Eckart Schrank

Palynology (pollen, spores and dinoflagellates) and cretaceous stratigraphy of the Dakhla Oasis, central Egypt

Abstract A re-assessment of the Cretaceous succession in the Dakhla area, central Egypt, is presented on the basis of new palynological evidence from the Six Hills and Maghrabi Formations. Miospore ages for the Six Hills Formation range from Early Neocomian to late Barremian-Early Aptian(?). The upper Six Hills (to lower Abu Ballas?) interval is the only unit that yielded marine dinoflagellates in addition to terrestrially derived miospores. Marine influence was thus effective below the base of the marine Abu Ballas Formation, which is here regarded as Early Aptian in age. The overlying Sabaya Formation could range down into the Aptian. Miospore assemblages from the Maghrabi Formation in the Dakhla area contain the new species Retimonocolpites variplicatus , tricolpates and tricolporates, but no triporates, which favours an Albian to Early Cenomanian age. Maghrabi assemblages in the Kharga area include triporates, which is broadly consistent with a Late Cenomanian to Turonian age. The formation may thus be diachronous, becoming younger from west to east. It is concluded that an eastward shift of the depocentre took place from the Dakhla area in Early Cretaceous time to the Kharga area in Albian to Late Cretaceous time.

Effects of chemical processing on the preservation of peridinioid dinoflagellates: A case from the late Cretaceous of NE Africa

Peridinioid dinoflagellates from the Late Campanian of Egypt revealed important morphologic alterations caused by routine palynological extraction techniques. Cysts of Andalusiella polymorpha aegyptica n. ssp., Senegalinium bicavatum Jain et Millepied, 1973, S. laevigatum (Malloy) Bujak et Davies, 1983, and S. granulostriatum Jain et Millepied, 1973 normally have a periphragm closely appressed to the endoblast and isolated apical and antapical cavations. After oxidation with cold HNO3 and subsequent alkali (KOH or NH4OH) treatment, an expansion of the periphragm was observed which resulted in the separation of the periphragm from the endophragm and consequently in the connection of the apical and antapical cavations. Originally cornucavate cysts, a diagnostic feature of the genera Andalusiella and Senegalinium, became circumcavate in this way, a characteristics one would rather expect to find in Palaeocystodinium Alberti, 1961 and Deflandrea Eisenack, 1938. A short systematic discussion of the dinoflagellate species involved is given and a new subspecies of Andalusiella polymorpha is described. After excessive oxidation most dinoflagellates are eliminated and the presence of a very resistant background microflora is revealed, consisting mainly of small acritarchs and prasinophyceans.

Pollen and spores from the Tendaguru Beds, Upper Jurassic and Lower Cretaceous of southeast Tanzania: palynostratigraphical and paleoecological implications

Two informal sporomorph assemblage zones can be distinguished in the dinosaur-bearing Tendaguru Beds of southeast Tanzanian. The first zone, the Classopollis—Araucariacites—Shanbeipollenites Assemblage Zone, ranges from the Lower to the Upper Saurian Bed, and a mid-Oxfordian to Tithonian age is suggested based on the presence of Shanbeipollenites quadratus. The second zone, the Classopollis—Cicatricosisporites—Ruffordiaspora Assemblage Zone, is restricted in the Trigonia schwarzi Bed, which overlies the Upper Saurian Bed. The combined ranges of Cicatricosisporites hughesii, Ruffordiaspora australiensis and Trilobosporites obsitus would be consistent with a late Berriasian to Hauterivian age of this zone. This is refined further to late Valanginian to Hauterivian on the basis of already existing evidence from fauna and dinoflagellate cysts. From a phytogeographic point of view the Tendaguru locality belongs to the southern Gondwana Trisaccates Province because of the presence of trisaccate podocarpaceous pollen. The quantitative composition of the palynofloras is characterized by the dominance or abundance of pollen produced by the two conifer families Cheirolepidiaceae (Classopollis) and Araucariaceae (mainly Araucariacites). Pollen of Cheirolepidiaceae, typically xerophytic, drought-resistant, thermophilic plants, is dominant throughout the Tendaguru Beds except in parts of the Middle Saurian Bed where pollen of Araucariaceae, a presumably mesic group, becomes most abundant. Classopollis attains the highest degree of dominance in the shallow marine deposits associated with the saurian beds. This may be related to paleoecological and taphonomic factors, namely abundance of Classopollis-producing plants in low-lying coastal environments close to the lagoonlike depositional sites and transportational sorting of sporomorphs leading to a relative enrichment of small and/or anemophilous pollen. The abundance of Araucariacites in the Middle Saurian Bed suggests that araucarians existed in coastal plain environments that were stable enough to allow the growth of large trees. This open araucarian forest, which may have been a source of food for high-browsing dinosaurs, was situated landward of the cheirolepidiacean belt not far from the depositional sites. Pteridophytes and bryophytes were concentrated at moist places and around water bodies. Podocarpaceous conifers producing bisaccate and trisaccate pollen grew in local uplands, while gnetaleans related to Ephedra and Welwitschia may have been present in dry places. The palynological evidence is consistent with a seasonally dry, tropical to sub-tropical paleoclimate. Three new combinations, Equisetosporites certus (Bolkhovitina), Jugella caichigüensis (Volkheimer and Quattrocchio) and Trichotomosulcites microsaccatus (Couper), are proposed, and Jugella semistriata is described as a new species.

