SOIL CHRONOSEQUENCE STUDY OF LONG VALLEY, NEW MEXICO: INSIGHTS INTO THE DEVELOPMENT OF SOILS ON PLEISTOCENE AND HOLOCENE MORAINE CATENAS

The history of glacial advance and retreat cycles in mountain watersheds is recorded in glacial landforms. The Sangre De Cristo mountain range in northern New Mexico contains evidence for some of the southernmost expansion of glacial activity in the Southwest during the Quaternary, barring only the Sacramento Mountains of southern New Mexico, but there have been few studies correlating its glacial chronology to the Rocky Mountain glacial record. Glacial deposits within Long Valley in the Sangre de Cristo Mountains were correlated with the glacial history of the southern Rocky Mountains and Wind River Range utilizing soil and landform properties. A soil profile development index (PDI) was calculated utilizing soil texture, structure, consistency, and color data. Organic carbon, hydroxalamine extractable (FeO) and dithionite extractable (FeD) iron oxides, and clay accumulation were also utilized to differentiate moraine age correlations. Soil development is observed to increase with age between soil catenas and at individual catenary positions. Utilizing the calculated PDI values, chemical and physical proxies, as well as field and DEM observations of moraine morphology, four Pleistocene glacial periods are observed within the Long Valley moraine sequence as well as two much smaller periods during the Holocene. Moraines were correlated to the Bull Lake, Pinedale, Oldest Dryas, Youngest Dryas, and two periods during the latter half of the Holocene. Among moraine morphology parameters, summit width and flank slope best distinguished moraines of different ages. Profile mass content of FeD iron and clays increased with age while FeO iron and organic carbon profile mass content decreased with age. The soil PDI values had the highest correlation with surface age, with chronofunctions for clay and the FeO/FeD ratio also representing good age discriminators. organic carbon, FeO, and FeD iron were not as useful in differentiation of moraine ages. Chronofunctions for soil catenas exhibited the greatest correlation with age with Summit position soils also exhibiting good correlations with age.