NEW SHORELINE-BASED CONSTRAINTS ON THE EXTENT AND TIMING OF LATEST PLEISTOCENE HIGHSTANDS OF PLUVIAL LAKE ESTANCIA, CENTRAL NEW MEXICO

Closed basin watersheds of western North America contain valuable paleo-hydrologic records in their alluvial, groundwater discharge, and lacustrine sediments that help inform the region’s response to past hydrologic change. These records are important for establishing sensitivity to drought, tracking past atmospheric patterns, and placing contemporaneous archaeological sites in environmental context. Lake deposits of the Estancia Basin of central New Mexico contain a detailed late Quaternary history of lake transgressions and regressions preserved in basin center deposits. Geochronologic constraints show these lake levels varied in sync with other hydrologic records of western North America and broader global changes. However, clear links between shoreline deposits defining past lake areas and the basin center stratigraphic horizons are obscured by flat basin slopes, sparse shoreline age data, and post-lake alluvial, eolian, and agricultural modification of the surface. We present new radiocarbon ages from gravel pit exposures of shoreline and near shore sediments of the northern basin margin that better define the extent and timing of three late Pleistocene highstands of Lake Estancia centered at 18.9, 17.7, and 16.1 ka. These align well with the last three highstands inferred from basin center deposits and suggest progressively increasing peak lake elevations of ~1893, 1895, and 1897 m, respectively. Notably, the lowermost lacustrine deposits dating to 18.9 ka lie directly on coarse alluvial fan deposits at ~1891 m, that feature well developed carbonate soils indicative of substantial age and surface stability. This indicates MIS 2 lake highstands prior to the late LGM did not reach above this elevation. Overall, this corroborates other evidence from New Mexico for increasing effective moisture during millennial scale wet periods of the LGM and Termination 1, culminating with the “Big Wet” coeval with Heinrich Stadial 1 at 16.1 ka.