Barremian Angiosperm Pollen and Associated Palynomorphs from the Dakhla Oasis Area, Egypt

Pollen grains characteristic of the local pre-tricolpate, pre-Aptian phase of angiosperm evolution have been recovered from the upper part of the Six Hills Formation in the Dakhla Oasis area, Egypt. Highest abundance (up to 16.5 per cent) and diversity of angiosperm pollen is attained in samples from the Tineida 2 borehole, which also display a remarkable variety of different aperture types for a palynoflora of late Barremian age. Monosulcate, columellate tectates such as Retimonocolpites are most important, but a single trichotomosulcate grain as well as monoporate and inaperturate types that have not been reported from many coeval palynofloras, are also present. The following new taxa are described using same-grain SEM/LM techniques: Tucanopollis annulatus Schrank, sp. nov., Retimonocolpites pennyi Schrank and Mahmoud, sp. nov. and Retiacolpites columellatus Schrank, gen. et sp. nov. Phytogeographic links are closest with palynofloras previously described from the late Barremian of West Africa (Gabon, Congo), that is within the Northern Gondwana or Dicheiropollis etruscus/Afropollis Province.

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

Abstract 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.

Biostratigraphic importance of microfloras from the Late Cretaceous clastic series of Northwestern Sudan

Abstract The poorly fossiliferous Late Cretaceous clastic series of Northwestern Sudan has been studied palynologically for the first time. Clay samples, rich in kaolinite, from the El Ghaba well, about 370 km NW of Khartoum, contain two terrestrial palynomorph assemblages dominated by tricolpate angiosperm pollen, but also include some gymnosperms ( Inaperturopollenites, Steevesipollenites ) and, very rarely, pteridophyte spores. The presence of Foveotricolpites giganteus, F. gigantoreticulatus, F. tienabaensis, Tricolpites sp. CI.13, and T. sp. SCI.294 suggests a Lower Senonian (Coniacian) age for the El Ghaba samples. Their sedimentary facies favours a possible correlation with the upper Wadi Howar or lower Kababisch Formation of the Gebel Abyad Basin in Northwestern Sudan.

Upper Cretaceous to Neogene Palynology of the Melut Basin, Southeast Sudan

Abstract The palynology of the Upper Cretaceous to Neogene non-marine succession in the Melut Basin, southeast Sudan was investigated. The palynomorphs are overwhelmingly of terrestrial origin, but rare brackish water dinoflagellate cysts and scolecodonts were encountered from the Lower Miocene and Oligocene-Miocene. Mangrove pollen, which is common in coeval West African coastal basins, is rare and inconsistent. Examples are Spinizonocolpites (Nypa) from the Campanian-Maastrichtian to Eocene and Rhizophoraceae (Zonocostites ramonae) from the Neogene. Based on the stratigraphic distribution of selected pollen and spores from four exploration wells, eight informal palynozones from the Campanian to the Neogene are proposed. The zones, in stratigraphically ascending order, are as follows: Assemblage Zone I, Campanian (lower Melut Formation); Assemblage Zone II, Campanian-Maastrichtian (middle Melut Formation); Assemblage Zone III, Maastrichtian (upper Melut Formation); Assemblage Zone IV, Paleocene (Yale Formation); Assemblage Zone V, Eocene (upper Yale and Adar formations); Assemblage Zone VI, Oligocene-Early Miocene (Jimidi and lower Miadol formations); Assemblage Zone VII, Early Miocene (uppermost Miadol and lowermost Daga formations); and Assemblage Zone VIII, Late Miocene-Pliocene (Daga Formation). The ages are based on stratigraphic positions and a series of first downhole appearances of key species such as Foveotricolpites cf. giganteus (Zone I), Auriculiidites reticulatus (Zone II), Ariadnaesporites spinosus (Zone III), Periretisyncolpites giganteus (Zone IV), Retistephanocolpites williamsii (Zone V), Cricotriporites camerounensis (Zone VI), Perfotricolpites digitatus (Zone VII), and Peregrinipollis nigericus (Zone VIII). Palynofacies investigations indicated differences between the Late Cretaceous and Paleogene-Neogene paleoenvironments of the sections studied. The coexistence of structured organic palynodebris with pteridophyte spores, including those of water ferns (Ariadnaesporites), in the Upper Cretaceous strata suggests swampy conditions within a predominantly fluvial setting. The frequent occurrence of Palmae pollen indicates warm, humid conditions during the Late Cretaceous, although seasonal or hinterland aridity is suggested because of the occurrence of ephedroid pollen. Late Paleogene and Neogene assemblages are characterized by amorphous organic matter, fern spores, freshwater algae, and Gramineae pollen. Deposition in lacustrine habitats under warm, humid conditions is inferred. The occurrence of Gramineae pollen, mainly in the Neogene, indicates the development of grassy areas in a seasonally dry climate. A short marine incursion may have taken place during the Oligocene-Miocene, due to the rare occurrence of brackish water dinoflagellate cysts and scolecodonts.

