Page 210 - Carbonate Facies in Geologic History

Description of an Early Pennsylvanian Field in Sutton County, West Texas 197

LOWER STRAWN SHELF EAST
WEST
15 km
8ASIN
81ack shale with
sp iculitk cherty
mudstone

abundant Komia Wackestone and mudstone
and crinoids with few algal pi ales, few Komia,
fusulinids, crinoids, foroms algal ploles,
crinoids
m Komio ~ forams I ~ I fusulinids 0 Platy algo. G Shelly biodosls

Fig. VI-24. Section across Middle Pennsylvanian field, west-central Sutton County, Texas.
Section is 15 km across field. Interval diagrammed is a few tens of meters thick~a minor shelf
margin buildup capped with Komia grainstone. It is of lower Desmoinesian age, zone of
Wedekindellina and Fusulina

Description of an Early Pennsylvanian Field in Sutton County, West Texas

The small Denison field in West Texas is known to produce oil from a reservoir
consisting of detritus of the tiny dendroid stromatoporoid, Komia (Fig. VI-24).
This is one of the many fields of Desmoinesian or Strawn age which developed in
shelf margin carbonate buildups along the shifting western margins of the eastern
shelf of the Midland basin. The textural and biological makeup of these fields has
not yet been well described in the literature. (See, however, Toomey and Winland,
1973.)
Komia was probably not capable of frame construction despite its known
branching growth form when seen intact (Ungdarella of Toomey and Johnson,
1968, see Wilson, 1969, for correction). It is a delicate organism and is commonly
found in micritic bedded limestones. In the Denison field it forms crinoid-rich
flank debris on the seaward, exposed side of a lime mud mound containing a few
algal plates and many foraminifera. The reservoir is composed of grainstone
sediment with original porosity preserved and with some diagenetic alteration of
Komia bioclasts. A good analogy may be made with the similarly shaped modern
red alga Goniolithon whose debris forms a seaward fringe on Rodriguez Bank in
the Florida Straits (Baars, 1963) and with the rapidly eroding red algae fringing
reefs around the northern end of the Qatar Peninsula in the Persian Gulf. Both
this field and the Nena Lucia buildup described by Toomey and Winland (1973)
show that the porous reservoir facies may be preferentially developed on the open
sea, winnowed side of these low-lying buildups.