Palynology and age of the Elko Formation (Eocene) near Elko, Nevada

Abstract

A well exposed section of Elko Formation in the Adobe Range, north of Elko, Nevada, was examined for plant microfossils. A diverse, well‐preserved assemblage of palynomorphs was recovered which indicates an early to middle Eocene age for the exposure. This age is based primarily on the presence of Platycaryapollenites, Pistillipollenites, Ilexpollenites, Ctenosporites, and pollen comparable to the extant genera Eucommia, Platanus, and Triumfetta. This age conflicts with radiometric age determinations from units within and below the Elko Formation at other localities, which indicate a late Eocene to early Oligocene age for the formation. This conflict suggests that stratigraphic units assigned to the Elko Formation on the basis of lithology may be of different ages at different localities.

The assemblage is dominated by probable algal microfossils, Pinaceae, Alnipollenites, Ulmipollenites, juglandaceous forms, and diverse tricolpate and tricolporate pollen of uncertain affinity. Rare specimens of a probable fresh water dinoflagellate cyst were encountered and tentatively assigned to the genus Phthanoperidinium. Warm‐temperate climatic conditions are suggested by the palynological assemblage, which contrasts with the subtropical to tropical conditions of age‐equivalent deposits in the central Rocky Mountains. Additional palynological studies of latest Oligocene and younger strata in the eastern Great Basin Province indicate warm, arid conditions prevailed, similar to the conditions of the present time.

Regional correlations of early Tertiary sediments in northeastern Nevada are difficult as a result of disjunct exposures and great variations in lithologies, both laterally and vertically. The Elko Formation consists of variable lithologies representing lacustrine and fluvial deposition and is characterized by shales rich in organic matter, even though these constitute a minor portion of the total section. The richness and diversity of plant microfossils in the Elko Formation suggest a potential means of dating and correlating Early Tertiary rocks in the Basin and Range Province using palynology.