Dakhla Shale Research Articles

A Prognathodontin Mosasaur from the Maastrichtian of the Dakhla Oasis, Western Desert, Egypt

Mosasaurs were diverse in the Upper Cretaceous in Africa, but relatively little is known about the mosasaur fauna of Egypt. Here, associated teeth and postcranial skeletal elements are reported for a mosasaur from the Maastrichtian Dakhla Shale of the Dakhla Oasis. The specimen includes tooth crowns, cervical, dorsal, and caudal vertebrae, and ribs. Teeth and bones exhibit features allowing referral to Prognathodontini. The teeth are relatively straight and blunt, suggesting affinities with Prognathodon overtoni or P. currii. Prognathodontins were important predators in the Maastrichtian of Africa, previously being recorded in Morocco, Congo, and Angola.

A new species of Halisaurus (Mosasauridae: Halisaurinae) from the lower Maastrichtian (Upper Cretaceous) of the Western Desert, Egypt

Mosasaurids were highly diverse and dominant as predators in late Cretaceous marine ecosystems. In the Maastrichtian, the Halisaurinae, a clade of relatively small-bodied mosasaurids, became common, especially in North Africa. Here, we report a new species of halisaurine from the lower Maastrichtian Dakhla Shale of the Western Desert of Egypt. Halisaurus hebae sp. nov. resembles Halisaurus platyspondylus and H. arambourgi in the shape of the frontal, suggesting close affinity with those species. A revised halisaurine phylogeny shows a cluster of species characterized by modification of the orbital bones to accommodate large eyes, suggesting a shift towards the use of visual cues to find prey, perhaps in low light conditions. The abundance and diversity of halisaurines in Africa contrasts with their relative rarity elsewhere in the world, emphasizing the regionalization of marine reptile faunas in the Maastrichtian.

Petrography, mineralogy, and geochemistry of nitrogenous shale in the Western Desert of Egypt: implications for paleoenvironment

Besides nitrate deposits located in the Atacama Desert of Chile and the Mojave Desert of California, the present work documents, for the first time, the occurrence of potassium nitrate as oval-suboval-shaped aggregations associated with the Late Maastrichtian-Early Paleocene Dakhla Shale and the Paleocene-Early Eocene Esna Shale encountered in the northeastern part of the Kharga Oasis, particularly at G. Um El-Ghanayem and G. Ghaneima. Consequently, integrated petrographic, mineralogical, and geochemical investigations were carried out for shale deposits and nitrate salts to reconstruct the paleoenvironmental conditions of shale, reveal the extent to which nitrate salts are genetically related to the paleoenvironment of shale deposits, and build up a complete scenario about the source and the formation mechanism of nitrate salts. The overall results showed that the studied shale deposits were sourced from mafic igneous and quartzose sedimentary provenances where humid climatic conditions were dominant; the transported detrital particles were then settled down under oxidizing bottom water and shallow depositional conditions. Moreover, the nitrate salts are of an epigenetic origin and sourced from the microbial nitrification of organic matter and the wet atmospheric deposition that is believed to be triggered by the active volcanic eruptions during the Late Eocene/Early Oligocene transition where warm climatic conditions prevailed.

Integrated foraminiferal biostratigraphy, bioevents and sea‐level reconstruction in the Campanian–Maastrichtian succession at Gabal Nezzazat, south‐western Sinai, Egypt

