A reconnaisance of organic maturation and petroleum source potential of Phanerozoic strata in northern Yukon and northwestern District of Mackenzie
Creators: name: Link, Christine Marie
Publisher: name: University of British Columbia
Year: 2010

description: The level of organic maturation, thermal history and petroleum source potential of Phanerozoic strata in northern Yukon and northwestern District of Mackenzie have been investigated by measurement of vitrinite (% Rorand) and graptolite (% Romax) reflectance, conodont alteration index (CAI) and Rock-Eval pyrolysis. The strata in general have lower maturity levels in southern Mackenzie Delta, Peel Plateau and Eagle Plain than in the Richardson and Ogilvie Mountains. The level of maturation varies from graptolite reflectance values of 4.0% to 6.5% Romax and CAI values of 3.5 to 5 in Upper Cambrian to Lower Devonian strata whereas vitrinite reflectance ranging from 0.2% to 3.75% Rorand occur in Middle Devonian to Upper Cretaceous strata. Time-averaged numerical modelling of measured maturation gradients (0.10 to 0.32 log Rorand/km) suggest paleogeothermal gradients on the order of 20 to 45°C/km in southern Mackenzie Delta and Peel Plateau, from 10 to 20°C/km in central Eagle Plain and from 20 to 45°C/km adjacent the Richardson and Ogilvie Mountains. The higher maturity levels in mountainous areas reflect higher maturation gradients and, in the Richardson Mountains, deeper burial due to rapid subsidence caused by the foundering of grabens within the Richardson Fault Array. Anomalously high maturation values (0.92% to 1.60% Rorand) measured in Lower Cretaceous strata on the Campbell Uplift are interpreted to reflect high paleoheat flow associated with basement uplift. Average TOC contents are generally low to moderate (0.1 to 2.0%) but organic-rich intervals occur throughout the studied succession. TOC values up to 14.5% are present in the Upper Cretaceous Eagle Plain Group, values up to 9.5% occur in the Middle Devonian Canol Formation and Upper Cambrian to Lower Devonian Road River Group and values up to 5.0% are present in the Lower Cretaceous map unit Kwr and Mount Goodenough Formation, the Lower Cretaceous and Jurassic Husky Formation, the Jurassic Porcupine River Formation and the Upper Carboniferous Blackie and Hart River Formations and the Ford Lake Shale. The organic matter (OM) is dominantly type III except for minor amounts of type I and II in Lower Paleozoic strata and a mixture of type II and III in parts of Middle Devonian, Carboniferous, Jurassic and Lower Cretaceous strata. The quality of organic matter varies significantly (QOM; 0.01 to 6.1 mg HC/g Corg) as a result of variation in organic maturity, the type of OM and, in some cases, migration. Average QOM values are generally low to moderate (0.01 to 1.5 mg HC/g Corg) and, along with low to moderate Hydrogen Index values (&lt;300 mg HC/g Corg), suggest poor to moderate petroleum source potential. Relatively few examples of potential oil prone source rocks occur, but these include parts of the Road River Group, the Hare Indian, Canol, Hart River, Blackie, Mount Goodenough and Arctic Red River Formations, the Ford Lake Shale, unnamed Carboniferous unit and map unit Kwr. Gas prone source rocks comprise parts of the Blackie, Porcupine River, Husky, Mount Goodenough and Arctic Red River Formations and the Bug Creek and Eagle Plain Groups and map unit Kwr. With respect to petroleum generation, Upper Cretaceous strata are generally immature. Lower Cretaceous to Permian strata are immature to mature, Carboniferous strata are immature to overmature, and Devonian and older rocks are mature to overmature. The timing of hydrocarbon generation from source rocks in the study area varied substantially both laterally and stratigraphically as a result of variations in the timing and magnitude of the maximum depths of burial. The variation in source rock quality appears to closely reflect the interpreted depositional environment of some of the strata which facilitates the interpretation of regional extent of. potential hydrocarbon source rocks. A correlation of graptolite and vitrinite reflectance, calibrated by conodonts, shows that a graptolite reflectance range of 5% to 6.5% Romax (CAI = 5) corresponds to a vitrinite reflectance of 4.0% Romax. Graptolite organic remains appear to behave similar to bitumen with increasing depth of burial; at higher levels of thermal maturity, graptolite reflectance increases more rapidly than vitrinite reflectance.