Laserfiche WebLink
apparently began prior to deposition of the Upper Cretaceous Williams Fork <br />Formation because this unit thickens across the basin and thins over the Douglas <br />Creek Arch. Basin development apparently continued throughout the Paleocene <br />and early to middle Eocene and allowed accumulation of the thick sequence of <br />lacustrine sediments which now constitutes the Green River Formation. Following <br />infilling of Lake Uinta, tectonism continued, as evidenced by the structurally <br />deformed Wasatch, Green River and Uinta Formations in the vicinity of the Grand <br />Hogback (Figure 4-9). This deformation was associated with continued uplift of the <br />White River Plateau in late Eocene time. The present-day structural relief between <br />the Piceance Creek Basin and the White River Uplift is about 30,000 feet (Tweto, <br />1980). <br />The Piceance Creek Basin is a relatively simple structure. It has a northwest- <br />southeast orientation, is asymmetric to the east and northeast, and has a slightly <br />sinuous longitudinal axis (Figure 4-9). Uplifts surrounding the basin include the Elk <br />and West Elk Mountains, Uncompahgre Uplift, Douglas Creek Arch, eastern Uinta <br />Mountains, Axial Basin Uplift and White River Uplift. The interior of the basin is not <br />strongly affected by structural deformation; high-angle normal faults and shallow, <br />elongate anticlines and synclines are the most common features (Figure 4-9). <br />The Grand Hogback monocline is the dominant fold in the Piceance Creek Basin. <br />Sandstones and shales of the Wasatch, Williams Fork and Iles Formations generally <br />have dips in excess of 60° along the monocline and are sometimes overturned <br />(Collins, 1976). In the north-central part of the basin, a series of northeast-trending <br />anticlines and synclines are present. The major structures include the Red Wash <br />Syncline, which is in the structurally deepest part of the basin, the Rangely Anticline, <br />the South Rangely Syncline, which crosses the Lease, Piceance Creek Dome, <br />Sulfur Creek Anticline and Hunter Creek Syncline (Murray and Haun, 1974). <br />Daub & Associates, Inc. Page 4-26 NSI Mine Plan 2010 Rev. <br />Printed: 7/5/2010 Section 4 Geology