Date of Award

Spring 1-1-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geological Sciences

First Advisor

Matthew J. Pranter

Second Advisor

Rex D. Cole

Third Advisor

Edmund R. Gustason III

Abstract

The middle Mesaverde Group of the Douglas Creek Arch, northwestern Colorado, is represented by a complex succession of fluvial to marine strata that serve as outcrop analogs to laterally equivalent natural gas reservoirs in the Piceance and Uinta basins. The interval includes ~380 ft (~115.9 m) of mudrock, coal, and sandstone within the lower (Kmvl) to main coal-bearing (Kmvc) intervals of the Mesaverde Group (equivalent to the upper Iles and lower Williams Fork formations). Based on 2,488 ft (758.5 m) of measured section, facies associations include: (1) coastal plain; (2) estuarine; (3) lagoon; and (4) shallow marine. Nine architectural elements are identified and include: (1) channel bodies; (2) crevasse splays; (3) discrete flood bodies; (4) a bayhead delta; (5) an estuarine assemblage; (6) foreshores; (7) tidal barforms; (8) middle shorefaces; and (9) washover fans. The study interval records an overall transgression from coastal-plain to shallow-marine facies associations to regression from shallow-marine to coastal-plain facies associations. Based on 38 sandstone-body measurements, channel bodies have an apparent width (W) of 287.7 ft (87.7 m), and thickness (T) of 4.9 ft (1.5 m) and are larger than crevasse splays (W=90.5 ft [28.0 m]; T=1.8 ft [0.5 m]) and discrete flood bodies (W=61.5 ft [18.8 m]; T=1.6 ft [0.5 m]). Net-to-gross ratios (N:G) create packages in the study interval and show direct ties to the sequence-stratigraphic framework. High N:G packages lie above sequence boundaries and fine upward into low N:G packages. Moderate N:G packages occur in late transgressive to early regressive strata.

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Geology Commons

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