R. Andrew MacRae

Late Cretaceous and Cenozoic fossil dinoflagellates and other palynomorphs from the scotian margin, offshore eastern Canada

Synopsis Palynomorphs, especially dinoflagellate cysts (dinocysts), have been at the forefront of research carried out on Mesozoic‐Cenozoic sediments on the Scotian Margin over the last 30–40 years: this research has been driven by the need to develop a stratigraphical framework to better understand the regions petroleum systems. To support the compilation of a detailed event strati‐graphical scheme for the Late Cretaceous to Cenozoic of the margin, emphasising dinocysts but with information from other fossil groups and non‐biostratigraphical data, there is a need to formalise the dinocyst taxonomy. In this paper, we fulfill this need by illustratingand, where appropriate, describing and discussing taxa used in our event biostratigraphical scheme. The following taxa (dinocysts except where indicated) are new: Areoligeracircumsenonensis,Axiodinium,Axiodiniumprearticulatum, Cordosphaeridium delimurum, Glaphyrocysta extensa, Hafniasphaera delicata, Impletosphaeridium capitatum, Mendicodinium robustum (validation of previously proposed name), Minisphaeridium,Oli‐gokolpoma, Oligokolpoma tubulus, Palaeocystodinium obesum, Palaeocystodinium teespinosum, Palaeohystrichophora palaeoinfusa, Pentadinium sabulum, Pervosphaeridium granaciculare, Tall‐adinium, Wetzeliella caviarticulata and Cingutriletes tyriskos (a trilete spore). The following are newly proposed combinations (with a former name in parentheses): Cerebrocysta waipawaensis (Pyxidinopsis waipawaensis), Cerodinium glabrum (Cerodinium speciosum subsp. glabrum), Din‐opterygium alatum (Xiphophoridium alatum), Kleithriasphaeridium cooksoniae (Florentinia cook‐soniae), Kleithriasphaeridium perforatum (Florentinia perforata), Minisphaeridium latirictum (Hys‐trichosphaeridium latirictum), Nyktericysta tripenta (Balmula tripenta), Pentadinium granulatum (Pentadinium laticinctum subsp. granulatum) Talladinium? clathratum (Charlesdowniea clathrata) and Talladinium wulagenense (Charlesdowniea wulagenensis). Emendations of the following taxa are proposed: Apectodinium, Dinopterygium, Distatodinium, Glaphyrocysta, Hafniasphaera, Isa‐belidinium, Kleithriasphaeridium, Manumiella, Nyktericysta, Palaeocystodinium, Rhombodinium, Wetzeliella and Wetzeliella articulata. Material from the Kiowa Formation of Kansas supports our concept of Dinopterygium. We review several morphological terms already in the literature and introduce the following new ones: mesotabular, obtabular, contabular, penicontabular, epeliform, equi‐epeliform and lati‐epeliform.

The last 100 million years on the Scotian Margin, offshore eastern Canada: an event-stratigraphic scheme emphasizing biostratigraphic data

