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Jeanne d’Arc Basin
The Jeanne d’Arc Basin is a relatively small passive-margin rift basin that underlies what is now the northeastern corner of the Grand Banks of Newfoundland. In the Late Cretaceous and early Paleogene, the basin formed an elongated depression where sediment accumulated in and along the margins of a shallow-shelf sea. Seismic and well data were used to examine the Late Cretaceous and Paleogene evolution of the basin and to formally revise the existing stratigraphic classification scheme. In the Late Cretaceous, the western margin of the basin was characterized by a well-developed shelf and slope system comprised of the sand-prone Otter Bay and Fox Harbour members and the distally equivalent shale-prone Red Island and Bay Bulls members, respectively. These members record two main progradational episodes that are separated by a regional unconformity and a thick shale interval corresponding to the Bay Bulls Member. East of the shelf-slope system, Upper Cretaceous shale and sparse sandstone of the Dawson Canyon Formation and chalk of the Petrel Member and Wyandot Formation were deposited in a relatively condensed section. In the early part of the Paleogene, two main sandstone units, herein named the Avondale and South Mara members, were deposited east of the well-developed latest Cretaceous slope in the lower part of the Banquereau Formation. The Avondale Member corresponds to small sand-prone submarine fans deposited on the basin floor in the early Paleocene. The submarine fans were fed primarily by two canyons that incised the western margin of the basin, eroding the Late Cretaceous shelf and slope. Also in the Paleocene, siliceous shale and siltstone of the Tilton Member were deposited above bathymetric highs along the western and southern basin margins. The exact temporal relationship between the Tilton and Avondale members is poorly understood. The South Mara Member was deposited in the latest Paleocene and early Eocene. In the southern parts of the basin, it forms a regressive sandstone unit above the Tilton Member, deposited during a period of renewed shelf-slope progradation. In the central and northern parts of the basin, the South Mara Member corresponds to small, sand-prone submarine fans, similar to those deposited in the early Paleocene.
The Jeanne d’Arc rift basin is located on the Grand Banks of Canada, offshore Newfoundland (Figs. 1 and 2). This basin is one of the most important oil provinces of Canada with four oil-producing fields: Hibernia, Whiterose, Terra Nova and North Amethyst. The basin developed during the breakup of the supercontinent Pangea during the Mesozoic (e.g. Louden, 2002; Seton et al., 2012; Withjack et al., 2012a), and it is part of the more extensive eastern North American rift system (Fig. 1).
Figure 1. a) Map of the eastern North America rift system showing location of the Jeanne d’Arc basin (blue polygon) and key tectonic features. Inset shows position of the rift system relative to Pangea during Late Triassic time. b) Regional transect from offshore Canada (location given by dashed line in a) showing key tectonostratigraphic features. Modified from Withjack et al. (2012).
Figure 2. a) Southern half of map shows faults cutting prominent Middle Jurassic reflection, and northern half shows faults cutting Aptian/Albian sequence (modified from Withjack and Schlische, 2005). b) Regional cross section (location given by red line in a) showing tectonostratigraphic packages (capital letters and colors) and main structural features. Dashed lines and gradational colors show uncertainty. Regional cross section is based on seismic line HBV83-195 (Appendix 3), modified from Withjack and Schlische, (2005), and line B, this study.
The onset of rifting in this rift system was relatively synchronous and began by the Late Triassic, but the cessation of rifting and onset of seafloor spreading was diachronous, ranging from latest Triassic in the southern segment (southeastern United States), to Early Jurassic in the central segment (northeastern United States and southern Canada) and Late Cretaceous in the northern segment (eastern Grand Banks of Canada) (Withjack et al., 1998; Schlische et al., 2002; Withjack and Schlische, 2005; Withjack et al., 2012a). In the Jeanne d’Arc basin, some authors suggest that rifting occurred in two or three distinct episodes with intervening periods of thermal subsidence (e.g. Hubbard et al., 1985; Tankard and Welsink, 1987; Hubbard, 1988; Sinclair, 1988; Grant and McAlpine, 1990; McAlpine, 1990; Sinclair and Riley, 1995; Sinclair et al., 1999) (Fig. 3).
