Summary

Understanding the interaction of mixed carbonate and siliciclastic sedimentation in areas that have experienced rapid subsidence is crucial in petroleum exploration because it enables one to predict stratigraphic relationships and geometries between potential reservoirs, seals, and traps. This paper presents an analogue study and sequence-stratigraphic model to address the possiblity of generating deep-water sedimentation from the combined effects of rapid subsidence and siliciclastic suppression of carbonate productivity, especially during times of relative sea-level fall.

Strata of the Late Cambrian Pterocephaliid Biomere in western Utah and eastern Nevada record two influxes of shale across a miogeoclinal carbonate platform. Although the shale-rich facies mostly reflect deepening, we interpret these units as lowstand deposits, products of two eustatic falls. A succession of relatively deep water outer-ramp facies in the lower shale unit (Prehousia Zone), which other sequence stratigraphy models might interpret as a maximum flooding zone, is correlated with hiatus on the craton. The upper shale unit (lower Elvinia Zone) is associated with the only carbonates in the biomere interval with microkarst features; correlative successions of peritidal and subtidal carbonates were deposited in basinward sections. These data indicate that relative falls in sea level may be correlated with the deepest water deposits on parts of the miogeocline.

Eustatic falls provided an efficient mechanism to disperse siliciclastic fines onto the miogeocline; the influx of siliciclastics at times effectively suppressed the carbonate factory, so that despite the eustatic falls, the rate of accommodation from rapid subsidence outstripped net sediment accumulation, resulting in upward-deepening successions.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas