Discontinuity Surfaces, Clinoforms, and Facies Architecture in a Wave-Dominated, Shoreface-Shelf Parasequence

Abstract

ABSTRACT Detailed outcrop analysis of a wave-dominated, shoreface-shelf parasequence exposed in the Book Cliffs, Utah reveals minor stratigraphic discontinuities, which define clinoforms. Two types of discontinuity are recognized, each with a distinctive lithologic character and geometry. Nondepositional discontinuities are marked by an abrupt decrease in the thickness and amalgamation of storm-generated event beds, and are interpreted to record hiatuses in sedimentation. These discontinuities define clinoforms with a concave-upward geometry that dip gently (0.02-0.58°) over distances of 800-6000 m down depositional dip. Erosional discontinuities are marked by an abrupt increase in event-bed amalgamation, grain size, and sand content, and are interpreted as enhanced storm-wave scours. These discontinuities define more steeply dipping (0.22-0.95°), concave-upward clinoforms that extend over 100-1600 m down depositional dip and 500-1500 m along depositional strike. The distribution and amalgamation of minor stratigraphic discontinuities defines linear zones of distinctive facies architecture that are oriented parallel to the paleoshoreline trend. Using the simple assumption that the shoreface-shelf equilibrium profile remained approximately constant for each type of discontinuity throughout shoreface migration (the Bruun rule), intra-parasequence facies architecture can be speculatively interpreted in terms of shoreline trajectory, which reflects the balance between sediment supply and accommodation. The resulting interpretations support the notion that shoreline trajectory exerts a strong control on intra-parasequence facies architecture and preservation of the shoreface-shelf profile.