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Regional Stratigraphic Architecture of the Prairie Canyon Member of the Mancos Shale, Uinta Basin, Utah: Development of a Constructional Shelf/Slope/ Basin Ramp

Anderson, Donna S.1, Michael H. Gardner2 (1) Colorado School of Mines, Golden, CO (2) Montana State University, Bozeman, MT  


The Campanian Prairie Canyon Member (PCM) of the Mancos Shale was deposited across a > 9,000 sq mi area of the Uinta basin, Utah. The distribution, distinctive facies successions, and resulting stratigraphic architecture of this 1600 ft-thick time-transgressive interval yields insight into the development of ramped slopes constructed during overfilling of a foreland basin. This analysis includes logs for 280 wells and eight cores, integration with previous and concurrent outcrop studies, including five measured sections in the Book Cliffs.


The PCM consists of thinly interbedded (< 2.5 in. average bed thickness) rippled sandstone and graded to ungraded mudstone that produces well-log responses that reflect the changing sandstone percent. PCM cycles are defined by correlating mudstone-rich intervals to the 4th-order condensed zones of deltaic/shoreface members of the Mesaverde Group. The resulting stratigraphic architecture consists of broad low-relief clinoforms (<< 0.1 degrees) that bound highly aggradational (older) to slightly progradational (younger) clinothems. Sediment progressively filled the basin from the southwest, west and northwest, with older PCM cycle strata constructing a platform for younger (middle to upper Blackhawk Formation) shoreline progradation. Coeval shorelines were consistently > 30 mi away from PCM depocenters, implying significant and consistent sand and mud delivery on a ramping slope to basin profile. The huge volume of sediment needed to fill the > 9000 sq mi basin in < 2 million years reflects sediment delivery in a tectonically active foreland from multiple moderate sized deltas likely to generate as hyperpycnal flows.

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana