A LATE PLEISTOCENE TO RECENT GLACIAL AND PERIGLACIAL RECORD FROM THE SOUTHERN ROCKY MOUNTAINS, NORTHERN NEW MEXICO

The southern Sangre de Cristo Mountains of northern New Mexico contain evidence of glacial activity ranging in age from the late Pleistocene to the late Holocene. A suite of sediment cores was recovered from an alpine bog trapped behind a Pinedale-age moraine that is located about 2 km down valley from a high-elevation cirque. Three of the cores reached glacial talus and recovered up to 6 m of sediment consisting of lake clays overlain by gyttja. Clear stratigraphic and sedimentologic changes are correlated with the relative glacial chronology established for the basin based on glacial landforms in the valley and talus flows in the cirque. Accelerator mass spectrometry (AMS) dating, sedimentology, variations in magnetic properties of the sediment, and organic carbon properties in the bog cores reveal six distinct periods of glacial/periglacial activity. These include a late Pleistocene Pinedale glacial termination just before 12,120 ¹⁴C yr B.P., a Younger Dryas chron cirque glaciation, an early Neoglacial periglacial event (~ 4,900 ¹⁴C yr B.P.), a late Holocene cirque glaciation (3,700 ¹⁴C yr B.P.), as well as late Holocene periglacial events at 2,800 ¹⁴C yr B.P., and during the Little Ice Age (~120 ¹⁴C yr B.P.). Each of these cold events correlates in time with subtle ice rafting events in the North Atlantic and with millennial-scale climate change elsewhere in the northern hemisphere. The cold phases in this drainage basin are marked by pulses of enhanced downslope sediment transport with coarser grain sizes. While glacial activity was clearly the dominant erosional agent in this landscape, the role of interglacial millennial-scale cold episodes with enhanced runoff was probably also important.