In North Greenland a geologic section is present that contains Precambrian crystalline basement, and strata of Precambrian, early Paleozoic, late Paleozoic, Mesozoic, and Tertiary strata.

The crystalline basement, which is exposed at places adjacent to the Inland Ice, is overlain with angular unconformity by the late Precambrian to early Paleozoic sedimentary section. These sediments have a gentle north dip and comprise a large platform area that extends from the west to the east coast. The oldest sedimentary formation of this platform (the Inuiteq S^phgr Formation) is at least 1,000 m.y. old, and the youngest strata are late Wenlockian-early Ludlovian. The lower Paleozoic strata, if traced northward, are part of the North Greenland fold belt, which occupies an approximately E-W-trending zone of folds and metamorphic rocks along the extreme northern coast of Greenland. In Peary Land, where the broadest section across the folded zone is exposed, metamorphic and deformat onal effects increase northward.

In eastern Peary Land, the folded Cambrian, Ordovician, and Silurian sediments are overlain unconformably by less severely deformed Pennsylvanian, Permian, Triassic, and Cretaceous-Tertiary strata. This younger cover shows the effects of Tertiary earth movements. In northern Peary Land, a bedded sequence of dominantly rhyolitic lava and tuff (the Kap Washington Group) crops out. These volcanic rocks post-date the main Paleozoic diastrophism of the surrounding metasediments, but are affected by later folding and thrusting. A minimum K-Ar age of 35 m.y. has been obtained from the lavas.

The metasediments of the North Greenland fold belt have been subjected to a complex structural and metamorphic history, which is not completely understood. Two distinct periods of deformation and metamorphism can be recognized: Paleozoic (between Late Silurian and Late Devonian times) and Cretaceous-Tertiary. Paleozoic orogenesis involved polyphase deformation in northern Peary Land with the second- and third-order folds facing northward, toward the assumed interior of the orogen. Cretaceous K-Ar ages of the metamorphic rocks suggest a subsequent thermal episode which produced Abukuma-type mineral assemblages, but no structural events can be assigned to this period. Tertiary movements are indicated by the northward thrusting of the metamorphic rocks over the Kap Washington Group, with accompanying mylonitization.

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