The foraminiferal assemblages are tracked in the Campanian–Early Danian succession at Gabal Nezzazat, south‐western Sinai, Egypt. Lithostratigraphically, the studied succession overlies the nearly barren Matulla Formation and includes the Sudr Chalk (Campanian–Maastrichtian) below and the lower part of the Dakhla Shale (Maastrichtian–Early Danian) above. Biostratigraphically, the planktonic foraminiferal assemblages enabled the recognition of 15 planktonic foraminiferal biozones ranging from the Lower Campanian Globotruncanita elevata Zone at the base to the Lower Danian Guembelitrea cretacea Zone at the top. The proposed planktonic biozones are compared with their equivalents in other Egyptian regions and globally correlated with their equivalents within the Tethyan Province and the equatorial Pacific Ocean. The vertical stratigraphic range of Bolivinoides allowed the recognition of eight benthic foraminiferal biozones. These benthic biozones show a similarity between the Tethyan Province and the Boreal and Western Interior successions. Fifteen lowest occurrence and two highest occurrence planktonic foraminiferal bioevents are also recognized and correlated all over the world. The stage boundaries are mainly delineated according to the diagnostic planktonic foraminifera. Based on the percentage of planktonics, the palaeobathymetry is estimated and hence the sea‐level fluctuation. The reconstructed sea‐level curve revealed seven sea‐level fall events within the Campanian and five within the Maastrichtian and the earliest Danian. These events were globally correlated and match in most parts with that of the worldwide sea‐level curve.

Appraisal for the environment, weathering and provenance of Upper Cretaceous-Lower Tertiary shales, Western Desert, Egypt

The combination of the mineralogical and geochemical composition of shales is considered a key to decipher their environment evolution, weathering, climatic conditions, and provenance. The Upper Cretaceous-Lower Tertiary succession is extensively dispersed in Egypt. The present work is devoted to studying the Dakhla shales of (Maastrichtian- Danian), Duwi (Campanian) and Quseir (pre-Campanian) formations. Chemical and mineralogical analyses were conducted by using seven representative surface sections from Dakhla Oasis. Dakhla shales are dominates by Smectite and kaolinite. The average percentages of SiO2, Al2O3, CaO, MgO, Na2O and K2O are subordinate values. In contrast, Al2O3 contents of Dakhla shale, TiO2, P2O5 and Fe2O3, contents are relatively higher than common shale composition. The CIA and CIW high values due to clay minerals and the absence of feldspars. This is also confirmed by the smectite domination and subordinate kaolinite in these formations. The ICV values for Dakhla and Duwi shales are 0.59 and 0.74 (ICV < 1). The shale is mature and deposited in a quiescent environment. Whereas the ICV for Quseir shale is 1.24, it can be incidental that it is immature. The shale is wholly detrital and a product of moderate to intensive weathering. The provenance was constituted of granitic and basaltic source rocks, and the parent provenance is basalt. Consequently, the shale is deposited under fluvio-marine environments, and the prevailed condition was of alkaline chemical affinity probably passed through different environments varying from a fluvial, eolian and shallow marine.

Biostratigraphy and depositional environments of the Palaeocene–Eocene succession at Um El Huwaitat area, Eastern Desert, Egypt

The Palaeocene–Eocene succession in southwest Safaga, Eastern Desert, Egypt has been studied to determine its lithostratigraphic units, biostratigraphic zonation, microfacies association, and depositional environments. The variation in lithofacies allows the subdivision of the Danian–Ypresian interval into four lithostratigraphic units that are arranged, from base to top, as the Dakhla Shale (only its upper part), Tarawan Chalk, Esna Shale, and Thebes Formation (only its lower part). Moreover, the Esna Shale is further subdivided into four members, arranged from base to top, as El Hanadi, Dababiya Quarry, El Mahmiya, and Abu Had. The depositional setting is interpreted to primarily reflect the relative sea‐level changes. The planktonic/benthic (P/B) foraminiferal ratio is indicative of oscillations of depositional settings in normal open marine conditions, ranging from shallow inner to outer neritic environments. Biostratigraphically, the Palaeocene–Eocene succession in the studied area is subdivided into 12 biozones and subbiozones. These are correlated with the standard biozonation of the Palaeocene–Eocene. Deposition of the Palaeocene–Eocene succession in the studied area took place on a relatively stable shelf. Three lithofacies were recognized: shale, marl, and limestone. The shale lithofacies is differentiated into two sub‐lithofacies; pure shale and calcareous foraminiferal shale, whereas marl lithofacies contains abundant planktonic foraminifera. The encountered carbonate rocks comprise eight microfacies types. In addition, the studied interval is correlated with the Global Standard Stratotype Section and Point in the Dababiya section, south of Luxor, Egypt.

