GLACIOEUSTATIC AND TECTONIC INDUCED STRATAL GEOMETRIES IN MIXED DELTAIC/CARBONATE STRATA, PENNSYLVANIAN HERMOSA GROUP, NORTH OF DURANGO, COLORADO

Exceptional exposures of the middle Pennsylvanian Hermosa Group north of Durango, Colorado display a range of lateral variability in facies geometries and cyclic frequency indicative of local tectonism (uplift of the Ancestral Rocky Mtns.), and glacioeustaic influences. Data gathered from fixed-wing side-view aerial photography combined with measured sections show two principle styles of lateral variation in stratal geometries. Deltaic sequences ranging from coarse-grained proximal fan deltas to more low-angle mud-dominated deltaic deposits show marked changes in thickness and facies over distances of 0.5 to 2 km. In contrast, thinner carbonate/siliciclastic parasequences similar to updip parasequences on the western part of the Paradox basin, produce tabular to low-angle progradational geometries that appear to extend across much of the 10km of exposed section. The exceptionally abrupt vertical facies changes, the wide extent, and the high frequency of the carbonate parasequences suggests a strong glacioeustatic influence. More biostratigraphic control is being sought to constrain the timing, and possible correlation of major deltaic progradation with previously documented thrust events in the eastern Paradox basin.