Papers by Ahmed A Abdelhady
Journal of Paleontology
The Jurassic rocks of Gebel Maghara, northern Sinai, Egypt, contain a well-preserved and highly d... more The Jurassic rocks of Gebel Maghara, northern Sinai, Egypt, contain a well-preserved and highly diverse macrobenthic fauna, dominated by bivalves. This fauna, particularly bivalves and gastropods, have received little attention in the last 100 years. In an attempt to provide a sound database on the marine bivalve diversity of Egypt during the Jurassic period, a first faunal group, the protobranch bivalves, is reviewed in detail. Sixteen taxa (three of them new), belonging to two orders, five families, and nine genera are systematically described and compared to closely related Jurassic taxa from various locations, particularly in Europe and India. New species are Nuculoma douvillei n. sp., N. sinaiensis n. sp., and Palaeoneilo aegyptiaca n. sp. In addition, Palaeonucula cuneiformis (J. de C. Sowerby), P. muensteri (Goldfuss), Dacryomya diana (d'Orbigny), D. lacryma (J. de. C. Sowerby), and Praesaccella juriana Cox are identified from Jurassic strata of Egypt for the first time. ...
Palaeontologia Electronica, 2019
Fossil groups are used for biochronological dating of rocks for decades. This manuscript presents... more Fossil groups are used for biochronological dating of rocks for decades. This manuscript presents a quantitative approach to appraise and compare the quality of selected taxa as biostratigraphic markers. Based on species occurrence of ammonites, bivalves, and planktic and benthic foraminifers we evaluate the potential of these to rank them quantitatively. The spatiotemporal analyses of occurrence data (species duration, geographic range) were integrated in results of the Unitary Association method, which measures superpositional contradictions in addition to the generation of a number of UAs. The results indicate that Jurassic ammonites have the lowest species duration, and that the majority of species is confined to a single UA-zone. Additionally, ammonites have the lowest numbers of contradicted bio-events. However, planktic foraminifers are more valuable at least in the Cenozoic as they have a high geographic reproducibility and diversity, and higher ISP values. The bivalves and benthic foraminifers both show longer average species durations and more superpositional contradictions per species. Therefore, their biostratigraphic potential is more limited at an interregional scale. The shorter species durations of ammonites and planktic foraminifers in the studied sections can be attributed to their higher extinction rates. As an advantage to simple spatio-temporal analyses, the UA-method can accurately assess the stratigraphic potential of a given taxonomic group. The results obtained herein indicate that the life-habit has direct impact on the species duration and thus, the stratigraphic potential of the fossil groups. Based on the results achieved from this study, an index for ranking fossil groups (Index of Stratigraphic Potential 'ISP') is introduced.
Journal of Paleontology, 2017
The nuculanid bivalveCostinuculana magharensisnew genus new species is described from the middle ... more The nuculanid bivalveCostinuculana magharensisnew genus new species is described from the middle to upper Bathonian Kehailia Formation of Gebel Maghara, North Sinai, Egypt.Costinuculanadiffers from other genera of the family Nuculanidae by the presence of opisthocline ribs along the rostrum. These ribs are variable in shape and size, straight to folded posteriorly, bifurcate ventrally and occasionally postero-dorsally, and cover an area~45% of the total valve length from the posterior end. The life position ofC.magharensisn. gen. n. sp. is reconstructed on the basis of a functional interpretation of its morphology and by comparison with closely related Recent forms. The asymmetrical commarginal ribs facilitated the burrowing process. The posterior oblique ribs are asymmetrical in cross-section with a steeply concave side in the burrowing direction and slightly convex side in the opposite direction. They probably kept the bivalve in a stable position once the desired depth had been r...
