Rates of Soil Development from Four Soil Chronosequences in the Southern Great Basin

Abstract

Four soil chronosequences in the southern Great Basin were examined in order to study and quantify soil development during the Quaternary. Soils of all four areas are developed in gravelly alluvial fans in semiarid climates with 8 to 40 cm mean annual precipitation. Lithologies of alluvium are granite-gneiss at Silver Lake, granite and basalt at Cima Volcanic Field, limestone at Kyle Canyon, and siliceous volcanic rocks at Fortymile Wash. Ages of the soils are approximated from several radiometric and experimental techniques, and rates are assessed using a conservative mathematical approach. Average rates for Holocene soils at Silver Lake are about 10 times higher than for Pleistocene soils at Kyle Canyon and Fortymile Wash, based on limited age control. Holocene soils in all four areas appear to develop at similar rates, and Pleistocene soils at Kyle Canyon and Fortymile Wash may differ by only a factor of 2 to 4. Over time spans of several millennia, a preferred model for the age curves is not linear but may be exponential or parabolic, in which rates decrease with increasing age. These preliminary results imply that the geographical variation in rates within the southern Great Basin-Mojave region may be much less significant than temporal variation in rates of soil development. The reasons for temporal variation in rates and processes of soil development are complexly linked to climatic change and related changes in water and dust, erosional history, and internally driven chemical and physical processes.

Radiocarbon and Soil Carbon Dynamics

“…One example of such a threshold is the ratio of annual precipitation to available soil pore space, which essentially determines whether weathering products remain in the soil profile or are leached out of it (Chadwick & Chorover 2001). Finally, soils have history, and the degree to which current soil conditions reflect past climatic regimes or even past land uses must be part of the overall view of soil development (Harden et al 1991.…”

“…Soil mineral composition, in turn, varies in predictable ways over time as soils develop (Harden et al 1991, Chadwick & Chorover 2001, Baisden et al 2002, Chorover et al 2004). Torn et al (1997) demonstrated very long (>50,000 years) residence times for the large amounts of C associated with allophane that are the initial weathering products in young soils with basalt parent material.…”

Gamma radioactivity on a chronosequence, Pinery Provincial Park, Ontario

“…Also, there are few true chronosequences in which there is great confidence that none of the other soil-forming factors are varying in any degree with soil age (Crocker 1952;Singleton and Lavkulich 1987 (Harden et al 1991), marine terraces in Oregon (Bockheim et al 1992) and river terraces in California (Harden et al 1987) (Birkeland 1990 (Myttenaere and Girardi 1982)' The soil chronosequence is the logical f,teld scenario for investigating these relationships.…”

Environmental history recorded in aeolian deposits under stone pavements, Mojave Desert, USA

“…With time the degree of soil development increases, expressed for example by increasing values of the profile development index (Harden et al, 1991) or increasing secondary carbonate contents and carbonate morphology stages. However, soil development can also vary remarkably on landforms of the same age within a few tens of metres, as demonstrated by Wood et al (2002Wood et al ( , 2005, who highlighted the close relationship between surface properties (pavement coverage, clast size, vegetation density and type) and subsurface properties.…”