The upper Cenozoic Gatuna Formation of southeastern New Mexico
Dennis W. Powers and Robert M. Holt
The Gatuna Formation of southeastern New Mexico has been studied in the field for two landfill projects and the Waste Isolation Pilot Plant project. Shafts, drilling and field mapping reveal the distribution, thickness and sedimentary features of the unit in an area where it was poorly known or assigned to other units. The Gatuna is at least 300 ft thick in the study area. The formation was deposited in the north and east as elastic beds ranging from conglomerates to laminar claystones. Fining upward cycles are common, though depositional features and facies associations are consistent with braided river/stream environments, not meandering rivers. Laminar and thinly bedded siltstones to claystones were deposited in floodplain to playa environments. Pedogenic features superimposed on many fining upward cycles include soil fractures, slickensides, MnO2 illuviated clay, bioturbation, probable ped structures and desiccation cracks. The upper Gatuna more consistently includes pedogenic development. Beds of poorly indurated "orange" sand, consisting of rounded and well-sorted grains, are interpreted as eolian deposits. From southern Nash Draw to Orla, the Gatuna is fine-grained and gypsiferous, including displacive crystals and probable subaqueous deposits. These outcrops represent low energy environments, including playas, which were near local base level. The age of the upper Gatuna is reasonably constrained by the Lava Creek B ash (0.6 Ma) within the Gatuna along Livingston Ridge. The age of basal deposits is poorly or not constrained. An ash within probable Gatuna near Orla, TX, is about 13 Ma based on both radiometric and geochemical data. The Gatuna represents an important piece of the geological history of southeastern New Mexico. Further studies could include efforts to better determine the age of the formation; to obtain paleontological data; and to map Gatuna structural relationships to older and younger beds in detail to determine the timing of and spatial evidence for, dissolution of evaporites and collapse of overlying beds, including the Gatuna.
- Powers, Dennis W.; Holt, Robert M., 1993, The upper Cenozoic Gatuna Formation of southeastern New Mexico, in: Carlsbad Region, New Mexico and West Texas, Love, David W.; Hawley, John W.; Kues, Barry S.; Adams, Jim W.; Austin, George S.; Barker, James M., New Mexico Geological Society, Guidebook, 44th Field Conference, pp. 271-282.