Cretaceous Floras of Chandler-Colville Region, Alaska: Stratigraphy and Preliminary Floristics

Abstract

Field studies of the stratigraphy of Cretaceous plant-bearing beds were undertaken in the Chandler and Colville Rivers region of northern Alaska during the summers of 1964 and 1966. Florules were discovered and sampled at 55 localities. Their superpositional relations and their relation to fossiliferous marine interbeds were determined in the field. The lower part of the section (about 4,700 ft) contains the Nanushuk Group of middle Albian to early Cenomanian age. The upper part (about 5,100 ft) contains the Colville Group of Turonian to Maestrichtian? age, which lies with angular unconformity on the Nanushuk Group. Invertebrate megafossils include species of ammonites, of Inoceramus, and of other mollusks and provide direct field evidence for referring floral records to uropean stages. Plant megafossils from nonmarine units include ferns, ginkgophytes, cycadophytes, conifers, and angiosperms. The numerical importance and the variety of each major plant taxon differ at different stratigraphic levels. Also noted is a striking change in floristics from bottom to top of local sections, similar to the floral records found earlier in the Kuk River area 200 mi northwest. Seven biostratigraphic units (plant megafossil zones) are distinguished, of which five were recognized previously by the author in the Kuk River section. Several of the floral zones appear to be present also in the Soviet Arctic 1,500 and 2,000 mi west, and in Greenland 2,500 mi east, all at approximately the same latitude. The floral zones in other Arctic regions seem to have the same sequential relations as in northern Alaska, suggesting that such zones may be holarctic in extent. It appears probable that the sequential floral records of northern Alaska, with their direct marine interties, may serve as reliable references for correlations of plant-bearing nonmarine deposits of similar age throughout Arctic regions.