Calcic and Petrocalcic Horizons - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 105

Chapter 12
Calcic and Petrocalcic Horizons

12.1 Introduction

The calcic horizon has significant accumulation of secondary calcium or other
carbonates. If these carbonates are cemented or indurated, it becomes a petrocalcic
horizon. Soils with such horizons are found in many parts of the world, though
mainly in the arid regions. The study of soils with calcic and petrocalcic horizons is
highly relevant because they (1) contain high concentrations of inorganic C (Schle-
singer 1982 ; Hirmas et al. 2010 ), (2) can be used to reconstruct paleo-environments
(Monger et al. 1991 ; Dhir et al. 2004 ; Durand et al. 2007 ; Shankar and Achyuthan
2007 ; Achyuthan et al. 2012 ), (3) have enabled an understanding of aeolian inputs
on pedogenesis (Reheis 1990 , 2006 ; Reheis et al. 1992 ; Reheis and Kihl 1995 ;
Gustavson and Holliday 1999 ; Amiotti et al. 2001 ), (4) contribute to our knowledge
of polygenesis (Kleber 2000 ; Brock and Buck 2009 ), (5) allow for relative dating
and determination of rates of soil formation (Gile et al. 1966 ; Machette 1985 ;
McFadden and Tinsley 1985 ; McFadden 1988 ; McFadden et al. 1989 ; Reheis
et al. 1989 ; Harden et al. 1991 ; Khokhlova and Kouznetsova 2004 ; Calero
et al. 2008 ; Bad´a et al. 2009 ; Zielhofer et al. 2009 ), and (vi) can be used to study
the impacts of desertification (Hirmas and Allen 2007 ; Sierra et al. 2009 ).
In Soil Taxonomy (Soil Survey Staff 2010 ), the requirements for a calcic horizon
include (1) a thickness of

5 or 15 % CaCO 3
equivalent (depending on the clay content), (3) a 5 % greater concentration of
CaCO 3 than in the underlying horizon, and (4) the lack of cementation or induration
by carbonates. A petrocalcic horizon is cemented or indurated by carbonates, has a
lateral continuity

15 cm, (2) a concentration of

1 cm if it consists of a
laminar cap directly over bedrock). The calcic horizon is defined similarly in the
WRB ( IUSS Working Group WRB 2006 ); however, the petrocalcic horizon is
defined as having a very strong reaction to 10 % HCl and an extremely hard dry
consistence; the WRB requirements for cementation or induration by CaCO 3 and
thickness are similar to Soil Taxonomy .

10 cm, and has a thickness 10 cm (or