Paleoclimatic Interpretations of Some Mesozoic Floral Sequences

Studies of Cretaceous floral sequences in northern Alaska were conducted during five field seasons from 1956 to 1966. Seven study areas across more than 350 miles of the Arctic Slope were examined in considerable stratigraphic detail. Marine invertebrate index fossils collected from deposits interbedded or intertonguing with plant-bearing units permit references to European stages of the Cretaceous. Comparisons of local floral sequences permit regional correlations of non-marine deposits across northern Alaska. Vegetational changes noted through thousands of feet of section in the various study areas provide a basis for inferring regional climates and climatic trends. Marine faunal interties indicate a time span from middle Albian to probably Maestrichtian, about 45 to 50 million years. Comparisons with selected North American Mesozoic floras and floral sequences at high latitudes (about 70° N.) and at middle latitudes (about 40° N.), and with Jurassic and Cretaceous records of Eurasia, suggest that vegetational and inferred climatic zonations were latitudinal as at present. Evidence suggests that vegetational zones shifted northward from Early Jurassic to medial Cretaceous (Albian) time, indicating a warming trend, followed by cooler climates in later Mesozoic time. Comparisons with floral records from other areas of the Northern Hemisphere, and of inferred climatic changes, do not favor concepts of wandering poles, drifting continents, or change in axial inclination as causal factors of climatic change since at least the beginning of Jurassic time.