Abstract

Upper Pennsylvanian strata of the Honaker Trail Formation exposed along the Colorado River and its tributaries in and near Canyonlands National Park consist of interbedded siliciclastic and carbonate facies deposited in open marine, littoral, and paralic environments. A total of 29 cycles defined by outcrop and wellbore data record the filling and subsequent tectonic inversion of the Paradox salt basin.

The lower 9 cycles of this interval (Desmoinesian through Early Missourian) have a protracted and northeastward stepping geometry which records the final stages of filling of the Paradox Basin. These cycles are composed of eolian fine-grained quartzarenite and lithic arenite sands delivered from the north at a low angle to the western shoreline of the Paradox Basin. Much of this sand was reworked and interbedded with carbonate sediments during episodic submergence of the western coastal margin.

The subsequent 10 cycles (middle Missourian-Virgilian) mark a gradual westward readjustment in the basin depocenter. The lower part of this succession is composed of die toesets of a series of westward stepping cycles. Internally, they are thin, compositionally diverse and lithoclastic with highly erosional flooding surfaces. The succeeding cycles are composed largely of restricted marine limestones, dolomites, and sandstones which thin and toplap to the east beneath a regionally correlative disconformity surface.

Nonmarine siliciclastics dominate the upper 10 cycles (Virgilian through Wolfcampian) which stack as a series of westward stepping depositional clinoforms. This stacking pattern apparently developed in response to an active sediment source located to the northeast which shed large quantities of arkosic fluvial and flood-plain sediments in a southwesterly direction. These deposits occupy the upper slope and topsets of the clinoforms whereas thick eolian sandstones and marine limestones occupy the lower slope and toesets.

The internal stacking pattern and distribution of lithofacies within a single cycle of sedimentation were closely examined in a high-resolution stratigraphic cross section along a dip-oriented outcrop exposure. The internal cycle architecture is strongly controlled by the rate and magnitude of base-level fluctuation, apparently linked to high-amplitude, glacio-eustatic sea-level change. A depositional model derived from analysis of this exposure demonstrates some key factors controlling the distribution of large-scale, crossbedded eolian sandstones, a potential hydrocarbon reservoir facies. Eolian dune sands migrate to basinal positions during sea-level lowstands commonly bypassing the exposed ramp margin. These deposits aggrade and are preserved when the rate of eolian sand delivered to the basin is in balance with the rate of sea-level rise.