Abstract: Origin of Navajo Sandstone
Five quartz sand samples of the Navajo Sandstone from near Green River, Utah, were examined by scanning electron microscopy (SEM) to determine if the surface textures present could be used for environmental discrimination. In addition, surfaces were etched with hydrofluoric acid (HF) in an attempt to resurrect possible mechanical textures; finally, the fine fraction of one sample was studied in thin section and with a scanning electron microscope (SEM).
Although individual sand grains in certain samples are covered with diagenetic textures, more than half of 150 grains examined with SEM contained some areas, particularly on well-rounded grains, that included relatively unmodified upturned plates. Textural evidence thus indicates that the last mechanical episode impressed on Navajo sand grains was Saharan eolian-type abrasion.
After hydrofluoric acid etching on grains, quartz crystal terminations were eliminated and eolian upturned plates clearly exposed over large areas. This probably occurred because the silica precipitated on plate surfaces was amorphous and therefore more soluble than the underlying quartz.
Thin section study of Navajo grains indicated that many had been fractured after deposition; SEM study showed individual silt grains with eolian surfaces on one side and fractured surfaces on the other. Thus size-frequency analyses that have been used in the past for environmental discrimination may be incorrect.
Finally, although primary mechanical features may be present to a very slight degree, they can be recognized with careful examination, and environmental discrimination then may be possible.
AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma