Nation River Formation

Unit symbol: Dnr
Age range Upper and Middle? Devonian (393.3 to 358.9 Ma)
Lithology: Sedimentary
Group name: Clastic and carbonate rocks of the Yukon Flats Basin
Commonly-graded, rhythmically interbedded mudstone, sandstone, gritstone, and conglomerate. Mudstone is olive-gray and nearly everywhere contains plant fragments and spores of Late Devonian age. Sandstone is olive-gray chert arenite and wacke, commonly with carbonate cement. Gritstone and conglomerate are mostly composed of varicolored chert granules and pebbles. Total thickness ranges from approximately 650 to 1,300 m (Brabb and Churkin, 1969). According to Clough and others (1995), in the northern part of the Charley River quadrangle, the Nation River Formation is yellow-brown to light-brownish medium-gray chert arenite sandstone and chert pebble- to cobble-conglomerate. Conglomerate is clast-supported, contains rounded to subangular clasts, and has gray, dark-gray, and black chert in a quartz and chert sand-size matrix; locally white-weathering tripolitic chert clasts are common. Nation River conglomerate is less sorted, has more rounded clasts, more chert clasts, is more siliceous, and is more clast-supported than Step Conglomerate (Pstc). Dover and Miyaoka (1988) mapped a large expanse of the western Charley River quadrangle as conglomerate of the Nation River Formation, whereas Brabb and Churkin (1969) considered these rocks to more likely be the Permian Step Conglomerate (Pstc), which is how they are shown here

Source map information

Correlated geologic units

Label Dnr
Description Nation River Formation of Charley River quad.
Geologic age Middle-Devonian to Late-Devonian
Geologic setting Undivided
Lithology Form Importance
Conglomerate < Clastic < Sedimentary Bed Major
Phyllite < Metaclastic < Metasedimentary < Metamorphic Indeterminate, major
Quartz-arenite < Arenite < Sandstone < Clastic < Sedimentary Bed Indeterminate, major
Siltstone < Clastic < Sedimentary Bed Indeterminate, major