In order to provide a detailed stratigraphic framework for the Late Cretaceous and Cenozoic basin fill of the Scotian Margin (the continental shelf and continental slope off Nova Scotia, eastern Canada), we have developed an event-biostratigraphic scheme based mainly on new analyses of several exploration wells. These include the following shelf wells — Demascota G-32, Hesper I-52, Onondaga E-84 and Wenonah J-75 — as well as Shelburne G-29 and Shubenacadie H-100 on the slope. Several fossil groups are involved in this study, most notably dinoflagellate cysts (dinocysts) and nannofossils, with the former generally providing more diverse assemblages and the latter more precise calibration with global correlations. Because most of the material studied is from cuttings samples, we have relied largely on Last Appearance datums (LADs). The scheme incorporates information from about 250 microfossil species (or groups of species), delimiting about 180 events. Not all events occur in all wells and the scheme needs to be tested against future observations: nevertheless, it represents a considerable advance on previous schemes, which were based mostly on broad zones rather than detailed events. Moreover, it allows for a more refined assessment of ages of geological events, such as the early Eocene gamma spike and the incision of the Wenonah Canyon. And it provides an accurate age context for ongoing stratigraphic, sedimentological and paleoenvironmental studies, and ultimately for a fuller understanding of petroleum systems on the Scotian Margin. RESUME Pour fournir un cadre stratigraphique detaille du remplissage du Cretace tardif et du Cenozoique du bassin de la marge Neo-Ecossaise (plateau continental et pente continentale au large de la Nouvelle-Ecosse, est du Canada), nous avons mis au point une formule evenementielle-biostratigraphique principalement basee sur de nouvelles analyses de plusieurs puits d’exploration. Ces derniers comprennent les puits Demascota G-32, Hesper I-52, Onondaga E-84 et Wenonah J-75 sur le plateau continental ainsi que Shelburne G-29 et Shubenacadie H-100 sur la pente continentale. L’etude touche plusieurs groupes de microfossiles, plus particulierement les kystes de dinoflagelles (dinokystes) et les nannofossiles, les premiers procurant generalement des assemblages plus diversifies et les derniers, un etalonnage plus precis avec des correlations mondiales. Comme la majeure partie du materiel etudie provient d’echantillons de deblais, nous nous sommes largement appuyes sur les plans de reference des dernieres manifestations. La formule incorpore des donnees provenant d’environ 250 especes (ou groupes d’especes) de microfossiles delimitant quelque 180 phenomenes, dont environ 50 % sont bases sur des nanofossiles, quelque 46 % sur des palynomorphes et 4 % sur des foraminiferes. Les phenomenes en question ne se manifestent pas tous dans tous les puits et il faut encore soumettre la formule a des essais en vertu des observations futures: elle represente neanmoins un progres considerable par rapport aux formules anterieures, qui etaient surtout basees sur des zones etendues plutot que sur des phenomenes detailles. Elle permet de plus une evaluation plus raffinee des âges des phenomenes geologiques, comme les pics gamma du Paleocene tardif et l’incision du canyon Wenonah. Elle procure par ailleurs un contexte de datation exact pour les etudes stratigraphiques, sedimentologiques et paleoenvironnementales courantes, et elle permettra en fin de compte une comprehension plus complete des systemes petroliers le long de la marge Neo-Ecossaise. [Traduit par la redaction]

Abstract: A revised biostratigraphic and well-log sequence stratigraphic framework for the Scotian Margin, offshore eastern Canada

As part of a Play Fairway Analysis (PFA) of the Scotian Margin, offshore eastern Canada, we have conducted quantitative multi-disciplinary biostratigraphic studies of the Upper Triassic-Cenozoic sections in 6 wells: Bonnet P-23, Chebucto K-90, Cohasset L-97, Glenelg J-48, Glooscap C-63 and South Griffin J-13. These wells were chosen to provide good spatial coverage and stratigraphic penetration, plus correlation with the seismic grid. Using the results from these new wells as calibration, we have also evaluated pre-existing biostratigraphic data and interpreted the well-log sequence-stratigraphy of 14 additional wells using a consistent multi-disciplinary event scheme. Our study provides accurate ties and clarifies the origin of seismic horizons mapped across the area within the PFA project. Key to the dating of some horizons has been integration of the palynology and micropalaeontology (most commonly used for biostratigraphy on the Scotian Margin) with new nannofossil and available calpionellid data. By integrating the biostratigraphic, lithofacies, well log and seismic data, we have enhanced resolution over previous efforts and thus have a better understanding of unconformities and major flooding events in the region. Our component of the PFA should enable better targeting of hydrocarbon exploration efforts on the underexplored Scotian Margin, especially in deeper water..

MICROBIAL MATS AND ICHNOFAUNA OF A FLUVIAL-TIDAL CHANNEL IN THE LOWER PENNSYLVANIAN JOGGINS FORMATION, CANADA

ABSTRACT A meandering fluvial channel body at Coal Mine Point in the Joggins Fossil Cliffs, Nova Scotia contains an unusual fossil assemblage. During an early stage of channel abandonment, a wrinkled surface attributed to microbial mats was traversed by large arthropleurids (Diplichnites cuithensis trackways). Closely associated are smaller Diplichnites gouldi trackways, probably made by myriapods, as well as tetrapod tracks (Pseudobradypus?, Dromillopus, Hylopus) and invertebrate traces (Cochlichnus, Gordia), collectively representing the Scoyenia ichnofacies. The mats stabilized the sediment surface, allowing excellent trackway preservation, and may have formed a food source, although no feeding traces were identified. Overlying strata yield Protichnites followed by a succession containing paired mud drapes and an impoverished Skolithos ichnofacies encompassing Skolithos, Arenicolites, Cochlichnus, and possible Rhizocorallium, collectively suggesting brackish influence. The channel deposits contain some logs and large plant axes, and were colonized in late stages by lycopsid and calamitalean trees. The assemblage indicates that Early Pennsylvanian channels on a vegetated coastal plain near the tidal limit had a diverse and interconnected aquatic and riparian ecosystem, with tetrapods and terrestrial arthropods entering the channel. Microbial mats may have been common components of Pennsylvanian channels, much as they are in modern fluvial and tidal channels.

