ABSTRACT: Eustatic Control on an Aggradational Parasequence Set, Cretaceous Emery Sandstone, Utah
Marjorie A. Chan
The Cretaceous Emery Sandstone exemplifies wave-dominated sedimentation in the Western Interior seaway, within exposures in Castle Valley, Utah. Ten partially developed, cyclic shoreface sequences are distinguished and can be recognized as benches in a stratigraphic section about 200-m thick. The individual vertical sequences (about 20-m thick) contain laminated to burrowed shale, hummocky cross-stratified to rippled sandstone, and amalgamated hummocky cross-stratified sandstone facies. These facies respectively represent offshore, lower shoreface, and middle shoreface deposits. The lack of developed upper shoreface deposits indicates that this portion of the basin remained below fair-weather wave-base conditions.
The ten cyclic shoreface sequences are interpreted to represent parasequences that formed an aggradational parasequence set of a shelf-margin systems tract. The ratio of the rate of deposition to the rate of accommodation was close to unity. Although other Upper Cretaceous formations along the western edge of the Interior seaway commonly display coastal plain and deltaic features, this Emery example demonstrates the seaward expression of aggradational shallow-marine sandstones during a sea level highstand.
AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990