|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.
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
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.
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.