MIDDLE ALBIAN (LOWER CRETACEOUS) GASTROPLITINID AMMONITES AND DINOFLAGELLATES FROM THE CHRISTOPHER FORMATION (DRAGON MOUNTAIN, AXEL HEIBERG ISLAND, CANADIAN ARCTIC ISLANDS) AND A REVISION OF THE GENUS PSEUDOGASTROPLITES JELETZKY, 1980

Abstract A large sample of excellently preserved ammonites from concretions concentrated at a single horizon near the base of the Macdougall Point Member of the Christopher Formation (Aptian–Albian age; Early Cretaceous) is the basis for recognizing a new species of the boreal ammonite genus Pseudogastroplites (P. draconensis). The dimorphic nature of the genus is established, two variants are recognized (P. draconensis var. robusta and P. draconensis var. gracile), and the generic diagnosis is emended. Retention of the genus Pseudogastroplites Jeletzky, 1980 as distinct from Gastroplites McLearn, 1930 is proposed. The concretions also yield Pseudopulchellia flexicostata (Imlay, 1961), inoceramid bivalves, fish remains, and a palynological flora, and are dated as late middle Albian.

Diagenesis and Porosity Reduction in the Late Cretaceous Wyandot Formation, Offshore Nova Scotia: A Comparison with Norwegian North Sea Chalks

Abstract Porous chalk units have produced significant oil and gas discoveries around the world, including the world-class Tor Field of the Norwegian North Sea. On the Scotian Shelf of eastern Canada, the Upper Cretaceous Wyandot Formation is widespread, extending approximately 500 km along the length of the margin, and consists primarily of limestone with major chalk intervals. These chalks have porosities of up to 30% and are the reservoir for a gas and oil discovery at the Primrose N-50 well (1972) and a gas show at the Eagle D-21 well (1972). However, despite its potential as a hydrocarbon reservoir and/or seal, the Wyandot Formation is under-studied. In this paper, the Wyandot chalk is studied using conventional core samples, petrophysical logs, isotope geochemistry and SEM images to enhance the understanding of the depositional history, diagenesis and porosity-reducing mechanisms within the Wyandot Formation. Results indicate that the Wyandot chalks are in situ pelagic deposits, as opposed to the allochthonous North Sea chalks, and that mechanical compaction and dissolution/re-precipitation are the dominant mechanisms of porosity reduction. Given that significant volumes of Wyandot chalk have been eroded on parts of the Scotian Shelf, it is possible that North Sea type allochthonous reservoirs exist is distal locations on the Scotian Slope, and therefore an increased understanding of the sedimentology and porosity distribution of the in situ Wyandot Formation is important for further exploration in this frontier area.

An Ichnotaxonomic Approach to Wrinkled Microbially Induced Sedimentary Structures

ABSTRACT Microbially induced sedimentary structures (MISS) are an important facet of recent paleoichnological work because of their taphonomic implications. MISS are extensively studied in terms of their formation processes, recognition in the ancient record, and their diverse morphologies. Classification and terminology schemes are based on their appearance and mode of formation; however, the taxonomic treatment of MISS remains debated. Traditionally MISS have been considered sedimentary structures, and arguments have been made that they cannot be treated as trace fossils under the International Code of Zoological Nomenclature (ICZN) due to MISS being formed by communities of microbiota including algae, cyanobacteria, and others, rather than a single tracemaker. Here, we reexamine MISS using an ichnotaxonomic approach and apply ichnologic terminology and binomial names. Upon reexamining the holotype of Kinneyia Walcott, a genus commonly used to describe some MISS, we argue it cannot be used to correctly describe wrinkle or ripple-like features seen in MISS, and we agree with previous authors that Kinneyia is likely not biogenic in origin. We here assign a new ichnogenus and ichnospecies, Rugalichnus matthewii, to ripple-like sedimentary wrinkle marks known as MISS, separating them from the nomen dubium genus Kinneyia.