The Albian-Cenomanian flora of the Kukpowruk River, western North Slope, Alaska: Stratigraphy, palaeofloristics, and plant communities

Cretaceous plant fossils were collected in the context of sedimentary facies at 34 localities along the Kukpowruk River, north-western Alaska. The river transects three mapped units: the predominantly marine Torok Formation, the transitional Kukpowruk Formation and the predominantly non-marine Corwin Formation. Fifty-seven taxa, mostly leaves but including several reproductive structures, were recognised and compared to similar aged fossil plants from north-eastern Russia and Alaska. Although divisible into upper and lower regional floral suites, most of the flora represents a single stage in floral evolution (we refer to these two plant suites together as the Kukpowruk flora). There are strong similarities to the very rich (more than 150 species) early–middle Albian flora of the Buor-kemuss floral type in north-eastern Russia. However, because several taxa are quite long-ranging those plants from the upper delta plain environments of the Corwin Formation are likely to be late Albian in age. A second, smaller, component of the flora (which we here refer to as the Corwin flora) contains angiosperms and is similar both to the Grebenka floral type of north-eastern Russia and the Upper Killik and Niakogon floras from the central and eastern North Slope of Alaska. From consistent associations between specific taxa and sedimentary facies distinct plant communities have been recognised: a marginal marine and early successional marsh/heath community dominated by Equisetites andBirisia ferns, shrubby to forested river margin communities dominated by Ginkgo, and mire forest communities dominated by Pityophyllum and Podozamites