Print this pageAbstract: Lower Triassic Hinge Line and Shelf Tar "Sand" Deposits, Central and Southern Utah
The Lower Triassic Moenkopi Formation contains numerous tar-impregnated and oil-stained sandstone and carbonate deposits from the San Rafael swell in central Utah to northern Mohave County, Arizona. The petroliferous deposits are within several different stratigraphic zones of the Moenkopi; most are associated with offshore-bar and delta-front sand bodies and oolitic and fossiliferous bar and shoreline calcarenites.
Although several sources for the hydrocarbons are possible, most probably the fluid hydrocarbons migrated updip from the Cordilleran miogeosyncline onto the hinge-line and shelf areas. Nearly all the traps are stratigraphic and involve the pinchouts of sand bodies into less permeable, finer grained rocks. Oil-stained deposits in southernmost Utah and northern Arizona are associated with oomoldic and crittermoldic porosity in the Timpoweap Member of the Moenkopi.
Many of the oil-impregnated deposits are in rocks of relatively low permeability and porosity but secondary porosity associated with major lineament and fault structures probably provides the most favorable areas for subsurface petroleum exploration.
AAPG Search and Discovery Article #90964©1978 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah