The significance of graptolite reflectance in regional thermal maturity studies, Queen Elizabeth Islands, Arctic Canada☆☆☆

Abstract Variations in reflectance and bireflectance of graptolites taken from the Cape Phillips Formation in the Queen Elizabeth Islands, Arctic Canada, are documented. Graptolites taken from core samples from Melville Island possess a wide range of reflectance (1.75–3.90% R 0 max). Graptolites taken from outcrop samples from the other islands have a much narrower reflectance distribution (0.57–0.81% R 0 max). The latter indicate that the organic matter is in the mature stage of hydrocarbon generation. Conodont colour-alteration indices in strata from Arctic Canada and in the Cape Phillips Formation in Eldridge Bay E-79, Melville Island, are low (1–1.5) and agree with the low reflectance of the Cape Phillips graptolites. The higher maximum reflectance values of the Melville Island graptolites indicate that the host sediments have experienced deeper burial and exposure to elevated temperatures compared to graptolites in the same formation of other islands. This study demonstrates that graptolite reflectance can delineate, relatively accurately, the thermal conditions that sediments enclosing them have experienced and, when combined with bitumen reflectance and stratigraphic and structural evidence, graptolite reflectance can be useful in assessment of thermal maturity and thickness of eroded section in lower Palaezoic successions.