DINOFLAGELLATE CYSTS AND ASSOCIATED AQUATIC PALYNOMORPHS FROM THE TENDAGURU BEDS (UPPER JURASSIC–LOWER CRETACEOUS) OF SOUTHEAST TANZANIA

Abstract Dinoflagellate cysts and associated aquatic palynomorphs have been recovered from the dinosaur-bearing Tendaguru Beds (Upper Jurassic–Lower Cretaceous) at Tendaguru, a hill in southeast Tanzania. Palynofloras from these beds are generally dominated by pollen grains of Mesozoic conifers (mainly Classopollis), but dinoflagellate cysts occur sporadically throughout the succession. They attain highest relative abundances and diversities in the marine intercalations between the Saurian Beds, namely in the Nerinea Bed (between the Lower and Middle Saurian Beds) and even more so in the Trigonia smeei Bed (between the Middle and Upper Saurian Beds). Peak levels of dinoflagellate cysts correspond to times when the shallow marine environments of the Nerinea and Trigonia smeei Beds had access to the open sea, while scarcity or absence of dinoflagellate cysts in the Saurian Beds is related to intervals of restricted access to the sea in tidal flat and coastal plain environments. Four informal dinoflagellate cyst assemblages can be distinguished in the Tendaguru Beds: the Rigaudella aemula-Chlamydophorella wallala assemblage from the Nerinea Bed (Oxfordian to Kimmeridgian); the Endoscrinium attadalense-Ctenidodinium sellwoodii group assemblage from the Middle Saurian Bed (late Kimmeridgian); the Dingodinium jurassicum-Kilwacysta assemblage from the Trigonia smeei Bed (Tithonian); the Muderongia-Oligosphaeridium assemblage probably from the Trigonia schwarzi Bed at Namunda Plateau, 8 km south of Tendaguru (late Valanginian to Hauterivian). The age determinations are based on correlation with known dinoflagellate cyst ranges and zonations in Australia, Europe and elsewhere. However, the stratigraphic position and previous biostratigraphic interpretations of the Tendaguru Beds based on ammonites, charophytes and ostracods were also taken into consideration. One new genus (Kilwacysta), three new species (Kilwacysta multiramosa, Kilwacysta semiseptata and Protobatioladinium lindiensis) and the new combination Barbatacysta capitata are proposed.

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

Abstract 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.

The marine Abu Ballas formation of southern Egypt: a clay-mineralogic and microfloral reconstruction of the Aptian paleoclimate

Abstract Combined investigations on the clay minerals and the microfloras of the backshore to shallow marine offshore strata of the Abu Ballas Formation (Aptian of southern Egypt), give evidence of warm and semi-arid climatic conditions. The sedimentary successions studied, predominantly consist of alternating pelitic and psammitic siliciclastic deposits. Their clay-mineral association with kaolinite, high-cristallinity illite, illite-dominated randomly interstratified illite-smectite and chlorite is inherited from continental areas under erosion. The Abu Ballas clay minerals reflect only subordinate pedogenetic chemical alteration which suggests a restricted humidity and the absence of a major vegetation. They were transported into the marine environment by periodic river systems. Aeolian processes played a minor role. The Abu Ballas microfloras are overwhelmingly dominated by terrestrial pollen and spores. Marine phytoplankton is extremely rare. Important changes in the local Jurassic to Early Cretaceous microfloras include a decline of ferns and Araucariaceae and, starting with Barremian-Aptian time, the appearance and rise in frequency of early angiosperms and of ephedroids. This seems to indicate a paleoclimatic trend towards less humidity and rising aridity which may be supported by other Abu Ballas fossils such as the lung-fish Ceratodus and the palm fruit Hyphaeneocarpon aegyptiaca Vaudois-Mieja and Lejal-Nicol, 1987.