Page 208 - Carbonate Facies in Geologic History

Townsend-Kemnitz Field- A Tubiphytes and Tubular Foraminiferal Reef 195

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40 28
o

IJopochJ 01
poro.ity in I •• ,
36 31 32 in Wolfcomp
• Well

Fig.VI-23. Porosity isopachous map of Kemnitz field, New Mexico. Isopach in ten foot
intervals of beds with between 8 and 18% porosity. Line of cross section on Fig. VI-22
indicated. Porosity clearly outlines fairway and reef at shelf margin. Numbered squares in
grid are square miles. (Sections within Townships)

micrite. Fusulinid and crinoid coquinas are common in places within this facies.
Very coarse talus also exists in the form of rudites of poorly sorted, varied litho-
clasts and bioclasts. The lithoclasts are from both shelf and shelf margin sedi-
ments and the bioclasts are large, broken, abraded, and somewhat blackened
fossils of brachiopods, horn corals, bryozoans, crinoids, and fusulinids. The Kem-
nitz north-south cross section (Fig. VI-22) shows a greater development of algal
plates downslope, presumably in slightly deeper water. Basinal facies consist of
argillaceous, dark, spiculitic micrite with lenses of purer carbonate micrite and
much ball and flow lamination.
According to Malek-Aslani porosity is best developed within the Tubiphytes
boundstone fabric. It reaches a maximum of 18%, but averages about 8%. There
is fair interconnection within the boundstone so that permeability may be good
although variable. By far the best production from Townsend-Kemnitz was from
the very narrow reef front belt or "fairway". Malek-Aslani considers that most of
this is primary porosity in a reef fabric. Some reservoir rock was formed by
interconnected algal plate porosity where the large amount of original pore space
was not filled by much micrite matrix and where brecciation, plate fracture and
mud flowage occurred. See Fig. VI-23 for isopach of porosity.
Dunham (1969b) presented compelling evidence of both leaching and infilling
ofthe fairway sediment in the vadose zone. This interpretation must be related to
an understanding of the typically complex geological history of Pennsylvanian
buildups which commonly record several sea level fluctuations and periods of