Palaeogeography, Palaeoclimatology, Palaeoecology, 2017
Middle to Late Jurassic equatorial seawater temperatures and latitudinal temperature gradients ba... more Middle to Late Jurassic equatorial seawater temperatures and latitudinal temperature gradients based on stable isotopes of brachiopods and oysters from Gebel Maghara,
Cretaceous Research, 2017
Based on rock and fossil data from the Upper Cretaceous of the El Hassana Dome (Abu Roash, Egypt)... more Based on rock and fossil data from the Upper Cretaceous of the El Hassana Dome (Abu Roash, Egypt), factors controlling facies architecture and the nature of biotopes are highlighted. The succession formed on a non-rimmed shelf, the architecture of which varied from an inner to an outer shelf setting upsection. Macrobenthic biotopes are reconstructed and their palaeoecological significance assessed using a novel ternary plot. Based on diversity and community structure (770 specimens assigned to 28 bivalve and gastropod taxa), four paucispecific associations are identified. These are: 1. the 'Cucullaea' Assemblage, a low-energy, soft-substrate, oligotrophic outer shelf environment with reduced terrigenous input dominated by infaunal bivalves and hexactinellid sponges; 2. the 'Plicatula' Assemblage, a lowenergy, restricted inner shelf lagoonal setting with soupy substrates and dysoxia below the sedimentwater interface dominated by plicatulid and ostreid bivalves, 3. the 'Durania' Assemblage, a highenergy, high-temperature, shoal environment dominated by elevator rudists with minor numbers of echinoids, corals and bryozoans, which together form several biostromes. and 4. The 'Trochactaeon' Assemblage, which share the same characteristics of the 'Durania' Assemblage. The paucispecific nature of these biotopes is indicative of different stress factors. Consequently, the predominant taxa exhibit different degrees of adaptive strategies. In addition to global sea level, local tectonics have significantly affected facies distribution and biotope structure. The shallower facies during the early Turonian and the dysoxia spanning the ConiacianeSantonian were linked to synsedimentary tectonics, which formed many barriers and led to circulation restrictions.
The Jurassic succession of Gebel Maghara North Sinai, Egypt, represents a mixed carbonate-silicic... more The Jurassic succession of Gebel Maghara North Sinai, Egypt, represents a mixed carbonate-siliciclastic sedimentary succession. Combining information from both fossils and rocks collected from four sections has allowed a plausible reconstruction of the palaeoenvironments and benthic communities of the area. As age-diagnostic fossils are rare, and in order to ensure maximal stratigraphic resolution, chronostratigraphic boundaries were determined based on quantitative biostratigraphy (Unitary Associations method). The proposed zones were found to be valid chronological markers and permitted correlation with the Tethyan ammonite zones. The Jurassic succession of G. Maghara was deposited on ramp, and the architecture of the ramp facies was strongly controlled not only by eustatic sea-level changes but also by the extensional tectonics in connection with rifting of the Tethys north of Gondwana. Seven tectonically enhanced third-order sequences (DS1 to DS7) have been recognized. The first...
Palaeogeography, Palaeoclimatology, Palaeoecology, 2015
Based on newly collected material from the Bajocian Oxfordian rocks of Gebel Maghara (North Sinai... more Based on newly collected material from the Bajocian Oxfordian rocks of Gebel Maghara (North Sinai, Egypt) and available published information, the palaeobiogeographic pattern and the dispersal potential of the macrofauna including bivalves, ammonites, corals, and brachiopods are investigated. Both clustering methods and ordination techniques were applied and evaluated. During Bajocian times, G. Maghara occupied an intracratonic setting and was isolated from the main ocean by islands and shallows. These barriers may have limited the dispersal potential of the macrofauna and impeded the faunal exchange with even nearby areas. Although these barriers had disappeared by rejuvenation of faults during an active rift stage in Bathonian times, the same biogeographic patterns continued, which may be related to the global sea level lowstand. By Callovian times, a time of global sea level highstand, in contrast, the fauna of the study area became very similar to that of northeastern Africa. Similarly, diversity and extinction rates increased from the Middle Bathonian onward, which may reflect immigration of cosmopolitan taxa due to the newly established open marine setting and the global sea level highstand. Towards the Oxfordian, lowering of temperature may have limited the dispersal ranges of the macrofauna within the Ethiopian Province. As a
Newsletters on Stratigraphy, 2015
