Plant megafossil sequences, north slope cretaceous

Abstract

An Albian to Maestrichtian plant megafossil sequence in northern Alaska is documented by assemblages from 250 localities distributed through about 23,000 feet of section in seven study areas across 350 miles of the North Slope. The megafossil records are referred to formal rock units that range upward from Albian Torok—Fortress Mountain levels through the Albian—Cenomanian Nanushuk Group and the Turonian—Maestrichtian Colville Group. More than 380 plant species are recognized at present. Eight biostratigraphic zones totaling 21 subzones have been established: IA (oldest) and IB—fern‐ginkgophyte‐cycadophy te ; II—fern‐ginkgophy te‐cycadophy te‐coni‐fer; III—fern‐ginkgophyte‐cycadophyte‐conifer‐dicot; IV—conifer‐dicot; V to VII—predominantly dicots with conifers subdominant. Floral data from numerous levels suggest rapidly fluctuating conditions over the northern Alaska region during Cretaceous time. Floras and climates may have changed as rapidly in the later part of the Mesozoic era as they did in the later part of the Cenozoic era, perhaps every 100‐ to 200,000 years.