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

摘要: Lacustrine stromatolites are layered accretionary structures formed in shallow water by cyanobacteria. They a precise indicator of high lake limits and their morphology structure provide an insight into paleoenvironments the time. Previous research on lacustrine from Etosha Pan Namibia based radiocarbon ages carbonates were close to limit method did not account for any possible 14C reservoir effect. The used suggest that basin was extensively flooded during last 40,000 yr. To assess effect, age characteristics stromatolite Poacher’s Point investigated dating both carbonate organic residue samples at different depths deposit. ~15-cm-diameter separated 12 zones center edge block cut each zone; residual dated separately. ranged 34,700 24,700 yr BP 15,700 2500 BP. Ages generally increased with increasing distance surface We believe accurate estimate stromatolite’s age, while much older reflect incorporation old carbon limestone bedrock ancient calcrete introduced stream spring flow. Excluding 2 oldest (15,700 13,600 BP), which may contamination material washed flooding, linear regression relationship between indicates effect ranges up ~24,000 but decreases slightly as true deposit increases. This correct finite Pelican Island obtained early 1980s, together our new Andoni Bay, document >8-m-deep Late Pleistocene, prior ~34,000–26,000 cal prolonged conditions middle Holocene (8000–6600 BP) extent seen Pleistocene. DOI:  10.2458/azu_js_rc.55.16401