ABSTRACT As age-diagnostic fossils are rare in the Middle to Upper Jurassic sedimentary successio... more ABSTRACT As age-diagnostic fossils are rare in the Middle to Upper Jurassic sedimentary succession of Gebel Maghara, North Sinai, Egypt Jenkins (1990), and in order to ensure maximal stratigraphic resolution, chronostratigraphic boundaries were determined based on quantitative biostratigraphy. A data matrix comprising 231 macrofaunal taxa in 93 samples from four sections has been processed with the Unitary Association (UA) Method. This led to construction of a sequence of 29 UAs (maximal sets of actually or virtually coexisting taxa), which have been grouped into 14 laterally reproducible association zones. The UA method allowed an in-depth analysis of the stratigraphically conflicting taxa, enabled the biostratigraphic subdivision of the studied interval, and also provided stratigraphic correlation among the measured sections and with the Tethyan ammonite zones
Journal of African Earth Sciences, 2014
Highlights 1. Cluster analysis and multivariate ordination were used to a reconstruct the palaeoc... more Highlights 1. Cluster analysis and multivariate ordination were used to a reconstruct the palaeocommunities. 2. The community structure was linked to environmental conditions and sequence stratigraphy. 3. Middle ramp setting during middle TST to MFZ provided the best conditions for the macrobenthos.
Journal of Palaeogeography, 2015
The Jurassic succession at Gebel Maghara, North Sinai, Egypt, represents a mixed carbonate-silici... more The Jurassic succession at Gebel Maghara, North Sinai, Egypt, represents a mixed carbonate-siliciclastic sequence. Combining information from both fossils and rocks allowed a plausible reconstruction of the depositional environments and of the basin evolution. The Jurassic succession of Gebel Maghara was deposited on a ramp, and the architecture of the ramp facies was strongly controlled not only by sea-level changes but also by extensional tectonics in connection with rifting of the Tethys, North Gondwana. Seven tectonically modified thirdorder sequences (DS 1-DS 7) have been recognized. The first three sequences (DS 1-DS 3), ranging from the Toarcian to the Bajocian, record sea invasion (intertidal to shallow subtidal conditions) across an intracratonic area as a result of eustatic sea-level changes during a quiescent rift stage. The remaining sequences (DS 4-DS 7) reflect open marine mid to outer ramp settings. Non-marine conditions around the Bajocian-Bathonian boundary, documented by caliche, represent the maximum regression of the sea. During an active extensional stage, horsts, which formerly acted as barriers separating the Maghara sub-basin from the main ocean, subsided. Subsequent rejuvenation and reactivation of faults shifted the homoclinal physiography of the ramp to a distally steepened ramp during the early Bathonian, creating a 200-m-thick deltaic wedge. Similar processes during the early Kimmeridgian created a calcirudite-calcarenite succession of slope origin. The diversity and the epifaunal/infaunal percentage of the macrofauna display a cyclic pattern which coincides more or less with the sequence stratigraphic architecture.
During the last decade, the desert fringes of the Nile Valley in Egypt witnessed a vast expansion... more During the last decade, the desert fringes of the Nile Valley in Egypt witnessed a vast expansion of groundwaterfed reclaimed lands. However, waterlogging and drainage-induced groundwater quality issues started to be of concern in many locations in these developed areas. In this study, an integrated methodology (landscape analysis, electric geophysical survey, geochemical and isotopic data) was applied to assess the causes of the waterlogging and to examine the impact of waterlogging and associated soil salinization on the groundwater quality, using the area east of the Nile Valley in the El Minia district as a test site. Using eighteen vertical electrical sounding (VES) measurements, the distribution and thicknesses of the impermeable shale layers, which potentially prevent the infiltration of excess irrigation water into the aquifer were delineated. Geochemical and isotopic data revealed that groundwater is not impacted by subsurface discharge of agricultural drainage water and it is mainly recharged from occasional rainfall and lateral seepage from the alluvial aquifer, mainly recharged from the Nile water. Our findings suggested that in addition to the occurrence of shales, the flood irrigation and non-planned cultivation without considering the natural stream networks as well as the wrong management decisions by local farmers significantly contributed to develop the waterlogging, which might further be expanded to impact the adjacent old and low cultivated floodplain lands. Local measures to dispose the excess irrigation water directly into the subsurface through tube wells were found to be inefficient. Since the geology and hydrogeology of new developed lands surrounding the Nile Valley are similar to the test site, the applied methodology can be applicable for all these locations for sustainable agricultural development in Egypt and similar arid regions.
