Late Ordovician to early Silurian acritarchs from the Qusaiba-1 shallow core hole, central Saudi Arabia

Well-preserved acritarchs are documented from Upper Ordovician and lower Silurian sections in the Qusaiba-1 shallow core hole of central Saudi Arabia. Sixty-nine genera comprising 68 named species and 62 forms under open nomenclature were recorded from forty core samples. At the base of the Upper Ordovician and lower Silurian succession in Qusaiba-1 is the Quwarah Member of the Qasim Formation. This is overlain by glacio-marine deposits of the Sarah Formation, which are overlain in turn by the Qusaiba Member of the Qalibah Formation. Four distinct acritarch assemblages are informally numbered 1 to 4 from the base of the core upwards. Assemblage 1 is from the Quwarah Member, and is independently dated by Chitinozoa as being late Katian to early Hirnantian in age (Late Ordovician). The assemblage contains a number of new species, plus species reported from low-latitude Late Ordovician Laurentia and Baltica as well as the Gondwanan margin. Assemblage 2 is from a glacitectonite at the base of the Sarah Formation and is early Hirnantian in age. Assemblage 3, from the Baq'a Shale Member of the Sarah Formation, is also Hirnantian in age and is characterized by a stratigraphically admixed Ordovician palynoflora. Assemblage 4 is restricted to three samples from the Qusaiba Member in the lowermost part of the Qalibah Formation and is dated as Rhuddanian (earliest Silurian). The highest of the three samples that comprise Assemblage 4 is from the same level as a gamma ray peak at 254.8 ft. Reworking of Middle Ordovician forms is evident in Assemblage 3 and is attributed to processes of glacial erosion and resedimentation during glacial melting. Reworked specimens are probably from the Hanadir Member and possibly also the Kahfah Member of the Qasim Formation. The extent of later Ordovician reworking in Assemblage 3, for example reworking from the Quwarah Member, is unclear. However, given that glacial erosion extended to levels below the Quwarah Member, Late Ordovician palynomorphs present in Assemblage 3 might also be reworked. The extent of any reworking in assemblages 1 and 2 is uncertain. There is no evidence for reworking in Assemblage 4. Two new acritarch genera, five new species and one new combination are proposed: Dorsennidium polorum (Miller and Eames, 1982) comb. nov., Falavia magniretifera gen. et sp. nov., Inflatarium trilobatum gen. et sp. nov., Nexosarium mansouri sp. nov., Orthosphaeridium orthogonium sp. nov. and Tunisphaeridium bicaudatum sp. nov. Samples from the same set were used for chitinozoan, scolecodont and miospore studies (this volume). Eurypterid and graptolite remains are also presen

Middle Ordovician acritarchs and problematic organic-walled microfossils from the Saq-Hanadir transitional beds in the QSIM-801 well, Saudi Arabia

Core samples from the QSIM-801 water well, drilled in central Saudi Arabia, cover a 93-foot interval spanning the transition between the Sajir Member of the Saq Formation, that consists mainly of sandstones of tidal sand flat environments, and the Hanadir Member of the Qasim Formation, characterized by argillaceous graptolitic mudstones, corresponding to a tidal delta front. The samples contain abundant, exceptionally well-preserved and diverse palynomorphs, which include cryptospores, acritarchs and chitinozoans, other problematic organic-walled microfossils as well as other organic particles such as cuticle-like fragments. The studied interval is biostratigraphically well constrained by the presence of chitinozoans of the formosa and pissotensis Zones of late-early to late Darriwilian age (Middle Ordovician) in the uppermost Saq Formation and Hanadir Member. The biostratigraphic age of the Sajir Member considered to span the Dapingian–Darriwilian boundary, is re-discussed based on the results herein. The uppermost part of the Sajir Member yielded the ichnofossil, Phycodes fusiforme. Acritarch assemblages from the Sajir Member of the Saq Formation are poorly diversified and dominated by sphaeromorphs. More diverse assemblages of acritarchs, associated with enigmatic forms, occur in the Hanadir Member of the Qasim Formation. The contact between the two formations and the transition between the palynomorph assemblages are sharp, suggesting a stratigraphic hiatus. A quantitative analysis allows us to discuss the paleoenvironmental changes and possibly climatic changes associated with an hypothesis of ice house conditions during this period. Among the diagnostic acritarch taxa observed are Frankea breviuscula, F. longiuscula, Baltisphaeridium ternatum, Dasydorus cirritus, Dicrodiacrodium ancoriforme, Poikilofusa ciliaris, Pterospermopsis colbathii and Uncinisphaera fusticula. These are associated with other typical forms known to range across the Lower–Middle Ordovician boundary, such as Aremoricanium rigaudae, Aureotesta clathrata, Barakella fortunata, B. rara, Baltisphaeridium klabavense, Glaucotesta latiramosa and Striatotheca spp. Galeate and peteinoid acritarchs are also well represented, as well as tiny forms of ultraplanctonic size. Three new species of acritarchs are proposed: Frankea longiuscula var. darriwilense var. nov, Micrhystridium regulum sp. nov, and Tyrannus proteus sp. nov. Repeated occurrences throughout the section of cryptospores, problematic microfossils such as organic filaments, cuticle-like tissues, striated and pigmented leiospheres frequently in clusters, are interpreted to reflect recurrent terrestrial and freshwater inputs in the depositional environment. Single-specimen, high-resolution analyses using Confocal Laser Scanning Microscopy on the enigmatic form Tyrannus proteus sp. nov. show fluorescence emission spectra and microstructural properties significantly different from those of typical marine acritarchs from the same levels