The Maastrichtian–Danian transition in the northern Farafra Oasis, Western Desert (Egypt): Implications from foraminiferal paleobathymetry and paleoenvironmental reconstructions

Two exposed sections of the Lower/Upper Maastrichtian to Danian at northern and northeastern Farafra Oasis, Western Desert (Egypt) namely, the Farafra–Ain Dalla road and the Ain Maqfi sections have been analyzed for their planktonic and benthonic foraminifera to constrain the biostratigraphy and infer the paleoenvironmental conditions. Lithostratigraphically, the successions of the present study are classified into the Khoman Chalk and the Dakhla Shale. Biostratigraphically, six planktonic foraminiferal zones; Gansserina gansseri, Racemiguembelina powelli and Plummerita reicheli of the Maastrichtian as well as the Praemurica inconstans (P1c), Praemurica uncinata (P2) and Morozovella angulata (P3a) of the Danian are recognized. A detailed quantitative benthonic foraminiferal analysis has been performed and yields a total of 172 identified benthonic foraminiferal species belonging to 62 different genera. The various foraminiferal parameters as well as cluster analysis provide good information about the paleoenvironmental conditions and sea–level fluctuations across the Maastrichtian–Danian transition. The Maastrichtian revealed outer neritic shelf with slightly shallowing conditions recorded only at the Ain Maqfi section, well oxygenated conditions with low organic matter influx coupled with sea–level rise. During the Maastrichtian–Danian transition, a paleoenvironmental shift to inner-shallow middle neritic shelf, low oxygenated conditions with moderate organic matter influx coupled with sea–level fall is interpreted. This transition is characterized by a major hiatus due to absences of Guembelitria cretacea (P0), Parvularugoglobigerina eugubina (Pα), Parasubbotina pseudobulloides (P1a) and Subbotina triloculinoides (P1b) zones and subzones. It is well marked in the field by an irregular contact and conglomeratic phosphatic dolostone bed at the Farafra-Ain Dalla road section while the disconformity surface can be detected by planktonic foraminifera in the Ain Maqfi section. The lowermost Danian is phosphatic argillaceous chalky limestone with intensive reworking. Low oxygen and/or relatively high–moderate organic matter influx within inner–middle neritic shelf paleoenvironmental conditions can be reconstructed for the lowermost Danian associated with a slight increase in sea–level during the Praemurica inconstans (P1c) zone. The uppermost Danian reflected very well oxygenated conditions and/or low organic matter influx in middle–outer neritic shelf conditions associated with sea–level rise during ages of the planktonic foraminiferal zones P2–P3a.

Order differences to enhance the delineation of rock units boundaries by using aerospectrometric data of Wadi Al Mushash area, Central Eastern Desert, Egypt: A new approach

The present work utilizes airborne gamma-ray spectrometric data, in a trial to refine the surface geological mapping of sedimentary rocks at Wadi Al Mushash, Central Eastern Desert of Egypt. The acquired aerospectrometric data were supported by the surface geology concerning the study area. This area is mainly covered by sedimentary rocks of Tertiary to upper Cretaceous as Nubian Sandstone Formations (Quseir Clastics and Tarif Sandstone), Duwi Phosphates Formation, Dakhla Shale Formation, Esna Shale Formation, Tarawan Formation, Thebes Formation, and Quaternary deposits. High-resolution airborne gamma-ray spectrometry can be very helpful in mapping the surface geology. The method provides estimation of the apparent surface concentrations of the most common naturally occurring radioactive elements, such as potassium (K), equivalent uranium (eU) and equivalent thorium (eTh). This work is based on the assumption that, the absolute and relative concentrations of these radioelements vary measurably and significantly with lithology. The composite image technique is used to display and simulate three parameters of the radioelements concentrations. The technique offered much in terms of lithologic discrimination, based on color differences and showed efficiency in defining areas, where different lithofacies occur within areas mapped as one continuous lithology. The Differences technique is used to delineate contacts of the rock units and the mainly structures of the study area. It is based mainly on varying in change of concentration of successive total count measurements within each line in the study area. Then, a suitable difference order is selected and matched to original measured line. Moreover, plotting the suitable order as grid and applied grid peaks on this grid. Then, these ridge grid peaks are symbolized over surface geological information and prepared radioelement composite map. This provides more detail about the surface geology, and addition more contacts occurred within original rock units. These subdivisions of rock units may be related to one formation that consists of more than one member having a different composition.

