ABSTRACT: Organic Maturation and Thermal History of the Queen Charlotte Islands, British Columbia
D. Vellutini, R. M. Bustin
The levels of organic maturation, thermal history, and petroleum source rock potential of Mesozoic and Tertiary strata of the Queen Charlotte Islands have been determined with vitrinite reflectance, numerical modeling (modified Arrhenius model), Rock-Eval pyrolysis, and total organic carbon analysis. The thermal history and consequently the levels of organic maturation and source rock potential closely reflect the tectonic evolution of the Queen Charlotte Islands from an early Mesozoic island arc system. The level of organic maturation increases from northern Graham to southern Moresby Island, which primarily reflects high heat flow resulting from Middle to Late Jurassic and Eocene to Oligocene plutonism and cospatial dyking. Upper Triassic-Lower Jurassic and most Cretace us strata are overmature on Moresby Island with vitrinite reflectance values ranging from 2.40 to 5.80%Ro. Jurassic, Cretaceous, and Tertiary strata are immature to overmature on Graham Island with values ranging from 0.15% Ro (Skonun Formation) to 2.4% Ro (Haida Formation). Locally vitrinite reflectance values up to 3.2% on Graham Island, and 8.3% on Moresby Island occur adjacent to igneous intrusives. Modeling of measured levels of organic maturation
suggest that elevated geothermal gradients ranging from 83 to 150°C/km existed during Yakoun (between 183 and 178 Ma) and Masset (between 35 and 10 Ma) volcanism on Graham Island. Numerical modeling further suggests that Triassic strata on Fredrick Island and Kennecott Point, Graham Island, entered the oil window during the early Miocene whereas Jurassic strata at Rennell Junction and Cumshewa Inlet entered the oil window during the Bajocian. Cretaceous strata on north and south Graham Island entered the oil window during the early Miocene and are currently within the oil window. The Tertiary Skonun Formation is generally immature except for strata on west and northeast Graham Island, which entered the oil window in the Late Miocene.
AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990