Cynthia Riediger

Unusual polycyclic alkanes in Lower Cretaceous Ostracode sediments and related oils of the Western Canada Sedimentary Basin

Several series of unusual polycyclic alkanes (ranging from tricyclic to heptacyclic) have been identified as major components in extracts of Lower Cretaceous Ostracode Zone sediments of the Western Canada Sedimentary Basin. These compounds appear to be specific markers for the Ostracode Zone-sourced oils in the Lower Mannville Group reservoirs of the Provost area and may represent a new class of molecules whose natural distribution and biological significance remains to be determined. The stable carbon isotopic data of the tri-, tetra- and pentacyclic alkanes appear to be related to pristane and phytane, yet the significant isotopic depletion observed in the hexacyclic compounds suggests that they may be derived from different groups of organisms or different biosynthetic routes.

The Gordondale Member: designation of a new member in the Fernie Formation to replace the informal “Nordegg Member” nomenclature of the subsurface of west-central Alberta

New biostratigraphic data and revised lithostratigraphic correlations reveal that the current stratigraphic nomenclature for the Lower Jurassic portions of the Fernie Formation in the subsurface of west-central Alberta is inadequate. This paper introduces a new member, the Gordondale Member, for highly radioactive, fine-grained strata previously referred to as either the lower Fernie Formation, the Lower Fernie shelf limestone and clastics, the Nordegg Member, or the “Nordegg Member”. A new occurrence of a late Toarcian ammonite, which constrains the age of the top of the Gordondale Member, is also reported. The Hettangian to upper Toarcian Gordondale Member is an important hydrocarbon source rock and consists of dark brown, finely laminated, organic-rich, phosphatic and highly radioactive calcitic mudstones, calcilutites and fine-grained calcarenites. Fish fragments, pectinoid bivalves, Ostrea , belemnoids, ammonites, coccoliths and radiolarians are abundant. The Gordondale Member is laterally extensive and thins westward from a maximum thickness of approximately 50 m in the subsurface of west-central Alberta to 19 m at Pink Mountain in northeastern British Columbia.

Oil families in Mannville Group reservoirs of southwestern Alberta, Western Canada sedimentary basin

Abstract Lower Cretaceous oils in southern Alberta have been assessed using column chromatography, sulphur analysis, gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). These oils can be divided into four oil families, E, Q, EQ and F, on the basis of biomarker characteristics. Family E oils are characterized by low pristane/phytane ratios and a C 35 homohopane prominence. Family Q oils are identified by the presence of so-called “Q compounds” (Q/R ratio > 0.5) and have high C 27 diasterane to regular sterane ratios. Family EQ oils are a mixture of Family E and Family Q oils, with biomarker characteristics intermediate between these two families and low abundance of “Q compounds” (Q/R ratio 1.2) and no C 35 homohopane prominence. Oil-source rock correlation to available source rock data suggest that Family E oils are derived from the Upper Devonian-Mississippian Exshaw Formation and Family Q oils correlate to the Lower Cretaceous Ostracode Zone. Family F oils are likely derived from shales of the Upper Jurassic Rierdon Formation, however additional geochemistry data from this potential source rock are required to confirm this interpretation.

Sedimentology of the Upper Triassic Charlie Lake, Baldonnel and Pardonet Formations from Outcrop Exposures in the Southern Trutch Region, Northeastern British Columbia

