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The AAPG/Datapages Combined Publications Database
The concept of gilsonite fracture and vein evolution is still, by nature, a theoretical argument. A historical review presented with recent observations and conclusions divides this period of origin into five stages of formation.
The Uncompahgre uplift established an initial ancestral pattern of northwest-trending anticlinal structures. These propagated northeastward throughout the Uinta and Piceance basins as a result of compression during the Pennsylvanian Period. Planes of weakness were imprinted vertically along the axes of these folds and subsequently affected the overlying Mesozoic sediments. Next, the Uinta uplift reenforced these northwest-trending folds and planes of weakness during the early Laramide orogeny. The third stage of formation involves contemporaneous deposition of Eocene sediments, including the kerogen of the Green River Formation. Differential compaction during diagenesis, over the northwest-trending residual highs formulated subperpendicular, localized tensile stresses. Vertical fractu es propagated rapidly in an en echelon fashion along the imprinted axial planes of weakness. In the fourth stage of formation, fractures penetrated overlying reservoir intervals, which contained various combinations of liquid hydrocarbons and connate water. Released fluids entered the low-pressure voids and spread laterally and vertically throughout the Eocene sediments. A final period of inspissation and/or metamorphosis quickly altered the various liquid hydrocarbon deposits to form gilsonite and other bitumens.
The variation of these bitumens is dependent on the original chemical composition of the individual reservoir zones during deposition.
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