DELINEATION OF THE J-1 UNCONFORMITY IN SOUTH-CENTRAL UTAH USING A PORTABLE XRF

The Navajo Sandstone in south-central Utah is overlaid by the White Throne Member of the Temple Cap Formation in the west, and the Page Sandstone in the east. All three of these sandstones are Jurassic in age and were deposited in an arid, eolian setting. The Page Sandstone and the White Throne Member of the Temple Cap Formation are separated from the Navajo Sandstone by an erosional surface called the J-1 Unconformity. This contact is obvious in many outcrop locations on the Colorado Plateau, however, in some locations it is quite difficult to delineate. This is due to the similar appearance and facies of these eolian sandstones. This relationship makes stratigraphic studies problematic.

We have begun analysis of these formations using a portable XRF to determine the bulk chemistry of each formation and to identify subtle changes that may help delineate the position of the J-1 Unconformity. Preliminary results are very promising. Analysis from three locations where the position of the J-1 Unconformity is well known has resulted in recognizable trends that differ between the Navajo Sandstone and the Temple Cap Formation/Page Sandstone. The next major step will be to analyze these formations in locations where the J-1 Unconformity is not so easily located to see if the same trends exist there.