach based on fault size and vertical displacement

For many countries, the methodology for offshore geohazard mitigation lags far behind the well-established onshore methodology. Particularly complicated is the assessment of fault hazard in the marine environment. The determination of whether a fault is active or not requires ultra-high-resolution seismic surveys and multiple coring and, unfortunately, frequently ends with uncertain results. Moreover, if a pipeline must cross a fault, it is not enough to determine whether the fault is active; slip rates are needed for resistant planning. Here we suggest a new approach for fault hazard assessment for the master planning of infrastructure. We provide planners a way to choose a route that will cross the least hazardous faults; these faults will then be investigated in site-specific surveys for slip rates that will allow seismic design. Instead of following the onshore practice that is hard to implement in the marine environment, we suggest taking advantage of the marine environment where seismic data are commonly better in quantity and quality. Based on existing industrial 3D seismic surveys, we measure for each fault in the study area the amount of its recent (in our specific case, 350 ka) vertical displacement and the size of its plane. According to these two independently measured quantities, we classify the faults into three hazard levels. This allows planners to choose infrastructure routes that cross the least hazardous faults at an early stage of planning and direct them to sites that need further investigation. Our case study is the Israeli continental slope, where numerous salt-related, thin-skinned, normal faults dissect the seabed, forming tens of meters high scarps. A particular hazardous zone is the upper slope south of the Dor disturbance, where a series of big listric faults rupture the seabed in an area where the sedimentation rate is 4 times faster than the vertical displacement rate. We suggest that this indicates exceptionally fast creep, seismic rupture, or rapid tremor and slip episodes.</p

Intra-Messinian truncation surface in the Levant Basin explained by subaqueous dissolution

The Messinian salinity crisis (MSC) is an extreme event in Earth history during which a salt giant (>1 × 106 km3) accumulated on the Mediterranean seafloor within ~640 k.y. Erosional unconformities extending from the continental margins into the deep basins are key features for reconstructing the MSC; however, the nature of the erosional processes and their subaerial versus subaqueous origin are highly controversial. This study focuses on the top erosion surface (TES) in the deep Levant Basin, which is notably flat, truncating a basinward-tilted Messinian evaporitic succession. Based on high-resolution seismic surveys and wireline logs, we show that (1) the TES is actually an intra-Messinian truncation surface (IMTS) located ~100 m below the Messinian-Zanclean boundary; (2) the topmost, post-truncation Messinian unit is very different from the underlying salt deposits and consists mostly of shale, sand, and anhydrite; and (3) the flat IMTS is a dissolution surface related to significant dilution and stratification of the water column during the transition from stage 2 to stage 3 of the MSC. Dissolution occurred upslope where salt rocks at the seabed were exposed to the upper diluted brine, while downslope, submerged in the deeper halite-saturated layer, the salt rocks were preserved. The model, which requires a stratified water column, is inconsistent with a complete desiccation of the eastern Mediterranean Sea

Sulfur isotopic compositions of individual organosulfur compounds and their genetic links in the Lower Paleozoic petroleum pools of the Tarim Basin, NW China

During thermochemical sulfate reduction (TSR), H2S generated by reactions between hydrocarbons and aqueous sulfate back-reacts with remaining oil-phase compounds forming new organosulfur compounds (OSCs) that have similar δ34S values to the original sulfate. Using Compound Specific Sulfur Isotope Analysis (CSSIA) of alkylthiaadamantanes (TAs), alkyldibenzothiophenes (DBTs), alkylbenzothiophenes (BTs) and alkylthiolanes (TLs), we have here attempted to differentiate OSCs due to primary generation and those due to TSR in oils from the Tarim Basin, China. These oils were generated from Cambrian source rocks and accumulated in Cambrian and Ordovician reservoirs. Based on compound specific sulfur isotope and carbon isotope data, TAs concentrations and DBT/phenanthrene ratios, the oils fall into four groups, reflecting different extents of source rock signal, alteration by TSR, mixing events, and secondary generation of H2S. Thermally stable TAs, that were produced following TSR, rapidly dominate kerogen-derived TAs at low to moderate degrees of TSR. Less thermally stable TLs and BTs were created as soon as TSR commenced, rapidly adopted TSR-δ34S values, but they do not survive at high concentrations unless TSR is advanced and ongoing. The presence of TLs and BTs shows that TSR is still active. Secondary DBTs were produced in significant amounts, sufficient to dominate kerogen-derived DBTs, only when TSR was at an advanced extent. The difference in sulfur isotopes between (i) TLs and DBTs and (ii) BTs and DBTs and (iii) TAs and DBTs, represents the extent of TSR while the presence of TAs at greater than 20 μg/g represents the occurrence of TSR. The output of this study shows that compound specific sulfur isotopes of different organosulfur compounds, with different thermal stabilities and formation pathways, not only differentiate between oils of TSR and non-TSR origin, but can also reveal information about relative timing of secondary charge events and migration pathways