Abstract Upper Triassic strata in the Trutch (94 G) NTS map area consist of the Charlie Lake, Baldonnel and Pardonet formations. These units comprise a mixed siliciclastic-carbonate succession, approximately 350 to 400 m thick. Sediments accumulated along a low gradient continental ramp deposited on the northwestern margin of Pangaea. Twenty-two lithofacies, deposited in distal offshore through supratidal settings are documented. Seven recurrent facies associations are identified in these strata; four reflecting deposition in continental to marginal marine settings, and three reflecting shallow to deep water marine deposition. Facies association 1 (FA1) consists of interbedded dolomitic mudstone/siltstone and dolomitic sandstone that was deposited in an intertidal flat depositional setting. Facies association 2 (FA2) consists of normally graded, trough cross-bedded to current ripple-laminated lenticular beds of mudclast-rich fine- to medium-grained sandstone, and was deposited by a series of small tidal channels. Facies association 3 (FA3) consists of well-sorted fine-grained sandstone beds characterized by high-angle tabular to wedge-shaped cross-beds, low-angle planar cross-beds, low-relief, translatent ripples and inversely graded lamina sets. FA3 is interpreted to represent deposition by a series of elongate, shore-parallel aeolian dunes. Facies association 4 (FA4) consists of a heterogeneous succession of solution collapse breccias, rooted, pedogenically-altered mudstone and siltstone, and wave-rippled very fine- to fine-grained sandstone. It is interpreted as ephemeral lacustrine and/or supratidal sabkha. Facies association 5 (FA5) consists of variably bioclastic quartzose sandstone, crinoidal packstone-grainstone and bivalve-dominated packstone beds. It is interpreted as a wave-dominated shoreface to foreshore on a shallow (inner) ramp. Facies association 6 (FA6) is dominated by very fine-grained calcareous sandstone and thin to thick-bedded bivalve-dominated wackestone, packstone and grainstone. It is interpreted as medial ramp (i.e., offshore transition to proximal offshore). Facies association 7 (FA7) consists primarily of organic-rich calcareous siltstone and mudstone (commonly with abundant carbonate concretions) and variably thick tightly packed bivalve packstone/grainstone beds. It is interpreted as outer ramp (proximal to distal offshore). Siliciclastic sediment in the study area was derived from a variety of sources, including fluvial input from the east-northeast, longshore drift from the north, and aeolian input sourced from marginal marine dune fields. Carbonate sediment in the study interval consists primarily of bioclastic detritus, although non-skeletal grains, particularly faecal pellets, and ooids are locally common. Skeletal carbonate material is dominated by disarticulated mollusc valves and crinoid skeletal debris but also includes ammonoids, articulate brachiopods, gastropods. Vertebrates (fish and reptiles) are also common.

Unusual polycyclic aromatic hydrocarbons in Lower Cretaceous Ostracode Zone sediments and related oils of the Western Canada sedimentary basin

Analyses of the aromatic hydrocarbon fractions of extracts of Lower Cretaceous Ostracode Zone sediments from the Western Canada sedimentary basin indicate the predominance of polycyclic hydroaromatic components. Most of these have not been previously reported in the literature, but are obviously diagenetically related to a new class of molecule whose natural distribution and biological significance remain to be determined. The components whose molecular structures have been confirmed, together with those for which tentative structural assignments are given, provide strong support for a pathway of progressive aromatisation of the presumed polyprenol precursors. These compounds appear to be specific markers for the Ostracode Zone sourced oils in the Lower Mannville Group reservoirs of the Provost area and may serve as excellent oil-source correlation parameters.

Hydrocarbon Source Rock Characterization and Thermal Maturity of the Upper Triassic Baldonnel and Pardonet Formations, Northeastern British Columbia, Canada

Abstract Numerous gas and oil fields are hosted in the Baldonnel and Pardonet formations of northeastern British Columbia, Canada. The source of the hydrocarbons in these fields has not been demonstrated using organic geochemical methods. However lithologic characteristics, interpreted depositional settings, and some published organic carbon content values have led to speculation that Upper Triassic strata of northeastern British Columbia, in particular the Pardonet Formation, may include important hydrocarbon source rocks. In order to assess the hydrocarbon source rock potential of Upper Triassic strata in northeastern British Columbia, nine outcrops and seven drillcores were measured, described and sampled for geochemical analyses. Geochemical analyses using Rock-Eval/TOC pyrolysis indicate a total organic carbon (TOC) content ranging from 0.03 to 2.08 weight percent for the Baldonnel (majority Geochemical data from outcrop and core suggest that the Pardonet Formation in northeastern B.C. had good to very good initial hydrocarbon potential, and has generated economically significant quantities of hydrocarbon. However, gas isotopic and gas compositional data, as well as biomarker analysis of oils and source rock extracts, are required to demonstrate whether the Pardonet, or some other, deeper unit, was the source of hydrocarbons found in Upper Triassic reservoirs in northeastern B.C. Mass balance calculations based on the geochemical data presented here for the Pardonet Formation, suggest that current initial in-place reserve estimates for Upper Triassic reservoir strata are four to five times less than expected. We speculate that some proportion of this calculated volume of hydrocarbons may have been retained within the Pardonet Formation itself, suggesting some potential as a fractured shale play. The Baldonnel Formation had only poor to fair initial hydrocarbon potential, and was not a significant hydrocarbon source.

Geochemistry of medium gravity crude oils in southern Alberta and northern Montana

ABSTRACT Petroleum geochemistry data from thirty-one oil samples from southern Alberta and northern Montana are used to distinguish oil families in this region. The highest quality oils (API gravity generally >35°, sulphur content End_Page 105------------------------