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~~h~bi+ C <br />i~ <br /> <br />\. <br />SENECA 11-WIYOAST <br />GEtIERAL GEOLOGIC DESCRIPTION <br />Regional Structure <br />The area lies in the southwest synclinal portion of the Washakie structural basin of <br />south-central Wyoming. {n northern Colorado, the syncline is bordered on the east by the <br />Park Range, a large faulted anticline, and on the southwest by the Axial E?asin anticline. <br />The regional synclinal structure has been modified by numerous folds, the largest of these <br />being the Tow Creek anticline, an asymmetrical fold trending towards the northeast. Other <br />prominent struttur al features include the Wolf Creek Dome, Chimney Creek Dome, Pagoda <br />Dome, Williams Park, and Beaver Creek anticlines, and Nat and Twenty-mile Park syncline. <br />The present structural fabric was initiated during the La ramide Orogeny, the second major <br />recorded episode of mountain building in the Rocky Mountain region, during the Late <br />Cretaceous and Early Tertiary. The forces responsible for the Laramide Oroge ny continued, <br />although at a diminished rate, and during the Miocene epoch were responsible for the <br />increased inland stress and strain which eventually elevated all of Colorado and parts of <br />Utah, Arizona, and New Mexico an additional 5,000 feet. <br />Regional Stratigr aphy <br />The exposed rock sequences present in the region consist of approximately 13,500 of Late <br />Cretaceous, Tertiary, and Oua to rnary age deposits. This sedimentary sequence is composed <br />of primarily marine, near shore, palludal, and fluvial sediments with occasional influxes <br />of volcanic esh, subsequently altered to bentonite (Figure 1). <br />The Late Cretaceous sediments were deposited along a transgressive, regressive <br />epicontinental seaway. The oldest of these formations exposed in [he region is the Mancos <br />shale. This formation is approxina tely 4,900 feet thick and consists chiefly of <br />homogeneous dark gray marine shale and highly fractured, [hi n-bedded, fine-graineu <br />fossiliferous limy sandstones and fossili (crows limestones. These limy beds, of Niobrara <br />age, have yielded shows of natural gas and oil in rvells drilled along areas of sir uc[ural <br />deformations. <br />The Mesaverde Croups o/ Lat r. Crrraceous age conformably overlies the MJ nf.nS shale. Ttie <br /> <br />