Page 205 - Carbonate Facies in Geologic History

192 Pennsylvanian-Lower Permian Shelf Margin Facies

LOWER WOLFCAMP
PALEOENVIRONMENTAL MAP
SOUTHEAST NEW MEXICO

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Fig. VI-20. Early Wolfcampian paleoenvironments, southern New Mexico showing details of
Fig.VI-19. From Malek-Aslani (1970, Fig.8), with permission of American Association of
Petroleum Geologists

Townsend-Kemnitz Field-A iilbiphytes and Tubular
Foraminiferal Reef (Dunham, 1969 b, Malek-Aslani, 1970)

Another type of organic buildup occurs in lower Permian strata in the southwest-
ern U.S.A.-a linear mud bank with a boundstone cap. A well-studied example
occurs in the subsurface around the northern end of the Delaware Basin in Lea
County, New Mexico. Earliest Wolfcampian beds here form an east-west curving
trend of carbonate buildups which cross several structurally high areas trending
north-south and formed by early Pennsylvanian block faulting (Figs. VI -19, VI -20).
Continued movement along these faults caused gentle scarps and shallow
water and resulted in carbonate buildups along them throughout the Pennsyl-
vanian. Where early Wolfcampian shelf margins cross the fault blocks, a struc-
tural culmination causes the Townsend-Kemnitz field. The trend has been exten-
sively studied using abundant core material available from numerous wells. Re-
gionally, the lowest Wolfcampian beds constitute a wedge thinning northward
from the thickest and most porous development in the shelf margin trend. Basinal
beds to the south are thin, dark, spiculitic limestone. The porous equivalent of