HEAVY MINERAL ANALYSIS OF THE GRAND CASTLE FORMATION, IRON COUNTY, UTAH

The Paleocene age grand castle formation crops out, principally in Iron County, Utah. This unofficially named rock unit is composed of three “members”. The lower and upper “members” are composed of coarse conglomerate with sand matrix; the composition of the middle “member” is dominantly fine-grained quartz sand with a minor fraction of pebbles. This rock unit is problematic because all three “members” seldom occur in the same outcrop. The conglomeratic material in the lower and upper “members” appears to have been derived from the Wah Wah thrust sheet to the northwest. The source area for the middle “member” has been suggested to be the Navajo Sandstone. To determine if all three “members” have the same sand source, samples were collected every fifty feet through the unit. Heavy mineral analysis was conducted on these samples, and then compared to a heavy mineral analysis of the Navajo Sandstone. This analysis indicates that the sand source of the grand castle formation is the Navajo Sandstone to the west.