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MICROMORPHOLOGICAL ANALYSIS OF SELECTED PALEOSOLS OF LATE
CARBONIFEROUS COAL-BEARING ROCKS EXPOSED AT JOGGINS, NOVA SCOTIA, CANADA
M.G. SMITH and I.P. MARTINI
Department of Land Resource Science, University of Guelph, Guelph, Ont.,
Canada
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The coal-bearing Late Carboniferous rocks exposed at Joggins, Nova
Scotia, contain numerous plant-rooted zones and paleosols. Microfacies analysis
of representative paleosols reveals that they retain significant amounts of
paleoenvironmental information, in spite of diagenetic modifications. Indeed,
diagenetic transformations may have been localized by pre-existent pedofeatures.
A case in point are numerous, varied Fe-rich glaebulae (siderite and other
Fe-oxide and hydroxide micro-nodules and micro-concretions). The glaebulae rim
pedotubules, grade out and become dispersed in the surrounding matrix. This is
what it would be expected on a thin section cut across a rhizosphere.
The
mineralogical paragenesis of root-fillings and surrounding micro-nodules has
developed at different stages during pedogenesis (Fe-oxides and hydroxides) or
very early diagenesis (siderite in the vadose zone) and, perhaps even late
diagenesis (cathodoluminescent calcite). The pedogenetic and early diagenesis
stages have been affected by local soil drainage related to fluctuating water
table, inundation and onset of hydromorphic conditions. In this context,
"shale-type" underclays are of particular interest, and microfacies
analyses support the hypothesis that they are polygenetic soils which started
forming in moderately drained sites prior to the emplacement of thick peatlands
(the precursors of the overlying coals). The underclay may have undergone
subsequent diagenetic transformation, as some researchers argue and as evidenced
by a slightly higher concentration of kaolinite in their uppermost horizon, but
that may have been the extent of such modification as suggested by the essential
homogeneity of clay minerals and of chemical composition throughout the rest of
the profile.
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