ABSTRACT:
Six distinctive limestone facies, plus shale and sandstone, have been defined by a detailed petrologic and paleontologic study of five cores through a Middle Pennsylvanian (Desmoinesian) carbonate buildup in the Nena Lucia field area, Nolan County, Texas. The limestone facies, designated according to their most outstanding characteristic(s) are: (1) crinoidal, (2) pelletal-foraminiferal, (3) algal-plate, (4) algal-intraclast, (5) intraclastic, and (6) micritic. The first four facies display a restricted distribution pattern relative to the carbonate buildup, whereas the last two facies may be present in any position within the carbonate sequence. Quantitative limits have been delineated for the characteristic petrographic parameters of each facies present within the line of cross section through Nena Lucia field. Subtle petrographic and paleontologic differences in the sandstone and shale from the northwest (front) side and southeast (back) side of the bank are present in the studied cores. Distinct vertical paleontologic changes corroborate and strengthen the petrographic criteria. In addition, certain paleontologic variables appear to show subtle lateral changes that may be applicable in attempting to determine relative position on, or proximity to, the algal-plate mound buildups.
