Abstract: Parasequence Sets, Parasequences, Facies Distributions, and Depositional History of the Upper Cretaceous Ferron Deltaic Clastic Wedge, Central Utah
Thomas A. Ryer, Paul B. Anderson
The upper part of the Ferron Sandstone (Kfu)includes a clastic wedge of deltaic sediment that has been divided into seven "data-front units" or genetic units" by previous investigators. These seven units (Kf-1 through Kf-7) correspond to parasequence sets in sequence stratigraphic terminology. The arrangement of parasequence sets is forward-stepping in the lower part of Kfu and aggradational to backward-stepping in the upper part. There are important differences in the facies content and architectural styles, particularly with respect to arrangement of parasequences, in the forward- and aggradational to backward-stepping parts.
Kf-1 and Kf-2 have a forward-stepping arrangement Each can be divided into numerous parasequences and many of these parasequences include river-dominated deltaic fades. Kf-3 through Kf-5 are essentially aggradational, while Kf-6 and Kf-7 display a strongly backward-stepping arrangement. The parasequences that they contain include a much greater percentage of wave-dominated shoreline fades. Although parasequences can be distingished in Kf-3 through Kf-7, the marine-flooding surfaces that separate them are commonly difficult to recognize.
One important characteristic shared by all of the Ferron parasequence sets is that each displays pronounced aggradation during the initial phase of progradation, resulting in a strong "stratigraphic rise" of fades in the seaward direction. This pattern suggests of a sinusoidal driving mechanism, possibly eustatic fluctuation of sea level. Because they include greatly thickened upper shoreface intervals, the landward most portions of the parasequence sets commonly contain the best reservoir fades. Furthermore, the periods of pronounced aggradation were the principal times of peat accumulation, resulting in proximity of reservoir and possible source beds for methane.
AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada