|North Pacific||AKSR-NASR||Anadyr-Koryak||Verkhoyansk-Chukotka||Okhotsk-Chukotka||N. Alaska||Yukon||Chignik|
The Yukon-Koyukuk Subregion
The depositional environments of the Yukon–Koyukuk Subregion (YKSR) consisted of a shallow-water sea basin and coastal lowlands, comparable in landscape terms to the Cretaceous depositional environments of the AKSR and NASR. However, non-marine sedimentation in the YKSR only lasted through the comparatively short interval of the Cenomanian (beginning most likely in the late Albian) and Turonian (possibly until the early Senonian). Remains of Cretaceous plants are known from two areas of the subregion: from the Yukon and Koyukuk river basins and from coastal exposures of the Nunivak and Nelson islands and of the Baird Inlet in western Alaska.
The Melozi and Kaltag formations of the Yukon and Koyukuk River Basins yielded the diverse Melozi-Kaltag Flora (Hollick, 1930; Spicer, 1987), which is mostly of Cenomanian age, though it probably spans the late Albian and part of the Turonian (Patton, 1973; Spicer, 1987). Angiosperms predominate in this flora, with several genera of large-leaved platanoids being numerous in local assemblages. Other plants are represented by abundant ginkgoaleans and the cycadalean genus Nilssonia. Conifers of the flora are diverse, whereas ferns are of low abundance. In its systematic composition, the Melozi-Kaltag flora is close to the Grebenka flora of the AKSR and the Niakogon flora of the NASR. Abundant remains of platanoids suggest its similarity with the Penzhina flora of the AKSR and Kaolak flora of the NASR.
Several taphofloras from the Nunivak and Nelson islands area are comparable to some extent with the Melozi-Kaltag flora and can be regarded as impoverished analogs of the latter (Spicer, 1987). It is possible that some of them are younger, corresponding in age to the Senonian.
Interactive map of western central Alaska showing the Yukon-Koyukuk Subregion.