Potassium-argon dates and the Cenozoic mammalian chronology of North America

Evernden, Jack F.; Savage, Donald E.; Curtis, Garniss H.; James, G. W.

doi:10.2475/ajs.262.2.145

Cited by 375 publications

(117 citation statements)

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“…ago, which suggests that the Pliocene-Pleistocene boundary, based on the climatic definition, may be as old as this. Other workers have also advanced the possibility that the Pleistocene is of considerably longer duration than has been previously thought [17,18].…”

Section: Geological Implicationsmentioning

confidence: 99%

Paleomagnetism and geochronology of the Pliocene-Pleistocene lavas in Iceland

McDougall

Wensink²

1966

Earth and Planetary Science Letters

155

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Potassium-argon dates are reported on five basalt samples from the Pliocene-Pleistocene sequence of lavas in the Jbkuldalur area, northeastern Iceland. These dates confirm the correlations previously made with the geological time scale by means of paleomagnetic stratigraphy. The R1 and N2 polarity epochs are shown to be equivalent to the Matuyama reversed and Gauss normal polarity epochs respectively. Within the N2 (Gauss) normal epoch up to three successive lava flows occur which are reversely magnetized. Dating of a normally magnetized basalt immediately below these reversed lavas gives a result of 3.10 ± 0.10 m.y., and confirms the reality of the Mammoth reversed event, first recognized in California. Two intercalations of normally magnetized lavas occur in the R1 (Matuyama) reversed epoch. The older of the normal flows may represent the Olduvai event; the younger normal polarity flow has been dated at 1.60 ± 0.05 m.y., and possibly indicates the presence of yet another normal event in the Matuyama reversed epoch. We propose the name Gils~ for this possible additional event.Immediately above the basalt dated at 3.10 ± 0.10 m.y. occurs a tillite, which suggests that regional glaciation commenced in Iceland at about this time. Hence, the base of the Pleistocene may be as old as 3 m.y.

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Section: Geological Implicationsmentioning

confidence: 99%

Paleomagnetism and geochronology of the Pliocene-Pleistocene lavas in Iceland

McDougall

Wensink²

1966

Earth and Planetary Science Letters

155

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“…White River lithostratigraphy has been debated for over a century, but was mostly clarified by Morris Skinner and other workers from the Frick Laboratory starting in the 1930's (Emry et al, 1987). Several intercalated ashes were dated by K-Ar methods (Evernden et al, 1964) and a paleomagnetic stratigraphy was established by Prothero et al (1983) and Prothero (1985a, b). Reanalysis of these ashes and paleomagnetic stratigraphies as well as several additional ashes and paleomagnetic sections with more precise 4°Ar/39Ar and paleomagnetic methods by Swisher and Prothero (1990), Prothero and Swisher (1992), and Evanoff et al (1992) provides an integrated regional geochronology of the White River Group.…”

Section: Samples and Stratigraphymentioning

confidence: 99%

Biologic and climatic signals in the oxygen isotopic composition of Eocene-Oligocene equid enamel phosphate

Bryant

Froelich

Showers

et al. 1996

Palaeogeography, Palaeoclimatology, Palaeoecology

138

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Oxygen isotope results for tooth enamel-phosphate (6p) from late Eocene-early Oligocene fossil horses are presented to determine if paleobiologic and paleoclimatologic information is recorded in fossil tooth enamel chemistry. Teeth from jaws of Mesohippus and Miohippus from the White River Formation (or Group) in the western Great Plains are well preserved and have excellent geochronologic control. Although there is clear evidence for post-depositional alteration of the enamel, a hydroxylapatite mineralogy is preserved and isotopic exchange of oxygen does not appear to be significant. There are distinctive patterns of 6p variation among individual teeth from the same jaw. These patterns reflect season of birth and timing of enamel mineralization. Most of the horses were born in the spring, and mineralization of the enamel is complete after 1-1.5 years. These results show that paleoclimate reconstruction from enamel 6p must account for tooth position and timing of mineralization. The observation that there are different intrajaw patterns of 6p variation among Mesohippus and Miohippus may provide a basis to reconstruct changes in climate seasonality in ancient environments.

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“…Stirton concluded "there is not sufficient identifiable material in our collection from Alturas for an accurate determination of the age of the stratum from which they were obtained." The general character of this fauna and a radiometric date from near Rattle- snake Butte (Evernden et al, 1964) suggested a Hemphillian age. Axelrod (1944) provided further discussion of the fossil flora from the Alturas Formation based on re-examination of previous materials and from additional material obtained from the "Alturas formation near Rattlesnake Butte."…”

Section: Introductionmentioning

confidence: 99%

“…Axelrod (1944) concluded a Pliocene age for the Alturas flora. Evernden et al (1964) published a K/Ar date from plagioclase in a tuff near the base of the Alturas Formation of 8.1 Ma.…”

Section: Introductionmentioning

confidence: 99%