Freshening of the Mediterranean Salt Giant: controversies and certainties around the terminal (Upper Gypsum and Lago-Mare) phases of the Messinian Salinity Crisis

The late Miocene evolution of the Mediterranean Basin is characterized by major changes in connectivity, climate and tectonic activity resulting in unprecedented environmental and ecological disruptions. During the Messinian Salinity Crisis (MSC, 5.97-5.33 Ma) this culminated in most scenarios first in the precipitation of gypsum around the Mediterranean margins (Stage 1, 5.97-5.60 Ma) and subsequently &gt; 2 km of halite on the basin floor, which formed the so-called Mediterranean Salt Giant (Stage 2, 5.60-5.55 Ma). The final MSC Stage 3, however, was characterized by a "low-salinity crisis", when a second calcium-sulfate unit (Upper Gypsum; substage 3.1, 5.55-5.42 Ma) showing (bio)geochemical evidence of substantial brine dilution and brackish biota-bearing terrigenous sediments (substage 3.2 or Lago-Mare phase, 5.42-5.33 Ma) deposited in a Mediterranean that received relatively large amounts of riverine and Paratethys-derived low-salinity waters. The transition from hypersaline evaporitic (halite) to brackish facies implies a major change in the Mediterranean’s hydrological regime. However, even after nearly 50 years of research, causes and modalities are poorly understood and the original scientific debate between a largely isolated and (partly) desiccated Mediterranean or a fully connected and filled basin is still vibrant. Here we present a comprehensive overview that brings together (chrono)stratigraphic, sedimentological, paleontological, geochemical and seismic data from all over the Mediterranean. We summarize the paleoenvironmental, paleohydrological and paleoconnectivity scenarios that arose from this cross-disciplinary dataset and we discuss arguments in favour of and against each scenario

The accretion of the Levant continental shelf alongside the Nile Delta by immense margin-parallel sediment transport

Following the termination of the Messinian salinity crisis ~5.3 million years ago, massive sedimentation in the Eastern Mediterranean Sea formed the huge Nile Delta. Alongside delta propagation, a continental shelf was accreted along the Levant margin. For several decades it was assumed that these two sedimentary structures were closely connected. Levant shelf deposits are composed of Nile-derived sediments and present-day measurements show that sand is currently being transported alongshore from the Nile Delta to offshore Israel. This study reexamines the existing paradigm about sediment transport and shelf-delta connection. We show that longshore sand transport is just a small part of a much larger process termed here margin-parallel sediment transport (MPST). Sand is transported in a nearshore shallow-water belt where marine currents are highly energetic. At the same time, shale is transported at greater depths over the deeper shelf and the continental slope where marine currents are weaker. To model the accretion of the Levant shelf alongside the Nile Delta we use a 3D, diffusion-based, stratigraphic modeling tool (DionisosFlow) with a new module representing MPST. Our results show that margin-parallel transport of silt and clay in the deeper waters accounts for the bulk of deposition offshore Israel and is responsible for the development of the Levant shelf. Moreover, though MPST has begun coevally with delta formation, massive accretion of the Levant shelf was delayed by 2–3 My. Initially, a continental shelf formed offshore Sinai, then offshore Israel, and most recently along the Lebanon coast. Our model also demonstrates the significant lithological differences observed between sedimentation in front of the Nile River mouth and along adjacent continental margin. High energy down-slope sediment transport carries sand, silt, and clay, whereas margin-parallel currents are relatively weak and carry mainly silt and clay. One exception within the margin-parallel system is the highly energetic nearshore current that transports sand. Thus, we point out, MPST is an efficient separator between shale and sand. © 2020 Elsevier LtdThis study was supported by the Israeli Ministry of Energy and by the Mediterranean Research Center of Israel (MERCI). The article is further based upon work of COST Action “Uncovering the Mediterranean salt giant” (MEDSALT) supported by the European Cooperation in Science and TechnologyPeer reviewe

Limited Mediterranean sea-level drop during the Messinian salinity crisis inferred from the buried Nile canyon

