DEPOSITIONAL CONTROLS ON THE DISTRIBUTION OF EARLY PERMIAN PHYLLOID ALGAL BIOHERMS ON THE WESTERN MARGIN OF THE OROGRANDE BASIN

Late Paleozoic organic carbonate buildups of North America are concentrated in basins associated with the development of the Ancestral Rocky Mountains. Spatial and temporal distribution of these buildups is primarily controlled by glacial-eustasy, regional and local tectonics, and depositional profile style. In south central New Mexico, the Orogrande basin is the western extent of the Permian Basin, and contains Permian phylloid algal buildups. Previous work on the Orogrande basin has focused primarily on the eastern shelf margin, where thick phylloid algal buildups are associated with restricted tidal flat and lagoonal facies, suggesting buildups formed a significant bank with topographic relief. In contrast, the western margin has been interpreted as a distally steepened ramp, progressively deepening from west to east.

Outcrop datasets of the Lower Permian Hueco Limestone on the western margin of the Orogrande basin were analyzed in regard to depositional facies distribution and sequence stratigraphy in order to reevaluate the geometry of the western margin. Eight stratigraphic sections were measured in the Lower Hueco member to create a northwest to southeast (landward-basinward) transect across the western margin. Five depositional facies are recognized: 1) tidal flat laminated dolomicrite with subordinated algal laminates, 2) restricted lagoonal ostracode-rich, cherty wackestones, 3) bank margin oolitic shoals, 4) bank margin phylloid algal bafflestones with crinoidal and calci-sponge packstones, and 5) upper slope open marine, intraclast packstones. Parasequence stacking patterns based on these depositional facies define prograding facies associations that shallow and thicken upsection. This suggests a switch in the depositional profile style from ramp to platform during the Wolfcampian related to progressive climatic aridification and waning tectonism in the late stages of the Ancestral Rocky Mountains development.