SOIL DEVELOPMENT AS AN INDICATOR OF RELATIVE PINGO AGE, NORTHERN ALASKA, USA

Soils of pingos in the Prudhoe Bay region of northern Alaska (70 degre es N, 148 degrees W) were examined to determine if their development c ould be used to support or nullify a hypothesis of differential age be tween two morphologically distinct groups of pingos. The two morpholog ical types, one with steep side slopes and small basal diameters (''st eep-sided'') and one with gentle side slopes and large basal diameters (''broad-based''), have been proposed to represent two different age groups. Steep-sided types are found on landscape surfaces of all ages, always within recognizable thaw-lake basins, and are all presumed to have formed within the last 10 kyr. Broad-based types are found only o n pre-Holocene surfaces and never within recognizable thaw-lake basins , leading to speculation that they formed during a previous thaw-take cycle on the older surfaces. Soils were described and collected from n ine localities on each of three steep-sided and two broad-based pingos . Profile development was quantified using an index that compares soil morphology with parent material characteristics. A second index quant ified profile anisotropy of various soil properties. Multiple lines of evidence from the pingo soils supports the differential age hypothesi s. Broad-based pingos have greater concentrations of clay and iron, lo wer pH, more developed color, structure, and consistence, and greater profile anisotropy. Absolute pingo ages were estimated by developing r egression equations for profile development of temperate soils from th e literature and applying these to the pingo soils. The regression res ulted in estimated ages of the steep-sided pingos of approximately 5 k y and of broad-based pingos of 14-22 kyr, which are thought to be mini mum age estimates.