Application of Sequence Stratigraphy Techniques for Interpretation of Clastic Depositional Systems: Abstract

Abstract Development of sequence stratigraphy techniques, as an outgrowth of the application of seismic stratigraphy principles to analysis of outcrop and subsurface geologic data, has provided a systematic, predictive approach for basin analysis. Cyclic depositional patterns can be divided into unconformity-bounded units comprised of depositional systems that record changes in relative sea level. Recognition of genetically significant physical surfaces, large-scale stratal patterns and depositional facies associations allows delineation of lowstand, transgressive and highstand systems tracts. Deposits of the lowstand wedge systems tract rest directly on the sequence boundary and typically include regressive deposits basinward of the shelf edge and gradational valley-fill deposits landward. Depositional processes in the lowstand wedge vary from stacked turbidite lobes at the base of clinoform strata to deltaic or shelfal sedimentation in the toplapping portion of clinoforms. Nested channel deposits of the Brushy Canyon Formation, Guadalupe Mountains, typify proximal lowstand wedge facies. Fluvial, estuarine to tidal flat deposits of the J sandstone interval, Denver Basin, are characteristic of valley-fill deposition. Upward-deepening retrogradational deposits of the transgressive systems tract rest upon a regional flooding surface at the top of the lowstand system. The transgressive surface is commonly sharp and erosional, often marked by a thin coarse grained lag deposit, as above the J incised valley deposits. Facies of the transgressive system vary from shelfal sandstones and shales to stacked shoreline deposits. Dominantly regressive deposits of the highstand systems tract lie above the maximum flooding surface that caps the transgressive system. The shallowing-upward deltaic succession of the Denver Basin Skull Creek interval characterizes highstand clinoform strata. Oversteepening of the highstand progradational shelf edge may result in slope and basinal turbidite deposition.