Architectural Variation and Ichnology of High Permeability Facies Associations in Disparate Accommodation Settings, Ferron Sandstone, Utah
The Late Cretaceous Ferron Sandstone of Emery County, Utah
is dominantly represented by fluvio-deltaic facies associations. The facies
associations display a regional stratigraphic architecture of progradational
(PPS) then retrogradational parasequence sets (RPS). Transgressive sandstones
within the upper Ferron have exhibited some of the greatest permeabilities.
This study compares two tidally influenced, reservoir-analogue geobodies that
occur at two major transgressive levels within the Ferron Sandstone. The nature
and abundance of ichnofossils differ between the two examples and provide a
tool for recognizing the larger geobodies of the PPS from the smaller RPS.
The largest potential reservoirs present in the transgressive intervals of the Ferron Sandstone generally fall into two facies
associations. Facies Association 1 (FA1) comprises clean, channelized,
cross-bedded sandstone with minor centimeter scale mudstones. FA1 is
interpreted to represent tidal-inlet deposits. These tidal-inlet deposits are
multiple shingled geobodies that stretch for kilometers over an erosional
surface. Rare to moderately abundant Ophiomorpha are observed at various
horizons. The intervening mudstones associated with the PPS, are sparsely
burrowed by Arenicolites, Planolites, and Thalassinoides.
In contrast, the extent of tidal-inlet sandstones within the RPS are much
smaller, only a few hundred meters in length, than the examples from the PPS.
The ichnology of the example from the RPS differs from the PPS in that heavy bioturbation is locally observed in the intervening mudstones, greater
abundance of Ophiomorpha is noted, and traces associated with comparably
marine conditions such as Rosselia may be present.
Facies Association 2 (FA2) represents channelized,
sparsely burrowed cross-bedded sandstones containing subangular to subrounded
mudstone clasts and large quantities of organic debris. Occasionally, shell
material and Teredolites are observed. FA2 is interpreted to represent
distributary channel deposits. Distributary channels lay above and below (i.e.,
sandwich) inlet deposits of the PPS and RPS. Importantly, the geobodies
represented by FA1 and FA2 provide more continuous reservoir in the PPS.
Whereas the distributary channel deposits of the RPS are disrupted by laterally
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California