Stratigraphy, facies, and paleotectonics, Mississippian System, New Mexico
— Augustus K. Armstrong and Bernard L. Mamet

In the San Juan Basin of northwestern New Mexico, lowermost Mississippian deposits are Kinderhookian/earliest Osagean (pre-zone 7, zone 7) in age, are restricted to the western margin of the basin and overlie rocks of Late Devonian age. These Mississippian rocks were laid down as carbonate sediments during a transgression of the sea across an abraded surface of very low relief. The Osagean marine transgression continued in an eastward and southeastward direction from the Four Corners region and northward from southcentral New Mexico, flooding a terrane of Precambrian igneous and metamorphic rocks. The Precambrian surface was irregular, and islands stood above the late Osagean sea. These major islands, parts of regional lineation trends, were the Zuni-Defiance uplift, the Uncompahgre uplift and the Pedernal uplift. The Osagean carbonate sediments adjacent to the highlands were supratidal and intertidal lime mudstones, anhydrites, gypsum, dolomites, quartz sandstones and shales. The sediments in more open marine environments were calcareous sand shoals composed of pellets, bioclasts of crinoids, brachiopods, bryozoans and ooids and oolites. The end of Osagean time was marked by regional marine regression, uplift and erosion of the carbonate platform. The next regional marine transgression is represented by Meramecian age limestones in the subsurface of southeastern Utah, the western part of the San Juan Basin and in outcrops of the Tererro Formation (Arroyo Peñasco Group), in the Nacimiento, San Pedro and Sangre de Cristo Mountains in northern New Mexico and the subsurface of northeastern New Mexico. These are marine, bioclastic, arenaceous, carbonate sediments composed of dolomites, lime mudstones, ooid-oolites, crinoids, Foraminifera, algae, brachiopods and pellets. A marine transgression represented by the Cowles Member of the Tererro Formation of early Chesterian age is found in the Sangre de Cristo Mountains. During the Late Mississippian the region was differentially uplifted, and large areas of Mississippian sediments were removed. The remaining carbonate rocks were subjected to solution and karst activity, resulting in the development of a thick regolith. In the San Juan Mountains and the subsurface, this regolith was reworked by the transgressive Pennsylvanian sea and formed the Molas Formation. On the eastern flank of the San Juan Basin in the San Pedro, Nacimiento and Sandia Mountains, the Mississippian carbonates of the Arroyo Peñasco Group are overlain unconformably by the continental red beds of the Chesterian Log Springs Formation. Everywhere, Mississippian sedimentary rocks are truncated by Pennsylvanian sedimentary rocks.