The Cenomanian shallow marine succession in the Southern Galala Plateau of Egypt contains rich be... more The Cenomanian shallow marine succession in the Southern Galala Plateau of Egypt contains rich benthic fauna and preserves enormous information on how paleo-communities respond to fluctuating environmental conditions. Based on rock and fossil data, the Galala Formation was interpreted to be the result of deposition on a tidedominated homoclinal ramp. Three main facies associations representing three depositional environments (intertidal, shallow subtidal, and deep subtidal) were recognized. Three distinct macroinvertebrate associations corresponding to these environments and dominated mainly by oysters were quantitatively identified. They show a gradational vertical increase in diversity as well as in the infaunal and mobile species. This trend can be attributed to the Cenomanian sea-level rise, where harsh marginal marine environments in the middle Cenomanian became more stable toward the latest Cenomanian. Sea flooding may have eliminated barriers, enhanced water circulation, and stopped hyperpycnal flow and/or terrigenous flux. Consequently, oxic mesotrophic conditions may have prevailed and siliciclastic starvation may have concentrated fossil materials, and therefore, diversity increased. Based on the vertical and lateral changes of the facies stacking pattern, two main parasequence types were recognized, the first includes deep subtidal deposits changed upwards to shallow subtidal and the second includes shallow subtidal deposits that pass upward into intertidal. Moreover, two and one-half third-order mixed sequences were identified and correlated to their regional and global counterparts.
The mechanisms underlying the evolutionary adaptation of animals that transcend the ecological ba... more The mechanisms underlying the evolutionary adaptation of animals that transcend the ecological barrier separating the intertidal and supratidal zones of rocky shores are poorly understood. Different wetting frequencies in these zones in tropical regions (daily vs. seasonally, respectively) impose different physical stressors, which should drive phenotypic variation and ultimately speciation in the animals that inhabit them. We studied morphological, physiological and genetic variation in a tropical high-shore gastropod that transcends these zones [Echinolittorina malaccana (Philippi, 1847)]. Variation in melanization, shell features and evaporative water loss was linked to regular seawater wetting, frequent activity and feeding, and solar exposure in intertidal snails, and to inactivity and prolonged aestivation in the shade during continuous air exposure in supratidal snails. Despite selective pressure for phenotypic divergence, and reproductive isolation of the populations in either zone, their mitochondrial COI gene sequences confirmed that they represent a single species. Speciation in our study case is probably constrained by the limitation on activity, mating and reproduction of supratidal snails, such that their populations can only be sustained through intertidal pelagic larval recruitment. Comparisons with other studies suggest that supratidal speciation and specialization for life in this zone probably require moderation of the abiotic (desiccative) conditions, to facilitate greater activity and interaction of animals during air exposure.
