A Reappraisal of the 40Ar/39Ar Stepwise Degassing Technique

Brereton, N. R.

doi:10.1111/j.1365-246x.1972.tb06102.x

Cited by 92 publications

(13 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Ar 40 /Ar 39 measurements (Brereton, 1972) were made to determine if excess radiogenic Ar could be detected, thereby confirming the hypothesis that the 1-m.y. age is indeed too old because of incomplete Ar outgassing.…”

Section: Figure 2 Oxygen-isotope Curves Showing Youngest Oxygen-isotmentioning

confidence: 93%

See 1 more Smart Citation

Late Quaternary Sediment of the Panama Basin: Sedimentation Rates, Periodicities, and Controls of Carbonate and Opal Accumulation

Pisias

1976

Geological Society of America Memoirs

View full text Add to dashboard Cite

Assuming a constant rate of quartz accumulation for deep-sea sediment core Y69-106P, from the Panama Basin, I have estimated the age of samples from the core and have constructed a curve for sedimentation-rate versus time. Stratigraphic controls for the calculated time scale include three C 14 measurements, the extinction of the radiolarian Stylatractus universus, correlation with oxygen-isotope curves from other dated cores, and an Ar 40 /Ar 39 age determination.The model sedimentation rates, when combined with data on mineralogic composition, allow the determination of accumulation rates for CaC0 3 , opaline Si0 2 , and remaining "detritus." Fluctuations in CaC0 3 accumulation rates over time correlate with variations in oxygen-isotope ratios in biogenous carbonate from two other equatorial Pacific cores; high oxygen-isotope ratios correlate with high CaC0 3 accumulation rates. Opaline Si0 2 accumulation rates reflect changes in the dominance of different radiolarian fossil groups, changes which can be related to surface circulation in the Panama Basin.Spectral analysis of the accumulation rate of CaC0 3 in core Y69-106P and of the oxygen-isotope record of core V28-238 indicates a 23,000-yr periodicity. Spectral analysis of the opal accumulation rate suggests a 100,000-yr periodicity, which is an important frequency in the oxygen-isotope record. Both these periodicities are close to those found in fluctuations in the Earth's orbital parameters. The eccentricity of the orbit fluctuates with an average period of 98,000 yr, and the precession of the equinoxes changes with a period of 22,000 yr.

show abstract

Section: Figure 2 Oxygen-isotope Curves Showing Youngest Oxygen-isotmentioning

confidence: 93%

“…age is indeed too old because of incomplete Ar outgassing. The Ar 40 /Ar 39 stepwise degassing technique (Brereton, 1972) gave an age of about 260,000 yr for this ash, and the measurements indicated that excess radiogenic Ar was present (J. Dymond, 1973, oral commun. ).…”

Section: Figure 2 Oxygen-isotope Curves Showing Youngest Oxygen-isotmentioning

confidence: 98%

Late Quaternary Sediment of the Panama Basin: Sedimentation Rates, Periodicities, and Controls of Carbonate and Opal Accumulation

Pisias

1976

Geological Society of America Memoirs

View full text Add to dashboard Cite

show abstract

“…K-Ar isochrons, which not only allow for initial argon but may furnish objective internal criteria for discrepancy detection, and in this respect rival the expensive and the time consuming 40 Ar/ 39 Ar step heating method for single samples (Fitch, Miller & Mitchell, 1969;Bryhni, Fitch & Miller, 1971;Brereton, 1972;Fitch, 1972;Miller, 1972;. AH quoted ages are based on the following constants: A 3 = 4.72 x 10~1 0 y 1 , A e = 0.584 x 10-10 y-1 , and 40 K/K = 0.0119 at.…”

Section: Geo 113mentioning

confidence: 99%

Single whole rock K—Ar isochrons

1976

View full text Add to dashboard Cite

Conventional K-Ar age determinations are frequently discrepant. A major factor is the failure of rocks to conform to the basic simplifying assumptions made in the total fusion method. Many rocks incorporate initial argon with an isotopic composition different from the present atmosphere and others have not remained closed systems. By careful sampling and the application of isochron geochronometry more reliable and geologically acceptable K-Ar ages can be obtained. K-Ar step heating isochrons from Kenyan Miocene volcanic sanidines are used to illustrate the accumulating evidence for the presence in ancient rocks of initial argon with an isotope ratio unlike that of the modern atmosphere. Single whole rock total fusion K-Ar isochrons from the Olduvai basalt, Tanzania and the Upper basalts of Antrim are presented to illustrate a new version of the K-Ar isochron technique. Special circumstance multiple rock K-Ar isochrons from the Belfast section of the Antrim basalts and from an ignimbrite-ash flow unit in Bed I, Olduvai Gorge, are used in a further discussion of the general applicability and usefulness of K-Ar isochrons.

show abstract

“…(1) The saddle-shaped age spectra have been presented by several authors (e.g., Lanphere and Dalrymple, 1971;Brereton, 1972;Kaneoka, 1974;Lanphere and Dalrymple, 1976). Lanphere and Dalrymple (1971) reported However, no definite criteria for the evaluation of disturbed 40 Ar- 39 Ar age results have been established.…”

Section: Introductionmentioning

confidence: 99%