EUSTASY AND TECTONISM IN THE ANCESTRAL ROCKY MOUNTAINS, EASTERN PARADOX BASIN,CO

The detailed timing of and style of uplift remains critical to constraining models of the origin of the Ancestral Rocky Mountains. Teasing apart tectonically driven pulses in sedimentation from eustatically driven sedimentation remains a challenge to this effort, however with adequate temporal resolution, progress is being made. On the eastern margin of the Paradox basin, adjacent to the Uncomphagre uplift, recent well log interpretations by Brown (2002) correlate the eastern side of the basin to the Honaker Trail area where Ritter et. al (2002) have tentatively correlated sequences to Midcontinent sequences using conodont and fusulinid faunas. Using these tentative correlations it appears that water depths on both sides of the basin reached maxima during the deposition of the late Desmoinesian, Midcontinent Verdigris-correlative sequence containing the Chimney Rock Shale. On the tectonically active, eastern margin of the basin, Chimney Rock Shale equivalent strata occur within back-stepping prodeltaic facies that are directly overlain by shallow water carbonate facies. Similar facies successions overlying this interval may correlate with a smaller maximum flooding associated with the sequence containing the Gothic Shale. On the tectonically quiescent western shelf of the Paradox basin, near Honaker Trail, maximum sequence thickness and inferred water depth also are associated with these depositional sequences. The Verdigris sequence is also marked as having produced a significant highstand in the Midcontinent. Hence it appears that even on the flanks of the tectonically active Uncompaghre Uplift, eustasy has left a distinctive signature that may be separated from the influence of tectonism.