Local Variations in Depositional Facies of the Honaker Trail Formation (Pennsylvanian, Hermosa Group), Durango, Colorado
On the eastern side of the Paradox Basin, thin sandstones in the Honaker Trail Fm. are minor hydrocarbon reservoirs. Exploitation is hampered by variability in reservoir quality. This outcrop study of contemporaneous strata provides analogs for understanding lithofacies in subsurface sands. Previous interpretations of the Honaker Trail Member in the Durango area of SW Colorado were based on a type section on Hermosa Mountain. In 2011 this author presented an update using a new measured section with outcrop gamma ray from a nearby canyon and a photo pan. The study area is now expanded to a zone up to eight miles long and three miles wide incorporating 3-6 measured sections, 2 outcrop gamma ray curves and 2 high-resolution photo pans. This integration facilitates analysis of stratal geometries, sand body dimensions, paleosol continuity and linkage between sub-environments. Results fall into three topics; the larger-scale evolution of the area through time, details of depositional facies and correlation to the subsurface. Similar to other locations in the Paradox Basin, the Honaker Trail records the transition from marine to terrestrial environments. Within this trend, the overall packaging of strata into five major sequences (non-marine lowstands and marine highstands) identified in 2011 is still valid, although placement of higher-order surfaces differs. Marine facies became more and more restricted with successive transgressions. Older units are lower shoreface to lagoonal. Younger are updip tidal. Marine sandstones are more widespread in older strata, but are fine-grained and carbonate-cemented. Younger are lenticular and contain abundant mud rip-up clasts. Carbonate tidal facies form multi-directional, prograding bars with grainstone topsets and mudstone toes. In non-marine facies, older sandstones are widespread, coarse-grained, multi-storied channel complexes (braided stream). Younger are more often single-storied with lateral accretion surfaces (meandering), separated by thick sections of red and green mudstone overbank deposits. Attempts to correlate the outcrop gamma ray curve to the closest wells in the subsurface (~12mi) are largely unsuccessful due to the presence of more updip tidal and non-marine facies in the study area. There is a large amount of lateral variability in these settings resulting in differing log responses. Comparison of outcrop GR between two measured sections separated by three miles illustrates this problem.
AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012