Figure 3. Lithostratigraphic chart of the Jeanne d’Arc basin highlighting tectonostratigraphic packages interpreted in this study (capital letters) and tectonic stages interpreted in previous studies. Modified from Sinclair et al. (1999) and Magoon et al. (2005). Results from my thesis work will show that Packages B, C and D are all syn-rift units.
Geologic and structural background
The Jeanne d’Arc basin is a funnel-shaped, 25-80 km wide, half graben that deepens and widens northward (Tankard and Welsink, 1987) (Fig. 4). The NNE-striking, Edipping Murre fault in the south and Mercury fault in the north bound the basin on the west (e.g. Enachescu, 1987; Tankard and Welsink, 1987). Intrabasinal faults generally strike NW-SE and detach on salt (e.g. Tankard and Welsink, 1987; Withjack and Schlische, 2005). The study area, in the northwestern corner of the basin, lies between the Mercury and the Murre faults. The Flying Foam anticline overlies the Murre fault in the north; in contrast, in the south, several basement-involved faults occur between the Mercury and the Murre faults.
Pre-rift rocks consist of Paleozoic igneous and metamorphic rocks from the Avalon and/or Meguma terrains (Tankard and Balkwill, 1989) (Fig. 5). Several orogenies (Ordovician Taconic, Devonian Acadian and Carboniferous-Permian Alleghanian) preceded rifting (Naylor, 1971; Rodgers, 1971; Murphy and Keppie, 1998; Williams, 1999; Cocks and Torsvik, 2011). The overlying sedimentary section (Fig. 5) consists of Late Triassic – Early Jurassic siliciclastic rocks from the Eurydice Formation and salt from the Argo Formation (e.g. Jansa and Wade, 1975; McAlpine, 1990). The overlying Early Jurassic to Late Jurassic section consists of dolomites, limestones, calcareous shales and some sandstones from the Iroquois, Downing, Voyager and Rankin formations (e.g. McAlpine, 1990; Sinclair et al., 1999). Within the Rankin Formation, an organicrich shale (the Egret Member) sources the hydrocarbons of the Jeanne d’Arc basin (e.g. Magoon et al., 2005). The overlying latest Jurassic – Early Cretaceous section consists of sandstones, shales and some limestones from the Jeanne d’Arc, Avalon, Whiterose, Catalina, Hibernia, Nautilus and Ben Nevis formations (e.g. McAlpine, 1990; Sinclair, et al., 1999). Sandstones from the Hibernia and Avalon formations are the main reservoir rocks in the Jeanne d’Arc basin (e.g. Magoon et al., 2005). Finally, the Late Cretaceous – Cenozoic section consists of shales and some sandstones from the Dawson Canyon and Banquerau formations (e.g. Deptuck et al., 2003). In general, studies suggest that the Late Triassic – Early Jurassic and the latest Jurassic – Early Cretaceous sections correspond to periods of active rifting, whereas the Early Jurassic to Late Jurassic section represents a period of tectonic quiescence (e.g. Hubbard et al., 1985; Tankard and Welsink, 1987; Hubbard, 1988; Sinclair, 1988; Grant and McAlpine, 1990; McAlpine, 1990; Grant and McAlpine, 1990; McAlpine, 1990; Sinclair and Riley, 1995; Sinclair et al., 1999; Welsink and Tankard, 2012). The Late Cretaceous – Cenozoic section corresponds to post-rift rocks that accumulated during the thermal subsidence of the basin (e.g. McAlpine, 1990; Sinclair, et al., 1999). This study focuses on the Late Triassic to Early Cretaceous sections.
