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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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