The effect of mineralogy of calcined shales on the alkali activation and geopolymerization reactions: A case study from Abu-Tartur plateau, Western Desert, Egypt

Abstract The effect of mineralogy of calcined shales on the alkali activation and geopolymerization reactions was studied. Shales under study included black and Dakhla shales, which were obtained from the Abu-Tartur plateau in the Western Desert of Egypt and characterized using optical microscope, SEM, XRF, XRD, and FTIR. The dehydroxylation of shale samples was performed at 550, 650, 750, and 850 °C for one hour. The mineral transformations on calcination were monitored using SEM, XRD and FTIR. The alkali activation process was then conducted on the calcined samples using a mixture of sodium hydroxide and sodium silicate at 1.2 solid/liquid mass ratio. The resultant pasts were molded in steel cubes (50 × 50 × 50mm in diameter) and cured at 70 °C for 48 h. The compressive strength of cured samples was measured to reveal the extent to which the dehydroxylation achieved. The maximum strength values were reported at 4.19 MPa and 2.49 MPa for the calcined black shale and Dakhla shale, respectively. By comparing with literature, the present strength is considered to be too much low. This indicates a deficiency of the dehydroxylation of clay minerals, a little amount of the active amorphous phases, and the dominance of low reactive crystalline phases through the whole range of calcination process.

Geochemistry, mineralogy and depositional environment of black shales of the Duwi Formation, Qusseir area, Red Sea coast, Egypt

This study focuses on the geochemistry of redox-sensitive elements of marine black shales at the Qusseir area of the Duwi Formation to infer their depositional environment. The black shales from the uppermost member of the Duwi Formation in the Qusseir area is conformably overlain by the Qusseir variegated shale and underlain by the Dakhla shale. Detailed mineralogical and geochemical characteristics were examined using several techniques, including X-ray diffractometry, scanning electron microscopy and X-ray fluorescence. Mineralogically, black shales in the Duwi Formation are composed mainly of montmorillonite, kaolinite, calcite, gypsum, quartz and pyrite. They are detrital and authigenic in origin. They are most probably derived from basic volcanic rocks by intensive chemical weathering under the prevalence of semiarid conditions. The redox-sensitive trace metals suggest anoxic sulfidic conditions that favoured the accumulation of these metals in the Qusseir area of the Duwi Formation.

Assessment of the wastewater effect on the shallow subsurface soil at Farafra Oasis, Egypt, by using geoelectrical and geochemical data analysis

Geoelectrical techniques have been used to detect the subsurface stratigraphy and structures around Farafra Oasis, Egypt. 1D inversion approaches have been applied to interpret the geoelectrical data obtained at six vertical electrical soundings (VES’s) using the well-known Schlumberger array with half-current electrode spacing (AB/2) varying from 3 to 400m in successive steps.A preliminary quantitative interpretation of the sounding curves was achieved firstly by using two-layer standard curves and generalized Cagniard graphs. The final models were obtained in 1D using IPI2WIN program. The modeling results were used to construct two geoelectrical sections.Two geoelectrical units were identified: the superficial geoelectrical layer is composed mainly of shale (Dakhla Shale Formation). It is characterized by relatively very low electrical resistivity values (3–5Ωm) with a maximum thickness of about 17.58m.The second layer reveals moderate electrical resistivity values (17–98Ωm). It is extended from the surface layer to the end of the investigated section and represents the Sandstone (upper aquifer) in the study area.

