Quantitative paleoenvironmental and paleoclimatic reconstruction ...
Quantitative paleoenvironmental and paleoclimatic reconstruction ...
Quantitative paleoenvironmental and paleoclimatic reconstruction ...
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ARTICLE IN PRESS<br />
28 N.D. Sheldon, N.J. Tabor / Earth-Science Reviews xxx (2009) xxx–xxx<br />
Fig. 17. Photomicrographs of paleosol carbonates. Mi=micrite, Sp=Sparite, MS =microspar (A) Nearly pure microcrystalline calcite (micrite; gray areas) that occludes mudstone<br />
from the matrix (red areas) in an Upper Triassic (Carnian) paleosol carbonate nodule of the Ischigualasto fm., Argentina. The area shown is appropriate for sampling, <strong>and</strong><br />
determination of δ 18 O <strong>and</strong> δ 13 C values, in order to approximate environmental conditions during pedogenesis. Field of view is 2 mm. (B) Nearly pure micrite from a cross-section of a<br />
vertically oriented rhizolith in a paleosol from the Middle Permian Quanzijie fm, Xinjiang Province, Northwest China. The area shown is appropriate for sampling, <strong>and</strong> determination<br />
of δ 18 O <strong>and</strong> δ 13 C values, in order to approximate environmental conditions during pedogenesis. The red areas are colored by stain from potassium ferricyanide, which indicates lowmagnesium<br />
calcite. The light gray areas are gypsum. Scale bar is 1 mm. (C) Domains of (1) micrite, (2) veins of sparry calcite, <strong>and</strong> (3) mixed micrite, microspar <strong>and</strong> Fe-oxide in a<br />
paleosol nodule from the Late Triassic (Carnian) Ischigualasto fm., Argentina. δ 18 O <strong>and</strong> δ 13 C values from domains of sparry calcite <strong>and</strong> mixed microspar <strong>and</strong> micrite are inappropriate,<br />
whereas δ 18 O <strong>and</strong> δ 13 C values from domains of micrite are appropriate, for sampling <strong>and</strong> measurement of oxygen isotope values in order to approximate environmental conditions<br />
during pedogenesis. Field of view is 4 mm. (D) Clotted micrite (dark areas) that is finely intergrown with microspar (light areas) from a paleosol nodule in Cretaceous<br />
(Kimmeridgian) strata of the Democratic Republic of Congo. Dark areas are stained by Fe-oxides. Field of view is 0.5 mm. While the areas of clotted micrite are appropriate for oxygen<br />
<strong>and</strong> carbon isotope analysis in order to approximate pedogenic conditions, very fine intergrowth of microspar <strong>and</strong> micrite makes sampling of the appropriate phase very challenging,<br />
<strong>and</strong> likely only feasible via a computer-assisted drill system. (E) Lamellar micrite intercalated with sparry calcite from a horizontal rhizolith in the Middle Permian Moradi fm., Niger.<br />
Field of view is 2 mm. While areas of micritic calcite are appropriate for sampling <strong>and</strong> oxygen <strong>and</strong> carbon isotope analysis in order to interpret environmental conditions during<br />
pedogenesis, domains of micrite are relatively narrow, <strong>and</strong> divided by complex networks of sparry <strong>and</strong> microspar cements. Samples such as this should be avoided for isotopic<br />
analysis, or employ a computer-assisted drill system. Sampling. (F) Sphaerosiderites in claystone matrix from an Upper Oligocene paleosol in Chilga Woreda, northwestern Ethiopia.<br />
Siderite spherules such as these are appropriate for carbon <strong>and</strong> oxygen isotope analysis in order to interpret environemtnal conditions during pedogenesis. (For interpretation of the<br />
references to colour in this figure legend, the reader is referred to the web version of this article.)<br />
paleosols from the mid-continent, U.S.A., Fox <strong>and</strong> Koch (2004)<br />
suggested that long-term trends in calcite δ 18 O values appear to track<br />
changes in rainfall δ 18 O values related global-scale paleoclimate<br />
factors, where the most positive δ 18 O values occur in strata from the<br />
mid-Miocene climatic optimum, <strong>and</strong> a stepped trend toward more<br />
negative δ 18 O values occurs in post mid-Miocene samples during the<br />
interval of Late Cenozoic cooling, <strong>and</strong> northern hemisphere glaciation.<br />
Levin <strong>and</strong> others (2004) observed a positive ~5.5‰ shift in δ 18 O<br />
values of paleosol calcite occurring in ~4.5 Ma strata of southern<br />
Ethiopia which they attributed to climatic change possibly including<br />
closure of the Indonesian seaway, long-term uplift of the East African<br />
highl<strong>and</strong>s, <strong>and</strong> aridification of eastern Africa. Koch et al. (2003) noted<br />
a small positive δ 18 O shift of approximately 1‰ in the Bighorn Basin,<br />
Wyoming, U.S.A., that is synchronous with the Paleocene–Eocene<br />
Please cite this article as: Sheldon, N.D., Tabor, N.J., <strong>Quantitative</strong> <strong>paleoenvironmental</strong> <strong>and</strong> <strong>paleoclimatic</strong> <strong>reconstruction</strong> using paleosols, Earth-<br />
Science Reviews (2009), doi:10.1016/j.earscirev.2009.03.004