Lithostratigraphic classification
The only formally defined stratigraphic units in the Upper Cretaceous through Paleogene succession in the Jeanne d’Arc Basin are the Dawson Canyon, Wyandot and Banquereau formations, and the Petrel Member of the Dawson Canyon Formation. These units were originally defined for Scotian Shelf rocks (McIver, 1972), but their use was later extended to the timeequivalent strata of the Grand Banks (e.g., by Amoco Canada Petroleum and Imperial Oil, 1973a; Jansa and Wade, 1975a, b). Later workers (e.g., Boudreau et al., 1986; Sinclair, 1988; McAlpine, 1990; de Silva, 1993; Agrawal et al., 1995; Deptuck, 1998) used informal nomenclature to subdivide the Dawson Canyon, Wyandot, and Banquereau formations in the Jeanne d’Arc Basin. This nomenclature, however, has not been applied consistently (e.g., ‘‘South Mara Member,’’ Sinclair, 1988; ‘‘South Mara unit,’’ McAlpine, 1990; ‘‘South Mara Formation,’’ Deptuck, 1998), and thus, a formally revised lithostratigraphic classification is proposed in this paper.
Dawson Canyon Formation
The Dawson Canyon Formation (McIver, 1972) consists of a variety of sedimentary rocks, ranging from fine- and coarse-grained clastics to chalky carbonates (Figures 4,5). On the Scotian Shelf, for which the formation was originally defined, its lower boundary is conformable and gradational and lies just below the Petrel Member (defined below). Its upper boundary is defined as the base of the nearly ubiquitous chalky Wyandot Formation (Jansa and Wade, 1975b). In the Jeanne d’Arc Basin, where the Wyandot Formation is only locally developed, the accepted convention is to place the upper boundary of the Dawson Canyon Formation at the top of the Fox Harbour Member (described in a subsequent section) that coincides with a prominent spike on gamma-ray curves (Figure 3b). Where the gamma-ray spike is absent, the boundary is defined biostratigraphically as the Cretaceous–Tertiary boundary, which closely coincides with the top of the Wyandot Formation and/or the base of the Tilton and Avondale members (described in subsequent sections).
Figure 4. Generalized lithochronostratigraphic chart for the Upper Cretaceous and the lower part of the Paleogene stratigraphic succession in the Jeanne d’Arc Basin (modified from Sinclair, 1987). Absolute ages on the timescale are from Gradstein et al. (1995) and Berggren et al. (1995). OB = Otter Bay; FH = Fox Harbour; SM = South Mara; Mb = Member; Fm = Formation.
Following Boudreau et al. (1986), Sinclair (1988), and de Silva (1993), we subdivide the Dawson Canyon Formation into the Petrel, Otter Bay, and Fox Harbour members. We also formally define two new stratigraphic units: the Red Island and Bay Bulls members (Figures 4,5). The Otter Bay, Fox Harbour, Red Island, and Bay Bulls members are restricted to the western margin of the Jeanne d’Arc Basin. Except for the identification of the Petrel Member, we do not subdivide the Dawson Canyon Formation farther east.
Figure 5. (a) Lithostratigraphic correlation of the Petrel, Otter Bay, Fox Harbour, Red Island, and Bay Bulls members (Mb) of the Dawson Canyon Formation, and the Tilton and South Mara members (Mb) of the Banquereau Formation along the western margin of the basin. Datum is a prominent gamma-ray spike that defines the top of the Fox Harbour Member. All wells are arranged from south to north (left to right), with Hibernia wells arranged from west to east (proximal to distal).
Wyandot Formation
The Wyandot Formation, consisting of pelagic coccolithic-foraminiferal chalks and marlstones, is widely distributed on the Scotian Shelf, but developed only locally in the Jeanne d’Arc Basin. The formation, originally termed the ‘‘Wyandot chalk’’ by McIver (1972), was formally defined by Jansa and Wade (1975b, p. 89), who described it as ‘‘a dominantly chalk formation with marl and calcareous shale interbeds’’.
In the Jeanne d’Arc Basin, the Wyandot Formation is thickest to the north, near Botwood G-89, Adolphus D-50 and 2K-41, and Conquest K-09, an area outlined in Figure 6b. In this area, the formation is similar to the type section on the Scotian margin. Gamma-ray logs have an overall upward-decreasing character, corresponding to a basal marl and calcareous shale interval passing upsection into an interval of cleaner chalky limestones (e.g., at Adolphus D-50, 2674–2910 m). A Santonian shale unit (part of the Dawson Canyon Formation) commonly underlies the Wyandot Formation (e.g., at Adolphus D-50, 2910–2945 m; Doeven, 1983).
