Fission-track dating of volcanically derived sedimentary rocks
Depositional ages of sedimentary rocks can be determined using fission-track single grain ages on zircons from layers of volcanic ash or bentonite, even when the layers have been contaminated by older grains. This is done by compiling an age probability distribution or age spectrum for a sample from individual grain ages. An age spectrum is a simple and unambiguous way of testing for contamination and extracting useful age information. The youngest peak in the age spectrum approximates the time of deposition. In most contaminated samples, 30 or more grains should be counted to produce a reliable spectrum. However, useful, reproducible ages can be obtained by counting less than 10 grains in samples where most of the older, contaminating grains can be removed. The few older grains that remain after removing the obviously abraded ones may then be eliminated by examining the age spectrum. Although ages determined in this way are probably not precise enough for use in defining stratigraphic boundaries, they still provide a means of obtaining an isotopic age in sediments that cannot be dated by other radiometric methods. 18 references, 3 figures, 3 tables.
- Research Organization:
- Brigham Young Univ., Provo, Utah
- OSTI ID:
- 5587678
- Journal Information:
- Geology; (United States), Vol. 14:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BENTONITE
ISOTOPE DATING
SEDIMENTARY ROCKS
AGE ESTIMATION
VOLCANIC ROCKS
FISSION TRACKS
GEOLOGIC DEPOSITS
MEASURING METHODS
MEXICO
SAMPLING
UTAH
ZIRCON
CLAYS
DEVELOPING COUNTRIES
FEDERAL REGION VIII
IGNEOUS ROCKS
LATIN AMERICA
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
PARTICLE TRACKS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
USA
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES
580100* - Geology & Hydrology- (-1989)