Abu Roash G dolomite reservoir characterization using seismic inversion technique, Horus field, Western Desert, Egypt

The main objective of this paper was the characterization of the reservoir (Abu Roash G dolomite) in terms of acoustic impedance from surface seismic data complemented by available well logs. To reach our target, a two-step procedure was followed: first, identification of the reservoir signatures using synthetic seismogram using Strata program in Hampson–Russell software and second, applying inversion technique to the post-stack seismic data using Strata program in Hampson–Russell software to obtain acoustic impedance profiles and maps. This procedure was applied to 12 3D seismic lines (six cross-lines, and six in-lines) from Horus field in Western Desert in Egypt after converting them from analog state to SEGY format by vectorization. Five wells had been used in this study. The outcome of this paper is an improved subsurface image of seismic data and achieving the reservoir characterization in a good way.     

Geochemistry and microprobe investigations of Abu Tartur REE-bearing phosphorite,Western Desert,Egypt

Phosphorites in Egypt occur in the Eastern Desert, the Nile Valley and the Western Desert at Abu Tartur area and present in Duwi Formation as a part of the Middle Eastern to North African phosphogenic province of Late Cretaceous to Paleogene age (Campanian–Maastrichtian). The Maghrabi-Liffiya phosphorite sector is considered as the most important phosphorite deposits in the Abu Tartur area due to its large reserve thickness and high-grade of lower phosphorite bed beside high content of REE. Back scattered electron (BSE) images show framboidal pyrite filling the pores of the phosphatic grains, suggesting diagenetic reducing conditions during phosphorites formation.Electron Probe Micro Analyzer (EPMA) chemical mapping was conducted to examine the variation and distributions of selected elements (P, F, La, Fe, Yb, Si, Ce, W, Eu, S, Ca, Y and Er) within the shark teeth, coprolites and bone fragments. In the teeth W, S, Fe are concentrated along the axis of the teeth, the bone fragments show high concentration of W, Yb, Er and Eu, whereas coprolites are nearly homogenous in composition contains S, Er with some Si as micro-inclusions. Fluorapatite is considered as main phosphate mineral whereas pyrite occurs as pore-filling within the phosphatic grains and cement materials. Maghrabi-Liffiya samples show a wide range in the P₂O₅ content, between 19.8 wt.% and 29.8 wt.% with an average of 24.6 wt.% and shows low U content ranging from 15 ppm to 34 ppm with an average of 22 ppm. The total REE content in nine samples representing the Maghrabi-Liffiya ranges from 519 to 1139 ppm with an average of about 879 ppm. The calculation of LREE (La–Gd) show indeed a marked enrichment relative to the HREE (Tb–Lu) where LREE/HREE ratio attains 8.4 indicating a strong fractionation between the LREE and HREE. Chondrite-normalized REE patterns of the studied phosphorite samples show a negative Eu anomaly.     

Recovery of some valuable elements from lamprophyre dykes in the Abu Rusheid area, Southeastern Desert, Egypt

In the Abu Rusheid area, Southeastern Desert of Egypt, polymineralized (HREEs, U, Zn and Pb) lam-prophyre dykes are recently recorded. The lamprophyre dykes cut cataclastic rocks along share zones in NNW-SSE trends. The secondary U-minerals are essentially represented by uranophane, kasolite, torbernite and autunite. Ex-perimental work was carried out on the lamprophyre dykes for the recovery of uranium and other valuable elements (e.g. Zn, Pb and Al) from 50 kg of technological sample. The optimum conditions were: 100 g/L sulfuric acid con-centration, 1:5 S/L (solid/liquid) and soaking for 15 days at room temperature. The leaching efficiencies for the re-covery of uranium and other elements like Al, Zn and Pb were 40, 33.6, 98.8 and 78, respectively.     

