Floral Zones and Correlations of Cretaceous Kukpowruk and Corwin Formations, Northwestern Alaska

Abstract

Abstract Cretaceous fossils, mainly plant megafossils, were collected from 140 localities in the Kukpowruk River-Corwin Bluff areas of northwestern Alaska. Mollusks, from 13 marine interbeds in the Kukpowruk Formation of the Kukpowruk River area, correlate with middle to late? Albian faunas of the Chandler-Colville area about 300 mi east. Correlations by plant megafossil zones suggest an early Albian to possibly Cenomanian age for the Kukpowruk and Corwin Formations of northwestern Alaska. Floral records in the type section of the Corwin Formation show three sequential stages: (1) an oldest stage, equivalent largely to the widespread marine Torok Formation; (2) a middle stage, found also in the Kukpowruk Formation and the lower part of the Corwin Formation in the Kukpowruk River area, and in the Tuktu Formation of the Chandler-Colville areas; (3) a youngest stage in the bentonitic clay member of the Corwin type section, correlative with medial Corwin units in the Kukpowruk River area, and with a floral zone in the lower part of the Killik Tongue (Chandler Formation) in the Chandler-Colville areas. Plants in upper Corwin beds along Kukpowruk River represent a floral zone younger than the zones in the type section at Corwin Bluff. The floral zone in Chapman and Sable’s upper sandstone member in the Corwin type section repeats a zone found in older beds of the type section. The upper sandstone member of the Corwin type section is thus a duplication of older beds, rather than a younger unit containing a later and continuing stage of floral development.