Ocean Water Mass Stratification as Scaffolding for Depositional Systems: Mississippian and Permian of New Mexico and Texas

The stratified nature of ancient basin water masses is rarely invoked to explain lateral and vertical depositional trends in ancient basins. The recent body of work addressing the vertical organization of modern ocean water masses and boundaries between them indicates the importance of the structure and processes to global nutrient and energy circulation and sediment movement. Study of modern internal waves along pycnoclines documents horizontal fluid velocities near the substrate as high as 80 cm/s, sand waves that are actively migrating, and the geochemical and biological characteristics of sediments associated with the OMZ. The interpretation of ancient basin data sets would benefit from the context and scaffolding provided by this vertical organization which drives processes that result in organic and carbonate productivity, bottom currents, and sediment transport. Mississippian strata of the Sacramento Mountains of New Mexico and Permian strata of the Guadalupe Mountains of Texas provide evidence for the stratified nature of the ancient ocean water masses. In the Mississippian example, the rise in the pycnocline and OMZ on the margins of a mudmound are documented with sedimentologic, biologic, and trace element evidence. In the Permian example, onlapping wedges of coated grain grainstone with up-slope migrating ½ meter scale sand waves restricted to the base of the onset of accretionary reef facies, as well as geochemical evidence, support the presence of a pycnocline. In both examples, ocean stratification contributes to the development of models for nutrient flow in line with modern mesophotic and deep-water reefs.