The Early Cretaceous evolution and subsequent geographic spread of flowering plants resulted in major global floristic changes. Studies of recently collected angiosperm fossil leaf-forms using analyses of comparative leaf architecture, facies associations, migrations, and community structure have resulted in a biostratigraphic tool for Alaskan Cretaceous nonmarine deposits, and a greater understanding of the Late Cretaceous terrestrial environment of the North Slope when substantial coal resources were being laid down.

Angiosperms first arrived in northern Alaska, from the south, in latest Albian time. The Brooks Range apparently acted as a filter for some taxa and may have locally modified the climate. There is no evidence for major plant radiations at high paleolatitudes at this time.

Putative evergreens form a large component of the pre-angiosperm floras. Throughout the Late Cretaceous, progressive loss of evergreen and thermophilic elements suggest a deteriorating climate. Paleoclimatic interpretations based on gymnosperm and angiosperm taxa are that: (1) there was no seasonal dark period on the North Slope in mid-Cretaceous times; (2) a mid-Cretaceous warm, mildly seasonal climate deteriorated to being cool temperate, with pronounced seasonality, by the Paleocene; and (3) vegetation may have been light- or cold-limited by latest Cretaceous times. The paleolatitude of greater than 70°N predicted for northern Alaska by paleogeographic reconstructions would appear to conflict with the interpretation that plants experienced no seasonal dark period. An obliquity of 15° could explain this conflict and a closer relative position to the rotational pole accounts for the apparent climatic deterioration.

A detailed study of high-latitude terrestrial-plant ecosystems provides information critical to global climate models and therefore our understanding of the biosphere as a whole.

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