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The upper contact of the Saline Zone is marked by a Dissolution Surface (Figures 4- <br />2) which represents the lowermost penetration of circulating groundwater into the <br />Parachute Creek Member. Where the Saline Zone reaches its maximum thickness <br />(i.e., the Lease), the Dissolution Surface is positioned stratigraphically about 110 <br />feet above the contact between the L-5 and R-5 oil shale zones. Laterally from this <br />location the Dissolution Surface progressively penetrates deeper into the Parachute <br />Creek Member, reducing the Saline Zone in thickness until it becomes nil. Thus, the <br />present-day extent of the Saline Zone (Figure 4-7) is a result of natural subsurface <br />dissolution processes operating since the Eocene. <br />Above the Dissolution Surface, rocks of the Parachute Creek Member are generally <br />disturbed. The intensity of disruption is directly proportional to the former <br />abundance of saline minerals in the oil shale host rock. High concentrations of <br />saline minerals are now represented by dissolution rubble and collapse breccias. <br />Removal of the saline minerals also produced subsidence in overlying oil shales, <br />thus creating numerous joints and partings. The most intense interval of dissolution <br />disturbance in the Parachute Creek Member occurs between the Mahogany Zone <br />and the R-5 zone. Where the Saline Zone is thick, the Leached Zone (Dissolution <br />Surface to uppermost vug or dissolution feature) has a minimum thickness of about <br />600 feet. As the Dissolution Surface penetrates further into the section, the Leached <br />Zone becomes proportionally thicker. It should be noted that evidence for leaching <br />of saline minerals is also present above the Mahogany Zone. The lower Mahogany <br />Zone, A groove and parts of the R-8 zone all have dissolution features (Daub and <br />others, 1985; Trudell and others, 1970, 1974). <br />4.2.3.4. Uinta Formation <br />Lake Uinta reached its maximum size, possibly 20,000 square miles (Donnell, 1982), <br />during deposition of the upper Mahogany Zone. At that time it covered large parts of <br />western Colorado and eastern Utah. In late Mahogany time, fluvial, deltaic, and <br />volcaniclastic sediments from the north and air-fall tuffs began to fill Lake Uinta. The <br />process was slow and accompanied by numerous contractions and expansions <br />Daub & Associates, Inc. Page 4-24 NSI Mine Plan 2010 Rev. <br />Printed: 7/5/2010 Section 4 Geology