Abstract: TECTONIC HISTORY The symposium begins with a comprehensive review of the history of faulting in the Eastern Uinta Mountains by HANSEN, who has spent much of his long and productive career studying the complex geology of these magnificent mountains. He points out that the east-trending deformational features of the Uintas date from Archean time, and that there is evidence for both normal and reverse fault movements through time, beginning no later than the Middle to Late Proterozoic and continuing intermittantly into the Quaternary. Strong evidence for recurrent fault movements along the UintaAxial arch is also presented by STONE. Seismic and borehole data clearly show that early normal faulting (Proterozoic) was followed by structural inversion (Pennsylvanian) causing thrust reversal along the old fault zones during development of the Ancestral Rockies and again during the Laramide orogeny. The fault-bordered distribution and thickness of Precambrian Uinta Mountain Group strata indicated on STONE'S isochore map, which is based largely on seismic information, will inevitably need some revision as more data are aquired, but the map reveals an astonishing tectonic instability within the northwest Colorado province. DE VOTO, BARTLESON, SCHENK, AND WAECHTER also discuss Pennsylvanian stratigraphic relationships in the area of the Eagle basin and Sawatch Range to the southeast where Late Paleozoic tectonism controlled depositional facies and basin configuration. Two, rather poor quality, seismic lines, one oriented north-south along the Douglas Creek arch, the other east-west across the Piceance basin, are presented by WAECHTER AND JOHNSON in support of a concept of Pennsylvanian-Permian block-faulting'' and Late Pennsylvanian paleostructural development (including the Rangely anticline). A new interpretation of oil-source and migration history is proposed for the giant Weber pool at Rangely. According to these authors, oil derived from the Pennsylvanian Belden Shale cciiij i-lzve iiiiyraiea norinwesieriy oui oi rne Eagie Lasiii il iio h iX&i=!sostructural trap at Rangely. This interpretation is quite different from the concept presented by FRYBERGER AND KOELMEL (also by OSMOND). Their proposed seqcence of events includes early long-range migration of Phosphoria oil into an original stratigraphic trap along the Weber-Maroon facies boundary and later remigration into the Laramide structural trap. Geochemical data appear to indicate a Phosphoria source (STONE, Rangely field summary). However, gener?.;ion of hydrocarbons from a Pennsylvanian Belden Shale source can not be ruled out. -, Compressional defwmation during the Ancestral Rockies orogeny is certainiy indicated ffjr the Uncompahgre Plateau as pointed out by HEYMAN, HUNTOON, AND WHITE-HEYMAN, and indeed there is ample evidence for pre-Laramide faulting transverse to the Douglas Creek arch at Garmesa arid Douglas Creek fields as reported by WAECHTER AND JOHNSON. With a series of isopach maps, JOHNSON AND FINN outline the Cretaceous through Holocene history of the Douglas Creek arch and conclude that its present north-trending geometry did not develop until Paleocene time when the arch served mostly as a hinge between the subsiding Uinta and Piceance basins. And at the end of the tectonics section, VERBEEK AND GROUT summarize the results of their studies of fracture systems in the Green River Formation of the Piceance basin. They conclude that in the Piceance basin, Late Laramide and post-Laramide horizontal stresses (6 hmax) rotated counterclockwise about a vertical axis with time. I
Publication Year: 2017
Publication Date: 2017-01-12
Language: en
Type: book-chapter
Indexed In: ['crossref']
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