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.
Sedimentologic and paleontologic analyses of a 10.5 m subsurface section from the Estancia Valley provides a high-resolution paleolimnologic record of a pre-late Wisconsin section that is suspected to represent early through middle Wisconsin time. Relative abundances of ostracodes, foraminifers, Ruppia, and charophytes, along with sedimentologic aspects, depict a time interval characterized by alternating dry and wet playas and shallow saline lakes. The saline lakes exhibit marked evolution from brackish to saline to, presumably, hypersaline conditions. The overall paleoenvironmental conditions are in great contrast to those represented by the overlying full glacio-pluvial sediments of late Wisconsin age.The pre-late Wisconsin section, as a whole, represents cold/dry paleoclimatic conditions. Minor climatic excursions from this norm are recognized, but the section is more notable for its quasistability. The lack of any fresh-water phase during this time implies that there was no regional climatic shift of the magnitude of the late Wisconsin. It is surmised here that if a cold/dry climate results in saline lakes, at the extreme, then full glacio-pluvial systems must require a significant increase in precipitation along with cold paleoclimatic conditions in order to maintain deep, fresh-water lakes in the currently arid southwestern United States.
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