Fragipan Horizon - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 159

Table 15.4 Hypotheses for the genesis of fragipans (Bockheim and Hartemink 2013 )
Hypothesis References

Physical
Lithologic discontinuities or paralithic/lithic
contact

James et al. ( 1995 ), Aide and Marshaus ( 2002 ),
Bockheim ( 2003 ) and Wilson et al. ( 2010 )

Architecture of soil pores Ajmone-Marsan et al. ( 1994 ), James

et al. ( 1995 ), Lindbo et al. ( 1994 ) and Falsone
and Bonifacio ( 2009 )

Hydro-consolidation Bryant ( 1989 ) and Assallay et al. ( 1998 )

Wetting/drying cycles Miller et al. ( 1971a , b ) and Attou and Brua

( 1998 )

Earthflows from earthquakes Certini et al. ( 2007 )

Relict periglacial features from permafrost Van Vliet and Langohr ( 1981 ), Habecker

et al. ( 1990 ) and Payton ( 1992 , 1993a , b )

Glacial compaction and pedogenesis Lindbo and Veneman ( 1993 ) and Miller

et al. ( 1993 )

Chemical
Silica bonding of clays and Fe oxides Steinhardt and Franzmeier ( 1979 ), Karathanasis

( 1989 ), Tremocoldi et al. ( 1994 ), Norfleet
and Karathanasis ( 1996 ) and Duncan and
Franzmeier ( 1999 )

Amorphous aluminosilicates (Al, Si) Hallmark and Smeck ( 1979 )

Physico-chemical
Hydro-consolidation; “ripening” (pore reorga-
nization); amorphous bonding (“proto-
fragipan”)

Weisenborn and Schaetzl ( 2005b )

Ajmone-Marsan and Torrent 1989 ; Karathanasis 1989 ; Tremocoldi et al. 1994 ;
Duncan and Franzmeier 1999 ; Szymanski et al. 2012 ). Alternatively amorphous Al
or a hydrous aluminosilicate may cement or bridge skeletal grains (Hallmark and
Smeck 1979 ; Norton et al. 1984 ). To explain fragipan formation in northern MI,
Weisenborn and Schaetzl ( 2005b ) offered the “Michigan Model of Fragipan Evo-
lution” that involves the self-weight collapse of a wet soil or parent material,
followed by “physical ripening” of the collapsed zone. These processes assist in
retaining the closely packed fabric and bridging in the collapsed zone, creating a
“proto-fragipan.” Amorphous bonding agents may later precipitate in the proto-
fragipan due to its position near a weathering-front discontinuity. The resulting
fragipan develops progressively and becomes better expressed with further pedo-
genesis. Fragipan degradation is eventually initiated by an increasingly prominent,
perched zone of saturation that forms seasonally above the fragipan (Szymanski
et al. 2011 ). With time, processes associated with fragipan degradation and trans-
location of materials to lower parts of the profile become greater than processes
associated with progressive development; as a result the fragipan is destroyed.
However, the mechanisms of fragipan degradation are not well-understood.
The role of silica in fragipan development has been emphasized by several
researchers. Duncan and Franzmeier ( 1999 ) obtained a strong correlation between
rupture-resistance strength and the molar ratio Si d /(Si d +Al d ) in fragipans. Other