The extreme Mediterranean sea-level drop during the Messinian salinity crisis has been known for >50 years, but its amplitude and duration remain a challenge. Here we estimate its amplitude by restoring the topography of the Messinian Nile canyon and the vertical position of the Messinian coastline by unloading of post-Messinian sediment and accounting for flexural isostasy and compaction. We estimate the original depth of the geomorphological base level of the Nile River at ~600 m below present sea level, implying a drawdown 2–4 times smaller than previously estimated from the Nile canyon and suggesting that salt precipitated under 1–3 km deep waters. This conclusion is at odds with the nearly-desiccated basin model (>2 km drawdown) dominating the scientific literature for 50 years. Yet, a 600 m drawdown is ca. five times larger than eustatic fluctuations and its impact on the Mediterranean continental margins is incomparable to any glacial sea-level fall.The article was supported by COST Action “Uncovering the Mediterranean salt giant” (MEDSALT), funded by the European Cooperation in Science and Technology. It was also supported by the SALTGIANT program, a European project funded by the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska Curie grant agreement number 765256.Peer reviewe

Evidence of Clastic Evaporites In the Canyons of the Levant Basin (Israel): Implications For the Messinian Salinity Crisis

The recognition of large clastic sulfate deposits in the Miocene Messinian onshore of the Mediterranean Basin appears to be in contrast with the hypothesis of a complete desiccation as a consequence of the salinity crisis. Below the sea floor the evaporite facies are virtually unknown, but the detailed review of the cores from onshore Israel cutting through the evaporite filling of the marginal canyons in the Levant Basin (Mavqi’im Formation) reveal exclusively clastic sulfate facies. The rocks are graded gypsrudite and gypsarenite associated with laminar and cross-bedded gypsarenite–gypsiltite and shale, whereas no primary, in situ evaporites are present. The clastic facies association is interpreted to have been deposited by subaqueous gravity flows sourced from dismantled selenite rocks originally located eastward and updip of the canyons. The absence of supratidal evaporites suggests that no pronounced sea-level drop can be inferred during the salinity crisis because the presence of the evaporite layers at different elevations along the canyons cannot mark oscillations in sea level, but instead is the result of subaqueous mass-wasting phenomena. These findings indicate that the other ancient canyons described around the Mediterranean Basin may not be necessarily related to a base-level drop due to basinwide desiccation. On the contrary, the widespread presence of clastic evaporites suggests that a water body persisted even during the acme of the salinity crisis. The clastic deposits onshore Israel are the first direct evidence that the widespread Lower Evaporite Unit lying below the floor of the Mediterranean may actually consist of deep-water resedimented evaporites and that one of the primary sources was originally located on the upper margin of the Levant Basin. If this hypothesis is correct, then the Mediterranean Basin may host the largest clastic sulfate deposit in the world

Evidence of Clastic Evaporites In the Canyons of the Levant Basin (Israel): Implications For the Messinian Salinity Crisis

The recognition of large clastic sulfate deposits in the Miocene Messinian onshore of the Mediterranean Basin appears to be in contrast with the hypothesis of a complete desiccation as a consequence of the salinity crisis. Below the sea floor the evaporite facies are virtually unknown, but the detailed review of the cores from onshore Israel cutting through the evaporite filling of the marginal canyons in the Levant Basin (Mavqi\u2019im Formation) reveal exclusively clastic sulfate facies. The rocks are graded gypsrudite and gypsarenite associated with laminar and cross-bedded gypsarenite\u2013gypsiltite and shale, whereas no primary, in situ evaporites are present. The clastic facies association is interpreted to have been deposited by subaqueous gravity flows sourced from dismantled selenite rocks originally located eastward and updip of the canyons. The absence of supratidal evaporites suggests that no pronounced sea-level drop can be inferred during the salinity crisis because the presence of the evaporite layers at different elevations along the canyons cannot mark oscillations in sea level, but instead is the result of subaqueous mass-wasting phenomena. These findings indicate that the other ancient canyons described around the Mediterranean Basin may not be necessarily related to a base-level drop due to basinwide desiccation. On the contrary, the widespread presence of clastic evaporites suggests that a water body persisted even during the acme of the salinity crisis. The clastic deposits onshore Israel are the first direct evidence that the widespread Lower Evaporite Unit lying below the floor of the Mediterranean may actually consist of deep-water resedimented evaporites and that one of the primary sources was originally located on the upper margin of the Levant Basin. If this hypothesis is correct, then the Mediterranean Basin may host the largest clastic sulfate deposit in the world