A 65,000-YEAR RECORD OF HYDROLOGIC VARIABILITY IN THE ESTANCIA BASIN OF CENTRAL NEW MEXICO

Pluvial Lake Estancia in the Estancia Basin of central New Mexico contains one of the most continuous records of late Pleistocene and Holocene climatic variability in the American Southwest. Previous work employing radiocarbon dating, ostracode biostratigraphy, sediment mineralogy, and geochemistry revealed that the lake oscillated in size between 400 km² lowstands and 1100 km² highstands at least 9 times immediately prior to, during, and after the Last Glacial Maximum (LGM), including a post-LGM lowstand and highstand and a small highstand during the Younger Dryas (Allen and Anderson, 2000; Anderson, Allen, and Menking, 2002). In addition, high resolution studies of the LGM sediment sequence have revealed decadal to millennial scale cycles consistent with solar forcing (Menking, 2015). Highstand shorelines were accompanied by deposition of thick bioturbated clay marls and ostracodes indicative of fresh water whereas lowstands were characterized by deposition of thinly laminated (1-2 mm) gypsum sand and algal mats and by ostracodes with salinity tolerances >200,000 ppm.

Here we present new work that extends the record of hydrologic variability in the Estancia Basin backward in time to ~65 ka. Based on the different degrees of lamination and bioturbation seen in lowstand versus highstand deposits from the late Pleistocene, we have devised a qualitative lake level index (LLI) and applied it both to previously studied outcrop sediments and to a new sediment core that spans lower stratigraphic levels. Age control for the combined sequences comes from a mixture of radiocarbon dates on ostracodes for the last 30 ka (Allen and Anderson, 2000) and U-Th dates on gypsum sands from ~30-65 ka (Polyak et al., 2012). Fluctuations in LLI values throughout the entire sequence reveal similarities to oxygen isotopic variations at Fort Stanton Cave in southern New Mexico and the Greenland ice sheet (Asmerom et al., 2010; Seierstad et al., 2014).