Improving exploration and development techniques of fossil fuels are essential for continuous res... more Improving exploration and development techniques of fossil fuels are essential for continuous reserves development. Although there are many oil discoveries in the Razzak Area (North Western Desert, Egypt), there are also many dry wells. Therefore, the tectonic setting and reservoirs characterization of the study area has to be fully understood. Twenty 2D highly filtered stack zero-phase seismic sections and logging data of four wells were analyzed. According to seismic sections and structure contour maps (both time and depth), there is one major structural high (horst). It is a part of the regional Jurassic rift system. The NE Jurassic rifts continued during the deposition of the Early Cretaceous strata as growth faults and have been rejuvenated or continued during the closure of the Neotethys Ocean. During the Late Cretaceous, the compressional stress resulting from the collision between African and Eurasian plates has led to the inversion of the Razzak basin, where some segments of the main faults are transformed from normal to reverse and the hanging walls formed plunging drag fold, which was dissected by a set of NW-SE normal faults. Four prospective closures in the Razzak Field were highlighted. Based on integrated petrophysical tools (Gamma Ray, Sonic Log, Resistivity Deep, Neutron Porosity, and Bulk Density) in four wells (NRZK-1, NRZK2, NRZK-3, and NRZK-4), the Aptian Alamein Formation (mainly dolomite) was interpreted to be a good reservoir and can be subdivided into two zones (Upper Alamein and Lower Alamein) with different reservoir quality. In addition, 3D structure, facies, and petrophysical models were built based on integrated geological and petrophysical data. The results indicated that integrating both seismic profiles with logging data, even from a small number of wells, is highly valuable in evaluating reservoir quality and defining future prospective.
Fifty-five ostracod species have been identified from 100 samples belonging to three stratigraphi... more Fifty-five ostracod species have been identified from 100 samples belonging to three stratigraphic sections in the Middle-Upper Eocene strata of the Beni Suef area (southern Tethys of Egypt). These ostracods have been used to subdivide the studied time interval into three zones that are correlated to the planktic foraminiferal zones E13 to E15. Based on clustering, non-metric Multidimensional Scaling (nMDS), and The Permutational MANOVA, sediment facies was found to be a significant factor controlling the ostracod fauna. Four assemblages were identified and their bio-ecological preferences were used to reconstruct paleoenvironments: 1) The upper Bartonian
ostracod assemblage (El Fashn Formation) is dominated by Paracypris eskeri Bassiouni and Morsi and Novocypris eocenana Ducasse and is characterized by lower Shannon Diversity and higher ‘Dominance’ of stenohaline species with preference for lower oxygen levels and deeper neritic water depths; 2) The uppermost Bartonian (Qurn Member of Beni Suef Formation) is dominated by Paracypris eskeri Bassiouni and Morsi and Bairdia gliberti (Keij) indicating better oxygenated environmental conditions, supported by higher diversity values; 3) The lower Priabonian (Tarbul Member of Beni Suef Formation) is dominated by Novocypris eocenana Ducasse and has the lowest diversity, linked to the significant decrease of species with preference for highly oxygenated conditions; 4) The uppermost Priabonian (Maadi Formation) contains the most diverse assemblage and is characterized by a very low ‘Dominance’ and very high Shannon Index, where 26 species constitute the trophic nucleus and most of them are indicative of shallow water-depths and inner shelf settings in addition to preferences for high oxygen levels. The general increase in diversity and decrease in dominance is attributed to improved environmental conditions at shallower depths, where enhanced water mixing increased the oxygen available for biological demands. Moreover, the strong similarity of the recorded ostracod assemblages with those reported from other southern Tethyan sites reflects migration through the Atlantic and/or the trans-Sahara seaway, while the low similarity with the northern Tethys province (Europe) may be related on the one hand to their benthic nature, which may have limited their ability to move for longer distances, on the other hand to prevailing cooler waters to the north at higher latitudes. Water depth and associated environmental changes in respect to oxygen levels is interpreted to be the main factor controlling the distribution of the ostracods in the Beni Suef area.
