Hostname: page-component-78c5997874-m6dg7 Total loading time: 0 Render date: 2024-11-03T00:57:48.119Z Has data issue: false hasContentIssue false
  • English
  • Français

14C Dating of Organic Residue and Carbonate from Stromatolites in Etosha Pan, Namibia: 14C Reservoir Effect, Correction of Published Ages, and Evidence of >8-m-Deep Lake During the Late Pleistocene

Published online by Cambridge University Press:  09 February 2016

George A Brook ,
A Cherkinsky ,
L Bruce Railsback ,
Eugene Marais  and
Martin H T Hipondoka
George A Brook
Affiliation:
Department of Geography, University of Georgia, Athens, Georgia 30602, USA
A Cherkinsky*
Affiliation:
Center for Applied Isotope Studies, University of Georgia, Athens, Georgia 30602, USA
L Bruce Railsback
Affiliation:
Department of Geology, University of Georgia, Athens, Georgia 30602, USA
Eugene Marais
Affiliation:
Entomology Centre, National Museum of Namibia, PO Box 1203, Windhoek, Namibia
Martin H T Hipondoka
Affiliation:
Department of Geography, History and Environmental Studies, University of Namibia, PB 13301, Windhoek, Namibia
*
Corresponding author. Email: [email protected].
Get access Rights & Permissions [Opens in a new window]

Abstract

Lacustrine stromatolites are layered accretionary structures formed in shallow water by cyanobacteria. They are a precise indicator of high lake limits and their morphology and structure provide an insight into paleoenvironments of the time. Previous research on lacustrine stromatolites from Etosha Pan in Namibia based on radiocarbon ages of carbonates were close to the limit of the method and did not account for any possible 14C reservoir effect. The ages were used to suggest that the basin was not extensively flooded during the last 40,000 yr. To assess the reservoir effect, the age characteristics of a stromatolite from Poacher's Point were investigated by 14C dating both carbonate and organic residue from samples at different depths in the deposit. The ∼15-cm-diameter stromatolite was separated into 12 zones from the center to the edge and block samples were cut from each zone; the carbonate and residual organic residue were dated separately. The carbonate ages ranged from 34,700 to 24,700 14C yr BP and the organic ages from 15,700 to 2500 14C yr BP. Ages generally increased with increasing distance from the surface of the deposit. We believe that the organic ages are an accurate estimate of the stromatolite's age, while the much older carbonate ages reflect incorporation of old carbon from limestone bedrock and ancient calcrete introduced by stream and spring flow. Excluding the 2 oldest organic ages (15,700 and 13,600 14C yr BP), which may reflect contamination by older organic material washed into the lake during flooding, a linear regression relationship between carbonate and organic ages indicates that the reservoir effect on carbonate ranges up to ∼24,000 14C yr BP but decreases slightly as the true age of the deposit increases. This regression relationship was used to correct 2 finite carbonate ages for stromatolites from Pelican Island obtained in the early 1980s, which together with our new organic age for a stromatolite from Andoni Bay, document a >8-m-deep lake in Etosha Pan during the Late Pleistocene, at and prior to ∼34,000–26,000 cal yr BP. The organic carbon ages from the Poacher's Point stromatolite suggest prolonged lacustrine conditions during the early to middle Holocene (8000–6600 cal yr BP) but not to the extent seen during the Late Pleistocene.

Type
Radiocarbon Reservoir Effects
Information
Radiocarbon , Volume 55 , Issue 3: Proceedings of the 21st International Radiocarbon Conference (Part 2 of 2) , 2013 , pp. 1156 - 1163
Copyright
Copyright © 2013 by the Arizona Board of Regents on behalf of the University of Arizona 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Brook, GA, Marais, E, Srivastava, P, Jordan, T. 2007. Timing of lake level changes in Etosha Pan, Namibia, since the middle Holocene from OSL ages of relict shorelines in the Okondeka region. Quaternary International 175(1):29–40.Google Scholar
Brook, GA, Railsback, LB, Marais, E. 2010. Reassessment of carbonate ages by dating both carbonate and organic material from an Etosha Pan (Namibia) stromatolite: evidence of humid phases during the last 20 ka. Quaternary International 229(1–2):24–37.Google Scholar
Cherkinsky, A, Culp, RA, Dvoracek, DK, Noakes, JE. 2010. Status of the AMS facility at the University of Georgia. Nuclear Instruments and Methods in Physical Research B 268(7–8):867–70.Google Scholar
Geyh, MA, Eitel, B. 1998. Radiometric dating of young and old calcrete. Radiocarbon 40(2):795–802.Google Scholar
Hogg, AG, McCormac, FG, Higham, TFG, Reimer, PJ, Baillie, MGL, Palmer, JG. 2002. High-precision radiocarbon measurements of contemporaneous tree-ring dated wood from the British Isles and New Zealand: AD 1850–950. Radiocarbon 44(3):633–40.Google Scholar
Lindeque, M, Archibald, TJ. 1991. Seasonal wetlands in Owambo and Etosha National Park. Madoqua 17(2): 129–33.Google Scholar
McCormac, FG, Hogg, AG, Blackwell, PG, Buck, CE, Higham, TFG, Reimer, PJ. 2004. SHCal04 Southern Hemisphere calibration, 0–11.0 cal kyr BP. Radiocarbon 46(3):1087–92.CrossRefGoogle Scholar
Miller, R. 2008. The Geology of Namibia: Volume 3, Upper Palaeozoic to Cenozoic. Windhoek: Ministry of Mines and Energy, Geological Survey.Google Scholar
Reimer, PJ, Baillie, MGL, Bard, E, Bayliss, A, Beck, JW, Blackwell, PG, Bronk Ramsey, C, Buck, CE, Burr, GS, Edwards, RL, Friedrich, M, Grootes, PM, Guilderson, TP, Hajdas, I, Heaton, T, Hogg, AG, Hughen, KA, Kaiser, KF, Kromer, B, McCormac, FG, Manning, SW, Reimer, RW, Richards, DA, Southon, JR, Talamo, S, Turney, CSM, van der Plicht, J, Weyhenmeyer, CE. 2009. IntCal09 and Marine09 radiocarbon age calibration curves, 0–50,000 years cal BP. Radiocarbon 51(4):1111–50.Google Scholar
Rust, U. 1984. Geomorphic evidence of Quaternary environmental changes in Etosha, South West Africa/ Namibia. In: Vogel, JC, editor. Late Cainozoic Palaeoclimates of the Southern Hemisphere. Rotterdam: A A Balkema. p 279–86.Google Scholar
Stuiver, M, Polach, HA. 1977. Discussion: reporting of 14C data. Radiocarbon 19(3):355–63.CrossRefGoogle Scholar
Wilczewski, N, Martin, H. 1972. Algen-Stromatolithen aus der Etoscha-Pfanne Südwestafrikas. Neues Jahrbuch für Geologie und Paläontologie 12:720–6.Google Scholar