Geologic summary report of the 1987 exploration program, Sunnyside Tar Sands project, Carbon County, Utah--volume 1

1. The distribution of tar sands in the Sunnyside deposit is related to both structure and lithology. The structural control is associated with a northwest trending flexure that segments a large monocline which slopes gently into the Uinta Basin. The lithologic control is determined by porous and permeable sandstones deposited in the Sunnyside delta complex. An excellent overview of the project area appears as Photo 1. 2. The Mt. Bartles-Bruin Point segmented flexure (Figure 2 and 24) acts as a mega control for the distribution of bituminous sandstones. The western segment contains 4-12wt% bitumen in sandstones that dip 7-12° northeast. The central segment contains 4-7wt% bitumen in sandstones that dip 4-7° northeast. The eastern segment contains 0-4wt% bitumen in sandstones that dip 3-4° northeast. The subtle surface expression of this segmented flexure is seen in Photo 2. Aeromagnetic, gravity and seismic information indicate the presence of a subsurface fault in the vicinity of the Roan Cliffs near the town of Sunnyside. This northwest trending subsurface fault has a vertical displacement of 2500-6000 feet with the relative movement up on the San Rafael side and down on the Uinta Basin side. The Mt. Bartles-Bruin Point segmented flexure represents the surface expression of this subsurface fault. 3. The bituminous sandstones are characterized by good lateral continuity and can be separated into sheet sands and channel sands. Sheet sands characterize the majority of the tar sands, while channel sands are a minority of the tar sands. The bitumen is of Tertiary age and is mainly associated with relatively uniformly fine grained to very fine grained quartz-feldspar sandstones with an average porosity of 27 percent and an average permeability of 812 milli-darcys. Minor amounts of bitumen are associated with siltstones (average porosity of 22 percent and average permeability of 64md) and limestones (average porosity of 18 percent and average permeability of 1 md). Fifteen numbered tar zones exist and can be correlated on the basis of surface and subsurface gamma ray logs coupled with stratigraphy. 4. The Sunnyside Tar Sands area exists within the Eocene Green River Formation that has been separated into three members. The Douglas Creek Member is at the base, characterized by bituminous sandstones with intervening red shales and represents the delta facies. The Garden Gulch Member is in the middle, characterized by bituminous sandstones with intervening green shales and limestones, and represents the shore facies. The Parachute Creek Member is at the top, characterized by gray shales, oil-shales and limited bituminous sandstones; it represents the lake facies. 5. Field work has defined three important stratigraphic markers and two tuff beds. The Mahogany Ledge, Blue Marker and carbonate-rich interval are important stratigraphic markers. The Mahogany Ledge outcrops near the top of exposures in the Parachute Creek Member and the Blue Marker is at the base of this member. The carbonate-rich interval exists within the middle portion of the Garden Gulch Member. All three of these markers prevail throughout the project area except where removed by erosion. An upper and lower tuff bed have been located within limited portions of *_the Parachute Creek Member. The lower tuff bed has an age' dated of 51.45±2.0 million years. These markers and tuff beds help to establish stratigraphic continuity within the project area and into the Uinta Basin. 6. The Tar Sand Isopach Map illustrates two distinct features about the Sunnyside Tar Sands deposit. First, the thickest portion of the tar sands exist near Bruin Point in the western segment of the flexure. Second, the tar sands are concentrated within a northwest trending belt with decreased bitumen in the lateral extremities. This belt is six to eight miles long parallel to depositional strike and one to two miles wide parallel to depositional dip. 7. The Sunnyside Tar Sands deposit formed within a delta complex that is divided into three subdeltas. The Bruin Point, Dry Canyon and Whitmore Canyon subdeltas are delineated on the Tar Sand Isopach Map. The most productive portions of the tar sands are in the proximal portions along the Roan Cliff face where the main saturated zones are thickest and of the highest and most consistent grades. Thinning of the bituminous sandstones is pronounced from proximal to medial to distal portions of the subdelta over distances along depositional dip that range from one to four miles. 8. The Sunnyside delta complex was formed in riverdelta- beach-nearshore environments associated with the margins of Lake Uinta during Eocene time some 58-45 million years ago. The Sunnyside delta complex consists of 15-36 stacked intervals of sandstone-shale-limestoneunconformity sequences. These lithologic sequences represent repeated cycles formed under fluctuating wet and dry climatic conditions associated with Milankovitch climatic cycles. The outcrops along the Roan Cliffs represent stacked fluvialdeltaic and shoreline sequences. 9. Detailed surface gamma ray logs coupled with detailed measured section data are a powerful field method to establish numbered tar zones and locate marker horizons. Gamma ray values are obtained from a portable mini-spectrometer used at continuous intervals along measured sections. When the surface gamma ray logs and lithology logs of different measured sections are compared and matched, numbered tar zones can be established with confidence. When surface gamma ray readings are taken at 1-3 foot intervals near marker horizons, the surface gamma ray log patterns are nearly identical to well log gamma ray patterns as seen in Figures 21 and 22.