Facies model of a fine‐grained,tide‐dominated delta: Lower Dir Abu Lifa Member (Eocene), Western Desert,Egypt

Existing facies models of tide‐dominated deltas largely omit fine‐grained, mud‐rich successions. Sedimentary facies and sequence stratigraphic analysis of the exceptionally well‐preserved Late Eocene Dir Abu Lifa Member (Western Desert, Egypt) aims to bridge this gap. The succession was deposited in a structurally controlled, shallow, macrotidal embayment and deposition was supplemented by fluvial processes but lacked wave influence. The succession contains two stacked, progradational parasequence sets bounded by regionally extensive flooding surfaces. Within this succession two main genetic elements are identified: non‐channelized tidal bars and tidal channels. Non‐channelized tidal bars comprise coarsening‐upward sandbodies, including large, downcurrent‐dipping accretion surfaces, sometimes capped by palaeosols indicating emergence. Tidal channels are preserved as single‐storey and multilateral bodies filled by: (i) laterally migrating, elongate tidal bars (inclined heterolithic strata, 5 to 25 m thick); (ii) forward‐facing lobate bars (sigmoidal heterolithic strata, up to 10 m thick); (iii) side bars displaying oblique to vertical accretion (4 to 7 m thick); or (iv) vertically‐accreting mud (1 to 4 m thick). Palaeocurrent data show that channels were swept by bidirectional tidal currents and typically were mutually evasive. Along‐strike variability defines a similar large‐scale architecture in both parasequence sets: a deeply scoured channel belt characterized by widespread inclined heterolithic strata is eroded from the parasequence‐set top, and flanked by stacked, non‐channelized tidal bars and smaller channelized bodies. The tide‐dominated delta is characterized by: (i) the regressive stratigraphic context; (ii) net‐progradational stratigraphic architecture within the succession; (iii) the absence of upward deepening trends and tidal ravinement surfaces; and (iv) architectural relations that demonstrate contemporaneous tidal distributary channel infill and tidal bar accretion at the delta front. The detailed facies analysis of this fine‐grained, tide‐dominated deltaic succession expands the range of depositional models available for the evaluation of ancient tidal successions, which are currently biased towards transgressive, valley‐confined estuarine and coarser grained deltaic depositional systems.     

Wrench tectonics of Abu Gharadig Basin,Western Desert,Egypt: a structural analysis for hydrocarbon prospects

Mapping based on the interpreted seismic data covering the Abu Gharadig Basin in the northern Western Desert has revealed that the deposition of the Upper Cretaceous succession was controlled by dextral wrench tectonics. This dextral shear accompanied NW movement of the African Plate relative to Laurasian Plate. Structural depth maps of the Cenomanian Bahariya Formation and the Turonian-Coniacian D and A members of Abu Roash Formation display a clear NE-SW anticline dissected by NW-SE normal faults. This anticline represents one of the en echelon folds characterizing the wrench compressional component. The interpreted normal faults reflect the extensional T-fractures associated with the wrenching tectonics. The interaction between the aforementioned NE-SW anticline with the NW-SE extensional faults further confirms the effect of the Upper Cretaceous dextral wrench tectonic. However, the influence of this wrench tectonics was gradually diminishing from the Cenomanian up to the Coniacian times. The NW-SE compressional stress of the dextral wrench compressional component during the Cenomanian up to Coniacian age was greater in NW direction than the SE direction. Three mapped structural closures which are predicted to be potential hydrocarbon traps belonging to the Bahariya Formation and Abu Roash D Member, and are recommended to be drilled in the study area, with potential reservoirs. The regularity of the en echelon array of both anticlines and normal faults within the wrench zones suggests additional closures may be located elsewhere beside the study area.     

Late Albian–Middle Cenomanian palynofacies and palynostratigraphy, Abu Gharadig-5 well, Western Desert, Egypt

Quantitative analyses of palynomorph assemblages, particulate organic matter (kerogen), and total organic carbon (TOC) have been made on samples of the Albian–Cenomanian Kharita and Bahariya formations encountered in the Abu Gharadig-5 well, Western Desert, Egypt. Two assemblage palynozones are defined: Assemblage Zone A (Kharita Formation) of late Albian–early Cenomanian age and Assemblage Zone B (Bahariya Formation) of early–middle Cenomanian age. Palynofacies of the Kharita Formation suggest that sedimentation of these strata took place in a warm, shallow, nearshore-marine environment. The deposition of the lower Bahariya Formation took place initially in similar conditions but subsequently further offshore in somewhat deeper water of the inner shelf. The relatively high percentage of Ephedripites, Afropollis and elaterate pollen in both formations indicates an arid climate. The Kharita Formation yields kerogen types III and IV whereas the assemblages recovered from the Bahariya Formation contain types II and III. The TOC is generally between 0.42 and 0.65% in the Kharita Formation, while it ranges between 0.42 and 0.80% in samples of the Bahariya Formation. The spores and pollen grains are pale in colour; hence little source potential for hydrocarbons is indicated.     