LES SPORES DU DEVONIEN INFERIEUR DU SYNCLINORIUM DE LAVAL (MASSIF ARMORICAIN). Systématique - Biostratigraphie - Relations microplancton-palëoenvironnement

No abstractGe travail présente les résultats de l'étude du microplancton des formations du Dévonien inférieur du synclinorium de Laval (Massif Armoricain), datées par la macrofaune et rapportées au Siegenien supérieur - Emsien inférieur. Le synclinorium de Laval appartient au Domaine Centre armoricain et constitue la terminaison orientale du synclinorium médian.Les sédiments épicontinentaux de cette unité paléozoïque présentent un intérêt particulier, en raison de la diversité des faciès et des milieux de dépôts rencontrés, traduisant des variations de l’environnement susceptibles d’influencer la composition du plancton actif (Acritarches, Chitinozoaires et Scolécodontes) et passif (spores et débris végétaux). Deux aspects principaux ont été abordés, une analyse qualitative et quantitative du microplancton. L’analyse qualitative a essentiellement comporté une étude systématique des spores, intéressante dans la mesure ou le contenu palynologique de la période considérée, à la limite Siegenien - Emsien, restait mal connu. L’utilisation du M.E.B. a permis de préciser la morphologie de certaines des 75 espèces recensées et décrites. Cette étude systématique a confirmé une évolution de la végétation, se traduisant par une diversification d’espèces et un développement de l'organisation des spores au cours de cette période.Les 3 assemblages définis dans nos coupes, ayant valeur de biozones, ont été comparés à ceux proposés dans d’autres régions d’Europe, d’Afrique du Nord ou d’Amérique du Nord.La comparaison des résultats de l’analyse quantitative (la fréquence absolue et relative des différents éléments au microplancton) et des données sêdimentologiques a permis d’aborder le problème de l’influence des facteurs biotiques et abiotiques sur la distribution des microfossiles

Biostratigraphy, taxonomic diversity and patterns of morphological evolution of Ordovician acritarchs (organic-walled microphytoplankton) from the northern Gondwana margin in relation to palaeoclimatic and palaeogeographic changes.

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Late Palaeozoic palynomorph assemblages from the Karoo Supergroup and their potential for biostratigraphic correlation, Kalahari Karoo Basin, Botswana

Late Carbonifeous to Permian core samples from two borehole sections, STRAT 1 and CKP 6, that penetrate the glacial to postglacial and coal-bearing Lower Karoo sequence, Kalahari Karoo Basin, Botswana, contain well preserved pollen and spore palynomorphs. The palynomorph assemblages comprise 165 species of spores and pollen, and few acritarchs and chlorophycean algae. This paper presents a local biozonation of three succeeding assemblage zones, recognisable in each borehole section. The assemblage zones are named: the Hamiapollenites bullaeformis Biozone, the Cyclogranisporites gondwanensis Biozone and the Platysaccus papilionis–Striatopodocarpites fusus Biozone, in ascending order of stratigraphy. Assemblages are compared and correlated with assemblages described from other Gondwana areas of Africa, Australia, Arabia, South America and Antarctica. A general analysis of taxa from the Kalahari Karoo Basin indicates a distinct similarity with assemblages from the Paraná Basin of South America. The Hamiapollenites bullaeformis Biozone is comparable with the Vittatina costabilis Interval Zone of the Paraná Basin. Assemblages from the Cyclogranisporites gondwanensis and the Platysaccus papilionis–Striatopodocarpites fusus zones are comparable with the Lueckisporites virkkiae Interval Zone. Age determination for the assemblages in the Kalahari Karoo Basin is inferred from comparison with similar assemblages from previous Gondwana studies, and ranges from the Late Carboniferous (Kasimovian–Gzhelian) to latest Early or possibly earliest Middle Permian (Late Cisularian to Early Guadalupian). • Key words: Kalahari Karoo Basin, Late Carboniferous–Permian, pollen, spores, assemblage zones

Structure and microstructure of Pachypora lamellicornis Lindström, 1873, a tabulate coral from the Silurian of Gotland, Sweden

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The end of a myth:Arpylorus antiquus Paleozoic dinoflagellate

International audienceArpylorus antiquus, erected by Calandra in 1964, was isolated from upper Silurian sedimentary rocks from the Mechiguig 1 borehole in southern Tunisia, with other palynomorphs. The folded vesicle and the quadrangular form of the aperture break down into platelike fragments, resembling the tabulation of dinoflagellates. The presence of these elements has been used to interpret A. antiquus as a dinoflagellate cyst. The morphology and affinity of A. antiquus is reinterpreted herein based on investigation of larger sets of samples, including material from the type locality, together with material of Algeria, Saudi Arabia, and Brazil. More complete specimens than those previously described have been observed using gentle laboratory techniques, showing a large development of a fine membrane at the periphery of vesicles. This element was destroyed using classical palynological treatments, implying that the holotype is an incomplete specimen. The membrane at the periphery of vesicles and dorsoventral differentiation of these vesicles suggest that A. antiquus is a part of a more complex biological structure. We suggest a possible relationship with eurypterids, arthropods related to phyllocarids, represented by abundant fragments in the assemblages. Arpylorus antiquus is possibly a structure of storage. The chemical composition of A. antiquus using a Fourier transform infrared FTIR microspectroscopy analysis, reveals a wall composed of biopolymer that is not consistent with dinosporin. We conclude that Arpylorus antiquus is definitively not a dinoflagellate cyst. Although dinoflagellates may have older Paleozoic or even Proterozoic ancestors as the biomarker record may suggest, the dinoflagellate tabulation evolved only in the early Mesozoic