Radiocarbon, Volume 33 (1991): Recent submissions
Now showing items 41-53 of 53
-
Lithium Contamination in AMS Measurements of 14CHigh count rates of lithium ions in an AMS measurement system for 14C were traced to the lithium content in the quartz tubes used in the graphitization of the samples. The lithium contamination was nearly eliminated by the use of borosilicate glass reaction tubes at a lower reaction temperature. The ion beam current and the measurement precision of the isotope ratio were not affected.
-
Late Quaternary Pteropod Preservation in Eastern North Atlantic Sediments in Relation to Changing ClimateAMS 14C measurements on pteropod shells from eastern North Atlantic deep-sea cores reveal distinct periods of aragonite preservation during the last 16,000 years. Most preservation spikes coincide with documented periods of climatic change on a scale of 2 x 101 to 2 x 103 years.
-
LaboratoriesDepartment of Geosciences, The University of Arizona, 1991-01-01
-
Gas Proportional Versus Liquid Scintillation Counting, Radiometric Versus AMS DatingI discuss here the basis of a comparison of methods for radiocarbon dating and introduce a new index for the relative merit of a system, factor of counting capacity, that is generally more appropriate than the commonly used factor of merit. The merit of a dating system cannot be based on a single figure but other factors must also be considered. A comparison of the gas proportional, liquid scintillation and accelerator mass spectrometry technique is presented that for gas proportional counters is based on a multi-detector system rather than a single detector.
-
Cuello: Resolving the Chronology Through Direct Dating of Conserved and Low-Collagen Bone by AMSIt is well known that 14C dating of fossil bone with seriously depleted protein levels, or bone that has been consolidated with preservatives, can produce erroneous results. In the tropics, warm and moist soil conditions lead to constant reworking of organic matter and add to the danger of bone contamination. Because of this, 14C dating of preservative-impregnated bone from such areas has rarely been successful. We report here a set of AMS dates on both unconsolidated animal bone and polyvinyl acetate/polyvinyl alcohol (PVA/PV-OH) impregnated human burials from the Maya site of Cuello, Belize. The steps needed to purify the samples are described, together with details on the use of qualitative infra-red (IR) spectra as a means of assessing sample purity.
-
A Radiocarbon Chronology for Human-Induced Environmental Change on Mangaia, Southern Cook Islands, PolynesiaA suite of 23 14C age determinations, from a well-stratified rockshelter and from 3 pollen cores on Mangaia Island is reported. The rockshelter has yielded significant evidence for avifaunal extinctions during the period cal. A.D. 1000-1600. The Lake Tiriara pollen cores span a period from ca. 6500 cal. b.p. to the present, and palynological analysis of the TIR 1 core indicates major anthropogenic disturbance on the island's vegetation after ca. 1600 cal. B.P. These sites, and the radiocarbon ages associated with them, provide the first chronologically secure evidence for human impacts on the island ecosystems of the southern Cook Islands.
-
A Late Quaternary Stratigraphic Framework for Eastern Mediterranean Sapropel S1 Based on AMS 14C Dates and Stable Oxygen IsotopesDetailed stable oxygen isotope analyses coupled with AMS 14C measurements on an eastern Mediterranean sapropel S1 sequence indicate that adverse bottom conditions persisted for ca 8000 years. AMS dates on additional sequences show that complete bottom anoxia lasted for 300-800 years. The S1 event is not synchronous throughout the eastern Mediterranean, but started earlier in the deeper parts of the basin.
