Pseudotachylite rocks are millimeter- to kilometer-size rock bodies that consist of rock fragments set in a fine-grained groundmass that crystallized from a melt. Pseudotachylite bodies are found in large meteorite impact structures and form intricate networks below crater floors. The melt portions of pseudotachylyte bodies are generally believed to have formed during the impact process and at the positions where they are observed today. Ulrich Riller and colleagues show that the melt portions are derived from large, super hot pools of impact melt ponded in the crater, and that they travelled, likely within minutes, many kilometers away from the crater floor to their present location during impact crater formation. This has important consequences for the formation of large impact craters on Earth and other planets.
Constraints on early Cambrian carbon cycling from the duration of the Nemakit-Daldynian-Tommotian boundary delta-13C shift, Morocco
Adam C. Maloof et al., Dept. of Geosciences, Princeton University, Princeton, New Jersey 08544, USA. Pages 623-626.
The early Cambrian (542-511 million years ago) represents the transition from four million years of Precambrian Earth history dominated by bacteria and algae to a world rapidly populated by nearly all the animal phyla that exist today. During the early Cambrian radiation, the first appearance of calcite biomineralizers and reefs constructed by animals is associated with the largest perturbation to the carbon cycle in the Phanerozoic Eon (542-0 million years ago). A team of scientists from the USA and Morocco led by Adam Maloof report sedimentological and carbon-isotope data from a new 2.5-km-thick stratigraphic section that spans the early Cambrian evolutionary explosion in the Moroccan Anti-Atlas Mountains. Three new uranium-lead zirconages from tuffs within the stratigraphy place the events of the Cambrian explosion in a framework
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Geological Society of America