Sandilands Formation Research Articles

2D petroleum systems modeling of Queen Charlotte Basin, offshore British Columbia, Canada

Abstract Two-dimensional petroleum systems models (PSMs) are calculated for a cross-section through Hecate Strait in order to estimate the timing of hydrocarbon generation, expulsion and migration in the Queen Charlotte Basin, offshore BC, Canada. Our PSMs account for dominant kerogen types in the potential source rocks, and predict timing of generation, expulsion, and migration patterns of petroleum. The PSMs highlight the importance of fault zones for migration and potential loss of petroleum through the seafloor. Rich marine Jurassic source rocks (Ghost Creek Formation, Sandilands Formation) are assumed to underlie Hecate Strait. We predict these source rocks to be overmature with more than 80% kerogen transformation into oil and gas (>27 kg petroleum/t rock), even if significant heating was only restricted to Tertiary rifting. Our PSMs predict that most of the petroleum has been expelled from the source beds, with some potential seepage loss to the surface. Cretaceous source rocks are thicker and more extensive with less structural deformation on Haida Gwaii. They have variable, but generally low total organic carbon (TOC) content. If time equivalent sediments exist under Hecate Strait, they are likely to be terrestrial, Type III kerogen. Basin-wide, these source rocks are not considered to be highly productive, and only where they are buried >4.1 km (an area of approximately 2700 km2) do we calculate a transformation ratio >50%. Only a minor amount of Cretaceous derived petroleum is anticipated to have migrated and accumulated in the overlying Skonun Formation sediments, which comprise the most extensive and suitable reservoir facies. No significant accumulations of hydrocarbon are expected from the terrestrial, Mio-Pliocene Skonun Formation source rocks. The area of the basin, where the anticipated transformation ratio exceeds 50% is less than approximately 1400 km2.

A new genus and species of polychelid lobster (Crustacea, Decapoda, Eryonidae) from the Early Jurassic (Hettangian) of British Columbia

A single specimen of decapod crustacean, preserved in ventral view and compressed, represents a new genus and species of eryonid lobster, Wrangelleryon perates. The discovery in Lower Jurassic (Hettangian) sediments of the Sandilands Formation in British Columbia represents the first occurrence of Eryonidae in North America and reinforces a global distribution of the family in the Jurassic. The occurrence in British Columbia on the Wrangellia terrane supports the lower latitude setting in which the species lived.

New Nassellaria (Radiolaria) from the Lower Jurassic of the Canadian Cordillera

New nassellarian radiolarians are described from the Insular and Intermontane belts of the Canadian Cordillera in British Columbia. Two new genera (Atalanta n.gen. and Nitrader n.gen.) and three new species (Atalanta emmela n.gen., n.sp., Atalanta epaphrodita n.gen., n.sp., and Nitrader montegufonensis n.gen., n.sp.) were found in Lower Jurassic carbonate concretions of the Sandilands Formation of the Queen Charlotte Islands and in a chert pebble extracted from a Cretaceous conglomerate of the Intermontane Belt possibly correlative with the Spences Bridge Group. The discovery of new taxa within two distinct belts of the Canadian Cordillera stresses their biostratigraphic significance.

Organic petrology and geochemistry of organic-rich rocks of the Late Triassic and Early Jurassic Sandilands and Ghost Creek Formations, Queen Charlotte Islands, British Columbia

