The Permian-Triassic boundary interval (circa 252 million years ago) saw unparalleled species loss in the marine realm, and biotic recovery was delayed relative to other mass extinctions. A major unresolved question has been about where the marine organisms that recovered from the extinction were housed. Trace fossils, which preserve the activity of organisms, are recorded from Early Triassic rocks found in western Alberta, northeast British Columbia, and the barren landscapes of the Canadian Arctic; they provide evidence for refuges from ongoing extinction pressures in the immediate aftermath of latest Permian mass extinction. These fossils present a record of ocean-bottom dwelling organisms and indicate locally well-oxygenated conditions in an ocean otherwise characterized by widespread anoxia. The habitable zone model of Beatty et al. proposes that a colonization window existed along ancient western Canadian shorelines that was controlled by aeration through wave action and enhanced by frequent storms. Within the habitable zone, latest Permian extinction levels are reduced and the recovery time is minimized, supporting the interpretation that oxygen stress was a major cause of the recovery delay from Earth's greatest extinction. It follows that the habitable zone provided the seed communities from which the marine realm was repopulated following a global return of well-oxygenated oceanic conditions.
Sulfidity controls molybdenum isotope fractionation into euxinic sediments: Evidence from the modern Black Sea
Nadja Neubert et al., Universitat Bern, Institut fur Geologie, Balzerstrasse 3, 3012 Bern, Switzerland. Pages 775-778. NSF funding received.
Molybdenum is a trace metal that is sensitive to redox (reduction/oxidation reaction) changes in the water column. It is used by biogeochemists who study changes within the ocean syste
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Geological Society of America