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Abstract: Lacustrine Delta, Sunnyside Tar Sands, Northeastern Utah


The southwest rim of the Uinta Basin contains a well-defined lacustrine delta determined by extensive surface and subsurface data. the strata strike northwest, dip 312 degrees east and outline a monoclinal flexure. The delta was defined on the basis of over 140,000 feet of drill core and measured sections during a ten year time.

Rock-stratigraphic units of the Green River Formation of Eocone age are separated into three members: Douglas Creek, Water Canyon and Parachute Creek. The Douglas Creek Member consists of red shales with thick intervals of sandstones that formed in fluvial to deltaic environments. Those porous and permeable sandstones contain the vast majority of the biodegraded bitumen. The Water Canyon Member consists of green shales, algal/ostracodal carbonates and thin intervals of sandstones that formed in shoreline environments. The Parachute Creek Member consists of gray shales with intervals of oil shale and tuff beds that formed in lake environments. The wavy bedded tuff (47 Ma) and Mahogany bed represent important time-stratigraphic units. Algal intervals are found with oil shale. The base of the Parachute Creek Member contains a distinct marker herein named the Bruin Point marker.

These three members contain eleven major lithologic cycles. The repetitive upward-fining cycles of basal sandstone, middle shale and upper limestone are consistently capped by a local unconformity. Anomalous gamma ray values noted in both well logs and surface logs along measured sections are frequently associated with unconformities and help establish stratigraphic correlations.

AAPG Search and Discovery Article #90946©1997 AAPG Rocky Mountain Section Meeting, Denver, Colorado