Delineating groundwater aquifer and subsurface structures by using geoelectrical data: Case study (Dakhla Oasis, Egypt)

Geoelectric technique has been used to detect the subsurface stratigraphy and structures around Dakhla Oasis, Egypt. 1D inversion approach has been applied to interpret the geoelectrical data obtained along 10 vertical electrical soundings (VES) using the well known Schlumberger array of AB/2 with electrode spacing varying from 3 to 400m in successive steps.A preliminary quantitative interpretation of the vertical electrical sounding curves was achieved firstly by using two-layer standard curves and generalized Cagniard graphs. The final models were obtained in 1D using IPI2 WIN program. The modeling results were used to construct a geoelectrical section.Three geoelectric units were identified: The superficial geoelectrical layer is composed mainly of sand and gravel with relatively high resistivity values (7.61–346Ωm) and thin thicknesses (0.252–9.19m), of late Pleistocene to Holocene (Quaternary deposits).The second geoelectrical layer is composed of shale (Dakhla Shale). It is characterized by relatively very low electrical resistivity values (0.3–8.68Ωm). The maximum depth of this layer ranges from 4.18 to 56.4m.The Nubian sandstone (upper aquifer) third layer with moderate electrical resistivity values (68.5–1585Ωm) can be detected at the maximum depth of penetration.

Application of electrical resistivity prospecting in waste water management: A case study (Kharga Oasis, Egypt)

Electrical resistivity technique has been used to detect the subsurface stratigraphy and structures around Kharga Oasis, Egypt. 1D inversion approaches have been applied to interpret the electrical data obtained along 10 vertical electrical soundings (VES) using electrode spacing from 3 to 400m.A preliminary quantitative interpretation of the vertical electrical sounding curves was achieved firstly using two-layer standard curves and generalized Cagniard graphs. The manual models were used as initials to prepare the final model using the algorithm IPI2Win program. Model results were used to construct a geoelectrical section.Three geoelectric units were identified: the superficial geoelectrical layer is composed mainly of sand and gravel with relatively high resistivity values (8–372ohmm) and low thicknesses (0.523–4.92m). The age of this layer is from late Pleistocene to Holocene (Quaternary deposits).The second geoelectrical layer is composed of shale (Dakhla Shale). It is characterized by relatively very low electrical resistivity values (0.3–4.92ohmm). The maximum depth to this layer ranges from 13.8 to 45.7m.The third layer represents the first Nubian Sandstone aquifer with moderate electrical resistivity values (23.9–233ohmm) detected at the maximum depth of penetration, a great contrast for values according to the lithological content.

Groundwater Modeling of Multi-Aquifer Systems Using GMS

The Nubian Sandstone complex in the western desert is a part of the major regional Nubian aquifer system comprising West Africa. The different rock strata deposited in localities forming the units of the aquifer system. Farafra Oasis lies in the northern part of the Dakhla basin. In its southern region, the Nubian Sandstone (deep aquifer) is overlained by Dakhla shale but in the central and northern regions by fissured chalky limestone (shallow aquifer). The two overlaying aquifers in Farafra Oasis represent a typical hydrogeological model of a huge multi-layered artesian basin extending over the territory of Egypt. The Post Nubian aquifer played an essential role in the development of Farafra Oasis for a long time through the many springs issued from this aquifer. The rapid drilling process of deep wells started in 1960s led to stop flowing of many springs and wells plus the depletion in discharges and pressure of many others. Therefore, there is a real danger of either dewatering or increasing the water depths to uneconomic lifting depths for both the shallow and deep aquifers. A two-dimension flow model GMS (Groundwater Modeling System) was used to investigate this problem. Application of the present conditions indicated that drawdowns in the Post Nubian aquifer range from 5 m to about 9 m. The second scenario tries to sustain the groundwater utilities in the Post Nubian aquifer through a group of procedures. Accordingly, drawdowns are expected to range from 5 m to 8.6 m in the Post Nubian aquifer. According to this scenario, 3 m decline in the Nubian Sandstone aquifer followed by declining in the Post Nubian by about 1 m.

Uppermost Cretaceous to lowermost Eocene benthic foraminifera of the Dababiya Corehole, Upper Nile Valley, Egypt

Benthic foraminiferal assemblages from the Dababiya Corehole have been analysed as part of a multi-disciplinary study. Upper Cretaceous to lowermost Eocene sediments (Dakhla Shale, Tarawan Chalk and Esna Shale Formations) recovered from this corehole contain abundant and diverse benthic foraminifera, which allowed us to carry out detailed quantitative analyses of their assemblages and to infer paleoenvironmental changes. Assemblages are dominated by taxa typical of the Midway-type fauna, and of outer shelf environments. In this paper, we document for the first time the benthic foraminiferal assemblage turnover and changes in the paleoenvironmental conditions in this part of the southern Tethys from the latest Cretaceous to the earliest Eocene.

Planktonic foraminiferal biostratigraphy of the upper Cretaceous to mid-Paleocene of the Dababiya Quarry Corehole, Upper Nile Valley, Egypt

Biostratigraphic studies of planktonic foraminifera on the Dababiya Quarry corehole suggest an eight-fold zonal subdivision of the lower (Dakhla Shale,Danian) and middle (uppermost Dakhla and Tarawan Chalk) Paleocene. Preliminary studies of the basal part of the hole (~137–140 m) and the uppermost Cretaceous (~80–81 m) indicate the presence of the lower Maastrichtian Globotruncana aegyptiaca and upper Maastrichtian Pseudoguembina palpebra Zones, respectively. It would appear that there is a short hiatus at the Cretaceous/Paleocene boundary (denoted by the P. palpebra/Parvulorugoglobigerina eugubina zonal boundary and apparent absence of the (uppermost Maastrichtian) Pseudoguembelina hantkeninoides Zone and the (basal Danian) Guembelitria cretacea (P0) Zone, which may be due to syn-sedimentary tectonic and/or inadequate sampling density. The Danian/Selandian (D/S) boundary is placed at the boundary between the Igorina albeari/Praemurica carinata (=lower part of Zone P3b) Zone and the Ig. albeari (=upper part of Zone P3b) Zone at a distinct phosphatic bed tentatively correlated with the Qreiya Bed (in the Qreiya section) and the “Neo-Duwi Event" at 44.5m. This bed is marked by the gradual disappearance of praemuricid taxa in general and the lowest occurrence of P. carinata in particular.

Lithostratigraphy of the upper Maastrichtian to lower Eocene succession in the Dababiya Corehole, Egypt

The Dababiya core has recovered, in descending order, the Esna Shale Formation (lower part), the Tarawan Formation and the Dakhla Shale Formation (upper part). In the Esna Shale Formation, the Mahmiya Member (lower part), the Dababiya Quarry Member and the Hanadi Member were delineated. The Mahmiya Member and the Dababiya Quarry Member are early Eocene in age. The Hanadi Member belongs to the Paleocene. In the Dakhla Shale Formation, three informal members were recognized. The formation has also been divided into eight smaller units on the basis of limestone/shale alternation. The Dakhla Shale Formation encompasses the K/Pg boundary and ranges from Maastrichtian to Paleocene.

Geophysical logging and magnetic susceptibility studies on the Dababiya Quarry Corehole, Dababiya Natural Park, southern Nile Valley, Egypt

Following the designation of a GSSP for the Paleocene/Eocene boundary in the Dababiya Quarry section in the southern Nile Valley of Egypt a continuously cored well was drilled in the hope of recovering better preserved lithologies and microfossils than in nearby outcrops. The well was continuously cored from the lower part of the El Mahmiya Member of the Esna Shale and penetrated the Dababiya Quarry Beds, El Hanadi Member of the Esna Shale, Tarawan Chalk and Dakhla Shale to a total depth of 140 m. Geophysical logging included Natural Gamma Ray (GR), Single-Point Resistivity (PR), Self-Potential (SP), and Resistivity, Short Normal (SN) and Long Normal (LN). Magnetic susceptibility was also measured. The Paleocene/Eocene and Cretaceous/Paleogene (K/P) boundaries. were recorded as sharp peaks on all logs particularly the GR and PR, and in the magnetic susceptibility log. Accordingly, in addition to the paleontological and lithological studies, the two boundaries are well delineated/characterized from the geophysical logging and magnetic susceptibility logs. This paper presents a brief description and discussion of the logging and magnetic susceptibility characteristics of the subsurface sequences encountered in the Dababiya Quarry Corehole (DQC).

