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| Titel |
Investigating the effects of diagenesis on the environmental signals within species of Gigantoproductus |
| VerfasserIn |
Leah Nolan, Melanie J. Leng, Lucia Angiolini, Sarah J. Davies, Flavio Jadoul, Vanessa J. Banks, Michael H. Stephenson |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250137841
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| Publikation (Nr.) |
 EGU/EGU2017-691.pdf |
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| Zusammenfassung |
| The stable isotope composition (δ18O and δ18C) of biogenic (low-magnesium) calcite is
commonly used as a palaeoenvironmental proxy. However, to validate the isotope data,
there needs to be an assessment of preservation of the calcite to ensure that the data
generated reflect the original environmental conditions. Most commonly, preservation
analyses include: scanning electron and cathodoluminescence microscopy (SEM
and CL), and measurement of trace element composition. The shells of species of
Gigantoproductus (Brachiopoda) have thick valves, which allows sampling from the inner
to the outer shell margin, perpendicular to the orientation of growth lines, on an
internal surface exposed by longitudinal sectioning of the shell. This sampling can be
conducted at high resolution, potentially revealing seasonal variability that may be
preserved in the shell isotope geochemistry. We collected Mississippian species of
Gigantoproductus from two locations on the Derbyshire carbonate platform and assessed
preservation through SEM and CL; 11 specimens were selected for trace element
abundances (primarily Mn, Fe, Mg, Sr, and Na), of these, 5 were chosen for stable isotope
analysis. δ18O and δ18C values of the well-preserved material range between –2.6
to –6.4‰ and –1.7 and +2.7‰ respectively. Assuming normal marine salinity,
the range in δ18O suggests a seasonal range of about 16∘C in shallow sea water
temperature at this time. The different shell fabrics (i.e. the secondary laminar shell
layer, the prismatic tertiary shell layer and growth lines) show trace element and
stable isotope values that lie outside of the normal range whilst still appearing to be
well-preserved from the SEM and CL data. Overall, this study illustrates the importance
of conducting systematic preservation tests in order to select the best-preserved
specimens for biogenic calcite isotope analysis, and sampling at very high resolution
(hundreds of μm) reveals heterogeneity of preservation within several specimens. |
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