LATE HOLOCENE RAPID HYDROCLIMATIC CHANGE AT CIENEGA AMARILLA, WEST-CENTRAL NEW MEXICO, USA

Cienega Amarilla is a late Holocene carbonate spring mound with associated wetland deposits located in west-central New Mexico near the Arizona border. Alluvial and groundwater discharge deposits at Cienega Amarilla provide a 4000-year record of geomorphic, paleoenvironmental, and hydroclimatic change on the southern Colorado Plateau. Six allostratigraphic units identified in the Cienega Amarilla vicinity include alluvial, intermittent wet meadow, marsh, and carbonate spring mound facies. Forty-four ¹⁴C dates provide the basis for a high-resolution (centennial-scale) chronostratigraphic framework. The isotopic composition (δD and δ¹⁸O) of Cienega Amarilla spring water indicates that groundwater discharge there is driven primarily by winter precipitation. Although modern summer precipitation totals in the study area are generally greater than winter amounts, regional groundwater recharge is derived primarily from winter precipitation. Compared to summer storms, winter storms are generally more widespread, lower intensity, longer duration, and coincide with cooler temperatures and dormant vegetation, resulting in more winter moisture infiltrating into the ground. Pollen, plant macrofossil, gastropod, ostracode, and soil analyses aided reconstruction of local paleoenvironmental conditions at Cienega Amarilla. Rapid spring mound growth and wetland expansion ~2.3–1.6 cal ka signify a period of enhanced groundwater discharge followed by a sudden and pronounced decline between 1.6 and 1.0 cal ka. Cienega Amarilla spring discharge changes are consistent with other southwestern U.S. paleoenvironmental records and closely parallel prehistoric El Niño proxy record trends. The ~2.3–1.6 cal ka period of peak Cienega Amarilla groundwater discharge appears linked to increased winter precipitation that may have been a catalyst for prehistoric cultural changes throughout the southwestern U.S. including increased sedentism and dependence on agriculture.