Geoscience Reference
In-Depth Information
12.6 Genesis of Calcic and Petrocalcic Horizons
The genesis of calcic and petrocalcic horizons has been considered in detail by Gile
et al. ( 1981 ), Machette ( 1985 ), McFadden and Tinsley ( 1985 ), Rabenhorst and
Wilding ( 1986b ), West et al. ( 1988b ), Reheis et al. ( 1992 ), Shankar and Achyuthan
( 2007 ), Brock and Buck ( 2009 ), Monger et al. ( 2009 ), Hirmas et al. ( 2010 ),
Achyuthan et al. ( 2012 ), and others.
A key concept that has arisen from these and other studies is that of polygenesis
and the concept of soil-forming intervals. For example, two pulses of aeolian
sedimentation and soil formation were observed in the Lake Lahontan basin, NV,
the most recent during the late Holocene and an earlier event during Isotope Stage
5 (Chadwick and Davis 1990 ). The Churchill soils have been influenced by a three-
phase process: infiltration of desert loess into a coarse, clast-supported fluvial or
alluvial deposit during the arid, interpluvial phase of a Quaternary climate cycle
(Isotope Stage 5); slow weathering of the emplaced loess during the longer pluvial
phase of the climate cycle (Isotope Stages 4, 3, and 2); and a final phase of desert
loess infiltration (Isotope Stage 1). Similar findings were reported in the northern
Great Basin of the USA that involved two cycles of colluviation along with loess
deposition, followed by periods of soil formation that included formation of argillic
horizons. Amiotti et al. ( 2001 ) recorded three phases of aeolian deposition in
petrocalcic horizons of semiarid Argentina since beginning in the Pliocene and
continuing to the Holocene. These studies suggest that the soils have undergone
episodic soil development in response to climate change.
At Lake Mojave, CA, Wells et al. ( 1987 ) recorded six alluvial fans over the past
15,000 yr in response to climatically controlled stands of Lake Mojave. In the High
Plains of TX and NM, a 110 m section contains aeolian sediments with intercalated
paleosols that have been forming since the early Pliocene (Gustavson and Holliday
1999 ). During the interpluvial phases clay movement occurred in the soils.
12.7 Summary
Soils with calcic and petrocalcic horizons comprise about 1 million km 2 ,or
approximately 13 % of the total US land area. These soils occur in six orders,
22 suborders, 46 great groups, 158 subgroups, and about 2,200 soil series. Calcic
and petrocalcic horizons are most common in the Aridisols (973 soil series)
followed by the Mollisols (918), Inceptisols (219), Alfisols (79), Vertisols (22),
and Andisols (two soil orders). Soils with calcic and petrocalcic horizons occur
primarily in aridic/torric (44 %), ustic (26 %), and xeric (17 %) soil-moisture
classes; mixed mineralogy classes (78 %); mesic (36 %), frigid/cryic (35 %), and
thermic (23 %) soil-temperature classes; and loamy and loamy-skeletal (75 %)
particle-size classes. These soils are found primarily in the Basin and Range
Province of western USA, but they also occur in glacial lake plains of MN and
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