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| Titel |
Carbonate speleothems from western Mediterranean gypsum karst: palaeoclimate
implications |
| VerfasserIn |
Andrea Columbu, Russell Drysdale, Jon Woodhead, Veronica Chiarini, Jo De Waele, John Hellstrom, Paolo Forti, Laura Sanna |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250121487
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| Publikation (Nr.) |
 EGU/EGU2016-238.pdf |
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| Zusammenfassung |
| Gypsum caves are uncommon environments for carbonate speleothems (cave deposits).
Contrary to limestone caves, the only source of non-atmospheric carbon is from biogenic
CO2 produced by the overlying soils. Enhanced CO2 content in soils is in turn related with
climate, where warm temperatures and high humidity favour plant activity .().....(Fairchild
and Baker, 2012).
Although poorly decorated, the exploration of northern Italian and Spanish gypsum karst
systems reveals the existence of several generations of carbonate speleothems, which have
been dated with the U-Th series method .()......(Hellstrom, 2003; Scholz and Hoffmann,
2008). Their ages coincide with current and previous two interglacials (MIS 1,
5e and 7e and Greenland interstadials (GIS) 19, 20, 21 and 24. Considering that
these periods are amongst the most pronounced warm-wet pulsations over the last
250,000 ...(Martrat et al., 2007; NGRIP, 2004), and that CO2 has a fundamental
role in this karst process, this study explores the climate-driven hydrogeological
conditions necessary to trigger carbonate deposition in gypsum voids. The further
correlation with sapropel events 5, 4, 3 and 1, considered symptomatic of enhanced
rainfall across the whole Mediterranean basin .(.)(Emeis et al., 1991), highlights the
importance of flow-rate in the fracture network and infiltration of meteoric water into the
caves.
The combination of high CO2 and a phreatic status of the fracture network is thus
indispensable for the formation of carbonate speleothems in gypsum karst. This condition
appears to be triggered by periods of orbital precession minimum, when the monsoonal
activity peaked in the Atlantic area. Stable oxygen isotope signatures suggest that the
speleothems did not grow during any interglacial-glacial or main interstadial-stadial
transitions, confirming that variations from optimum climate conditions may hamper the
formation of this category of speleothems.
New speleological exploration and sampling campaign may extend this model in
space (extra-Mediterranean regions) and time (500,000 BP – the limit of U-Th
dating), enhancing knowledge on the latitudinal impact and timing of such climate
variability.
References
.Emeis, K.-C., Camerlenghi, A., McKenzie, J. A., Rio, D., and Sprovieri, R., 1991, The
occurrence and significance of Pleistocene and Upper Pliocene sapropels in the Tyrrhenian
Sea: Marine geology, v. 100, no. 1, p. 155-182.
Fairchild, I. J., and Baker, A., 2012, Speleothem science: from process to past
environments: John Wiley & Sons, Chichester.
Hellstrom, J., 2003, Rapid and accurate U/Th dating using parallel ion-counting
multi-collector ICP-MS.: Journal of Analytical Atomic Spectrometry, v. 18.
Martrat, B., Grimalt, J. O., Shackleton, N. J., de Abreu, L., Hutterli, M. A., and Stocker,
T. F., 2007, Four climate cycles of recurring deep and surface water destabilizations on the
Iberian margin: Science, v. 317, no. 5837, p. 502-507.
NGRIP, N. G. I. C. P. M., 2004, High-resolution record of Northern Hemisphere climate
extending into the last interglacial period: Nature, v. 431, no. 7005, p. 147-151.
Scholz, D., and Hoffmann, D., 2008, 230Th/U-dating of fossil corals and speleothems:
Quat. Sci. J, v. 57, p. 52. |
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