Sandstones that crop

Sandstones that crop out along the Roan Cliffs near Sunnyside, Utah, are estimated to contain
approxi- | matcly 6 billion barrels of bitumen, making it one of the largest deposits in the United
States. Little is known ¿ of the geologic aspects, particularly scdimentology, mineralogy (especially
clays), and diagenesis, of these sandstones. These aspects of tar sands must be characterized before
the feasibility of bitumen recovery can be assessed. Preliminary results of this ongoing study indicate
that the sandstones were deposited in fluvial and marginal lacustrine environments. Sandstone
geometry is dependent on depositional environment: Fluvial sandstones tend to be more extensive
basinward but arc less laterally extensive than the marginal lacustrine sandstones. The sandstones are
mainly feldspathic arenitcs, containing both plagioclase and K-feldspar. Authigenic cements include
calcite, dolomite, ankerite, siderite, and analcime. Authigenic clay minerals include kaolinite, illite, and
smectite. The percentages of clays and cements vary considerably from sample to sample, particularly
between bitumen-bearing sandstones and adjacent lithologies. Some of these authigenic minerals
have replaced framework grains. Dissolution has produced secondary porosity, and the bitumen
appears to occupy secondary porosity, preferentially in the coarser grained sandstones.