The Santonian/Campanian boundary interval (calcareous nannofossil zones CC16 to CC18) sediments i... more The Santonian/Campanian boundary interval (calcareous nannofossil zones CC16 to CC18) sediments in the Kurdistan region (northeastern Iraq) is analyzed for paleoenvironmental analysis. Based on the stratigraphic distribution of calcareous nannofossil taxa, four intervals were quantitatively identified, two within the Zone CC16 and two corresponding to CC17 and CC18, respectively. The assemblages are dominated by Watznaueria barnesiae (that forms 58% of the total population) and yielded a statistically significant and negative relationship with species diversity (Shannon Index) suggesting digenetic overprinting of the primary ecological signal. However, the presence of dissolution-susceptible taxa of Eiffellithus, Lucianorhabdus, Tranolitus, Lithastrinus and Zeugrhabdotus (albeit in low relative abundances), the ease of species-level identifications, the relatively high species diversity index (up to 2.6) and species richness (up to 22) suggests that the primary ecological signal is still preserved and can be used to infer the broad paleoenvironment. The entire studied interval is marked by a warm and oligotrophic water mass that is punctuated by cooler waters in the middle of Zone CC16 (Interval 2), beginning of zones CC17 (Interval 3) and CC18 (Interval 4; at the Santonian/Campanian boundary). These brief intervals are marked by increased relative abundances of cooler water species (Micula decussata, Eiffellithus turriseiffelii and Broinsonia enormis) and are interpreted as brief upwelling events associated by higher species diversity and species richness. As in the present study, globally also, the Santonian/Campanian boundary is marked by cooler waters.
Although the Essaouira-Agadir Basin (EAB) in Morocco is one of the most complete successions of t... more Although the Essaouira-Agadir Basin (EAB) in Morocco is one of the most complete successions of the Lower Cretaceous in Northern Africa, recent investigations have indicated major basinal-scale hiatuses, which may hinder interregional correlation. To test the quality of the existing stratigraphic scheme and provide a robust biozonation, nannofossil occurrence data from four sections were processed using the Unitary Association (UA) method. Based on critical evaluation of the singletons, which are all of a very important stratigraphic value, they were included in the analyses. The UA range chart of the studied time interval indicates six distinct segments, which are all comparable to the Standard Tethys Zones. The Aptian/Albian contact is also well defined. The results demonstrated that empirical index nannofossil zones have different quality depending mainly on their vulnerability to dissolution. In addition, some secondary marker species (i.e., their appearance/disappearance is located within a specific nannofossil zone), which exclusively occur in only one UA, can substitute the zonal index species. Although marker nannofossil species are different from section to section due to poor preservation, the UA method still provides a robust stratigraphic scheme at considerable resolution. The Aptian/Albian boundary was marked by a dramatic increase in the extinction rates and decrease in the species richness, whereas the Early Albian interval was characterized by relatively low diversity and high turnover rates.
The analysis of high-resolution stratigraphic data from the Cenomanian-Turonian successions in th... more The analysis of high-resolution stratigraphic data from the Cenomanian-Turonian successions in three sections from Sinai (northeast Egypt) revealed the mechanisms behind water depth-driven biological responses (visible in changes of biodiversity and community structure) of macroinvertebrates. Quantitative biostratigraphical analysis of 127 samples containing 6203 specimens representing 41 genera of molluscs, corals, and echinoids were used to construct changes in the community structure of Cenomanian-Turonian macroinvertebrates. We identified six assemblages that we assigned to two main categories and linked to regional sea-level changes. The first group of assemblages is associated with the initiation of transgression and/or late normal regression, is dominated mainly by opportunistic, epifaunal suspension feeders (oyster bivalves) and is characterized by lower diversity values (low Shannon Index and high dominance). The second category is associated with the maximum flooding zone and dominated by infaunal deposit feeders such as irregular echinoids and by nektonic ammonites and is characterized by higher diversity. The increase in nektonic and decrease in benthic taxa during the latest Cenomanian suggest deepening of the environment. Moreover, the change in the water depth was accompanied by a change in the structure of the macrobenthos.
The nuculanid bivalve Costinuculana magharensis new genus new species is described from the middl... more The nuculanid bivalve Costinuculana magharensis new genus new species is described from the middle to upper Bathonian Kehailia Formation of Gebel Maghara, North Sinai, Egypt. Costinuculana differs from other genera of the family Nuculanidae by the presence of opisthocline ribs along the rostrum. These ribs are variable in shape and size, straight to folded posteriorly, bifurcate ventrally and occasionally postero-dorsally, and cover an areã 45% of the total valve length from the posterior end. The life position of C. magharensis n. gen. n. sp. is reconstructed on the basis of a functional interpretation of its morphology and by comparison with closely related Recent forms. The asymmetrical commarginal ribs facilitated the burrowing process. The posterior oblique ribs are asymmetrical in cross-section with a steeply concave side in the burrowing direction and slightly convex side in the opposite direction. They probably kept the bivalve in a stable position once the desired depth had been reached. The thick oblique ribs probably also increased the strength of the rostrum and offered resistance against durophagous predators, being presumably partly exposed above the sediment-water interface. Based on the associated fauna, Costinuculana n. gen. lived in a low-energy environment characterized by a fine-grained, soft substrate. Materials and methods The present study is based on 10 specimens with preserved shells that were collected from the middle to upper Bathonian
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Papers by Ahmed A Abdelhady
ostracod assemblage (El Fashn Formation) is dominated by Paracypris eskeri Bassiouni and Morsi and Novocypris eocenana Ducasse and is characterized by lower Shannon Diversity and higher ‘Dominance’ of stenohaline species with preference for lower oxygen levels and deeper neritic water depths; 2) The uppermost Bartonian (Qurn Member of Beni Suef Formation) is dominated by Paracypris eskeri Bassiouni and Morsi and Bairdia gliberti (Keij) indicating better oxygenated environmental conditions, supported by higher diversity values; 3) The lower Priabonian (Tarbul Member of Beni Suef Formation) is dominated by Novocypris eocenana Ducasse and has the lowest diversity, linked to the significant decrease of species with preference for highly oxygenated conditions; 4) The uppermost Priabonian (Maadi Formation) contains the most diverse assemblage and is characterized by a very low ‘Dominance’ and very high Shannon Index, where 26 species constitute the trophic nucleus and most of them are indicative of shallow water-depths and inner shelf settings in addition to preferences for high oxygen levels. The general increase in diversity and decrease in dominance is attributed to improved environmental conditions at shallower depths, where enhanced water mixing increased the oxygen available for biological demands. Moreover, the strong similarity of the recorded ostracod assemblages with those reported from other southern Tethyan sites reflects migration through the Atlantic and/or the trans-Sahara seaway, while the low similarity with the northern Tethys province (Europe) may be related on the one hand to their benthic nature, which may have limited their ability to move for longer distances, on the other hand to prevailing cooler waters to the north at higher latitudes. Water depth and associated environmental changes in respect to oxygen levels is interpreted to be the main factor controlling the distribution of the ostracods in the Beni Suef area.
ostracod assemblage (El Fashn Formation) is dominated by Paracypris eskeri Bassiouni and Morsi and Novocypris eocenana Ducasse and is characterized by lower Shannon Diversity and higher ‘Dominance’ of stenohaline species with preference for lower oxygen levels and deeper neritic water depths; 2) The uppermost Bartonian (Qurn Member of Beni Suef Formation) is dominated by Paracypris eskeri Bassiouni and Morsi and Bairdia gliberti (Keij) indicating better oxygenated environmental conditions, supported by higher diversity values; 3) The lower Priabonian (Tarbul Member of Beni Suef Formation) is dominated by Novocypris eocenana Ducasse and has the lowest diversity, linked to the significant decrease of species with preference for highly oxygenated conditions; 4) The uppermost Priabonian (Maadi Formation) contains the most diverse assemblage and is characterized by a very low ‘Dominance’ and very high Shannon Index, where 26 species constitute the trophic nucleus and most of them are indicative of shallow water-depths and inner shelf settings in addition to preferences for high oxygen levels. The general increase in diversity and decrease in dominance is attributed to improved environmental conditions at shallower depths, where enhanced water mixing increased the oxygen available for biological demands. Moreover, the strong similarity of the recorded ostracod assemblages with those reported from other southern Tethyan sites reflects migration through the Atlantic and/or the trans-Sahara seaway, while the low similarity with the northern Tethys province (Europe) may be related on the one hand to their benthic nature, which may have limited their ability to move for longer distances, on the other hand to prevailing cooler waters to the north at higher latitudes. Water depth and associated environmental changes in respect to oxygen levels is interpreted to be the main factor controlling the distribution of the ostracods in the Beni Suef area.