Vitrinite reflectance measurements on coals and dispersed organic matter in the Spitsbergen Tertiary are reported. Maturity profiles through the Tertiary sequence (950 m) show gradual increase ranging from R_o = 0.40 at the top to R_o = 0.68 at the base. The maturity level along the economically important coal horizon at the base of the Tertiary sequence shows considerable regional variation ranging from R_o = 0.41 to R_o = 1.1. Maturity is highest in central and southern parts of the basin and decreases toward the western and eastern flanks.

Isoreflectance lines are interpreted in terms of isopachs. The main conclusions are: the area of greatest sediment-accumulation migrated eastward during deposition owing to tectonic activity related to the early opening of the Norwegian-Greenland sea. During the subsequent post-orogene uplift and denudation of Spitsbergen, approximately 1.0 to 1.5 km of the Tertiary deposits were eroded.

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