Small acritarchs from the Upper Cretaceous: taxonomy, biological affinities and palaeoecology

A systematic study of small acritarchs (most commonly around 10 μm) from the Late Campanian (Duwi (Phosphate) Formation) and Maastrichtian (Dakhla Shale) of Egypt, based on scanning electron miscroscopy, resulted in the identification of nine genera and 27 species, among them the new genus Recticystis and 14 new species, namely Operculites bigranulatus, Bacillidinium partitum, Mecsekia acuta, M. curvispina, M. triangula, Recticystis hemispinosus, Clavaticystis septatus, C. furcatus, Odontothrix multiornatus, Filisphaeridium paucigranulosum, Cymatiosphaera parvirugosa, C. muralis, C. polyornata and C. triradiata. In addition, the following new combinations are proposed: Cymatiosphaera coronis (Habib and Knapp), Mecsekia minor (Takahashi) and Mecsekia ariakense (Takahashi). Small acritarchs are thought to include cysts of dinoflagellates because of significant morphological similarities (cyst shape, chasmic and tremic archeopyles, spinose and septate ornaments) to certain organic-walled and calcareous dinoflagellate cysts. Small size in acritarchs is regarded as an adaptation to a planktonic and possibly to an interstitial mode of life. Small acritarchs attain the highest diversity and abundance in the well agitated environment of the phosphoritic sandstones. In the pores between the sand grains they were protected from the wave action and currents which moved away most of the larger dinoflagellates. Dinoflagellates are common in the associated shales representing a more quiet marine environment. The interpretation of some small spinulose acritarchs as interstitial dinoflagellates may also be supported by the presence of spinose cysts with a chasmic archeopyle in the modern dinoflagellate Polykrikos which includes interstitial forms.

Mesozoic palynology and continental sediments in NE Africa (Egypt and Sudan) - a review

In Egypt and Sudan most palynogical data are derived from predominantly clastic sequences in research wells for oil, water and other sedimentary deposits. The partly coal-bearing Middle Jurassic is characterized by dominance of pteridophytes while increasing percentages of gymnosperms may be noted in the Late Jurassic. The Jurassic-Cretaceous boundary is difficult to define, but Ischyosporites-Cicatricosisporites assemblages have been interpreted as Late Jurassic and overlying assemblages with Impardecispora, Geicheniidites, Classopollis etc. as Neocomian. The appearance of rare early angiosperms and their subsequent rise is documented e.g. in the Six Hills (Barremian) and in the shallow marine Abu Ballas Formation (Aptian). More advanced angiosperm types (tricolpates, tricolporates, triporates) occur in the post-Aptian. Elater-bearing spores ( Elaterosporites) associated with Afropollis form a distinctive element of the Albian (to Early Cenomanian) palynofloras known from Northern Egypt and recently discovered in Northern Sudan. In the Coniacian-Santonian, the spinose tetrads of Droseridites senonicus and large tricolpate pollen of the Foveotricolpites giganteus group become the most characteristic members of the terrestrial palynofloras. Distinctly marine palynomorphs reach the middle latitudes of Egypt for the first time with the Campanian-Maastrichtian transgression. Reduced salinity in the Phosphate Formation is reflected by peridinoid (e.g. Andalusiella, Senegalinium) communities interfingering with pollen and spores dominated associations. More open marine conditions in the overlying Dakhla Shale are documented by the rise of cosmopolitan gonyaulacoids such as Spiniferites, Glaphyrocysta and Florentinia.