Integrated potential field study on the subsurface structural characterization of the area North Bahariya Oasis, Western Desert, Egypt

The present study aims mainly to delineate and outline the regional subsurface structural and tectonic framework of the buried basement rocks of Abu El Gharadig Basin, Northern Western Desert, Egypt. The potential field data (Bouguer gravity and total intensity aeromagnetic maps) carried out in the Abu El Gharadig Basin had been analyzed together with other geophysical and geological studies. The execution of this study is initiated by transformation of the total intensity aeromagnetic data to the reduced to pole (RTP) magnetic map. This is followed by applying several transformation techniques and various filtering processes through qualitative and quantitative analyses on both of the gravity and magnetic data. These techniques include the qualitative interpretation of gravity, total intensity magnetic and RTP magnetic maps. Regional–residual separation is carried out using the power spectrum. Also, the analytic signal and second vertical derivative techniques are applied to delineate the hidden anomalies. Aeromagnetic anomalies in the area reflect significant features on the basement tectonics, on the deep-seated structures and on the shallow-seated ones. Major faults and intrusions in the area are indicated to be mainly along the NE–SW, NW–SE, ENE–WSW and E–W directions. The Bouguer gravity map indicates major basement fracturing, as well as variations in the sedimentary basins and ridges and subsequent tectonic disturbances. The most obvious anomalous trends on the gravity map, based on their frequencies and amplitudes, are along the NE–SW, ENE–WSW, E–W and NW–SE trends. The main of Abu EL Gharadig Basin depositional center does not show sharp variations, because of the homogeneity of the marine rocks and the great basement depths.     

Alam El Bueib reservoir characterization,Tut oil field,North Western Desert,Egypt

An integrated petrophysical well log and core data analysis of the Alam El Bueib-3D (AEB-3D) and Alam El Bueib-3E (AEB-3E) reservoirs, Tut oil field, North Western Desert, Egypt, allows the evaluation of those parameters critical to their reservoir characterization. The determined reservoir properties investigated are lithology, depositional paleoenvironments, shale volume, porosity, fluid saturation and net pay thickness. As the analysis of reservoir pressure is essential to specify the driving mechanisms that control the behavior of fluids within reservoirs, pressure analysis identified the Alam El Bueib-3D reservoir to be partial water drive and Alam El Bueib-3E to be an active water drive. In addition, the pressure analysis identified two additional hydrocarbon-bearing reservoirs in the Alam El Bueib-3D. Stacking patterns of the Alam El Bueib-3D reservoirs are generally fining upward sequences reflecting fluvial to braided fluvial paleoenvironments. The Alam El Bueib-3E channel shows blocky patterns with sharp bases and tops diagnostic of distributary channels. Statistical analysis of core permeability and porosity values of the Alam El Bueib reservoirs indicate very good reservoir quality. Scatter diagrams of porosity values derived from core analysis for the AEB-3D and AEB-3E reservoirs reveal correlation coefficient (r) values of 0.93 and 0.64, respectively, indicating strong linear relationships. Plots of porosity values against permeability values also show strong linear relationships in all the reservoirs indicating that the AEB-3D and the AEB-3E are permeable and with strong pore communication. The permeability measurements indicate restricted reservoir heterogeneity as plots of vertical permeability values against horizontal permeability values exhibit linear trends. Altogether, the reservoir characterization of the Alam El Bueib reservoirs demonstrates their excellent potential for hydrocarbon production.     

Groundwater potential for irrigation in the East Oweinat area,Western Desert Egypt

The Nubia Sandstone aquifer system is one of the most extensive groundwater systems in North Africa, covering an area of about 2,000,000 km², including parts of Egypt, Libya, Sudan, and Chad. In the Western Desert of Egypt, the Nubian formation has a thermal gradient of 1.1–5°C 100 m^–1 with the exception of the East Oweinat area, located in the southern part of the Western Desert. This is the only part of this huge system where ground-water occurs under unconfmed conditions in an area where the Nubian sandstone crops out and is underlain by shallow basement rocks; in this area groundwater has no thermal characteristics. The aquifer system in the East Oweinat area attains a relatively high hydraulic conductivity. The direction of groundwater flow is generally northeastwards but is distorted at faults and fracture zones. Chemical analyses of groundwater in the area indicate a low salt content and suitability for irrigation purposes. As the estimated recharge to the area is low compared with the foreseen irrigation water requirement, the development of groundwater in the East Oweinat should be based on groundwater mining. Although the evaluation of the groundwater resources in East Oweinat has indicated that groundwater can be extracted at a rate of 4.7×10⁶ m³ d^–1, the long-term economics of extraction that can sustain large-scale development projects has to be assessed.     

