Barremian—Aptian (Early Cretaceous) dinoflagellate cysts from the Scotian Margin, offshore eastern Canada
Bibliographic record
Abstract
The Scotian Margin is located in offshore Nova Scotia, Atlantic Canada, and includes a well-developed succession of Mesozoic strata that accumulated during the opening of the North Atlantic Ocean following the breakup of Pangea. Biostratigraphic studies of Mesozoic–Cenozoic strata along the Scotian Margin began in the early 1970s and focused on zonation schemes for each fossil group. Subsequent work, however, has emphasized an event-stratigraphic approach, combining palynologic with micropaleontologic and nannofossil events, as well logs and seismic horizons. Extensive taxonomic treatment of Late Cretaceous and Cenozoic palynomorphs from the Scotian Margin were also undertaken, but did not extend to the Triassic to Early Cretaceous interval. Thus, our present aim is to develop a detailed taxonomic review and a comprehensive event-stratigraphic scheme for this earlier interval of the Scotian Margin based mainly on palynology, integrated with macrofossil, nannofossil and sequence stratigraphic analyses. In our initial research, we are focusing on Lower Cretaceous conventional cores, including studies at the Panuke B-90 well. Data from sedimentary facies, including macrofossil and ichnofossil assemblages, suggest that, up from the base of the section studied there is an initial, regressive transition from a shelfal (neritic) to a mainly estuarine-brackish setting. The regressive trend is followed by a transgressive trend through most of the Upper Member of the Missisauga Formation, culminating in a return to fully marine conditions near the base of the overlying Naskapi Member. The presence of the dinoflagellate cyst (dinocyst) species Muderongia microperforata and Palaeoperidinium cretaceum, considered tolerant to low-salinity waters, indicates a brackish-estuarine setting in much of the Upper Member of the Missisauga Formation. However, the relatively abundant and rich dinocyst assemblages in specific intervals within this member indicate frequent fluctuations in and out of the estuarine complex, with intermittent connections with a fully marine environment. The dinocyst assemblages and key bioevents recorded in this study indicate a Barremian age for the Upper Member of the Missisauga Formation in Panuke B-90. This includes the co-occurrence of Odontochitina operculata and Tenua anaphrissa at the base of the section, indicating a probable early Barremian age, and higher, the Cerbia tabulata abundance is a reliable bioevent for the late Barremian to early Aptian interval. The palynological data confirm also an early Aptian age for the overlying Naskapi Member of the Logan Canyon Formation, based on the presence at its base of the age-diagnostic ammonite Deshayesites sp. Near the boundary between the Missisauga and Logan Canyon formations, the δ13C isotope ratio results show a negative carbon isotope excursion and subsequent recovery, which we interpret as the Cretaceous Oceanic Anoxic Event 1a (OAE1a, or Selli Event). At the onset of the event, dinocysts show a relatively high abundance and species richness; but this trend changes upwards, and at the top of the Selli Event both abundance and species richness decreases and Cerbia tabulata temporary disappears. Based on the above results, our ongoing study of the Panuke B-90 conventional cores and coeval successions will contribute to a comprehensive event-stratigraphic framework for the Scotian Margin.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".