Abstract

Lowermost Mississippian deposits of New Mexico and southern Arizona are Tournaisian (pre-Zone 7) in age and unconformably overlie rocks of Late Devonian and Precambrian age. These Mississippian rocks were laid down as sediments during transgression of the sea across an abraded surface of very low relief. An early and middle Tournaisian marine transgression across southern Arizona deposited the Escabrosa Limestone (200-300 m) and, in southwestern and south-central New Mexico, deposited the Keating (207 m), Caballero (18 m), and Lake Valley (180 m) Formations. By the end of Tournaisian (Osagean) time, epicontinental seas had flooded much of southern and central Arizona, depositing the Escabrosa and Redwall Limestones, Osagean seaways extended to the central and northern part of New Mexico, depositing the Kelly (35 m) and Espiritu Santo Formations (35 m). The latter is a sequence of subtidal to supratidal quartz sandstones and carbonate rocks. The Leadville Limestone (50-100 m) in the San Juan Basin of New. Mexico is a time-stratigraphic equivalent to the Espiritu Santo Formation and an eastern extension of part of the Redwall Limestone of Arizona. Two low islands in New Mexico were the Zuni-Defiance highlands and remnants of the transcontinental arch, the Pedernal highlands.

The end of Tournaisian (Osagean) time was marked by marine regression, regional uplift, and erosion of Tournaisian carbonate sediments.

A major regional marine transgression of Visean (Meramecian) age is represented by the upper part of the Escabrosa Limestone of southern Arizona, the upper part of the Hachita Formation (107 m) in southwestern New Mexico, the deeper water basin carbonates of the lower part of the Rancheria Formation (46 m) in south-central New Mexico, and part of the subtidal Tererro Formation (18 m) in north-central New Mexico.

The youngest unit of the Tererro Formation is the Cowles Member (10 m) which suggests that marine sedimentation ceased in northern and central New Mexico in late Visean time (early Chesterian), In southwestern New Mexico, the Paradise Formation (134 m) represents shallow marine sedimentations and ranges from Zone 15 (Meramecian) into Zone 19 (late Visean and Namurian or end of Chesterian). The upper part of the Rancheria Formation (69 m) and the Helms Formation (50 m) of south-central New Mexico are deeper water facies of the Paradise Formation.

Mississippian sedimentary rocks of Namurian, Visean, and Tournaisian age in southern Arizona and in northern, central, and southern New Mexico are truncated by Pennsylvanian marine deposits.