Abstract

The type section of the Nugget Sandstone in southwestern Wyoming was designated in 1907. By the early 1920s, the formation was defined in southwestern Wyoming and adjacent areas of Idaho, Utah, and Colorado. In the mid-1940s, the Nugget was traced from southwestern Wyoming into central Wyoming. The unit is not present in eastern and northern Wyoming. The Nugget is correlative to all or part of the Glen Canyon Group of the Colorado Plateau and the Aztec Sandstone of southwestern Nevada.

The Nugget Sandstone contains few fossil remains. Age estimates of the unit are based primarily on stratigraphic relationships. It is generally assigned a Triassic-Jurassic age, but may be entirely Jurassic.

Lithologically, the Nugget is composed primarily of fine-graned, moderately well-sorted subarkose and quartz arenite, with interbedded siltsone, mudstone, and limestone. In many areas, the sandstone is characterized by medium to large-scale cross-stratification, but in some locations, it is rippled and wavy-bedded or massive. Paleo-current studies of the cross-stratification indicate the general direction of sediment transport was to the south.

The majority of the cross-stratified sandstone is eolian in origin, but water-laid sediment is dominant at some locations and is present at almost all locations.