ern Uplands of Scotland are built from sandstones and shales that were deposited during the Ordovician and Silurian periods, between about 450 and 420 million years ago, on the edge of an ocean known as Iapetus. Waldron et al. used isotopic dating to determine the ages of sand grains within the sandstones, so as to provide evidence for the sources of sediment in the adjoining continents. This method uses laser ablation to release uranium and lead atoms from grains of the mineral zircon, extracted from the sandstones, and a multicollector inductively coupled-mass spectrometer to measure the amounts of their isotopes. The results show that zircon grains were derived from sources characteristic of the Laurentian continent, comprising most of North America, together with the Scottish Highlands and Greenland. Many of the grains are much older than the sandstones in which they are now found. Grains as old as 3.6 billion years were recorded, older than any within the British Caledonides southeast of the Moine Thrust. The results support a model for the origin of the Southern Uplands in an ocean trench along the margin of Laurentia, where the floor of the Iapetus Ocean was being consumed under the adjacent continental margin.
Astronomical climate control on paleosol stacking patterns in the upper Paleocene-lower Eocene Willwood Formation, Bighorn Basin, Wyoming
Hayfaa Abdul Aziz et al., Utrecht University, Faculty of Geoscience, Budapestlaan4, Utrecht 3584 CD, Netherlands. Pages 531-534.
The Late Paleocene to Early Eocene, between 60 and 50 million years ago, was associated with high carbon dioxide concentrations, similar to those expected for the coming centuries due to fossil fuel burning. Superimposed on this "Greenhouse World" was an episode of dramatic, short-lived global warming caused by an enhanced greenhouse effect, called the Paleocene-Eocene Thermal Maximum (PETM). The PETM coincides with the evolution of modern mammals,Page: 1 2 3 4 5 6 7 8 Related biology news :1
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