Lacustrine depositional environments of the Upper Triassic Redonda Formation, east-central New Mexico
Patricia C. Hester and Spencer G. Lucas
The Redonda Formation of the Chinle Group represents deposition in lacustrine and lake margin depositional environments during the Late Triassic (Norian-Rhaetian?) in east-central New Mexico, but not in a single, large lake. Lake margin facies in the Redonda depositional basin correspond to basement highs that delineated the Paleozoic Tucumcari structural basin, indicating that older structures influenced deposition during the Late Triassic. Paleozoic structures were either topographically high, or a reactivation of the Tucumcari basin initiated changes in drainage systems. Coarse, terrigenous sediment was deposited in Gilbert deltas where fluvial systems flowed into the Redonda depositional system along its eastern edge. Delta progradation at the northern edge of the depositional system produced delta-front sheet sands that were deposited and reworked by waves or currents. Beach environments produced carbonate mud on shallow mudflats along some shorelines, whereas sand beaches prograded at other shorelines. In the deepest lake settings, deposition inevitably gave way to shallowing, and alternations of sandstone and mudstone recorded climatically induced changes in lake level and sediment influx throughout Redonda history. Evidence of Late Triassic climatically influenced lacustrine deposition at low paleolatitudes in the Southwest corresponds to other evidence for climate control of lacustrine deposits of similar age along the present East Coast. The frequency of the response in lakes of the Redonda depositional system is consistent with the interpretation that orbital forcing of climate influenced lacustrine sedimentation over a broad region of Pangea.
- Hester, Patricia C.; Lucas, Spencer G., 2001, Lacustrine depositional environments of the Upper Triassic Redonda Formation, east-central New Mexico, in: Geology of the Llano Estacado, Lucas, Spencer G.; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, 52nd Field Conference, pp. 153-168.