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| Titel |
Stromatolite laminae (Lagoa Vermelha, Brasil) as archives for reservoir age
changes |
| VerfasserIn |
Sylvie Bruggmann, Crisogono Vasconcelos, Irka Hajdas |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250122165
|
| Publikation (Nr.) |
 EGU/EGU2016-1122.pdf |
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| Zusammenfassung |
| As laminated biogenic or abiogenic sedimentary structures [1], stromatolites record
environmental changes along growth profiles, revealing possible changes in reservoir ages
due to input of older carbon. A modern stromatolite sample was collected in Lagoa Vermelha
(100 km east of Rio de Janeiro, Brasil) an area known for upwelling of South Atlantic Central
Water (SACW).
34 samples from a transect cutting the lamination were collected with a hand-driller for
standard geochemistry and 14C AMS analyses. Shells collected in 2015 were analysed for
estimation of the present-day reservoir age. 14C ages of laminae and the reservoir age were
used to apply the age-depth model to the stromatolite transect with the OxCal depositional
model (Marine13 calibration curve; [2]).
Small-scale changes in the composition of laminae report environmental changes, e.g.
upwelling. The well-laminated middle part (laminated boundstone; ca. 4cm) of the
stromatolite transect was found to have grown in a short time period of less than 100 years
(1163-1210 14C y BP), with four excursions towards older 14C ages (ca. 1200 14C y BP). To
detect possible changes of marine 14C, calendar years assuming a stable modern reservoir
age were used to simulate atmospheric 14C ages with the southern hemisphere
IntCal13 atmospheric calibration curve [3]. The offset between the measured and
simulated 14C ages indicates a variability of the reservoir age between -99 and
268 14C y with highest reservoir correction found for the layers with indication of
environmental changes (e.g. upwelling). Thus, this simulation confirms the occurrence of
older carbon and points out the sensitivity of stromatolites for changing reservoir
ages.
[1] M.A. Semikhatov, C.D. Gebelein, P. Cloud, S.M. Awramik, W.C. Benmore (1979).
Stromatolite morphogenesis - progress and problems. Canadian Journal of Earth Sciences,
19:992-1015.
[2] P.J. Reimer, E. Bard, A. Bayliss, J. W. Beck, P. G. Blackwell, C. Bronk Ramsey, C. E.
Buck, H. Cheng, R.L. Edwards, M. Friedrich, P.M. Grootes, T.P. Guilderson, H. Haflidason, I.
Hajdas, C. Hatté, T.J. Heaton, D.L. Hoffmann, A.G. Hogg, K.A. Hughen, K.F.
Kaiser, B. Kromer, S.W. Manning, M. Niu, R.W. Reimer, D.A. Richards, E.M. Scott,
J. R. Southon, R.A. Staff, C.S.M. Turney, J. van der Plicht (2013). IntCal13 and
Marine13 radiocarbon age calibration curves 0-50,000 years cal BP. Radiocarbon
55(4):1869-1887.
[3] A.G. Hogg, Q. Hua, P.G. Blackwell, M. Niu, C.E. Buck, T.P. Guilderson, T.J. Heaton,
J.G. Palmer, P.J. Reimer, R.W. Reimer, C.S.M. Turney, S.R.H. Zimmerman (2013). Shcal13
southern hemisphere calibration, 0-50,000 years cal BP. Radiocarbon, 55(2):1-15. |
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