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TitleA paleoenvironmental model for the Labrador margin, Canada based on sedimentology, ichnology and quantitative palynology
AuthorDafoe, L TORCID logo; Williams, G L
Source35th IAS Meeting of Sedimentology Virtual Meeting, book of abstracts; by Bábek, O (ed.); Vodrázková, S (ed.); 2021 p. 127 Open Access logo Open Access
LinksOnline - En ligne (complete volume - volume complet, PDF, 3.05 MB)
Alt SeriesNatural Resources Canada, Contribution Series 20200740
PublisherInternational Association of Sedimentologists (Olomouc, Czech Republic)
Meeting35th IAS Meeting of Sedimentology; Prague; CZ; June 21-25, 2021
Mediaon-line; digital
File formatpdf
ProvinceEastern offshore region; Newfoundland and Labrador
NTS3; 13; 14; 15
AreaLabrador Sea
Lat/Long WENS -63.0000 -54.0000 63.0000 53.0000
Subjectsmarine geology; paleontology; tectonics; Science and Technology; Nature and Environment; Paleogene; Eocene; Paleocene; continental margins; paleoenvironment; depositional environment; ichnology; ichnofossils; ichnofacies; trace fossils; palynology; palynomorphs; miospores; tectonic history; rifting; sea floor spreading; observation wells; core samples; sedimentary structures; sedimentation rates; Labrador Margin; Greenland Plate; Ancestral North American Plate; Bjarni Formation; Markland Formation; Gudrid Formation; Dinoflagellates; Acritachs; Bisaccates; Cruziana; Phanerozoic; Cenozoic; Tertiary; Mesozoic; Cretaceous
ProgramGEM2: Geo-mapping for Energy and Minerals Baffin Region
Released2021 06 01
AbstractThe Labrador Sea developed during rifting that began in the Early Cretaceous, with eventual seafloor spreading between the Greenland plate and the paleo-North American plate from the Maastrichtian to late Eocene. A record of this tectonism is preserved along the Labrador margin, offshore eastern Canada in a succession with an established lithostratigraphic framework. We aim to establish comparative relationships between ichnofossil and palynomorph trends in paleoenvironmental analyses of these rocks using 23 conventional core intervals from 14 wells for the: Lower Cretaceous Bjarni Formation (syn-rift), Upper Cretaceous Markland Formation (late rift), and Middle Paleocene to lowermost Eocene Gudrid Formation (post-rift). Palynomorph counts were conducted on 64 samples from unsieved palynomorph slides for the following groups: dinoflagellate cysts (dinocysts), acritarchs, bisaccates, other miospores, and other palynomorphs, with ratios providing a sense of the depositional distance from the shoreline. We see expected relationships within fully marine strata. Shales of the Markland Formation deposited in slope-equivalent water depths, possibly deposited under dysoxic conditions, show high proportions of dinocysts and acritarchs (marine indicators) relative to miospores. From the same formation, homogenized sandy mudstones contain trace fossil suites of the Cruziana Ichnofacies, again with high proportions of dinocysts to miospores within inner to outer shelf deposits. Brackish bay or lagoonal deposits are generally devoid of dinocysts and acritarchs, suggesting significantly reduced salinity, in agreement with the depauperate trace fossil assemblages and early rift setting of the Bjarni Formation. However, they do contain bisaccates and a few other miospores. Both storm and wave-influenced deltaic strata in the Bjarni and Gudrid formations show small influxes of dinocysts and acritarchs, as would be expected where riverine influx is mitigated by wave or storm action. These strata contain trace fossil suites consistent with weakly stressed expressions of the Cruziana Ichnofacies, mostly lacking in vertical structures of inferred dwellings. Some bisaccates and limited numbers of dinocysts and acritarchs are found in cores of the Bjarni Formation, presumably reflecting deposition in river-influenced deltaic settings. Here, sedimentary structures dominate over bioturbation, with a highly stressed expression of the Cruziana Ichnofacies indicating high sedimentation rates and reduced salinity. One exception is the river-influenced deltaic strata of the Markland Formation, which contain samples overwhelmed by dinocysts and explained by progradation of the delta into deeper water. Finally, river-dominated deltaic deposits in the Bjarni Formation and a tidal channel succession of the Gudrid Formation lack dinocysts and acritarchs. These strata are dominated by sedimentary structures showing high sedimentation rates, ample current and wave activity, and rare trace fossils. In summary, well constrained paleoenvironmental results can be generally obtained by combining sedimentology and ichnology. Dinocyst and acritarch abundances generally parallel that of the marine trace fossils, but can be misleading in highly brackish settings where a paucity suggests nonmarine conditions. However, palynomorph counts can provide key evidence where macroscopic observations are not conclusive and can also highlight unique mixing of shallow and deeper water conditions.
Summary(Plain Language Summary, not published)
Analysis of rock cores from industry wells along the Labrador margin, eastern Canada provide new insights into paleoenvironmental changes during deposition of sediment from the Cretaceous through to the early Cenozoic. Different methodologies strengthen the interpretations, with quantitative fossil counts of microfossils tied to observations from the rock samples, including the presence of trace fossils (the preserved activity of animals, as opposed to fossilized remains).

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