ANDERSON, PAUL B., Consulting Geologist, Salt Lake City, UT

ABSTRACT: Stratigraphic and Sedimentologic Characteristics of the Lower Portion of the Ferron Sandstone Member of the Mancos Shale Along a Portion of Muddy Creek, Emery County, Utah

Characteristics of the no. 1 and no. 2 delta-front units were mapped on photomosaics from a portion of Muddy Creek. Both the no. 1 and no. 2 were divided into two localized parasequences based on transgressive surfaces, perhaps related to delta switching.

The no. 1a parasequence generally is a coarsening-upward sequence of sandstone/siltstone/mudstone. Occasionally its top exhibits an anomalously thick sandstone with sharp nondepositional lateral contacts. The sand is a slump feature related to downslope movement of the first regressive deposits on unstable muds of the Tununk Member of the Mancos Shale.

The overlying no. 1b parasequence is traceable regionally and locally exhibits typical wave-dominated deltaic facies. Upper shallower water and higher energy deltaic facies thin and/or pinch out locally.

The no. 2a delta-front unit directly overlies no. 1b, and they are separated by a transgressive surface. Locally, 1- to 10-m-thick channel deposits incise into lower shoreface deposits at the base of the no. 2. Occasionally, the channels cut into the upper portions of no. 1b. Cross-bedding suggests an east to southeast transport direction. No. 2b is 3-10 m thick and consists of a mouth-bar complex or unidirectional troughs facies. The top of the mouth bar is planar to convoluted bedded followed by steeply (20-30 degrees) seaward inclined parallel beds that thin, fine, and flatten seaward to flat-lying bottomset beds. Landward of the mouth-bar complex is a sequence of interbedded unidirectional trough, cross-bedded, and massive bioturbated sandstone. The troughs suggest north-northeast directed transport.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.