Peter B. Jones1
(1) International Tectonic Consultants Ltd, Calgary, AB
ABSTRACT: Wedge Tectonics, Basement Uplifts, and Fractured Hydrocarbon Traps
Although the uplift of the Colorado Front Range has frequently been attributed to west-dipping reverse faulting, no major west-dipping faults are exposed along the west edge of the Denver Basin. Even the west-dipping Golden fault, immediately west of Denver, and the largest fault in the Front Range, has an inadequate offset and too local an extent to have caused the uplift of the Front Range.
Seismic profiles and balanced cross-sections support reinterpretation of the Front Range as a basement-involved triangle zone formed by tectonic wedging. The Golden fault can be explained as a local pre-Laramide east-dipping extensional fault, incorporated into the basement thrust wedge and transported to its present position by the major Laramide thrust that uplifted the Front Range. That blind thrust, uplifting and tilting the adjacent shallow section of the Denver Basin clockwise, giving it a steep east dip, also converted the east dip of the ancestral Golden fault into a west-dipping pseudo-reverse fault. This fault flattens upward into a regional detachment within the Upper Cretaceous Pierre Formation.
Triangle zone geometry is applicable to other basement uplifts involving steeply-dipping leading edge faults that merge upward into detachment horizons in their Phanerozoic cover. Recognition of triangle zone geometry can lead to a systematic approach to exploration for and development of fractured hydrocarbon reservoirs in apparently anomalous structural settings on the flanks of uplifts. Examples presented include fractured hydrocarbon reservoirs in Western Canada, the Caucasus, and the Soda Lakes "oilfield" west of Denver.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado