Nile Fan Research Articles

Modes of gas migration and seepage on the salt-rooted Palmahim Disturbance, southeastern Mediterranean

Mass transport complexes often form key elements of petroleum systems, affecting sedimentary structures, seepage pathways and biodiversity hotspots on the seafloor. Yet, the feedback and interaction between these elements is not well constrained. This study investigates the modes of gas accumulation, migration, and seepage at the toe of Palmahim Disturbance (PD), a major salt-rooted mass transport complex across the southeastern Mediterranean margin, and adjacent edge of the eastern deep-sea fan of the Nile. Interpretation of a 3D time migrated seismic reflection dataset was calibrated with visual seafloor observations of active seepage. The toe of PD, in the eastern part of the study area, comprises four km-scale NE-SW oriented bathymetric ridges. At the crests of the eastern three of these ridges are six, hundreds-of-meters wide pockmark systems, four of which host verified seeps. Multiple sub-circular tens-of-meters wide pockmarks are mapped in the Nile fan west of PD. Active seepage was also identified within two elongate pockmarks along the flanks of the bordering Levant Channel. The seismic data reveal that the PD toe pockmarks and ridges overlie anomalous high amplitude seismic reflections (HASRs) from just beneath the surface to hundreds-of-meters deep intervals - below, at the base of and within a buried paleo mass transport deposit (MTD). These HASRs are interpreted to represent multiple gas-bearing intervals within thrust-faulted and folded blocks and their intermittent sealing, primarily at the base of the MTD. The Nile fan pockmarks overlie pervasive sub-seafloor HASRs that are overlain by low amplitude reflections, interpreted as gas-bearing channel-lobe sediments. Gas migration occurs via lateral to updip flow within depositional features and deeper folded sediments, and via sub-vertical flow, associated with the formation and leakage of transient reservoirs. Extension of fan sediments towards the PD pockmarks suggests additional updip focusing of gas, complementing sub-vertical gas flow to the PD pockmarks.

Multilevel Composition: A new method for revealing complex geological features in three-dimensional seismic reflection data

Advanced seismic data and multi-attribute visualization techniques, such as color blending of attributes, have considerably enhanced the capability of interpreters to characterize geological features in three-dimensional (3D) seismic reflection datasets. However, high resolution investigation of complex, vertically linked geological features such as channel systems and fluid conduits, remains challenging. These features may appear in the dataset as pronounced attribute anomalies, such as high-amplitude or spectrally or structurally enhanced seismic reflectivity bands, at several depth levels. Vertical linkages between these features, however, may not be readily established. We have developed an innovative method, Multilevel Composition, for an intuitive display of vertically connected features. Our method involves the composition of attribute maps from three different depth/time windows or slices onto a single map, in which inter-window/layer depth information is coded in colors. Multilevel Composition starts with the identification of suitable seismic attributes, such as high amplitudes in the examples displayed here, to map features of geological interest. At least one reference horizon is then identified and mapped in the vicinity of the target window of interest. Three sub-windows are then defined with respect to the reference horizon(s) based on the vertical and spatial distribution of the geological features. Relevant seismic attributes are computed for each of the sub-windows, and the resulting maps, one from each sub-window, are assigned basic color channels and are co-rendered to reveal multilevel linkages between these features. We demonstrate the efficacy of this method by applying it to two 3D seismic datasets, one illuminating deep-water depositional elements in the eastern Nile fan, eastern Mediterranean and the other targeting seafloor seeps and underlying gas migration systems beneath the Omakere Ridge, offshore New Zealand. The new method is simple and should be easy to implement to enhance seismic interpretation workflows.

On the Nile Fan's wave power potential and controlling factors integrating spectral and geostatistical techniques

Wave energy is foreseen to contribute largely to the renewable energy projected to supply 20% of Egypt's electricity budget to meet burgeoning energy demand. Therefore, this research analyses the Nile Fan wave energy forecasted from numerical modeling for 2020 of the Copernicus Marine Environment Monitoring Service (CMEMS) database, hourly spatially sampled at 0.042° as the finest scale remotely-sensed data available. Wave energy spatial distribution is analyzed using data from 259 points proposed as Wave Energy Converters (WECs). Spectral analyses techniques were appraised for disclosing the frequency and energy return periods of the significant wave height and peak periods and to understand the similarity among selected WECs of varied conditions. Factor analysis is conducted to investigate the magnitude of factors controlling the wave dynamic and energy potential. K-means clustering was used to distinguish energy classes with large inter-class variances. The obtained resources (average wave energy density, around 5.32 KWh/m; maximum recorded value of 112.9 KWh/m; annual wave energy density sum of about 46.96 MWh/m) are among the largest found in the Mediterranean Sea. Spectral analysis clarified a strong periodicity at 21 days, intermittent periods of 2.66 days, and 7.5 days dominate over the year while a 22.6 hourly period dominates in summer. January attained the strongest peak frequency of 8.4 in the west, 6.6 between the NW and SE sites, 5.20 for the near shore sites. Directional analysis indicated a bimodal wave system (325° and 285°-295°) in the west and unimodal (285°295°) in the east, while the central area showed combined distribution; bimodal in the deep water and unimodal near the shore. The 285°-295° wave direction showed largest contribution to the wave energy density. The northwest is the most energetic and most productive area. Monthly and seasonal wave energy clarified maximum of 9.98 MWh/m in January and 22.6 MWh/m in winter that contributes to 21% and 53% of the yearly mean, respectively. The wave energy resource is more than 3.5 times greater in winter than in summer. Exploitable energy density level exceeding 2 KWh/m are recorded for 250 sites out of the 259 site. Factor and detrended correspondence analyses confirmed that more than 98% of the Nile Fan's wave energy variance is controlled, in decreasing order of influence, by the depth, distance to shore, significant wave height, wave peak period, and wave principal direction. Four classes of varied statistics and hence different wave behavior were distinguished affected by the depth, morphology of the shoreline, and the dominating wave direction. Deepest water and near shore classes attained the largest wave energy. Further details on the effect of the environmental factors on the wave shape and corresponding energy are concluded.

On the Nile Fan's Wave Power Potential and Controlling Factors Integrating Spectral and Geostatistical Techniques

Wave energy is foreseen to contribute to the 20 % renewable energy supply of Egypt’s electricity budget to meet burgeoning energy demand. This research analyses the Nile Fan wave energy forcasted from numerical modeling for 2020 of the Copernicus Marine Environment Monitoring Service (CMEMS) database, hourly sampled at 0.042° as the finest remotely-sensed data available. Wave power spatial distribution is analyzed using data from 259 points proposed as Wave Energy Converters (WECs). Spectral analyses techniques were appraised for disclosing the frequency and power return periods of the significant wave height and peak periods and to understand the similarity among selected WECs of varied conditions. K-means clustering was used to distinguish energy classes with large inter-class variances. The obtained wave power resources ( av . 5.32 kW/m; maximum of 112.9 kW/m; annual mean of 46.96 MW/m) are among the largest found in the Mediterranean Sea. More than 98 % of the wave power variance is controlled, in decreasing order of influence, by the depth, distance to shore, significant wave height, wave peak period, and the wave principal direction. Deepest water and near shore classes attained the largest wave power. Detailed environmental factors induced the wave shape and power is concluded.

Impacts of Neotectonics and Salt Diaper on the Nile Fan Deposit, Eastern Mediterranean

Impacts of Neotectonics and Salt Diaper on the Nile Fan Deposit, Eastern Mediterranean

Anoxic development of sapropel S1 in the Nile Fan inferred from redox sensitive proxies, Fe speciation, Fe and Mo isotopes

Redox conditions and the mechanisms of redox development are a critical aspect of Eastern Mediterranean sapropels, whose formation in oxygen-depleted waters is closely related to water column stratification at times of global sea level rise and insolation maxima. Sapropels in the Nile Fan formed at relatively shallow water depths under the influence of the monsoon-driven freshwater output from the River Nile. This work evaluates the redox evolution of Holocene sapropel S1 in VALPAMED cruise core MD9509, recovered at 880 mbsl in the NE Nile Fan, using a combination of geochemical element proxies, Fe speciation, Fe and Mo isotopes studies. The productivity and redox proxies (Ba/Al, Mo/Al, U/Al, V/Al, Sb/Al) show well-defined enrichments in the sapropel, but with a marked minimum at ca 8.2ka indicative of reventilation corresponding to a well known global cooling event. Peak productivity and reducing signals occur close to the initiation of sapropel formation. The proxy signals in sapropel 9509 are stronger and of longer duration than those of a second sapropel S1, recovered at the same depth, but 380km to the north (MD9501), supporting the notion (suggested in previous studies) of more reduced conditions in the Nile Fan.The MoEF vs. UEF enrichment factor variations in core 9509 infer a transition from open marine suboxic conditions in the enclosing non-sapropel sediments to anoxic non-sulphidic water column conditions in the sapropel. Correspondingly, the highly reactive Fe pool (FeHR) measured in Fe speciation studies is dominated by Fe(oxyhydr) oxide minerals in the background sediments, whereas pyrite (Fepy) becomes the dominant component of the FeHR pool in the sapropel. Maximum Fepy values in the sapropel coincide with peak productivity and reducing conditions, implying a clear link between trace element uptake, diagenetic bacterial sulphate reduction in anoxic porewater and Fe mobilization in the sapropel. Iron isotope compositions (δ56Fe) in the sapropel do not show any departure from primary (marine and detrital) source sediment values, and the absence of an Fe/Al vs. δ56Fe trend strongly argues against an Fe shuttle. Molybdenum isotopes, however, show marked non-conservative fractionation patterns. Background sediment δ98/95Mo values (0.2 to 0.7‰) are compatible with fractionation upon absorptive uptake by Fe (oxyhydr)oxides and pyrite. In contrast, minimum δ98/95Mo values exhibited at peak sapropel (reducing and pyrite producing) conditions are most closely modeled by Mo isotope fractionation during kinetically controlled conversion of aqueous molybdate to thiomolybdate species. The conservative Fe isotope behavior/Mo isotope fractionation minima in the sapropel may be a characteristic of organic-rich sediment diagenesis below an anoxic non-sulphidic water body, without the operation of a benthic Fe shuttle.

Interconnectivity vs. isolation of prokaryotic communities in European deep-sea mud volcanoes

Abstract. During the past two decades, European cold seep ecosystems have attracted the scientific interest and to date there are several studies which have investigated the community structure and biodiversity of individual sites. In order to gain a better insight into the biology, biodiversity, and biogeography of seep-associated microbial communities along Europe's continental margins, a comparative approach was applied in the present work. By exploiting the publicly available data on 16S rRNA gene sequences retrieved from sediments of the Håkon Mosby mud volcano, Gulf of Cádiz and the eastern Mediterranean mud volcanoes/pockmarks (Anaximander area and Nile Fan), we investigated the prokaryotic biological components connecting these geographically isolated systems. The construction of interaction networks for both archaeal and bacterial shared operational taxonomic units (OTUs) among the different sites, revealed the presence of persistent OTUs, which can be considered as "key-players". One archaeal OTU (HQ588641) belonging to the ANME-3 group and one δ-Proteobacteria (HQ588562) were found in all five investigated areas. Other Archaea OTUs shared between four sites or less, belonged to the ANME-2c, -2a, MBG-D, -B and Thaumarchaeota. All other shared Bacteria belonged to the δ- and γ-Proteobacteria, with the exception of one JS1 affiliate OTU. The distribution of the majority of the shared OTUs seems to be restricted in cold seeps, mud volcanoes and other marine methane-rich environments. Although the investigated sites were connected through a small number of OTUs, these microorganisms hold central ecophysiological roles in these sediments, namely methane- and sulfur-mediated mineralization.

High- and low-latitude forcing of the Nile River regime during the Holocene inferred from laminated sediments of the Nile deep-sea fan

Sediments deposited on deep-sea fans are an excellent geological archive to reconstruct past changes in fluvial discharge. Here we present a reconstruction of changes in the regime of the Nile River during the Holocene obtained using bulk elemental composition, grain-size analyses and radiogenic strontium (Sr) and neodymium (Nd) isotopes from a sediment core collected on the Nile deep-sea fan. This 6-m long core was retrieved at ∼700m water-depth and is characterized by the presence of a 5-m thick section of finely laminated sediments, which were deposited between 9.5 and 7.3ka BP and correspond to the African Humid Period (AHP). The data show distinct changes in eolian dust inputs as well as variations in discharge of the Blue Nile and White Nile. Sedimentation was mainly controlled by changes in fluvial discharge during the Holocene, which was predominantly forced by low-latitude summer insolation and by the location of the eastern African Rain Belt. The changes in relative contribution from the Blue Nile and White Nile followed changes in low-latitude spring/autumn insolation, which highlights the role of changes in seasonality of the precipitation on the Nile River regime. The relative intensity of the Blue Nile discharge was enhanced during the early and late Holocene at times of higher spring insolation (with massive erosion and runoff during the AHP at times of high summer insolation), while it was reduced between 8 and 4ka at times of high autumn insolation. The gradual insolation-paced changes in fluvial regime were interrupted by a short-term arid event at 8.5–7.3ka BP (also associated with rejuvenation of bottom-water ventilation above the Nile fan), which was likely related to northern hemisphere cooling events. Another arid event at 4.5–3.7ka BP occurred as the apex of a gradually drier phase in NE Africa and marks the end of the AHP.

Nature and origin of sedimentary clasts associated with mud volcanoes in the Nile deep-sea fan. Relationships with fluid venting

During the last 10 years several marine geological/geophysical surveys conducted on the Nile deep-sea fan have provided much new information about the large fluid seepage phenomenon, which characterizes this passive margin segment. Among the data, more than 60 sediment cores have been recovered in this area. Rock clasts were collected from eight of them as well as during deep-sea dives, notably in the area of Isis, Osiris and Amon mud volcanoes. In few areas, especially in the Western and the North-eastern provinces of the Nile fan, some clasts consist of crust fragments resulting from cementation of muddy sediment by precipitation of high-Mg calcite. These clasts correspond to a simple cementation of the mud by precipitation of high-Mg calcite: as a consequence no obvious textural or faunal difference with the ambient matrix mud can be observed. These clasts are made of autochthonous crusts derived from microbial anaerobic oxidation of methane and release of bicarbonate and sulphide in the surrounding pore water. These clasts also lack aragonite. In most of the other cases (Menes caldera, Isis, Osiris, and Amon mud volcanoes), allochthonous clasts characterized by low-Mg calcite cement, siderite or dolomite mixed with expelled mud outcrop on the seafloor. Nannofossils have allowed us to date some of these clasts. Most of the ages range from Pliocene to Pleistocene; one clast is Lower Cretaceous in age. The lithological facies often indicate coastal or deltaic environments. Some clasts are closely linked to an evaporite-rich environment (halite, gypsum, and analcime); they all provide useful information on the nature of buried sedimentary series covering the margin. Their presence on the seafloor is due to the expulsion of a pressurized mixture of sediment, water, and gas. This process is believed to have used pre-existing tectonic conduits.

Nd isotopic compositions of Eastern Mediterranean sediments: tracers of the Nile influence during sapropel S1 formation?

Abstract Nd isotopic composition of Eastern Mediterranean sediments are used to investigate the influence of Nile flux variations during the formation of the youngest sapropel S1. Four box cores located on an east–west transect (around 35°N) at increasing distance from the Nile source were studied. ϵ Nd(0) signatures were measured in the lithogenic (alumino-silicate residue) fraction and the authigenic/biogenic (carbonates, organic matter and Fe, Mn oxyhydroxides) fraction of the sediment after 1 M HCl leaching. The ϵ Nd(0) profiles of the residual fraction show more radiogenic values in the sapropel layers than in the adjacent sediments. These profiles follow the Gaussian-shaped Ba/Al profile shape which defines S1. The ϵ Nd(0) variations can be related to changes in the proportions of two continental sources of particulate material: Nile particles and Saharan aerosols. A simple mixing model reveals that the contribution of Nile particulates to the sediments increases relative to Saharan aerosols during sapropel formation, indicating a higher Nile discharge and a decrease in eolian input at that time. For the cores located closest to the Nile fan, the ϵ Nd(0) signatures of the leachable fraction are always higher in the sapropel layer (−5 to −4) than in the adjacent sediments (∼−6). The sapropel layer ϵ Nd(0) values increase with decreasing distance to the Nile towards values close to the Nile particulates. All the results obtained on the leachable fraction point towards a massive input of Nile freshwater during S1 deposition.