Todd D. Gibbs and Dr. Thomas H. Morris, Geology

In order to find natural resources, whether it be precious metals or fossil fuels, one must understand the geological history. Further, one must be familiar with how different environments will affect where the resource is found. When dealing with fossil fuels, it is vital that the person understands the environment in which the sedimentary rocks were deposited. For example, in order to find coal, you must determine what depositional environment the outcrop of rocks you are presently looking at are in the depositional sequence. If there are beach deposits to the east of you and marine deposits to the west, then coal will be found in deposits to the east of the beach deposits. The same basic rules are applicable when searching for petroleum deposits.

The Uinta Basin of Eastern Utah contains many of the necessary elements for trapping petroleum. However, when searching for new deposits, understanding the depositional chronology of an area becomes critical. During a geological field course which was looking at the depositional chronology, an unidentified structure was found within the Green River Formation. The importance of this structure is that it may shed some light about the type of environment in which the deposition took place.

In order to accurately determine the environment in which the structure was deposited, it was necessary to conduct a fairly extensive literature review. By doing this, it was possible to first, determine whether or not this type of structure had been described previously and second, to find sources of information about the Green River Formation in which the structure is found.

Throughout the literature search, an analysis of the structure was conducted. This analysis was done by slabbing the sample rock that contained the structure into multiple 1″ slabs. The slabs were then polished and photographed. This was done in attempt to determine how the structure propagated in three dimensions through the sample. The slabs then became the focus of an intense descriptive process. Having completed the description of each slab, the focus then shifted to the review of five hypothetical modes of formation. It became apparent that no one mode of formation would adequately and completely explain the structures occurrence. Therefore, in order to describe how the structure formed, it was necessary to draw from multiple hypothesis, creating a synthesis of formational modes.

This particular sedimentary structure appears to have been formed as pressurized fluids from underlying layers were forced upward through overlying sediments. The fluids became pressurized as sedimentation due to rapid flocculation of clay particles increased. What was intriguing about this structure is that apparently a cycle of rapid flocculation and de-watering, followed by the re-introduction of water in the pore spaces occurred at least three distinct times. This cycle created what is now called a multiple generation fluid escape structure.

References

1. Picard, M. Dane., 1966, Oriented, Liner-Shrinkage Cracks in Green River Formation (Eocene), Raven Ridge Area, Uinta, Utah: Journal of Sedimentary Petrology., v.36, no.4, p. 1050-1057.
2. Picard, M. Dane and Lee R. High, Jr., 1972, Paleo-environmental Reconstructions in an Area of Rapid Facies Change, Parachute Creek Member of Green River Formation (Eocene), Unita Basin, Utah: Geological Society of America Bulletin, v.83, p.2689-2708.
3. 1968, Sedimentary Cycles in the Green River Formation (Eocene) Uinta Basin, Utah Journal of Sedimentary Petrology, v. 38, p. 378-383.
4. Ryder, Robert T. et al., 1976, Early Tertiary Sedimentation in the Western Uinta Basin, Utah: Geological Society of America Bulletin, v. 87, p. 496-512.
5. White, W. A., 1961, Colloidal Phenomena in Sedimentation o Argillaceous Rocks: Journal of Sedimentary Petrology, v. 31, p. 560-570.
6. The assistance and aid of Dr. Morris is gratefully acknowledged.