Geochemical characterization of zoned zircon from Wadi Abu Rusheid psammitic gneiss, south Eastern Desert, Egypt

A unique zircon was studied in the gneiss samples collected from the Wadi Abu Rusheid psammitic gneiss using electron scanning microscope and electron probe microanalyses. This zircon can be categorized into two types according to the texture and trace element content: (l) magmatic zircon slightly enriched in HfO₂ with ordinary zone. (2) Overgrowths of zircon occur as two species, the first species being highly enriched in HfO₂ with irregular zoning. The second species is highly enriched in HfO₂ forming a rim around the second species with a very sharp thinner boundary. The first type shows a distinct oscillatory internal zoning pattern without change in shape of this zone and has conspicuous inclusion-free zircon overgrowths with distinct poor concentrations in Y, Hf, Th, U, Nb, and Ta in both rim and core. The second type shows two species, the first one displays distinct irregular interval zoning and irregular overgrowth with abrupt change in composition of these zones with distinct enrichment in Y, Hf, Th, U, Nb, and Ta in the rim relative to the core. The second species is forming a rim around the first species also with distinct enrichment in Y, Hf, Th, U, Nb, and Ta content. These indicate that two events (crystallization environment) have played an important role in the formation of this zircon and largely reflect differences in whole-rock trace element contents between the successive generations of this zircon. The first event is believed to be of magmatic origin giving rise to normal composition of magmatic zircon. The second event shows an intense successive process of metasomatic activity during the formation of the Abu Rusheid radioactive gneiss. Electron microprobe analysis indicates that oscillatory zoned zircon shows poor content of Y, Hf, Th, U, Nb, Ta, and rare earth elements (REE) in the rim and core, while overgrowths of zircon are slightly enriched by these elements. Also, these analyses indicate that the Abu Rusheid psammitic gneiss has been significantly enriched by the thorite mineral (Th content up to 54.72% ThO₂) and columbite-bearing minerals (Nb content up to 64.74% Nb₂O₅, Ta content up to 9.32% Ta2O₅). The poor content of REE in overgrowths of zircon indicates mobilization of REE during the metamorphism processes of gneiss.     

Khatatba Formation as an active source rock for hydrocarbons in the northeast Abu Gharadig Basin,north Western Desert,Egypt

Arabian Journal of Geosciences - Rock samples and a suite of oil samples collected from wells drilled in the northeastern part of the Abu Gharadig Basin were studied to determine the petroleum...     

Interpretation of aeromagnetic and gravity data in East Qattara Depression, North Western Desert, Egypt

The study area lies to the east of Qattara Depression at the north of the Western Desert, Egypt. It is bounded by latitudes 29°00?? and 30°00?? N and longitudes 28°00?? and 29°30?? E, including Abu Gharadig basin, which is the most petroliferous basin in the Egyptian Western Desert. Numerous exploratory wells show that the area is characterized by a thick sedimentary section, unconformably overlying the basement rocks. The main objective of the present study is to outline the structural parameters controlling the area under consideration. Aeromagnetic and gravity data were subjected to the analytic signal, 3D Euler deconvolution and edge enhancement techniques. The Analytic signal and 3D Euler deconvolution were utilized mainly to locate the main subsurface contact zones and to determine the depth and structural indices of the expected causative subsurface structural elements. However, the edge enhancement technique was used with various windows to enhance the edges of subsurface structures. The structural indices were estimated to be ranging between 0.16 and 0.26, indicating that the area is mainly controlled by faults. The depth of these structural elements was also estimated to be ranging between <1.37 and 5.29?km. It has been shown that the structural elements of the study area have different directions, trending E-W, ENE, NW, and N-S.     

Sequence Stratigraphy and Rudist Facies Development of the Upper Barremian‐Lower Cenomanian Platform,Northern Sinai,Egypt

The Lower Cretaceous sections in northern Sinai are composed of the Risan Aneiza (upper Barremian-middle Albian) and the Halal (middle Albian-lower Cenomanian) formations. The facies reflect subtle paleobathymetry from inner to outer ramp facies. The inner ramp facies are peritidal, protected to open marine lagoons, shoals and rudist biostrome facies. The inner ramp facies grade northward into outer ramp deposits. The upper Barremian-lower Cenomanian succession is subdivided into nine depositional sequences correlated with those recognized in the neighbouring Tethyan areas. These sequences are subdivided into 19 medium-scale sequences based on the facies evolution, the recorded hardgrounds and flooding surfaces, interpreted as the result of eustatic sea level changes and local tectonic activities of the early Syrian Arc rifting stage. Each sequence contains a lower retrogradational parasequence set that constituted the transgressive systems tracts and an upper progradational parasequence set that formed the highstand systems tracts. Nine rudist levels are recorded in the upper Barremian through lower Cenomanian succession at Gabal Raghawi. At Gabal Yelleg two rudist levels are found in the Albian. The rudist levels are associated with the highstand systems tract deposits because of the suitability of the trophic conditions in the rudist-dominated ramp.     

Dokhan volcanics of Gabal Monqul area,North Eastern Desert,Egypt: geochemistry and petrogenesis

The Dokhan volcanics are represented by a thick stratified lava flows succession of basalt, andesite, imperial porphyry, dacite, rhyodacite, rhyolite, ignimbrites, and tuffs. These lavas are interbanded with their pyroclastics in some places including banded ash flow tuffs, lithic tuffs, crystal lapilli tuffs, and agglomerates. They are typical calc–alkaline and developed within volcanic arc environment. All rocks show moderate enrichment of most large ion lithophile elements relative to high field strength elements (HFSE). The incompatible trace elements increase from basalt through andesite to rhyolite. The felsic volcanics are characterized by moderate total rare earth elements (REE) contents (162 to 392 ppm), less fractionated patterns {(Ce/Yb)_N = (1.24 to 10.93)}, and large negative Eu anomaly {(Eu/Eu*) = (0.15 to 0.92)}. The mafic volcanics have the lowest REE contents (61 to 192 ppm) and are relatively steep {(Ce/Yb)_N = (3.2 to 8.5)}, with no negative Eu anomalies {(Eu/Eu*) = (0.88 to 1)}. The rhyolite displays larger negative Eu anomaly (Eu/Eu* = 0.28) than those of other varieties, indicating that the plagioclase was an early major fractionating phase. The mineralogical and chemical variations within volcanics are consistent with their evolution by fractional crystallization of plagioclase and clinopyroxene.     

Campanian-Lower Paleogene gastropods from the Kharga Oasis,south Western Desert,Egypt

The Campanian-Lower Paleogene successions exposed at the Kharga Oasis contain well-preserved gastropods. Nineteen gastropod species are identified and described in detail. Two new species are established: Gisortia khargaensis from the lower Eocene El Rufuf Formation and Ornopsis? barisensis from the lower Paleocene Kurkur Formation. In addition to, Turritella (Torquesia) derbesi Coquand is recorded herein for the first time from Egypt. The studied gastropods belonging to four clades: Sorbeoconcha (Metacerithium abictiforme (Wanner), Mesalia hofana Mayer-Eymar, Mesalia sp., Turritella (Torquesia) derbesi Coquand, Turritella (Torquesia) forgemoli Coquand, Turritella kaserensis Hewaidy and Azab, Turritella sp.), Littorinimorpha (Cypraedia bullina Oppenheim, Gisortia khargaensis nov. sp., Natica farafrensis Wanner, Aporrhais schweinfurthi (Quaas), Drepanocheilus bicarinatus Abbass, Drepanocheilus? sp., Anchura? unicarinatus (Abbass), Epitonium sp.), Neogastropoda (Ornopsis? barisensis nov. sp., Rostellana daniensis (Quaas), Vouta sp.), and Heterobranchia (Avellana cretacea Quaas).     

Hydrogeological studies for the Nubia sandstone aquifers in Garf Hussein area,Western Desert,Egypt

The lithology of the studied aquifers has an important effect on their hydrogeologic setting. Moreover, the structural patterns have their imprint on the geologic setting and consequently the hydrogeologic conditions of the area. Lake Nasser recharges the groundwater in the study area by large amount of water increasing the groundwater level. A comparison of the depth to water in the same wells at two different periods (1998 and 2014 ) shows that the depth to water increases with average rise 11.1 m during 16 years. The constructed water table map shows that the groundwater flow is mainly towards the northwest direction reflecting recharge from Lake Nasser. The hydraulic parameters of the Abu Aggag and Sabaya sandstone aquifers are determined in the present work from pumping tests. The transmissivity of the studied aquifers reflects the moderate to high potentiality. The groundwater salinity of the studied aquifers is fresh water and varies from 353 to 983 ppm (part per million) and suitable for all purposes. It increases due to the west direction coinciding with groundwater flow direction. The main result of the present study shows that the seepage water from Lake Nasser attains 17 mcm/year.     

The Ediacaran volcanosedimentary succession of Gabal Abu Had,North Eastern Desert,Egypt: geological study,facies analyses,and depositional setting

Gabal Abu Had is an exposure of a volcanosedimentary succession in the North Eastern Desert Basement Complex. This succession includes intercalation of two major rock units, which are Dokhan Volcanics and Hammamat Group with different styles of formation, deposition environments, and genesis. Gabal Abu Had succession (GHS) is a northward dipping, c. 700-m-thick volcanosedimentary succession that rests on metavolcanic and old granitoid rocks with erosion unconformity. The lower part of GHS is dominated by volcaniclastic mass flow deposits and andesitic lava with interbedded gravely sandstone, whereas the upper sequence is composed of pyroclastic flow deposits including welded to no welded ignimbrite intercalated with gravely sandstone and massive clast-support conglomerate toward the top. Facies analysis study of GHS presented eight lithofacies types, which grouped into five lithofacies associations. The GHS basin started with effusive eruption of silica-poor volcanic center, which produced andesitic lava. A part of lava underwent hyaloclastic fragmentation due to the presence of fluvial water in places producing the volcaniclastic mass flow deposits. Later, an explosive silica-rich volcanic center affected the GHS basin and created the pyroclastic plain deposits (ignimbrite and bedded tuff). The fluvial braided river is still in action since the first eruption, producing gravely sandstone, which is intercalated with the volcanic sequence. The upper GHS is characterized by thick, massive, and clast-supported conglomerate (well rounded clasts up to 100 cm) of alluvial fan facies. Several silica-rich and silica-poor subvolcanic intrusions were emplaced in the GHS. The GHS development displays a cycle from low- to high-energy sedimentation under humid climatic conditions, in addition to extension and down faulting of basin shoulders. In comparison with Gabal El Urf, located to the north of GHS and was studied by El-Gameel (2010), the GHS is a lava-rich succession rather than Gabal El Urf succession which is mainly pyroclastic rich.     

Seismic structural analysis at Abu Darag area,Gulf of Suez,Egypt

This study is an attempt to clarify the subsurface geological settings at Abu Darag area in the N part of the Gulf of Suez through the analysis of the available seismic data. The time contour maps of three different reflectors (Top Kareem, Within Rudeis and Top Nukhul) present in this area were constructed and several structures were detected. Generally, the area is considered as a tilted fault block dipping in NE-SW direction and it is dissected by different faults. Major and minor NW-SE faults are the strongest trend in the area while other fault trends are with very weak magnitude and limited extent. All these fault trends restrict between them some high and low areas. Also, two geo-seismic sections were built to confirm the structural prospects on Top Nukhul time contour map.     

The offshore to backshore environments of the Abu Ballas Formation of the SE Dakhla Basin (Western Desert,Egypt)

The Abu Ballas Formation in the Western Desert of Egypt represents a marine intercalation within fluvial, Nubia-type sandstones. These deposits document an extensive transgression of Aptian age flooding the Dakhla Basin from north to south. Due to this first advance of the Tethyan sea during the Cretaceous, sediments of open and marginal marine provenance were accumulated in the SE of the basin.The sedimentary succession of the open marine facies is divided into five lithostratigraphic units which reflect that deposition was largely controlled by one single transgressive-regressive event. The transgressive sequence in the lower part of the formation comprises sandstones of a backshore to foreshore environment (unit 1) which are overlain by offshore claystones (unit 2). The middle portion of the sedimentary succession consists of silty and sandy strata (unit 3) which are attributed to large-scale redepositional processes due to intensified bottom currents during the maximum extension of the sea. These sediments are capped by offshore originated claystones (unit 4) grading upwards into siltstones and sandstones of transition-zone to backshore environments (unit 5), which indicate a gradual regression.This stratigraphic sequence documenting a retrograding-prograding shoreline due to the transgression and regression of the Aptian sea, interfingers with silty and sandy deposits of the marginal marine facies of the Abu Ballas Formation. Comparable to the lithostratigraphic units 1 and 5 these strata represent a variety of sedimentary environments ranging from the backshore to the transition zone. They were accumulated on the western slope of the Kharga Uplift bounding the Dakhla Basin towards the east, which was partially flooded while the sea had its maximum extension.

