--> Abstract: The Autochthonous Component of Cyclicity in Shoreline Deposits of the Upper Cretaceous Ferron Sandstone, Central Utah, by T. A. Ryer; #90987 (1993).

Datapages, Inc.Print this page

RYER, THOMAS A., The ARIES Group, Inc., Louisville, CO

ABSTRACT: The Autochthonous Component of Cyclicity in Shoreline Deposits of the Upper Cretaceous Ferron Sandstone, Central Utah

Shoreline deposits of the Ferron Sandstone Member of the Mancos Shale display a complete range between river-dominated and wave-dominated. Deposits interpreted to represent river-dominated deltas are characterized by thin (usually less than 30 feet) sequences, numerous mudstone interbeds within the middle delta-front facies, minor burrowing, common distributary channel andmouth bar facies, and a high degree of variability. Wave-dominated deposits display a typical shoreface sequence. They are characterized by thicknesses of 30-60 feet. The middle shoreface parts of these sequences are commonly bioturbated; they contain few or no interbeds of mudstone.

Seven transgressive-regressive cycles have previously been recognized and mapped in the Ferron. Field studies demonstrate that regressive shoreline deposits of the first and second cycles can be subdivided into small-scale genetic units defined on the basis of their positions within the river- to wave-dominated spectrum of depositional styles. They typically extend a mileor two in the depositional dip direction. The boundaries between small-scale units are commonly abrupt, indicating that the changes from one depositional style to another were geologically instantaneous. In some cases, the boundaries are marked by localized transgressive surfaces characterized by minor amounts of erosion; in others, the boundaries are nonerosional andconform to gently seaward-inclined bedding surfaces

The small-scale units are interpreted to record autocylic processes within the Ferron fluvial-deltaic system. Avulsion of the river system played aprimary role in their genesis; lobe switching within the delta complex probably was a secondary contributing factor.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.