EVANS, KEVIN R.
U.S. Geological Survey, Western Energy Resource Surveys Team, Menlo Park, CA
Abstract: Reciprocal Sedimentation in the Cambrian of Utah: Reevaluating the Cyclostratigraphic Record
Stacking patterns of fifth-order cycles are thought to reflect third-order fluctuations of accommodation, but cyclostratigraphy largely ignores the influence of reciprocal sedimentation. Where reciprocal sedimentaton was an active control, interpreted thirdorder signals may be as much as 180<deg> out-of-phase.
Middle and Upper Cambrian strata of the House Range and Wah Wah Mountains of western Utah are approximately 2500 m thick on a trend parallel to depositional strike. Thicknesses and depositional facies of selected intervals in these successions vary significantly. Thick intervals of mixed siliciclastics and carbonates in the House Range correlate with thinner carbonate-rich intervals in the Wah Wah Mountains. Carbonate-rich intervals in the central House Range correlate with thicker successions in the Wah Wah Mountains. Alternate juxtaposition of thick-to-thin correlations suggests that reciprocal sedimentation played a key role. These patterns are coincident with a structural boundary that lies perpendicular to strike, separating the Southern Shelf from the House Range Embayment. The Southern Shelf was locus of aggradational carbonate cycles during sea-level highstands, and the House Range Embayment was a principal depocenter during lowstands.
Selected Upper Cambrian intervals illustrate the difficulties of correlating packages of fifth-order cycles between these areas. In the Wah Wah Summit Formation and Red Tops Member of the Notch Peak Formation, peritdal cycles cannot be correlated confidently over a few kilometers because of erosion, nondeposition, or complexities in stratal architecture. In the Orr Formation, cycles in subtidal, mixed carbonates and shale are abbreviated due to bevelling by storms, and elsewhere may have been expanded by bypass and redeposition.
AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California