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Zusammenfassung Die Abu Balks-Formation in der Western Desert Ägyptens stellt eine marine Einschaltung innerhalb von fluviatilen Sandsteinen Nubischen Typs dar. Diese Schichtenfolge dokumentiert eine weitflächige, nach Süden hin in das Dakhla-Becken vorgreifende Transgression aptischen Alters. Im Verlauf dieses ersten Vorstoßes der Tethys während der Kreide wurden im SE des Beckens Sedimente offen und randlich mariner Provenienz abgelagert.Die Ablagerungen der offen marinen Fazies werden in fünf lithostratigraphische Einheiten unterteilt, deren vertikale Abfolge eine Sedimentakkumulation im Rahmen einer Transgression und einer nachfolgenden Regression widerspiegelt. Die transgressive Schichtenfolge im unteren Teil der Formation umfaßt Sandsteine mit Merkmalen einer Strandsedimentation (Einheit 1), die von Peliten eines untiefen Schelfs (Einheit 2) überlagert werden. Höher folgen siltige und sandige Schichten (Einheit 3), die auf großräumige Umlagerungsvorgänge im Becken durch bodennahe Strömungen während der maximalen Ausdehnung des Meeres zurückgeführt werden. Die regressive Entwicklung setzt ein mit einer erneuten Ablagerung von pelitischen Sedimenten eines flachen Schelfmeeres (Einheit 4). Diese gehen zum Hangenden hin über in Siltsteine und Sandsteine (Einheit 5), die zwischen dem Schelf und dem Strandbereich vermitteln und das Ende der Verflachungsphase andeuten.Diese Schichtenfolge, die auf ein anfängliches Zurückweichen und späteres Vorrücken der Küstenlinie im Rahmen von Transgression und anschließender Regression hinweist, verzahnt sich mit siltigen und sandigen Ablagerungen der randlich marinen Fazies der Abu Ballas-Formation. Ähnlich wie die lithostratigraphischen Einheiten 1 und 5 entstammen sie einem Strandbis küstennahen Schelf-Milieu und wurden während der maximalen Ausbreitung des Meeres an der westlichen Flanke des Kharga-Uplifts akkumuliert. Diese Schwellenregion, die das Dakhla-Becken nach Osten begrenzt, war im Apt vermutlich nur teilweise überflutet.

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Résumé La formation Abu Ballas du désert occidental d'Egypte représente une intercalation marine dans les grès fluviatiles de type nubien. Cette séquence illustre une large transgression d'âge aptien pénétrant vers le Sud dans le bassin de Dakhla. Au cours de cette première progression de la Téthys pendant le Crétacé, des sédiments d'origine marine et marginolittorale se sont déposés dans la partie SE du bassin.Les couches de facies marin sont diversées en cinq unités lithostratigraphiques, dont la succession verticale refléte une accumulation de sédiments au cours d'une transgression et d'une régression successives. La série transgressive, dans la partie inférieur de la formation, comprend des grès typiques d'une sédimentaion de haute et de basse plage (unité 1), surmontés par des pélites de plate-forme continentale peu profonde (unité 2). Plus haut viennent des chouches silteuses et sableuses (unité 3) qui sont attribuées à des processus de remaniements dans le bassin par les courants de fond pendant l'extension maximale de la mer. La phase régressive commence par un nouveau dépôt de sédiments pelitiques de mer peu profonde (unité 4). Ceux-ci sont suivis vers le haut par des siltites et des grès (unité 5) déposés dans une zône de transition arrière plage/plateforme continentale et indiquant la fin de la régression.Cette série qui indique un recul puis une avancée de la ligne de rivage, par transgression et régression, est interstratifiée de dépôts silteux et sableux de facies marin marginal de la formation Abu Ballas. Semblables aux unités lithostratigraphiques 1 et 5, ces couches témoignent d'un milieu variant de la basse plage à la partie haute du shelf. Elles se sont accumulés au bord ouest du seuil de Kharga au cours de l'extension maximale de la mer aptienne. A cette époque, cette region élevée limitant le bassin de Dakhla vers l'est, n'était probablement inondée qu'en partie.

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