At Botwood G-89, the upper boundary of the formation is sharp and unconformable (2265 m). In other locations, the chalky limestone is overlain by a thin Maastrichtian shale (e.g., at Adolphus D-50, 2660–2674 m), which is, in turn, unconformably overlain by Danian shale (Doeven, 1983). A calculated sedimentation rate of 1.5–2.0 cm/k.y. led Doeven (1983) to suggest that late Santonian to middle Campanian chalk deposition at Adolphus D-50 took place in deeper water, farther offshore than correlative chalk on the Scotian margin.
South of Botwood G-89, the Wyandot Formation is much thinner (e.g., at North Ben Nevis P-93, 2176– 2184 m) or absent (e.g., at West Ben Nevis B-75). Some wells penetrate a relatively thick Coniacian limestone that could also be regarded as the Wyandot (e.g., at South Mara C-13, 2099–2156 m, shown in Figure 4), although it appears to be older than the chalky limestone recognized elsewhere.
Banquereau Formation
The Banquereau Formation, formally defined by McIver (1972), consists generally of deep-neritic to bathyal shales with minor chalks, siliceous mudstones, and locally developed sandstone units (McAlpine, 1990). The formation extends for the entire Tertiary succession above the Wyandot Formation and until now has never been formally subdivided.
In the Jeanne d’Arc Basin, an interval containing outer neritic to bathyal sandstone and siltstone is found stratigraphically above the Dawson Canyon and Wyandot formations, in the lower parts of the Banquereau Formation (Thomas, 1994). McAlpine (1990) designated this sandy interval, including intercalated shale-prone intervals, as the South Mara unit. In this study, we recognize two distinct sandstone units deposited near or at the base of the Banquereau Formation (Figures 4,6). The lower sandstone unit is defined here as the Avondale Member, and the upper sandstone unit is designated the South Mara Member, a formalization of the 31-m-thick lower Tertiary sandstone unit originally described by Sinclair (1988) at South Mara C-13 (1864–1895 m).
In addition to the sandstone members, we formally define a siltstone and shale dominated unit found directly above the Dawson Canyon Formation. This unit, herein referred to as the Tilton Member of the Banquereau Formation, was originally described by the CanadaNewfoundland Offshore Petroleum Board (1998) as the ‘‘Paleocene porcelaneous mudstone.’’ It appears to be more lithologically diverse than their informal nomenclature implies; hence, it is renamed here.
Figure 6. Schematic diagram illustrating the inferred stratigraphic relationships between the different members and formations identified in this and previous studies. Dashed lines are unconformities and their correlative conformities identified from wells and seismic ties. Note that the Otter Bay unconformity is located above the Otter Bay sandstones and represents the probable stratigraphic situation in the southern parts of the basin, where a prominent toplap surface is observed near Cormorant N-83. Near Hibernia, the Otter Bay unconformity may be located in or even below the sandstones of the Otter Bay Member. Similarly, the Fox Harbour unconformity is shown above the Fox Harbour sandstones, but in some areas, the unconformity may be located in the upper parts of the Fox Harbour Member. This uncertainty is caused by sparse palynology assemblages in the Fox Harbour and Otter Bay members. N.B.N. = North Ben Nevis.
Data source: Evolution of the Jeanne d’Arc basin, offshore Newfoundland, Canada: 3D seismic evidence for >100 million years of rifting. Elena Serrano Suarez, 2013
Revised Upper Cretaceous and lower Paleogene lithostratigraphy and depositional history of the Jeanne d’Arc Basin, offshore Newfoundland, Canada. Mark E. Deptuck, R. Andrew MacRae, John W. Shimeld, Graham L. Williams, and Robert A. Fensome. AAPG Bulletin, v. 87, no. 9 (September 2003), pp. 1459–1483
Следующий Бассейн: Flannan - Lewis