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TitreDeltaic and fully marine settings interpreted from conventional core, offshore Labrador, Canada
AuteurDafoe, L T; Williams, G L; Dickie, K
SourceGeoconvention 2015, abstracts; 2015 p. 1-3
Année2015
Séries alt.Secteur des sciences de la Terre, Contribution externe 20150375
ÉditeurCanadian Society of Petroleum Geologists
RéunionGeoconvention 2015; Calgary, AB; CA; mai 4-8, 2015
Documentlivre
Lang.anglais
Mediapapier; en ligne; numérique
Formatspdf
ProvinceRégion extracotière de l'est; Terre-Neuve-et-Labrador
SNRC3; 13I; 13N; 13O; 13P; 14
Lat/Long OENS -64.0000 -52.5000 60.0000 53.0000
Sujetssédiments deltaïques; dépôt deltaïque; sédiments marins; sédiments marins; milieux marins; Formation de Markland ; Formation de Bjarni ; Formation de Gudrid ; géologie marine; sédimentologie
Illustrationslocation maps; photographs
ProgrammeSystèmes pétroliers de Baffin, GEM2 : La géocartographie de l'énergie et des minéraux
LiensOnline - En ligne
Résumé(disponible en anglais seulement)
Previous work in the Labrador Sea has led to development of the Labrador Sea Atlas (Bell, 1989), as well as lithostratigraphic, paleoenvironmental, and seismic interpretations involving the Saglek and Hopedale basins (e.g., Miller and D¿Eon, 1987; Dickie et al., 2011; Jauer et al., in press). Dickie et al. (2011) revised the stratigraphic framework for the Labrador margin with a focus on seismic and biostratigraphic identification of unconformities. Despite these detailed studies, the work thus far has not assessed the data from a rigorous sequence stratigraphic approach. A sequence stratigraphic framework can provide an understanding of the nature of horizons, stratal packages and provide a predictive framework for understanding the stratigraphic succession. Our initial work on a sequence stratigraphic framework that can be used as an analogue to understand the succession in Baffin Bay involves the assessment of sedimentary cores from offshore Labrador to better understand the paleoenvironments of deposition.

Methods
Available sedimentary Mesozoic and Cenozoic conventional cores from wells offshore Labrador (Fig. 1) were analyzed in terms of lithology, sedimentary structures, degree of bioturbation, trace fossil suites and presence of fossil material. These data were used to interpret depositional environments in samples from the Bjarni, Markland and Gudrid formations. As fossil material was extremely rare within the core materials, sedimentological and trace fossil observations were primarily used to assess depositional settings. Samples were collected for palynological analysis to provide additional biostratigraphic ages and to augment the paleoenvironmental interpretations. While core materials are limited, they provide ground truth to depositional environments that can be extrapolated vertically in the wells and tied to seismic facies.

Results
Offshore Labrador conventional cores sampled the Bjarni, Markland (Freydis), and Gudrid formations with the Gudrid Formation sampled in southern Saglek Basin and the Markland and Bjarni formations sampled across the Hopedale Basin and into the southern Saglek Basin.

In the Bjarni Formation, massive to cross-bedded sandstones and conglomerates are present in Skolp E-07 (core 6), Ogmund E-72 (core 3) and North Bjarni F-06 (core 1) and are interpreted as alluvial to fluvial successions. In addition to these coarse-grained facies, heterolithic sandstone and shales and shale-dominated facies preserve sedimentological and trace fossil evidence of marine deposition. Early Bjarni sediments in both the Herjolf M-92 (core 2) and Hopedale E-33 (core 1) wells are characterized by dark grey shales with a low abundance and diversity trace fossil suite including grazing traces primarily observed from within sideritized intervals (Phycosiphon, Helminthopsis, Chondrites and Schaubcylindrichnus). Coal fragments are also present. The fine-grained nature of the sediment, presence of coaly material and trace fossil suite predominated by grazing traces suggests deposition in a restricted bay setting with poor oxygenation and little coarse clastic input. Heterolithic sandstones and shales are prevalent in Ogmund E-72 (core 2), Herjolf M-92 (core 1), Bjarni H-81 (core 1), Roberval K-92 (core 2), and North Leif (cores 1 and 2). These deposits are characterized by: cross bedding; planar lamination; soft-sediment deformation; thick mudstone beds of likely hypopycnal origin; unbioturbated, carbonaceous mudstone beds; microfaulting; organic detritus; coal fragments; and common sideritized intervals. The trace fossil suites comprise a generally low abundance and diversity of trace fossils with grazing traces most common. There is also evidence of opportunistic colonization, and overall the deposits are characterized by a stressed Cruziana ichnofacies. Based on the sedimentological and ichnological evidence, these sediments were deposited in delta front (possibly distributary channels) and prodeltaic settings. Differences in the nature of the sediments suggest that some core intervals represent river-dominated deltaic deposition while others reflect wave-influenced deposition.

