Underclays and related paleosols associated with coals

Hughes, Robert; DeMaris, Philip J.; White, W.A.

doi:10.1016/b978-0-444-89198-3.50024-6

Cited by 5 publications

(2 citation statements)

References 28 publications

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“…This is how the underclay profiles were interpreted by many previous workers including Huddle and Paterson (1961), Rimmer and Eberl (1982) and Hughes et al (1992). In the investigated case, the reaction cannot be regarded as a soil process, because the potential starting material--that is, the illitic fraction of the limestone--is identified as a product of burial diagenesis.…”

Section: Timing and Mechanism Of The Alterationssupporting

confidence: 51%

Illite-Smectite Alteration and Accompanying Reactions in a Pennsylvanian Underclay Studied by TEM

Elsass

1997

Clays and clay miner.

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Abstract--Pennsylvanian underclay from Illinois is characterized by well-developed mineral zonation: towards the coal bed, marly limestone gradually evolves into carbonate-free clay, chlorite becomes undetectable and illite/smectite changes from ordered and illite-dominated into random and smectite-dominated, with both types present in the middle of the profile. Transmission electron microscopy (TEM) observations of the bulk material imply that disappearance of calcite is due to dissolution. Movement of SiO 2 in the upper part of the profile is evidenced by quartz cementation of clay aggregates; crystallization of kaolinite, by the presence of vermicular aggregates absent from less-altered samples. Illitic material in unaltered (limestone) samples consists of rare, large, Al-rich crystals of mica, interpreted as detrital, and abundant thin crystals of illite/smectite intimately mixed in approximately equal proportions with even thinner crystals of discrete illite. Both are more Mg-and Fe-rich than the large mica crystals and are interpreted as diagenetic, based on their 1Md polytype and the correlation with coal rank. Illitic material of the upper, carbonate-free section of the profile contains the same 3 types of crystals, but in different proportions: illite/smectite crystals dominate and their composition is more smectitic. Two distinct morphologies of the aggregates of crystals with different proportions of the component layers are observed. It explains why 2 different illite/smectites are detectable by X-ray diffraction (XRD) in these samples. The analysis of chemical data suggests that the underclay is a residue after dissolution of all of the calcite and half of the quartz from the original limestone (paleosol and/or telogenetic process). The TEM observations are not decisive regarding the origin of variation within the illitic material. It may result from burial diagenetic illitization of more-smectitic material, similar to the composition preserved in the center of underclay profile, or it may represent telogenetic alteration of illitic clay by acid waters penetrating down from the coal bed. The aggradation model explains the increase in percent K20, MgO and illite layers in the uppermost part of the profile, Whichever is the direction of reaction, it proceeds on an aggregate-by-aggregate basis and not fundamental particle-by-particle, and cannot be explained by simple opening or collapse of interlayers.

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Section: Timing and Mechanism Of The Alterationssupporting

confidence: 51%

Illite-Smectite Alteration and Accompanying Reactions in a Pennsylvanian Underclay Studied by TEM

Elsass

1997

Clays and clay miner.

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“…This is perhaps to be expected in that the very name ''underclay'' was initially defined as a consequence of superjacent coal. Moreover, while there has been some debate concerning the origins of underclays and other ''seat rocks'' (e.g., Huddle and Patterson, 1961), many favor an interpretation that underclay units generally record biogenic and diagenetic alteration of subjacent clayey sediment prior to and during plant growth and peat formation (e.g., Elsass et al, 1997;Hughes et al, 1992;Alonso and Brime, 1990). To the degree that underclays (as opposed to shale, clay, and other mudrocks) owe their existence primarily to the postdepositional alteration (of some argillaceous precursor) by acidic pore fluids, excess underclay-to-coal transitions may have little to do with deposi- WILKINSON et al tional order.…”

Section: Underclay-to-coal Transitionsmentioning

confidence: 99%

Stratal order in Pennsylvanian cyclothems

Wilkinson

Merrill

Kivett

2003

Geo. Society Am. Bull.

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Interpretation of continental to shallowmarine sedimentary sequences is commonly based on a perception of the presence of order in the upsection recurrence and/or arrangement of one or more rock types. These patterns of stratal organization span a spectrum of scales, ranging from thick transgressive-to-regressive ''sequences'' within passive continental margins, to thin upward-shallowing ''parasequences'' reported from many peritidal carbonate successions. However, in spite of the widespread acceptance of this idea, little quantitative assessment has been conducted to ascertain the relative dominance of stratal order and disorder in sedimentary sections. Because perception of high-frequency stratigraphic repetition is especially prevalent in Pennsylvanian ''cyclothemic'' terrestrial to marine successions generally coeval with Gondwanan glaciation, hypotheses of stratal order have also been widely linked to possible periodic changes in global sea level. Because of the general importance of implied relations between stratal order and glacioeustasy, lithofacies thicknesses, recurrences, and transition frequencies were examined in outcrops of west-central Illinois which comprise the type region of ''cyclothem'' deposition in order to evaluate the incidence of depositional cyclicity at this rather intermediate scale of consideration. Data on compositions, thicknesses, and vertical stratigraphic arrangement of 1031 units were derived from measured sections of Wanless, these comprise 11 distinct lithofacies types that span 868 m of section exposed at 44 localities.Philosophically, stratigraphic cyclicity could be represented as expectation in lith- † ofacies thickness, lithofacies recurrence, or as some regular pattern in lithofacies ordering. Frequency distributions of lithofacies thicknesses and stratigraphic separations between recurrent lithofacies are exponential in form; these distributions of stratigraphic intervals would result if horizons of lithologic change or recurrence occurred independently (randomly) in sedimentary successions. Stratigraphic cyclicity manifested as lithofacies ordering is evaluated by considering frequencies with different rock types succeed each other in stratigraphic sections; presumption of cyclothemic order requires that lithofacies' transitions exhibit some manifestation of statistical predictability. Markov chain analyses indicate that most high-frequency transitional order exists at underclay-tocoal horizons. Because underclay development may, in part, reflect a post-depositional (diagenetic) process that was associated with plant growth and coal formation, underclay-to-coal couplets may exist as one lithofacies association (as opposed to two genetically unrelated superjacent units). Few other transitions exhibit statistically significant predictability that cannot be ascribed to linkages between gradational rock types or to low-frequency (formation scale) variation in the bulk rock composition of the aggregate Illinois succession. In addition to these statistical attributes, cyclo...

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2001

Soils of the Past

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Underclays and related paleosols associated with coals

Cited by 5 publications

References 28 publications

Illite-Smectite Alteration and Accompanying Reactions in a Pennsylvanian Underclay Studied by TEM

Illite-Smectite Alteration and Accompanying Reactions in a Pennsylvanian Underclay Studied by TEM

Stratal order in Pennsylvanian cyclothems

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