Genesis of a Holocene soil chronosequence from the southernmost Andes Mountains, Tierra del Fuego

Abstract

At the southernmost Andes Mountains, the Martial cirque glacier has retreated 2km in distance and 500m in elevation since the mid-Holocene. This study examines soil properties, processes, and classification in relation to soil age and elevation. Soils were sampled at elevations from 430 to 925m a.s.l. on drifts periodically influenced by volcanic ash that represent five age classes: 5.0 to 6.0kyrBP under deciduous Nothofagus pumilio forest; 1.3 to 3.2kyrBP under N. pumilio and N. antarctica forest and tundra; 0.3 to 1.4kyrBP under tundra; 0.3KyrBPCE under tundra; and 0.007KyrBPCE under scattered lichens and mosses. The soils represent a developmental sequence on metapellitic rocks ranging from: Cryorthents, Dystrocryepts, Humicryepts, and Humicryods. In general the soils contain abundant coarse fragments, sandy loam textures, and high levels of organic C. Clays have been altered in the soils from chlorite to a hydroxyl-interlayered vermiculite and ferrihydrite. The most developed soils are very strongly acid, Al saturated, and have illuvial horizons enriched in fulvic-acid C and organic-bound forms of free Fe and Al. The following properties are highly correlated with soil age: pyrophosphate soluble iron (Fep) in the B horizon (R2=0.97), color-development equivalence in the B horizon (R2=0.87), clay content of the B horizon (R2=0.68), and fulvic-acid C in the B horizon (R2=0.65). The results of this study imply that soil formation in magellanic subantarctic forests and tundra is rapid and involves podsolization, andisolization, and humification as primary soil-forming processes.