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| Titel |
A comparison of the organic carbon isotope composition of whole rock with that of isolated palynomorph groups (chitinozoans and scolecodonts) from the early Silurian of Gotland |
| VerfasserIn |
T. R. A. Vandenbroucke, A. Munnecke, M. J. Leng, T. Bickert, Olle Hints, G. Maier, T. Servais |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069351
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| Zusammenfassung |
| In the Early Palaeozoic, the carbon isotope composition of marine carbonates (δ13Ccarb) are
variable and at times much higher (exceeding +7) than values through the rest of the
geological column. Organic matter associated with the carbonates have a variable carbon
isotope composition (δ13Corg). However, the interpretation of δ13C from bulk organic carbon
is complex because of a whole number of poorly known factors that influence the signal.
Despite these difficulties, Early Palaeozoic global δ13Corg events are widely used and
interpreted in terms of global climate variation.
Here, we focus on one of these poorly understood influences on the signal, i.e. the variety
of sources that could constitute the bulk organic carbon that is measured for δ13C in rocks.
We compared the carbon isotope composition of bulk rock with that of two palynomorph
groups, scolecodonts (jaws of benthic annelid polychaetes) and chitinozoans (marine
mixed-layer epipelagic zooplankton). The samples were taken from the Llandovery-Wenlock
strata of the Lusklint 1 section on Gotland (E Sweden), which spans the typical rhythmic
limestone-marl alternations of the Upper and Lower Visby formations, and incorporates the
lower half of the famous Ireviken extinction Event and its associated oxygen and carbon
isotope excursion.
δ13C of the palynomorphs are consistently lower than bulk δ13C, and the δ13C of
the benthic scolecodonts are lower than of the planktonic chitinozoans. While the
difference between bulk and palynomorphs data may be in part a function of trophic
state, the difference between the scolecodonts and chitinozoans in the well-mixed
water column may imply an infaunal mode of life for the scolecodonts. Even more
negative values for the scolecodonts in the middle of the section may represent
variations in primary marine productivity, oxidation of organic matter in the bottom
waters, or genera effects. In general however, trends between the three datasets are
parallel indicating similarities in the low frequency, environmentally forced controls. |
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