Latest Triassic and Early Jurassic marine mudrocks on the Queen Charlotte Islands comprise a composite interval up to 600 m thick of organic-rich potential petroleum source rocks. These strata, assigned to the Sandilands and Ghost Creek Formations, are the only known significant potential petroleum source rocks on Canada's western continental margin. Regionally, the strata range from immature (0.33 R o,rand.) on northern Graham Island to overmature (>5 R o,rand.) on Moresby Island. Anomalously high levels of maturity exist in sediments adjacent to intrusive rocks and dyke swarms. The weight per cent total organic carbon (TOC) content of the strata ranges up to 6.1% and the organic matter as defined by Rock-Eval is predominantly types I and II, with hydrogen indexes ranging up to 589 mg HC/g C org. Petrographically, the organic matter is predominantly algal in origin, although minor to major amounts of vitrinite occur in many samples. Lateral variations in TOC closely reflect lateral variations in maturity. Based on the n-alkane distribution of the saturate fraction, the strata of the Sandilands Formation are divisible into two groups: (1) samples characterized by high concentrations of C 11 to C 31 with C 15 to C 17 dominant; and (2) samples characterized by n-alkanes of higher molecular weight with C 20 to C 23 dominant. In most samples, pristane is the dominant isoprenoid, but in all samples the pristane to phytane ratio is less than 2. Gas chromatography-mass spectrometry (GC-MS) of representative samples indicates the presence of both diasteranes and regular steranes with a predominance of C 29 regular homologues and a series of extended tricyclic terpanes from C 19 to at least C 35. There is a predominance of terpanes over steranes, the rearranged to regular sterane ratio is less than 1 and the 18α(H) trisnorhopane/17α(H) trisnorhopane + 18α(H) trisnorhopane ratio varies from 0.49 to 0.62. Samples from the Ghost Creek Formation have a similar n-alkane distribution to group 1 from the Sandilands Formation and GC-MS of two samples suggests less abundant terpanes and steranes than found in the Sandilands Formation. The carbon isotope composition of the organic fraction of all the strata is relatively homogenous, ranging from δ 13C, of −25 to −30% with a mean value of −28.8%; there is no consistent stratigraphic trend in δ 13C, nor is there significant correlation between δ 13C and any of the other geochemical indexes studied. In general, vitrinite-rich, terrestrially-derived organic matter is isotopically heavier than strata dominated by marine organic matter, the reverse from that found today, but similar to that reported during some oceanic anoxic events. Both organic petrology and geochemistry indicate that the organic matter is comprised of a mixture of terrestrial and marine organic matter with marine organic matter of algal origin predominating in most samples. The observed geochemical variation between samples is considered to reflect variations in maturity, relative abundance of terrestrial and marine organic matter and, to a lesser extent, biodegradation.

Evolutionary trends in Latest Norian through Hettangian radiolarians from the Queen Charlotte Islands, British Columbia

Uppermost Triassic and lowermost Jurassic (Hettangian) radiolarians from continuous sequences of the Sandilands Formation (Kunga Group), Queen Charlotte Islands, British Columbia, Canada, provide a rare glimpse into faunal patterns of evolution, radiation, extinction, and regeneration near a major stratigraphic boundary. The radiolarians are dated by Triassic ammonoids and conodonts, and Jurassic ammonites. Uppermost Triassic radiolarians are from strata equivalent to the Amoenum and Crickmayi ammonoid zones. Lowest Jurassic faunas are Planorbis Zone equivalent. The direction and pace of evolution in the highly diverse uppermost Triassic fauna is variable. Conservative taxonomic groups such as the pantanelliids and canoptids evolve gradually with only minor morphological change. Species extinctions occur regularly throughout the interval and across the boundary, with most genera ranging into the Jurassic. Current data confirm that Betraccium persists to the topmost Triassic but not into the Jurassic. Architecturally complex forms such as Squinabollela and Praecitriduma apparently have short ranges; they are common in uppermost Triassic beds but not found in the Lower Jurassic. Other radiolarian groups experience periodic bursts of radiation evidenced by multiple new species, and even new genera, most of which survive to the topmost Triassic but not beyond e.g. Ferresium and Laxtorum.. Finally, ancestral forms of some typical Lower Jurassic taxa are first recognized in uppermost Triassic beds e.g. Bipedis, Canutus, Crucella,, and Droltus.. Lowermost Jurassic radiolarians are easily distinguished from uppermost Triassic ones by their primitive appearance and low diversity, and by the absence of all distinctive uppermost Triassic taxa. Lower Hettangian faunas are characterized by latticed, spherical, irregularly spinose forms with poorly organized meshwork; non-distinctive spongy forms with spines; very simple nassellarians; and Archaeocenosphaera laseekensis. Pantanellium tanuense is the only pantanelliid species in Lower Hettangian collections.

The Triassic-Jurassic (T-J) boundary in Queen Charlotte Islands, British Columbia defined by ammonites, conodonts and radiolarians

In the Queen Charlotte Islands, on the Pacific shore of Birtish Columbia, Canada, Triassic-Jurassic boundary beds are present in several well-exposed sections of the Sandilands Formation. Triassic and Jurassic ammonoids, Triassic conodonts and Triassic and Jurassic radiolarians indicate the position of the boundary to within a few metres. The section may be essentially continuous across the boundary. The evidence suggests more or less simultaneous extinction of ammonoid, conodont and radiolarian faunas at the T-J boundary.

An Early Jurassic ichthyosaur from the Sandilands Formation, Queen Charlotte Islands, British Columbia

A partial skeleton, including a skull with part of the axial skeleton, part of a second skull, and fragments of ribs have been recovered from the Sinemurian of the Sandilands Formation exposed at Kennecott Point in the northwestern Queen Charlotte Islands. This material is the most complete Early Jurassic collection from North America reported to date; other occurrences include a forefin from the Nordegg Formation (Sinemurian) of Alberta positively identified as Ichthyosaurus (McGowan, 1978) and vertebral centra from the Nicely Formation (Pliensbachian), Oregon, not assigned conclusively to a genus (McGowan, 1978). The discovery of ichthyosaurs in the allochthonous insular belt of British Columbia adds weight to the contention that ichthyosaurs were cosmopolitan in their distribution (McGowan, 1978; Orr, 1986).

New biostratigraphic elements for dating upper Norian strata from the Sandilands Formation, Queen Charlotte Islands, British Columbia, Canada

Upper Norian radiolarians have been recovered from the basal Sandilands Formation on northwest Graham Island (Kennecott Point), Kunga Island, and Louise Island, Queen Charlotte Islands. Rare conodonts and ammonoids are associated with the radiolarians at several levels. At Kennecott Point over 90 m of the lower Sandilands Formation is coarser and less tuffaceous than is typical of the formation elsewhere and appears to represent continuous sedimentation. Diverse, well preserved radiolarians have been found in limestone concretions in the lower 75 m of section which has also yielded conodonts from the Epigondolella bidentata Zone (approximates Cordilleranus to basal Crickmayi ammonoid zones) and ammonoids from the Crickmayi Zone. At Kunga Island in the southern Queen Charlotte Islands, excellent radiolarian faunas have also been recovered from a 30 m interval beginning 80 m above the final occurrence of Monotis (=Cordilleranus Zone) and from a second 90 m interval lying structurally above the former that contains the upper Norian conodont Epigondolella bidentata at the base. Three preliminary radiolarian assemblages are recognized for upper Norian strata lying above the Monotis beds. Assemblage 1, the lower one, is tentatively correlated with the upper part of the Cordilleranus Zone; Assemblage 2 approximates the Amoenum Zone and Assemblage 3 is correlated with the Crickmayi Zone. The age of the Sandilands Formation is now confirmed to be late Norian and Hettangian as well as Sinemurian. Considering the record of apparently uninterrupted sedimentation, the section thickness and the excellent fossil recovery, the Sandilands Formation has been shown to contain an unusually thick upper Norian sequence and probably the Triassic-Jurassic boundary.

Biomarker characterisation and hydrous pyrolysis of bitumens from Tertiary volcanics, queen Charlotte islands, British Columbia, Canada

A number of bitumen samples have been recovered from vugs and fractures in outcropping Tertiary basalts of the Queen Charlotte Islands off the west coast of British Columbia, Canada. n-Alkanes and acyclic isoprenoids are not present and the polycyclic biomarker distribution of the four samples analyzed by GC and GC-MS has been altered. One sample contains no remaining recognizable biomarkers. Two bitumens were also obtained from Lower Jurassic potential source rocks, including one from the Sandilands Formation, which was considered previously to be the most likely source of the Tertiary bitumens. Although these two bitumens were also taken from outcrops, they are considerably less biodegraded. The Sandilands Formation bitumen contains 28, 30-bisnorhopanes and since these compounds were not detected in the Tertiary bitumens, there is no evidence from the initial results for a Sandilands Formation contribution to the hydrocarbons in the Tertiary basalts. The presence of 18α(H)-oleanane in the saturate fraction of two of the Tertiary bitumens from widely separated locations indicates that they are at least partially sourced from Tertiary organic matter. Because the distribution of biomarkers in some samples has been severely affected by biodegradation, the asphaltenes of the bitumens were hydrously-pyrolysed and the saturate fractions of the resulting pyrolysates analysed for possible additional information on the origin of the bitumens. The pyrolysates from the more degraded samples contain compounds not detected in the saturate fractions of the original bitumen and show some of the expected characteristics of the original non-degraded bitumen. However, the compounds most useful for correlation are not present in the pyrolysates apparently due to their non-incorporation into the kerogen macromolecule. Our results suggest that hydrous-pyrolysis of asphaltenes is of limited use in the correlation of biodegraded samples and in determining their origins.