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

A distinctive marginal marine palynological assemblage from the Přídolí of northwestern Saudi Arabia

A rare occurrence of a rich and diverse palynological assemblage from the Tawil Formation is described from well JLMD-EW-8 in northwestern Saudi Arabia. The composition of this assemblage strongly indicates a middle Přídolí age. The assemblage encountered contains very characteristic chitinozoans, acritarchs, tasmanitids, freshwater algae, scolecodonts, eurypterid cuticle and other organic remains. Land-derived miospores are also common and two new cryptospore species (Cymbohilates jalamidensis and Gneudnaspora sordida) are herein formally described. Most taxa of taxonomic interest and useful for regional and intercontinental correlation are illustrated. The palaeogeographic distribution of this assemblage is also discussed as organic-walled microphytoplankton, chitinozoans and miospores encountered in the studied samples correlate well with similar assemblages from various Algerian, Libyan, and Ibero-armorican localities (i.e. Ibarmaghian regions). This corresponds to what is considered as a transgressive middle Přídolí event in the Algerian Sahara, with non-marine intervals bracketing this brief marine sea-level rise. This event is likely to have extended into all of north Gondwana, including Arabia, and can be correlated to the S50 Maximum Flooding Surface from the sequence stratigraphic framework defined in the Neftex Geodynamic Earth Model

The life and scientific work of William R. Evitt (1923-2009)

Occasionally (and fortunately), circumstances and timing combine to allow an individual, almost singlehandedly, to generate a paradigm shift in his or her chosen field of inquiry. William R. (‘Bill’) Evitt (1923-2009) was such a person. During his career as a palaeontologist, Bill Evitt made lasting and profound contributions to the study of both dinoflagellates and trilobites. He had a distinguished, long and varied career, researching first trilobites and techniques in palaeontology before moving on to marine palynomorphs. Bill is undoubtedly best known for his work on dinoflagellates, especially their resting cysts. He worked at three major US universities and spent a highly significant period in the oil industry. Bill's early profound interest in the natural sciences was actively encouraged both by his parents and at school. His alma mater was Johns Hopkins University where, commencing in 1940, he studied chemistry and geology as an undergraduate. He quickly developed a strong vocation in the earth sciences, and became fascinated by the fossiliferous Lower Palaeozoic strata of the northwestern United States. Bill commenced a PhD project on silicified Middle Ordovician trilobites from Virginia in 1943. His doctoral research was interrupted by military service during World War II; Bill served as an aerial photograph interpreter in China in 1944 and 1945, and received the Bronze Star for his excellent work. Upon demobilisation from the US Army Air Force, he resumed work on his PhD and was given significant teaching duties at Johns Hopkins, which he thoroughly enjoyed. He accepted his first professional position, as an instructor in sedimentary geology, at the University of Rochester in late 1948. Here Bill supervised his first two graduate students, and shared a great cameraderie with a highly motivated student body which largely comprised World War II veterans. At Rochester, Bill continued his trilobite research, and was the editor of the Journal of Paleontology between 1953 and 1956. Seeking a new challenge, he joined the Carter Oil Company in Tulsa, Oklahoma, during 1956. This brought about an irrevocable realignment of his research interests from trilobites to marine palynology. He undertook basic research on aquatic palynomorphs in a very well-resourced laboratory under the direction of one of his most influential mentors, William S. ‘Bill’ Hoffmeister. Bill Evitt visited the influential European palynologists Georges Deflandre and Alfred Eisenack during late 1959 and, while in Tulsa, first developed several groundbreaking hypotheses. He soon realised that the distinctive morphology of certain fossil dinoflagellates, notably the archaeopyle, meant that they represent the resting cyst stage of the life cycle. The archaeopyle clearly allows the excystment of the cell contents, and comprises one or more plate areas. Bill also concluded that spine-bearing palynomorphs, then called hystrichospheres, could be divided into two groups. The largely Palaeozoic spine-bearing palynomorphs are of uncertain biological affinity, and these were termed acritarchs. Moreover, he determined that unequivocal dinoflagellate cysts are all Mesozoic or younger, and that the fossil record of dinoflagellates is highly selective. Bill was always an academic at heart and he joined Stanford University in 1962, where he remained until retiring in 1988. Bill enjoyed getting back into teaching after his six years in industry. During his 26-year tenure at Stanford, Bill continued to revolutionise our understanding of dinoflagellate cysts. He produced many highly influential papers and two major textbooks. The highlights include defining the acritarchs and comprehensively documenting the archaeopyle, together with highly detailed work on the morphology of Nannoceratopsis and Palaeoperidinium pyrophorum using the scanning electron microscope. Bill supervised 11 graduate students while at Stanford University. He organised the Penrose Conference on Modern and Fossil Dinoflagellates in 1978, which was so successful that similar meetings have been held about every four years since that inaugural symposium. Bill also taught many short courses on dinoflagellate cysts aimed at the professional community. Unlike many eminent geologists, Bill actually retired from actively working in the earth sciences. His full retirement was in 1988; after this he worked on only a small number of dinoflagellate cyst projects, including an extensive paper on the genus Palaeoperidinium

