Late Pennsylvanian phylloid-algal bioherms, Orogrande Basin, south-central New Mexico and west Texas
Donald F Toomey
Phylloid-algal bioherms are relatively common attributes of Late Paleozoic cyclical/repetitive sedimentation. Upper Pennsylvanian (Virgilian) rocks of the Orogrande Basin, south-central New Mexico and west Texas, contain bioherms composed of upright phylloid algae that display the relationship of facies to growth history and paleotectonics. Three outcrop locations rimming the Orogrande Basin contain excellent exposures of phylloid-algal bioherms, some of which attain a thickness of up to 34 m. Bioherms of the Panther Seep Formation in the San Andres Mountains are within an active military reservation, and information from those outcrops is limited. Exposures in the Sacramento Mountains have been studied extensively and demonstrate bioherm morphology and growth history on relatively narrow shelf margins, during intervals when regional tectonic activity on the La Luz anticline produced a distinct progression of bioherm growth stages on the western flank of the anticline, clearly showing bioherm accretion during upward-shoaling phases. Late Pennsylvanian phylloid-algal bioherms exposed in the Hueco Mountains of west Texas, along the southeastern rim of the Orogrande Basin, have a similar paleotectonic setting as the bioherms in the Sacramento Mountains. However, the biohermal interval is thicker and stratigraphically ranges through the entire Virgilian. Also, individual bioherms have rather different morphologies and associated flanking and inter-biohermal lithologies. All phylloidalgal bioherms rimming the Orogrande Basin are oriented with their long axes parallel to the trend of the depositional strike of the shelf margins.
- Toomey, Donald F, 1991, Late Pennsylvanian phylloid-algal bioherms, Orogrande Basin, south-central New Mexico and west Texas, in: Geology of the Sierra Blanca, Sacramento and Capitan Ranges, New Mexico, Barker, James M.; Kues, Barry S.; Austin, George S.; Lucas, Spencer, G., New Mexico Geological Society, Guidebook, 42nd Field Conference, pp. 213-220.