Measurements of both the granitic rocks from surrounding areas and the granitic xenoliths included in pumices give ages around 330 Ma and show that most of the xenocrysts included in the pumices did not lose significant amounts of argon during the eruption. As previously suggested by Lo Bello and co-workers for the pumice flow of Neschers belonging to the same volcanic massif, the saddle-shaped age spectra are ascribed to the different Ar-release patterns of two populations of K-feldspars: (1) young sanidine phenocrysts of the pumices; and (2) old K-feldspars plucked from the Hercynian basement during the explosive eruption.
Moreover, the occurrence of stegodons on islands that have never been connected to continents means they were commonly the only large- or medium-sized mammals to inhabit these until the later arrival of anatomically modern humans.In the absence of these, we propose that their extinction was possibly the result of long-term demographic and genetic declines associated with an isolated island population.Stegodons (Stegodontidae: Proboscidea) were a widespread and diverse family of proboscideans dating from the late Miocene to the Late Pleistocene of Africa and Asia. Because pumice flows of the Monts-Dore massif crop out over large areas, these new ages will be useful for establishing a precise stratigraphy of the European Plio-Quaternary. Géodynamique, Faculté de Sciences de Nice, 06034 Nice cedex, France), AB(Laboratoire et U. With the Ar step-heating method, we were able to detect contamination of Quaternary K-feldspars by Hercynian K-feldspars as low as 0.25ℵ. The laser-probe ages are lower than the minimum ages measured on the populations of grains by the step-heating method.
Laser-probe analysis of hand-picked single grains gives ages in agreement with those of overlying and underlying lava flows previously dated by the conventional K-Ar method.
Stegodons are thus important for understanding some key biological phenomena including the dispersal abilities of large-bodied mammals and the evolutionary mechanisms of island dwarfing.
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Here we report on uranium-series dating of a stegodon tusk recovered from the Ainaro Gravels of Timor.