Ages of Quaternary Rio Grande terrace-fill deposits, Albuquerque area, New Mexico

Results from luminescence dating on 13 samples from the Albuquerque area show that major-drainage fluvial deposits represent significant periods of aggradation that formed paired, correlatable terraces on the east and west margins of the Rio Grande valley . The youngest terrace fills (Primero Alto) formed during late Pleistocene as a result of streamflow variations with climate cooling during Marine Oxygen-Isotope Stage 3; our ages suggest aggradation of the upper part of the fill occurred at about 47–40 ka . Deposits of the second (Segundo Alto) terraces reached maximum height during climate cooling in the early part of Marine Oxygen-Isotope Stage 5 as late as 90–98 ka (based on dated basalt flows) . Our luminescence ages show considerable scatter and tend to be younger (range from 63 ka to 162 ka) . The third (Tercero Alto) and fourth (Cuarto Alto) terraces are dated on the basis of included volcanic tephra . Tercero Alto terrace-fill deposits contain the Lava Creek B tephra (639 ka), and Cuarto Alto terrace-fill deposits contain tephra of the younger Bandelier Tuff eruption (1 . 22 Ma), the Cerro Toledo Rhyolite (1 .47 Ma), and the older Bandelier Tuff eruption (1 . 61 Ma) . These periods of aggradation culminated in fluvial terraces that are preserved at maximum heights of 360 ft (Cuarto Alto), 300 ft (Tercero Alto), 140 ft (Segundo Alto), and 60 ft (Primero Alto) above the modern floodplain . Despite lithologic differences related to local source-area contributions, these terracefill deposits can be correlated across the Rio Grande and up- and down-valley for tens of miles based on maximum height of the terrace above the modern floodplain .