SOURCE ROCK ANALYSIS OF THE LOWER JURASSIC NORDEGG MEMBER AND OIL-SOURCE ROCK CORRELATIONS, NORTHWESTERN ALBERTA AND NORTHEASTERN BRITISH-COLUMBIA

The "Nordegg Member" comprises dark grey to black, variably phosphatic limestone and calcareous mudstone, and is easily identified in the subsurface of Alberta and British Columbia by a high gamma-ray log response. Rock-Eval/TOC analyses of more than 200 samples yielded Total Organic Carbon (TOC) contents up to 28%, Hydrogen Index (HI) values up to 800 mg HC/g TOC, and Tmax values of from less than 430-degrees-C to greater than 460-degrees-C. A plot of HI vs. OI (Oxygen Index) indicates Type I/II kerogen in the "Nordegg Member". Petrographic analyses indicate a high abundance of amorphous material (bituminite) and alginite, which is typical of Type I/II kerogen. Inertinite, phosphate, and framboidal pyrite are less abundant. Thermal maturity, based on Rock-Eval Tmax data, increases to the southwest, in a pattern that generally parallels the edge of the disturbed belt. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analysis of "Nordegg" core extracts yielded low pristane/phytane ratios (generally < 1.0), low Ts/Tm, low diasteranes/regular steranes and a predominance of hopanes over steranes. The biomarker signatures and lithotypes of the "Nordegg" indicate an anoxic, and possibly hypersaline, carbonate depositional environment. On the basis of these data, and also of tectonic evidence indicating that terrane obduction was occurring to the west during Early Jurassic time, we suggest that the "Nordegg" was deposited in a silled basin with restricted oceanic circulation. Biomarker signatures of "Nordegg" extracts are positively correlated with some oils contained in Upper Triassic reservoirs.