Paleoecology of Marine Foraminifera in the Pluvial Estancia Valley, Central New Mexico

Abstract

Two species of marine Foraminifera have been identified in the Quaternary pluvial sequence of the Estancia Valley, central New Mexico. Besides being an unusual occurrence of marine organisms in an inland body of water remote from the marine environment, the Foraminifera yield useful paleolimnological and paleoclimatological information about two major late Wisconsin pluvial lakes. In addition, the geographic location of the Estancia Valley relative to the closest marine environment requires foraminiferal introduction by avian means. Paleontologic evidence verifies the freshwater nature of the pluvial maxima of Late Lake Estancia (18,000-10,500 BP) and Lake Willard (8500-6000 BP) but early lake conditions were considerably different. The occurrence of foraminifers Cribroelphidium selseyense and Protelphidium orbiculare, both extant species, in the sediments from the early part of each pluvial stand indicates that initial lake development was characterized by a salinity range of 25 to 35‰. At these times lake depth approximated 6 m. By comparison, the freshwater maximum of Late Lake Estancia attained a minimum depth of 90 m. The modern holarctic distribution of the Foraminifera could suggest a mean August lake temperature of 10°C during the developmental stages of Late Lake Estancia and Lake Willard. Because of the shallow-water nature of the lake basins it is likely that this temperature was reflective of mean August air temperature. Therefore, a lowering of mean August air temperature of 9.7°C from that of the present is possible.