Geology Reference
In-Depth Information
N
River
Juan
8-Foot
Studied Cores
Outcrop Locations
Oil-producing Fields
Fig. 3.
Map showing location of the four primary outcrop locations on the Paradox shelf and the cored wells studied
through the same interval in the basin. The focus of this paper is the exposed algal mounds around the 8-Foot Rapids loca-
tion in the southwest part of the map. Note also how the individual mound fi elds (except for the giant Aneth fi eld), located
in the basin to the northeast, are generally of limited aerial extent and trend in a NW-SE direction. Strike of the basin is
also in a NW-SE orientation.
preserved only by micrite envelopes around the
perimeter of the grains. Wispy and low-amplitude
(subcentimetre scale) sutured-seam stylolites are
typically present.
The intermediate facies (diverse) is interpreted
as a low to moderate energy, open-marine plat-
form facies with good circulation, deposited when
fl ooding of the platform had proceeded to a point
that was conducive to the establishment of a nor-
mal subtidal carbonate factory. Lower contacts are
gradational. The upper contact is gradational with
the incipient mound facies.
(Fig. 4a). This low-energy facies is found as a
regionally pervasive, muddy phylloid algal unit
present at the base of algal mounds in both out-
crop and subsurface. The incipient mound facies
forms a laterally persistent, fl at bed at the base of
algal mounds in outcrop that is approximately
1.5-2.0 m thick, with a sharp basal contact and
a gradational transition into the overlying phyl-
loid algal mound. The facies is interpreted as a
low-energy accumulation of phylloid algal plates
and carbonate mud on an open platform. The
mechanism(s) responsible for the transition from
muddy algal facies to well-developed phylloid
algal mounds is unknown, but probably results
from changes in environmental conditions such
as wave and/or current energy, and therefore cir-
culation, which would then affect temperature,
salinity and water quality.
Incipient mound facies
The incipient mound facies is a phylloid algal
mudstone to wackestone with a matrix of peloi-
dal mud and scattered diverse skeletal grains
