Composition and organic maturity of Middle Jurassic coals, North-East Greenland: evidence for liptinite-induced suppression of huminite reflectance

Middle Jurassic coals from Kuhn Ø, North-East Greenland, may contain up to 85 vol.% liptinite, principally resinite (up to 68.6 vol.%). The coals are thus petrographically comparable to the Middle Jurassic Muslingebjerg Formation coals at Hochstetter Forland approximately 40–50 km to the north, and they are inherently excellent petroleum source rocks. Liptinite-poor (≤6.0 vol.%) coal samples from both Kuhn Ø and Hochstetter Forland yield mean random huminite reflectance values of 0.49–0.53%Ro, implying a rank of sub-bituminous A. Above a threshold value somewhere between 3 and 24 vol.% resinite and 6 and 35 vol.% total liptinite, significant reflectance suppression is induced, and between 24 and 69 vol.% resinite and 35 and 85 vol.% total liptinite, a nearly linear inverse relationship exists between the content of liptinite/resinite and the mean random reflectance values. At the highest liptinite/resinite contents, reflectance suppression may be up to 0.23%Ro. The reflectance suppression is related to bitumen-adsorption caused by bitumen-expulsion from resinite, and total reflectance distributions of the huminite fractions suggest that the reflectance of all huminite macerals is lowered with increasing liptinite/resinite content.