Albian-Cenomanian depositional cycles transgressed from Chihuahua trough to Western Interior
R. W. Scott, J. M. Holbrook, M. J. Evetts, and F. E. Oboh-Ikuenobe
The Upper Albian to Lower Cenomanian stratigraphic record in the Chihuahua Trough at El Paso, Texas is more than 250 m thick and records six depositional cycles averaging 1.6 million years in duration. Five of these cycles are identified in the much thinner Albian-Lower Cenomanian stratigraphic sections of northeastern New Mexico, Colorado, Kansas, and Wyoming, and the cycle of the Mesilla Valley Formation correlates into the regional unconformity between the Glencairn and Mesa Rica Formations.
Three transgressive-progradational cycles were deposited continuously from Texas north to Wyoming and Montana and the associated seaways provided opportunities for south to north biotic exchange. The first early Late Albian connection is represented by correlation of the two cycles of the Del Norte and Smeltertown fonnations at El Paso with the Tucumcari/Purgatoire/Kiowa/Skull Creek formations in New Mexico, Colorado, and Kansas, and the Thermopolis Formation in Wyoming and Montana. Part of the third cycle represented by the Muleros Formation may be partly represented locally in Kansas-Colorado, but its record is absent in most places.
The second potential connection is represented by the Anapra Formation at El Paso, the Pajarito Formation in New Mexico and the Van Bibber Member of the Muddy Formation in eastern Colorado. The Anapra correlates with the Pawpaw and Main Street formations in north Texas, which includes the range of the uppermost Albian oyster in the Fajardo, Peilinia levicostata Kues [formerly Rastellum quadriplicata (Shumard)]. But the Van Bibber contains a sparse non-marine biota indicating that little northward exchange occurred across the Transcontinental Arch with deposition of the Mowry Formation in Wyoming and Montana. The third connection in the Early Cenomanian is indicated by the Del Rio/Buda formations in El Paso and the lower part of the Graneros Shale northward. However, during this time little biotic exchange occurred, and the foraminiferal faunas are quite different. Full and open exchange was resumed during the Middle Cenomanian when the Thatcher Member of the Graneros was deposited.
The geographic pathways of the ancestors of the endemic ammonites and inoceramids of the Mowry Formation in Wyoming and Montana are as yet unclear. It is possible that these species are relics of the earlier Late Albian connection between the Caribbean and North Temperate Provinces. The geographic range of one of the ammonites is expanded by a new occurrence in the basal Cenomanian section in northwestern France (Cobban and Amedro, personal commun., 2001). Most of the benthic foraminifers in the Mowry are from the northern area, but a sparse plank-tic foraminiferal assemblage indicates a filtered connection with the Tethyan Realm. This connection was not necessarily southward with the Gulf Coast Caribbean Province.
- Scott, R. W.; Holbrook, J. M.; Evetts, M. J.; Oboh-Ikuenobe, F. E., 2001, Albian-Cenomanian depositional cycles transgressed from Chihuahua trough to Western Interior, in: Geology of the Llano Estacado, Lucas, Spencer G.; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, 52nd Field Conference, pp. 221-228.