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TitleNew insights into the age and nature of lower Paleozoic cores from the Labrador margin, offshore eastern Canada
AuthorBingham-Koslowski, NORCID logo
Source20th International Sedimentological Congress ISC, abstracts volume; 2018 p. 1
Alt SeriesNatural Resources Canada, Contribution Series 20180114
PublisherInternational Sedimentological Congress
MeetingISC2018 - 20th International Sedimentological Congress; Québec, QC; CA; August 13-17, 2018
Mediapaper; digital
File formatpdf
ProvinceNewfoundland and Labrador; Eastern offshore region; Northern offshore region
NTS14; 15
Lat/Long WENS -65.0000 -52.0000 61.0000 56.0000
Subjectssedimentology; paleontology; continental margins; continental shelf; core samples; core descriptions; thin section microscopy; depositional environment; bedrock geology; lithology; sedimentary rocks; sedimentary structures; fossils; microfossils; palynology; Labrador Margin; Gudrid H-55 Well; Freydis B-87 Well; Indian Harbour M-52 Well; Roberval K-92 Well; Iapetus Ocean; Phanerozoic; Paleozoic; Ordovician
ProgramGEM2: Geo-mapping for Energy and Minerals Baffin Region Atlas
Released2018 08 01
AbstractThe lower Paleozoic of the eastern Canadian Atlantic margin is poorly understood due to the scarcity of offshore samples and the occurrence of diagenetic alteration and tectonic deformation. These strata underlie the Mesozoic rift succession of the Hopedale Basin along the Labrador margin, offshore eastern Canada. Paleozoic-aged rocks were penetrated by seven industry wells (Freydis B-87, Gudrid H-55, Hopedale E-33, Indian Harbour M-52, Roberval K-92, South Hopedale L-39, and Tyrk P-100), with six corresponding conventional core samples available from four of the wells (Gudrid H-55, Indian Harbour M-52, and two cores from each Freydis B-87 and Roberval K-92). These six cores and their associated thin sections are described as part of a regional study aimed at understanding the lower Paleozoic depositional environments that existed along the western margin of the Iapetus Ocean. Five of the six cores are carbonates with one of the cores from Freydis B-87 and the core from Indian Harbour M-52 being composed of limestone, whereas the cores from Gudrid H-55 and Roberval K-92 are dolostones.
The uppermost core recovered from Freydis B-87 is siliciclastic and is dominated by mudrock with cross-bedded and laminated sandstone beds. The second core consists primarily of fossiliferous wackestone with fragments of undifferentiated shells, brachiopods, echinoids, bivalves, gastropods, trilobites, and bryozoans. Ostracods, sponge spicules, and calcimicrobes are also observed in thin section. The Indian Harbour M-52 core consists predominantly of limestone with dolomite occurring in localized patches and along stylolites. Fragments of shells, bivalves, echinoids, gastropods, trilobites, and brachiopods, along with radiolarians and sponge spicules are also present. The core from Gudrid H-55 and the two cores from Roberval K-92 are composed entirely of fabric-destructive diagenetic dolomite resulting in no identifiable fossil components. Ordovician scolecodonts, chitinozoa, and acritarchs were recovered using conventional cores and cuttings from six of the seven Paleozoic wells on the Labrador margin with varying degrees of preservation. No identifiable lower Paleozoic palynomorphs were found in Roberval K-92; however, given the lithological similarities with Gudrid H-55 and its proximity to the other Paleozoic wells, it is likely also Ordovician in age.
The diverse fossil assemblages observed in the lower core from Freydis B-87 and the core from Indian Harbour M-52 implies that these sediments were deposited under normal marine conditions, with low to moderate energy levels. The high abundance of fossils in the Freydis B-87 carbonate core and the presence of calcimicrobes suggests a somewhat shallow depositional environment, at, or near the base of the photic zone. The identification of radiolarians, and the overall lower fossil content noted in Indian Harbour M-52 reflects its deposition in a deeper-water, open marine environment. A transition from carbonate to siliciclastic sediments in Freydis B-87 signifies the termination of the carbonate factory later in the Ordovician and is likely correlative to a major, possibly eustatic, shift in depositional conditions.
Summary(Plain Language Summary, not published)
Six conventional lower Paleozoic cores and associated thin sections from the Labrador margin, offshore eastern Canada as part of a regional Paleozoic study. Five of the six cores were composed of carbonates with two cores consisting of limestone and the remaining three, composed entirely of dolomite. Fossils identified include fragments of shells, bivalves, echinoids, gastropods, trilobite, bryozoans, and brachiopods, along with radiolarians, ostracods, sponge spicules, and calcimicrobes. Preliminary interpretations suggest that the sediments composing the limestone cores were deposited under normal marine conditions in somewhat shallow to deep water depths.

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