Pedon Distribution of Minerals in Coastal Plain Paleudults

Abstract

Mineral distributions in three Florida Paleudults were investigated with respect to particle size, horizon, depth, and location within the soil matrix. Mineralogy of sand, silt, and clay was determined using optical microscopy, x‐ray diffraction, and thermal analysis. Also, mineralogy of sand‐grain coatings was compared with intergrain matrix material. Elemental‐oxide composition of siltsized phyllosilicate grains was determined by electron microprobe analysis. Sand fractions consisted mainly of quartz, with lesser amounts of feldspar and mica, which were more prevalent in lower horizons. Coarse‐ and medium‐silt fractions were also dominated by quartz, but contained appreciable feldspar and mica in B horizons. Kaolinite and hydroxy‐interlayered vermiculite (HIV) were most prevalent in fine‐silt and clay fractions. Abrupt changes in silt and clay mineralogy across the E‐ and B‐horizon boundary (E‐B) included a decrease in quartz and HIV and an increase in kaolinite. Relative amounts of HIV did not markedly change with depth in arenic epipedons, but decreased steadily below the E‐B boundary for all pedons. Sand‐grain coatings from Bt horizons contained more mica than did the intergrain matrix, whereas coatings in A and E horizons contained appreciably more HIV. Distribution of phyllosilicates in these pedons could be explained by a hypothetical sequence of processes which includes (i) illuviation of kaolinite formed from weathering or dispersed from clay lenses in the sediments, (ii) comminution of sand‐ and silt‐sized mica, (iii) incorporation of finegrained mica in sand‐grain coatings, and (iv) transformation of finegrained mica to HIV in highly permeable eluvial horizons.

Occluded Mica in Hydroxy-Interlayered Vermiculite Grains from a Highly-Weathered Soil

“…A mica precursor is consistent with the prevalence of HIV in sandy horizons (Cabrera et al, 1989;Harris et aL, 1989). Mica, as a relatively coarse-grained phyllosilicate in sediments, would likely have weathered in place during the period when colloidal components such as kaolinite eluviated to deeper zones.…”

“…It tends to be particularly abundant in near-surface horizons, rivaling kaolinite as the primary clay component (Bryant and Dixon, 1963;Carlisle and Zelazny, 1973;Harris et al, 1989;Rich, 1968a;Rich and Obenshain, 1955). Its properties are important to consider given its prevalence in the root zone, its reactivity relative to other mineral components present, and its potential for selective cation sorption (Rich and Black, 1964;Rich, 1968b).…”

Dehydration of Hydroxy-Interlayered Vermiculite as a Function of Time and Temperature

“…Mechanisms and conditions of polymer formation within interlayers of vermiculite (Rich, 1960;Hsu and Bates, t 964) and montmoriUonite (Shen and Rich, 1962;Brydon and Kodama, 1966) have been studied via artificial synthesis of polymers within interlayers. Many soils of humid regions (i.e., the southeastern U.S.) contain abundant HIV in clay fractions (Fiskell and Perkins, 1970;Carlisle et al, 1978Carlisle et al, , 1981Carlisle et al, , 1985Carlisle et al, , 1988, particularly in near-surface horizons (Rich and Obenshain, 1955;Bryant and Dixon, 1963;Rich, 1968;Carlisle and Zelazny, 1973;Harris et aL, 1989).…”

Highly weathered mineralogy of select soils from Southeastern U.S. Coastal Plain and Piedmont landscapes

“…Rich (1968) suggested that relatively acid (pH 4.5 to 5.8) -oxidizing conditions in low organic matter environments with seasonal wetting and drying, conditions commonly found in upland, well drained settings of the Southeastern U.S., promote hydroxyinterlayered vermiculite formation. Several studies have noted the enrichment in near-surface horizons and sandy epipedons of hydroxyinterlayered vermiculite, and its relative depletion with corresponding increases in kaolinite either with depth and/or across eluvial/illuvial boundaries (Rich and Obenshain, 1955;Harris et al, 1987;Harris et al, 1989;Cabrera-Martinez et al, 1989). As an example, the depth distribution of gibbsite, kaolinite, and hydroxy-interlayered vermiculite are shown for representative Alabama Piedmont (Kanhapludult) and Coastal Plain (Kandiudult) soils ( Fig.…”