Late Ordovician-earliest Silurian palynomorphs from northern Chad and correlation with contemporaneous deposits of southeastern Libya

International audienceWell preserved assemblages of cryptospores, chitinozoans, acritarchs, leiospheres, tasmanitids, colonies of Gloeocapsomorpha, scolecodonts and eurypterid fragments from 23 core samples of the Moussegouda core hole in the Erdi Basin, northern Chad, and from two samples from well KW-2 in Kufra Basin, South East Libya are investigated. These palynomorphs were recovered from the southernmost North African marine deposits of Late Ordovician and possibly early Silurian age. The palaeoenvironment evolves from late Hirnantian glacio-marine diamictites to silt-dominated sequences suggesting a marginal marine environment of possibly latest Hirnantian to earliest Rhuddanian age (post-elongata-pre-fragilis chitinozoan assemblages). The recovered palynomorph assemblages are compared and correlated with contemporaneous assemblages recorded in other northern Gondwana localities (Mauritania, Morocco Algeria, Libya, Africa, Saudi Arabia, Jordan), and in South Africa, in order to evaluate possible effects of the ice cap melting on palynomorph assemblages and sedimentation. Our goal is also to improve the regional biostratigraphy across the Ordovician-Silurian boundary. The composition of the recovered palynomorph assemblages, with mixed terrestrial and marine microflora, suggests that the topmost Ordovician or earliest Silurian in northern Chad and southeastern Libya, reflects nearshore conditions, with obvious fresh water influences. The lack of black shale or grey shale in the uppermost Ordovician and of "hot shale" in the lower Silurian in these areas, and their replacement by siltstones, are probably related to an isostatic readjustment that rapidly starved the marine sedimentation in the areas previously overlain by a thick ice cover during the climax of the Hirnantian glaciation. Tasmanites tzadiensis Le Herisse sp. nov. and Euconochitina moussegoudaensis Paris sp. nov., two new palynomorphs of biostratigraphical interest are described and illustrated

Palynology and sedimentary environments of the Devonian from the Saida area (northwestern Algeria)

International audienc

Crassiangulina variacornuta sp. nov. du Llandovérien et son rôle dans la taxonomie des acritarches

Une nouvelle espèce caractéristique d’acritarche, Crassiangulina variacornuta sp. nov., est observée dans les régions de basse latitude de Balonia (Belgique, Angleterre et Suède) et dans les régions de haute latitude de Gondwana (Algérie, Brésil, Libye et Arabie Saoudite). Cette espèce semble posséder une extension stratigraphique limitée au Télychien (Silurien). Cela montre le bon potentiel de Crassiangulina variacornuta sp. nov. comme marqueur biostratigraphique international pour le Llandovery supérieur. De plus, elle semble restreinte aux milieux déposés sous la limite d’action des vagues de tempête. Le genre Crassiangulina JARDINÉ et al. 1972 est amendé pour incorporer cette nouvelle espèce et pour rassembler dans un seul genre les acritarches triangulaires et autres acritarches à contour polygonal possédant des processus pleins. Le genre ainsi amendé contient l’espèce type Crassiangulina tesselita JARDINÉ et al. 1972 emend., C. grotesca CRAMER et al. 1976 comb. nov. et emend. et C. variacornuta sp. nov. Une étude biométrique de 138 spécimens de C. variacornuta sp. nov., issus de deux sections en Angleterre et d’une section en Belgique, et son traitement statistique montrent la cohérence biologique de la population étudiée et mettent en évidence des différences de moyennes entre les sections, différences dues à des facteurs taphonomiques ou environnementaux. Ces résultats montrent le besoin de décomposer les variations morphologiques des acritarches selon les axes de la variabilité morphologique : génotypique, écophénotypique, chronotypique et taphonotypique