 |
| Titel |
Removing the effects of metamorphism from the Neoproterozoic carbon isotope
record: a case study on Islay, western Scotland |
| VerfasserIn |
Alasdair Skelton |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250134046
|
| Publikation (Nr.) |
 EGU/EGU2016-14727.pdf |
|
|
|
|
|
| Zusammenfassung |
| The Port Askaig Formation on Islay, western Scotland is the first discovered tillite (glacial
sediment) of Neoproterozoic age. This formation is sandwiched between carbonate rocks
which preserve an extreme negative carbon isotope excursion. This so called “Islay anomaly”
has been correlated with other such anomalies worldwide and together with the tillites has
been cited as evidence of major (worldwide) glaciation events. During subsequent mountain
building, this carbonate-tillite- carbonate sequence has been folded, producing a major
en-echelon anticlinal fold system. Folding was accompanied by metamorphism at greenschist
facies conditions which was, in turn, accompanied by metamorphic fluid flow. Mapping of
the δ18O and δ13C values of these carbonate rocks reveals that metamorphic fluids were
channelled through the axial region of the anticlinal fold. The metamorphic fluid was found
to have a highly negative δ13C value, which was found to be in equilibrium with
metamorphosed graphitic mudstones beneath the carbonate-tillite-carbonate sequence.
Devolatilisation of these mudstones is therefore a likely source of this metamorphic
fluid. Removal of the effects of metamorphic fluid flow on δ13C values recorded
by metamorphosed carbonate rocks on Islay allows us to re-evaluate the isotopic
evidence used to reconstruct Neoproterozoic climate. We are able to show that
extreme negative δ13C values can partly be attributed to metamorphic fluid flow. |
|
|
|
|
|
|