The Markland Formation is characterized by shaly successions and sandstone-dominated intervals (Freydis Member). Dark grey, laminated shales in Roberval K-92 (core 1) are devoid of trace fossils, but green mineralizations suggest possible reduced conditions and a likely distal marine (bathyal) setting during early Markland deposition. Significant thicknesses of shales, sandy mudstones and muddy sandstones characterize cores 1-5 of the Skolp E-07 well (Fig. 2A). Here, intense bioturbation and trace fossil suites of the Cruziana ichnofacies indicate alternating deposition in lower shoreface to outer shelf successions in the early Markland. Similar to successions from the Bjarni Formation, heterolithic sandstone and shales in Gilbert F-53 (core 1) show massive to cross-bedded units with scattered trace fossils including: Phycosiphon, Helminthopsis, Rhizocorallium, Ophiomorpha, Planolites and Chondrites suggestive of a stressed Cruziana ichnofacies. This core interval is interpreted as a river-dominated deltaic succession of the Freydis Member.

The late Gudrid Formation is only sampled by two conventional core intervals from the southern Saglek Basin reflecting two different depositional settings. Core 1 of Snorri J-90 consists of fine-grained, cross-bedded sandstones with coal fragments, wave ripples and mudstone rip-up clasts show varying degrees of bioturbation from 0 to 80% (Fig. 2B, C). The trace fossil succession is dominated by grazing traces (Helminthopsis) and deposit-feeding structures including intense burrowing by Macaronichnus and Spirophyton trace-makers. This weakly stressed Cruziana ichnofacies suggests deposition within a wave or storm-dominated delta front. In the Karlsefni A-13 well (core 1), sandy, wave-rippled mudstones are highly bioturbated, but some beds of carbonaceous shale and sandstone remain unburrowed or show opportunistic colonization. The trace fossil suite is predominated by Phycosiphon and Helminthopsis with Chrondrites, Planolites, Rhizocorallium, Diplocraterion, Skolithos and Schaubcylindrichnus also common. Here, the deposits are interpreted to reflect a deltaic-influenced proximal inner shelf to prodelta setting.

Conclusions
While non-marine deposition in the Bjarni Formation is well known, indications from a number of core intervals show shallow marine deposition in deltaic and restricted marine settings across the Labrador shelf as early as the Aptian. Trace fossil occurrences suggest the presence of both wave-influenced and river-dominated successions which suggest varying degrees of marine and fluvial influence. Marine deposits in the Markland Formation are expected; however, the presence of bathyal shales above the Bjarni Formation in Roberval K-92 suggests a major flooding event. The thickness of fluctuating inner and outer shelf deposits in Skolp E-07 indicates that sedimentation rates kept pace with subsidence at that time. Finally, the late Gudrid Formation appears to be influenced by deltaic deposition in the southern Saglek Basin, which contrasts significantly with previous interpretations of bathyal deposition in the case of the Karlsefni A-13 well (Miller and D'Eon, 1987). This assessment of the core materials from the Labrador margin has refined the paleoenvironmental interpretations and allows us to extrapolate this understanding within the wells and to the seismic data.
Résumé(Résumé en langage clair et simple, non publié)
Intervalles de base conventionnelle de 15 puits au large du Labrador ont été étudiés en détail, échantillonné pour datation biostratigraphique et seront liées à un réseau sismique régional. Ces carottes illustrent une tranche de temps (au Crétacé et au début du Cénozoïque) dans le développement du bassin sédimentaire de l'offshore et la variété des marins peu profonds et paramètres sédimentaires entièrement marins présent dans ces moments. Grâce à l'analogique, ces données peuvent fournir aperçus de la géologie de la baie de Baffin et le potentiel pour source et réservoir roches dans la zone.
GEOSCAN ID297483